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1/*
2 * fs/userfaultfd.c
3 *
4 * Copyright (C) 2007 Davide Libenzi <davidel@xmailserver.org>
5 * Copyright (C) 2008-2009 Red Hat, Inc.
6 * Copyright (C) 2015 Red Hat, Inc.
7 *
8 * This work is licensed under the terms of the GNU GPL, version 2. See
9 * the COPYING file in the top-level directory.
10 *
11 * Some part derived from fs/eventfd.c (anon inode setup) and
12 * mm/ksm.c (mm hashing).
13 */
14
15#include <linux/hashtable.h>
16#include <linux/sched.h>
17#include <linux/mm.h>
18#include <linux/poll.h>
19#include <linux/slab.h>
20#include <linux/seq_file.h>
21#include <linux/file.h>
22#include <linux/bug.h>
23#include <linux/anon_inodes.h>
24#include <linux/syscalls.h>
25#include <linux/userfaultfd_k.h>
26#include <linux/mempolicy.h>
27#include <linux/ioctl.h>
28#include <linux/security.h>
29
30static struct kmem_cache *userfaultfd_ctx_cachep __read_mostly;
31
32enum userfaultfd_state {
33 UFFD_STATE_WAIT_API,
34 UFFD_STATE_RUNNING,
35};
36
37/*
38 * Start with fault_pending_wqh and fault_wqh so they're more likely
39 * to be in the same cacheline.
40 */
41struct userfaultfd_ctx {
42 /* waitqueue head for the pending (i.e. not read) userfaults */
43 wait_queue_head_t fault_pending_wqh;
44 /* waitqueue head for the userfaults */
45 wait_queue_head_t fault_wqh;
46 /* waitqueue head for the pseudo fd to wakeup poll/read */
47 wait_queue_head_t fd_wqh;
48 /* a refile sequence protected by fault_pending_wqh lock */
49 struct seqcount refile_seq;
50 /* pseudo fd refcounting */
51 atomic_t refcount;
52 /* userfaultfd syscall flags */
53 unsigned int flags;
54 /* state machine */
55 enum userfaultfd_state state;
56 /* released */
57 bool released;
58 /* mm with one ore more vmas attached to this userfaultfd_ctx */
59 struct mm_struct *mm;
60};
61
62struct userfaultfd_wait_queue {
63 struct uffd_msg msg;
64 wait_queue_t wq;
65 struct userfaultfd_ctx *ctx;
66 bool waken;
67};
68
69struct userfaultfd_wake_range {
70 unsigned long start;
71 unsigned long len;
72};
73
74static int userfaultfd_wake_function(wait_queue_t *wq, unsigned mode,
75 int wake_flags, void *key)
76{
77 struct userfaultfd_wake_range *range = key;
78 int ret;
79 struct userfaultfd_wait_queue *uwq;
80 unsigned long start, len;
81
82 uwq = container_of(wq, struct userfaultfd_wait_queue, wq);
83 ret = 0;
84 /* len == 0 means wake all */
85 start = range->start;
86 len = range->len;
87 if (len && (start > uwq->msg.arg.pagefault.address ||
88 start + len <= uwq->msg.arg.pagefault.address))
89 goto out;
90 WRITE_ONCE(uwq->waken, true);
91 /*
92 * The implicit smp_mb__before_spinlock in try_to_wake_up()
93 * renders uwq->waken visible to other CPUs before the task is
94 * waken.
95 */
96 ret = wake_up_state(wq->private, mode);
97 if (ret)
98 /*
99 * Wake only once, autoremove behavior.
100 *
101 * After the effect of list_del_init is visible to the
102 * other CPUs, the waitqueue may disappear from under
103 * us, see the !list_empty_careful() in
104 * handle_userfault(). try_to_wake_up() has an
105 * implicit smp_mb__before_spinlock, and the
106 * wq->private is read before calling the extern
107 * function "wake_up_state" (which in turns calls
108 * try_to_wake_up). While the spin_lock;spin_unlock;
109 * wouldn't be enough, the smp_mb__before_spinlock is
110 * enough to avoid an explicit smp_mb() here.
111 */
112 list_del_init(&wq->task_list);
113out:
114 return ret;
115}
116
117/**
118 * userfaultfd_ctx_get - Acquires a reference to the internal userfaultfd
119 * context.
120 * @ctx: [in] Pointer to the userfaultfd context.
121 *
122 * Returns: In case of success, returns not zero.
123 */
124static void userfaultfd_ctx_get(struct userfaultfd_ctx *ctx)
125{
126 if (!atomic_inc_not_zero(&ctx->refcount))
127 BUG();
128}
129
130/**
131 * userfaultfd_ctx_put - Releases a reference to the internal userfaultfd
132 * context.
133 * @ctx: [in] Pointer to userfaultfd context.
134 *
135 * The userfaultfd context reference must have been previously acquired either
136 * with userfaultfd_ctx_get() or userfaultfd_ctx_fdget().
137 */
138static void userfaultfd_ctx_put(struct userfaultfd_ctx *ctx)
139{
140 if (atomic_dec_and_test(&ctx->refcount)) {
141 VM_BUG_ON(spin_is_locked(&ctx->fault_pending_wqh.lock));
142 VM_BUG_ON(waitqueue_active(&ctx->fault_pending_wqh));
143 VM_BUG_ON(spin_is_locked(&ctx->fault_wqh.lock));
144 VM_BUG_ON(waitqueue_active(&ctx->fault_wqh));
145 VM_BUG_ON(spin_is_locked(&ctx->fd_wqh.lock));
146 VM_BUG_ON(waitqueue_active(&ctx->fd_wqh));
147 mmdrop(ctx->mm);
148 kmem_cache_free(userfaultfd_ctx_cachep, ctx);
149 }
150}
151
152static inline void msg_init(struct uffd_msg *msg)
153{
154 BUILD_BUG_ON(sizeof(struct uffd_msg) != 32);
155 /*
156 * Must use memset to zero out the paddings or kernel data is
157 * leaked to userland.
158 */
159 memset(msg, 0, sizeof(struct uffd_msg));
160}
161
162static inline struct uffd_msg userfault_msg(unsigned long address,
163 unsigned int flags,
164 unsigned long reason)
165{
166 struct uffd_msg msg;
167 msg_init(&msg);
168 msg.event = UFFD_EVENT_PAGEFAULT;
169 msg.arg.pagefault.address = address;
170 if (flags & FAULT_FLAG_WRITE)
171 /*
172 * If UFFD_FEATURE_PAGEFAULT_FLAG_WRITE was set in the
173 * uffdio_api.features and UFFD_PAGEFAULT_FLAG_WRITE
174 * was not set in a UFFD_EVENT_PAGEFAULT, it means it
175 * was a read fault, otherwise if set it means it's
176 * a write fault.
177 */
178 msg.arg.pagefault.flags |= UFFD_PAGEFAULT_FLAG_WRITE;
179 if (reason & VM_UFFD_WP)
180 /*
181 * If UFFD_FEATURE_PAGEFAULT_FLAG_WP was set in the
182 * uffdio_api.features and UFFD_PAGEFAULT_FLAG_WP was
183 * not set in a UFFD_EVENT_PAGEFAULT, it means it was
184 * a missing fault, otherwise if set it means it's a
185 * write protect fault.
186 */
187 msg.arg.pagefault.flags |= UFFD_PAGEFAULT_FLAG_WP;
188 return msg;
189}
190
191/*
192 * Verify the pagetables are still not ok after having reigstered into
193 * the fault_pending_wqh to avoid userland having to UFFDIO_WAKE any
194 * userfault that has already been resolved, if userfaultfd_read and
195 * UFFDIO_COPY|ZEROPAGE are being run simultaneously on two different
196 * threads.
197 */
198static inline bool userfaultfd_must_wait(struct userfaultfd_ctx *ctx,
199 unsigned long address,
200 unsigned long flags,
201 unsigned long reason)
202{
203 struct mm_struct *mm = ctx->mm;
204 pgd_t *pgd;
205 pud_t *pud;
206 pmd_t *pmd, _pmd;
207 pte_t *pte;
208 bool ret = true;
209
210 VM_BUG_ON(!rwsem_is_locked(&mm->mmap_sem));
211
212 pgd = pgd_offset(mm, address);
213 if (!pgd_present(*pgd))
214 goto out;
215 pud = pud_offset(pgd, address);
216 if (!pud_present(*pud))
217 goto out;
218 pmd = pmd_offset(pud, address);
219 /*
220 * READ_ONCE must function as a barrier with narrower scope
221 * and it must be equivalent to:
222 * _pmd = *pmd; barrier();
223 *
224 * This is to deal with the instability (as in
225 * pmd_trans_unstable) of the pmd.
226 */
227 _pmd = READ_ONCE(*pmd);
228 if (!pmd_present(_pmd))
229 goto out;
230
231 ret = false;
232 if (pmd_trans_huge(_pmd))
233 goto out;
234
235 /*
236 * the pmd is stable (as in !pmd_trans_unstable) so we can re-read it
237 * and use the standard pte_offset_map() instead of parsing _pmd.
238 */
239 pte = pte_offset_map(pmd, address);
240 /*
241 * Lockless access: we're in a wait_event so it's ok if it
242 * changes under us.
243 */
244 if (pte_none(*pte))
245 ret = true;
246 pte_unmap(pte);
247
248out:
249 return ret;
250}
251
252/*
253 * The locking rules involved in returning VM_FAULT_RETRY depending on
254 * FAULT_FLAG_ALLOW_RETRY, FAULT_FLAG_RETRY_NOWAIT and
255 * FAULT_FLAG_KILLABLE are not straightforward. The "Caution"
256 * recommendation in __lock_page_or_retry is not an understatement.
257 *
258 * If FAULT_FLAG_ALLOW_RETRY is set, the mmap_sem must be released
259 * before returning VM_FAULT_RETRY only if FAULT_FLAG_RETRY_NOWAIT is
260 * not set.
261 *
262 * If FAULT_FLAG_ALLOW_RETRY is set but FAULT_FLAG_KILLABLE is not
263 * set, VM_FAULT_RETRY can still be returned if and only if there are
264 * fatal_signal_pending()s, and the mmap_sem must be released before
265 * returning it.
266 */
267int handle_userfault(struct vm_fault *vmf, unsigned long reason)
268{
269 struct mm_struct *mm = vmf->vma->vm_mm;
270 struct userfaultfd_ctx *ctx;
271 struct userfaultfd_wait_queue uwq;
272 int ret;
273 bool must_wait, return_to_userland;
274 long blocking_state;
275
276 BUG_ON(!rwsem_is_locked(&mm->mmap_sem));
277
278 ret = VM_FAULT_SIGBUS;
279 ctx = vmf->vma->vm_userfaultfd_ctx.ctx;
280 if (!ctx)
281 goto out;
282
283 BUG_ON(ctx->mm != mm);
284
285 VM_BUG_ON(reason & ~(VM_UFFD_MISSING|VM_UFFD_WP));
286 VM_BUG_ON(!(reason & VM_UFFD_MISSING) ^ !!(reason & VM_UFFD_WP));
287
288 /*
289 * If it's already released don't get it. This avoids to loop
290 * in __get_user_pages if userfaultfd_release waits on the
291 * caller of handle_userfault to release the mmap_sem.
292 */
293 if (unlikely(ACCESS_ONCE(ctx->released)))
294 goto out;
295
296 /*
297 * We don't do userfault handling for the final child pid update.
298 */
299 if (current->flags & PF_EXITING)
300 goto out;
301
302 /*
303 * Check that we can return VM_FAULT_RETRY.
304 *
305 * NOTE: it should become possible to return VM_FAULT_RETRY
306 * even if FAULT_FLAG_TRIED is set without leading to gup()
307 * -EBUSY failures, if the userfaultfd is to be extended for
308 * VM_UFFD_WP tracking and we intend to arm the userfault
309 * without first stopping userland access to the memory. For
310 * VM_UFFD_MISSING userfaults this is enough for now.
311 */
312 if (unlikely(!(vmf->flags & FAULT_FLAG_ALLOW_RETRY))) {
313 /*
314 * Validate the invariant that nowait must allow retry
315 * to be sure not to return SIGBUS erroneously on
316 * nowait invocations.
317 */
318 BUG_ON(vmf->flags & FAULT_FLAG_RETRY_NOWAIT);
319#ifdef CONFIG_DEBUG_VM
320 if (printk_ratelimit()) {
321 printk(KERN_WARNING
322 "FAULT_FLAG_ALLOW_RETRY missing %x\n",
323 vmf->flags);
324 dump_stack();
325 }
326#endif
327 goto out;
328 }
329
330 /*
331 * Handle nowait, not much to do other than tell it to retry
332 * and wait.
333 */
334 ret = VM_FAULT_RETRY;
335 if (vmf->flags & FAULT_FLAG_RETRY_NOWAIT)
336 goto out;
337
338 /* take the reference before dropping the mmap_sem */
339 userfaultfd_ctx_get(ctx);
340
341 init_waitqueue_func_entry(&uwq.wq, userfaultfd_wake_function);
342 uwq.wq.private = current;
343 uwq.msg = userfault_msg(vmf->address, vmf->flags, reason);
344 uwq.ctx = ctx;
345 uwq.waken = false;
346
347 return_to_userland =
348 (vmf->flags & (FAULT_FLAG_USER|FAULT_FLAG_KILLABLE)) ==
349 (FAULT_FLAG_USER|FAULT_FLAG_KILLABLE);
350 blocking_state = return_to_userland ? TASK_INTERRUPTIBLE :
351 TASK_KILLABLE;
352
353 spin_lock(&ctx->fault_pending_wqh.lock);
354 /*
355 * After the __add_wait_queue the uwq is visible to userland
356 * through poll/read().
357 */
358 __add_wait_queue(&ctx->fault_pending_wqh, &uwq.wq);
359 /*
360 * The smp_mb() after __set_current_state prevents the reads
361 * following the spin_unlock to happen before the list_add in
362 * __add_wait_queue.
363 */
364 set_current_state(blocking_state);
365 spin_unlock(&ctx->fault_pending_wqh.lock);
366
367 must_wait = userfaultfd_must_wait(ctx, vmf->address, vmf->flags,
368 reason);
369 up_read(&mm->mmap_sem);
370
371 if (likely(must_wait && !ACCESS_ONCE(ctx->released) &&
372 (return_to_userland ? !signal_pending(current) :
373 !fatal_signal_pending(current)))) {
374 wake_up_poll(&ctx->fd_wqh, POLLIN);
375 schedule();
376 ret |= VM_FAULT_MAJOR;
377
378 /*
379 * False wakeups can orginate even from rwsem before
380 * up_read() however userfaults will wait either for a
381 * targeted wakeup on the specific uwq waitqueue from
382 * wake_userfault() or for signals or for uffd
383 * release.
384 */
385 while (!READ_ONCE(uwq.waken)) {
386 /*
387 * This needs the full smp_store_mb()
388 * guarantee as the state write must be
389 * visible to other CPUs before reading
390 * uwq.waken from other CPUs.
391 */
392 set_current_state(blocking_state);
393 if (READ_ONCE(uwq.waken) ||
394 READ_ONCE(ctx->released) ||
395 (return_to_userland ? signal_pending(current) :
396 fatal_signal_pending(current)))
397 break;
398 schedule();
399 }
400 }
401
402 __set_current_state(TASK_RUNNING);
403
404 if (return_to_userland) {
405 if (signal_pending(current) &&
406 !fatal_signal_pending(current)) {
407 /*
408 * If we got a SIGSTOP or SIGCONT and this is
409 * a normal userland page fault, just let
410 * userland return so the signal will be
411 * handled and gdb debugging works. The page
412 * fault code immediately after we return from
413 * this function is going to release the
414 * mmap_sem and it's not depending on it
415 * (unlike gup would if we were not to return
416 * VM_FAULT_RETRY).
417 *
418 * If a fatal signal is pending we still take
419 * the streamlined VM_FAULT_RETRY failure path
420 * and there's no need to retake the mmap_sem
421 * in such case.
422 */
423 down_read(&mm->mmap_sem);
424 ret = 0;
425 }
426 }
427
428 /*
429 * Here we race with the list_del; list_add in
430 * userfaultfd_ctx_read(), however because we don't ever run
431 * list_del_init() to refile across the two lists, the prev
432 * and next pointers will never point to self. list_add also
433 * would never let any of the two pointers to point to
434 * self. So list_empty_careful won't risk to see both pointers
435 * pointing to self at any time during the list refile. The
436 * only case where list_del_init() is called is the full
437 * removal in the wake function and there we don't re-list_add
438 * and it's fine not to block on the spinlock. The uwq on this
439 * kernel stack can be released after the list_del_init.
440 */
441 if (!list_empty_careful(&uwq.wq.task_list)) {
442 spin_lock(&ctx->fault_pending_wqh.lock);
443 /*
444 * No need of list_del_init(), the uwq on the stack
445 * will be freed shortly anyway.
446 */
447 list_del(&uwq.wq.task_list);
448 spin_unlock(&ctx->fault_pending_wqh.lock);
449 }
450
451 /*
452 * ctx may go away after this if the userfault pseudo fd is
453 * already released.
454 */
455 userfaultfd_ctx_put(ctx);
456
457out:
458 return ret;
459}
460
461static int userfaultfd_release(struct inode *inode, struct file *file)
462{
463 struct userfaultfd_ctx *ctx = file->private_data;
464 struct mm_struct *mm = ctx->mm;
465 struct vm_area_struct *vma, *prev;
466 /* len == 0 means wake all */
467 struct userfaultfd_wake_range range = { .len = 0, };
468 unsigned long new_flags;
469
470 ACCESS_ONCE(ctx->released) = true;
471
472 if (!mmget_not_zero(mm))
473 goto wakeup;
474
475 /*
476 * Flush page faults out of all CPUs. NOTE: all page faults
477 * must be retried without returning VM_FAULT_SIGBUS if
478 * userfaultfd_ctx_get() succeeds but vma->vma_userfault_ctx
479 * changes while handle_userfault released the mmap_sem. So
480 * it's critical that released is set to true (above), before
481 * taking the mmap_sem for writing.
482 */
483 down_write(&mm->mmap_sem);
484 prev = NULL;
485 for (vma = mm->mmap; vma; vma = vma->vm_next) {
486 cond_resched();
487 BUG_ON(!!vma->vm_userfaultfd_ctx.ctx ^
488 !!(vma->vm_flags & (VM_UFFD_MISSING | VM_UFFD_WP)));
489 if (vma->vm_userfaultfd_ctx.ctx != ctx) {
490 prev = vma;
491 continue;
492 }
493 new_flags = vma->vm_flags & ~(VM_UFFD_MISSING | VM_UFFD_WP);
494 prev = vma_merge(mm, prev, vma->vm_start, vma->vm_end,
495 new_flags, vma->anon_vma,
496 vma->vm_file, vma->vm_pgoff,
497 vma_policy(vma),
498 NULL_VM_UFFD_CTX);
499 if (prev)
500 vma = prev;
501 else
502 prev = vma;
503 vma->vm_flags = new_flags;
504 vma->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX;
505 }
506 up_write(&mm->mmap_sem);
507 mmput(mm);
508wakeup:
509 /*
510 * After no new page faults can wait on this fault_*wqh, flush
511 * the last page faults that may have been already waiting on
512 * the fault_*wqh.
513 */
514 spin_lock(&ctx->fault_pending_wqh.lock);
515 __wake_up_locked_key(&ctx->fault_pending_wqh, TASK_NORMAL, &range);
516 __wake_up_locked_key(&ctx->fault_wqh, TASK_NORMAL, &range);
517 spin_unlock(&ctx->fault_pending_wqh.lock);
518
519 wake_up_poll(&ctx->fd_wqh, POLLHUP);
520 userfaultfd_ctx_put(ctx);
521 return 0;
522}
523
524/* fault_pending_wqh.lock must be hold by the caller */
525static inline struct userfaultfd_wait_queue *find_userfault(
526 struct userfaultfd_ctx *ctx)
527{
528 wait_queue_t *wq;
529 struct userfaultfd_wait_queue *uwq;
530
531 VM_BUG_ON(!spin_is_locked(&ctx->fault_pending_wqh.lock));
532
533 uwq = NULL;
534 if (!waitqueue_active(&ctx->fault_pending_wqh))
535 goto out;
536 /* walk in reverse to provide FIFO behavior to read userfaults */
537 wq = list_last_entry(&ctx->fault_pending_wqh.task_list,
538 typeof(*wq), task_list);
539 uwq = container_of(wq, struct userfaultfd_wait_queue, wq);
540out:
541 return uwq;
542}
543
544static unsigned int userfaultfd_poll(struct file *file, poll_table *wait)
545{
546 struct userfaultfd_ctx *ctx = file->private_data;
547 unsigned int ret;
548
549 poll_wait(file, &ctx->fd_wqh, wait);
550
551 switch (ctx->state) {
552 case UFFD_STATE_WAIT_API:
553 return POLLERR;
554 case UFFD_STATE_RUNNING:
555 /*
556 * poll() never guarantees that read won't block.
557 * userfaults can be waken before they're read().
558 */
559 if (unlikely(!(file->f_flags & O_NONBLOCK)))
560 return POLLERR;
561 /*
562 * lockless access to see if there are pending faults
563 * __pollwait last action is the add_wait_queue but
564 * the spin_unlock would allow the waitqueue_active to
565 * pass above the actual list_add inside
566 * add_wait_queue critical section. So use a full
567 * memory barrier to serialize the list_add write of
568 * add_wait_queue() with the waitqueue_active read
569 * below.
570 */
571 ret = 0;
572 smp_mb();
573 if (waitqueue_active(&ctx->fault_pending_wqh))
574 ret = POLLIN;
575 return ret;
576 default:
577 BUG();
578 }
579}
580
581static ssize_t userfaultfd_ctx_read(struct userfaultfd_ctx *ctx, int no_wait,
582 struct uffd_msg *msg)
583{
584 ssize_t ret;
585 DECLARE_WAITQUEUE(wait, current);
586 struct userfaultfd_wait_queue *uwq;
587
588 /* always take the fd_wqh lock before the fault_pending_wqh lock */
589 spin_lock(&ctx->fd_wqh.lock);
590 __add_wait_queue(&ctx->fd_wqh, &wait);
591 for (;;) {
592 set_current_state(TASK_INTERRUPTIBLE);
593 spin_lock(&ctx->fault_pending_wqh.lock);
594 uwq = find_userfault(ctx);
595 if (uwq) {
596 /*
597 * Use a seqcount to repeat the lockless check
598 * in wake_userfault() to avoid missing
599 * wakeups because during the refile both
600 * waitqueue could become empty if this is the
601 * only userfault.
602 */
603 write_seqcount_begin(&ctx->refile_seq);
604
605 /*
606 * The fault_pending_wqh.lock prevents the uwq
607 * to disappear from under us.
608 *
609 * Refile this userfault from
610 * fault_pending_wqh to fault_wqh, it's not
611 * pending anymore after we read it.
612 *
613 * Use list_del() by hand (as
614 * userfaultfd_wake_function also uses
615 * list_del_init() by hand) to be sure nobody
616 * changes __remove_wait_queue() to use
617 * list_del_init() in turn breaking the
618 * !list_empty_careful() check in
619 * handle_userfault(). The uwq->wq.task_list
620 * must never be empty at any time during the
621 * refile, or the waitqueue could disappear
622 * from under us. The "wait_queue_head_t"
623 * parameter of __remove_wait_queue() is unused
624 * anyway.
625 */
626 list_del(&uwq->wq.task_list);
627 __add_wait_queue(&ctx->fault_wqh, &uwq->wq);
628
629 write_seqcount_end(&ctx->refile_seq);
630
631 /* careful to always initialize msg if ret == 0 */
632 *msg = uwq->msg;
633 spin_unlock(&ctx->fault_pending_wqh.lock);
634 ret = 0;
635 break;
636 }
637 spin_unlock(&ctx->fault_pending_wqh.lock);
638 if (signal_pending(current)) {
639 ret = -ERESTARTSYS;
640 break;
641 }
642 if (no_wait) {
643 ret = -EAGAIN;
644 break;
645 }
646 spin_unlock(&ctx->fd_wqh.lock);
647 schedule();
648 spin_lock(&ctx->fd_wqh.lock);
649 }
650 __remove_wait_queue(&ctx->fd_wqh, &wait);
651 __set_current_state(TASK_RUNNING);
652 spin_unlock(&ctx->fd_wqh.lock);
653
654 return ret;
655}
656
657static ssize_t userfaultfd_read(struct file *file, char __user *buf,
658 size_t count, loff_t *ppos)
659{
660 struct userfaultfd_ctx *ctx = file->private_data;
661 ssize_t _ret, ret = 0;
662 struct uffd_msg msg;
663 int no_wait = file->f_flags & O_NONBLOCK;
664
665 if (ctx->state == UFFD_STATE_WAIT_API)
666 return -EINVAL;
667
668 for (;;) {
669 if (count < sizeof(msg))
670 return ret ? ret : -EINVAL;
671 _ret = userfaultfd_ctx_read(ctx, no_wait, &msg);
672 if (_ret < 0)
673 return ret ? ret : _ret;
674 if (copy_to_user((__u64 __user *) buf, &msg, sizeof(msg)))
675 return ret ? ret : -EFAULT;
676 ret += sizeof(msg);
677 buf += sizeof(msg);
678 count -= sizeof(msg);
679 /*
680 * Allow to read more than one fault at time but only
681 * block if waiting for the very first one.
682 */
683 no_wait = O_NONBLOCK;
684 }
685}
686
687static void __wake_userfault(struct userfaultfd_ctx *ctx,
688 struct userfaultfd_wake_range *range)
689{
690 unsigned long start, end;
691
692 start = range->start;
693 end = range->start + range->len;
694
695 spin_lock(&ctx->fault_pending_wqh.lock);
696 /* wake all in the range and autoremove */
697 if (waitqueue_active(&ctx->fault_pending_wqh))
698 __wake_up_locked_key(&ctx->fault_pending_wqh, TASK_NORMAL,
699 range);
700 if (waitqueue_active(&ctx->fault_wqh))
701 __wake_up_locked_key(&ctx->fault_wqh, TASK_NORMAL, range);
702 spin_unlock(&ctx->fault_pending_wqh.lock);
703}
704
705static __always_inline void wake_userfault(struct userfaultfd_ctx *ctx,
706 struct userfaultfd_wake_range *range)
707{
708 unsigned seq;
709 bool need_wakeup;
710
711 /*
712 * To be sure waitqueue_active() is not reordered by the CPU
713 * before the pagetable update, use an explicit SMP memory
714 * barrier here. PT lock release or up_read(mmap_sem) still
715 * have release semantics that can allow the
716 * waitqueue_active() to be reordered before the pte update.
717 */
718 smp_mb();
719
720 /*
721 * Use waitqueue_active because it's very frequent to
722 * change the address space atomically even if there are no
723 * userfaults yet. So we take the spinlock only when we're
724 * sure we've userfaults to wake.
725 */
726 do {
727 seq = read_seqcount_begin(&ctx->refile_seq);
728 need_wakeup = waitqueue_active(&ctx->fault_pending_wqh) ||
729 waitqueue_active(&ctx->fault_wqh);
730 cond_resched();
731 } while (read_seqcount_retry(&ctx->refile_seq, seq));
732 if (need_wakeup)
733 __wake_userfault(ctx, range);
734}
735
736static __always_inline int validate_range(struct mm_struct *mm,
737 __u64 start, __u64 len)
738{
739 __u64 task_size = mm->task_size;
740
741 if (start & ~PAGE_MASK)
742 return -EINVAL;
743 if (len & ~PAGE_MASK)
744 return -EINVAL;
745 if (!len)
746 return -EINVAL;
747 if (start < mmap_min_addr)
748 return -EINVAL;
749 if (start >= task_size)
750 return -EINVAL;
751 if (len > task_size - start)
752 return -EINVAL;
753 return 0;
754}
755
756static int userfaultfd_register(struct userfaultfd_ctx *ctx,
757 unsigned long arg)
758{
759 struct mm_struct *mm = ctx->mm;
760 struct vm_area_struct *vma, *prev, *cur;
761 int ret;
762 struct uffdio_register uffdio_register;
763 struct uffdio_register __user *user_uffdio_register;
764 unsigned long vm_flags, new_flags;
765 bool found;
766 unsigned long start, end, vma_end;
767
768 user_uffdio_register = (struct uffdio_register __user *) arg;
769
770 ret = -EFAULT;
771 if (copy_from_user(&uffdio_register, user_uffdio_register,
772 sizeof(uffdio_register)-sizeof(__u64)))
773 goto out;
774
775 ret = -EINVAL;
776 if (!uffdio_register.mode)
777 goto out;
778 if (uffdio_register.mode & ~(UFFDIO_REGISTER_MODE_MISSING|
779 UFFDIO_REGISTER_MODE_WP))
780 goto out;
781 vm_flags = 0;
782 if (uffdio_register.mode & UFFDIO_REGISTER_MODE_MISSING)
783 vm_flags |= VM_UFFD_MISSING;
784 if (uffdio_register.mode & UFFDIO_REGISTER_MODE_WP) {
785 vm_flags |= VM_UFFD_WP;
786 /*
787 * FIXME: remove the below error constraint by
788 * implementing the wprotect tracking mode.
789 */
790 ret = -EINVAL;
791 goto out;
792 }
793
794 ret = validate_range(mm, uffdio_register.range.start,
795 uffdio_register.range.len);
796 if (ret)
797 goto out;
798
799 start = uffdio_register.range.start;
800 end = start + uffdio_register.range.len;
801
802 ret = -ENOMEM;
803 if (!mmget_not_zero(mm))
804 goto out;
805
806 down_write(&mm->mmap_sem);
807 vma = find_vma_prev(mm, start, &prev);
808 if (!vma)
809 goto out_unlock;
810
811 /* check that there's at least one vma in the range */
812 ret = -EINVAL;
813 if (vma->vm_start >= end)
814 goto out_unlock;
815
816 /*
817 * Search for not compatible vmas.
818 *
819 * FIXME: this shall be relaxed later so that it doesn't fail
820 * on tmpfs backed vmas (in addition to the current allowance
821 * on anonymous vmas).
822 */
823 found = false;
824 for (cur = vma; cur && cur->vm_start < end; cur = cur->vm_next) {
825 cond_resched();
826
827 BUG_ON(!!cur->vm_userfaultfd_ctx.ctx ^
828 !!(cur->vm_flags & (VM_UFFD_MISSING | VM_UFFD_WP)));
829
830 /* check not compatible vmas */
831 ret = -EINVAL;
832 if (cur->vm_ops)
833 goto out_unlock;
834
835 /*
836 * Check that this vma isn't already owned by a
837 * different userfaultfd. We can't allow more than one
838 * userfaultfd to own a single vma simultaneously or we
839 * wouldn't know which one to deliver the userfaults to.
840 */
841 ret = -EBUSY;
842 if (cur->vm_userfaultfd_ctx.ctx &&
843 cur->vm_userfaultfd_ctx.ctx != ctx)
844 goto out_unlock;
845
846 found = true;
847 }
848 BUG_ON(!found);
849
850 if (vma->vm_start < start)
851 prev = vma;
852
853 ret = 0;
854 do {
855 cond_resched();
856
857 BUG_ON(vma->vm_ops);
858 BUG_ON(vma->vm_userfaultfd_ctx.ctx &&
859 vma->vm_userfaultfd_ctx.ctx != ctx);
860
861 /*
862 * Nothing to do: this vma is already registered into this
863 * userfaultfd and with the right tracking mode too.
864 */
865 if (vma->vm_userfaultfd_ctx.ctx == ctx &&
866 (vma->vm_flags & vm_flags) == vm_flags)
867 goto skip;
868
869 if (vma->vm_start > start)
870 start = vma->vm_start;
871 vma_end = min(end, vma->vm_end);
872
873 new_flags = (vma->vm_flags & ~vm_flags) | vm_flags;
874 prev = vma_merge(mm, prev, start, vma_end, new_flags,
875 vma->anon_vma, vma->vm_file, vma->vm_pgoff,
876 vma_policy(vma),
877 ((struct vm_userfaultfd_ctx){ ctx }));
878 if (prev) {
879 vma = prev;
880 goto next;
881 }
882 if (vma->vm_start < start) {
883 ret = split_vma(mm, vma, start, 1);
884 if (ret)
885 break;
886 }
887 if (vma->vm_end > end) {
888 ret = split_vma(mm, vma, end, 0);
889 if (ret)
890 break;
891 }
892 next:
893 /*
894 * In the vma_merge() successful mprotect-like case 8:
895 * the next vma was merged into the current one and
896 * the current one has not been updated yet.
897 */
898 vma->vm_flags = new_flags;
899 vma->vm_userfaultfd_ctx.ctx = ctx;
900
901 skip:
902 prev = vma;
903 start = vma->vm_end;
904 vma = vma->vm_next;
905 } while (vma && vma->vm_start < end);
906out_unlock:
907 up_write(&mm->mmap_sem);
908 mmput(mm);
909 if (!ret) {
910 /*
911 * Now that we scanned all vmas we can already tell
912 * userland which ioctls methods are guaranteed to
913 * succeed on this range.
914 */
915 if (put_user(UFFD_API_RANGE_IOCTLS,
916 &user_uffdio_register->ioctls))
917 ret = -EFAULT;
918 }
919out:
920 return ret;
921}
922
923static int userfaultfd_unregister(struct userfaultfd_ctx *ctx,
924 unsigned long arg)
925{
926 struct mm_struct *mm = ctx->mm;
927 struct vm_area_struct *vma, *prev, *cur;
928 int ret;
929 struct uffdio_range uffdio_unregister;
930 unsigned long new_flags;
931 bool found;
932 unsigned long start, end, vma_end;
933 const void __user *buf = (void __user *)arg;
934
935 ret = -EFAULT;
936 if (copy_from_user(&uffdio_unregister, buf, sizeof(uffdio_unregister)))
937 goto out;
938
939 ret = validate_range(mm, uffdio_unregister.start,
940 uffdio_unregister.len);
941 if (ret)
942 goto out;
943
944 start = uffdio_unregister.start;
945 end = start + uffdio_unregister.len;
946
947 ret = -ENOMEM;
948 if (!mmget_not_zero(mm))
949 goto out;
950
951 down_write(&mm->mmap_sem);
952 vma = find_vma_prev(mm, start, &prev);
953 if (!vma)
954 goto out_unlock;
955
956 /* check that there's at least one vma in the range */
957 ret = -EINVAL;
958 if (vma->vm_start >= end)
959 goto out_unlock;
960
961 /*
962 * Search for not compatible vmas.
963 *
964 * FIXME: this shall be relaxed later so that it doesn't fail
965 * on tmpfs backed vmas (in addition to the current allowance
966 * on anonymous vmas).
967 */
968 found = false;
969 ret = -EINVAL;
970 for (cur = vma; cur && cur->vm_start < end; cur = cur->vm_next) {
971 cond_resched();
972
973 BUG_ON(!!cur->vm_userfaultfd_ctx.ctx ^
974 !!(cur->vm_flags & (VM_UFFD_MISSING | VM_UFFD_WP)));
975
976 /*
977 * Check not compatible vmas, not strictly required
978 * here as not compatible vmas cannot have an
979 * userfaultfd_ctx registered on them, but this
980 * provides for more strict behavior to notice
981 * unregistration errors.
982 */
983 if (cur->vm_ops)
984 goto out_unlock;
985
986 found = true;
987 }
988 BUG_ON(!found);
989
990 if (vma->vm_start < start)
991 prev = vma;
992
993 ret = 0;
994 do {
995 cond_resched();
996
997 BUG_ON(vma->vm_ops);
998
999 /*
1000 * Nothing to do: this vma is already registered into this
1001 * userfaultfd and with the right tracking mode too.
1002 */
1003 if (!vma->vm_userfaultfd_ctx.ctx)
1004 goto skip;
1005
1006 if (vma->vm_start > start)
1007 start = vma->vm_start;
1008 vma_end = min(end, vma->vm_end);
1009
1010 new_flags = vma->vm_flags & ~(VM_UFFD_MISSING | VM_UFFD_WP);
1011 prev = vma_merge(mm, prev, start, vma_end, new_flags,
1012 vma->anon_vma, vma->vm_file, vma->vm_pgoff,
1013 vma_policy(vma),
1014 NULL_VM_UFFD_CTX);
1015 if (prev) {
1016 vma = prev;
1017 goto next;
1018 }
1019 if (vma->vm_start < start) {
1020 ret = split_vma(mm, vma, start, 1);
1021 if (ret)
1022 break;
1023 }
1024 if (vma->vm_end > end) {
1025 ret = split_vma(mm, vma, end, 0);
1026 if (ret)
1027 break;
1028 }
1029 next:
1030 /*
1031 * In the vma_merge() successful mprotect-like case 8:
1032 * the next vma was merged into the current one and
1033 * the current one has not been updated yet.
1034 */
1035 vma->vm_flags = new_flags;
1036 vma->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX;
1037
1038 skip:
1039 prev = vma;
1040 start = vma->vm_end;
1041 vma = vma->vm_next;
1042 } while (vma && vma->vm_start < end);
1043out_unlock:
1044 up_write(&mm->mmap_sem);
1045 mmput(mm);
1046out:
1047 return ret;
1048}
1049
1050/*
1051 * userfaultfd_wake may be used in combination with the
1052 * UFFDIO_*_MODE_DONTWAKE to wakeup userfaults in batches.
1053 */
1054static int userfaultfd_wake(struct userfaultfd_ctx *ctx,
1055 unsigned long arg)
1056{
1057 int ret;
1058 struct uffdio_range uffdio_wake;
1059 struct userfaultfd_wake_range range;
1060 const void __user *buf = (void __user *)arg;
1061
1062 ret = -EFAULT;
1063 if (copy_from_user(&uffdio_wake, buf, sizeof(uffdio_wake)))
1064 goto out;
1065
1066 ret = validate_range(ctx->mm, uffdio_wake.start, uffdio_wake.len);
1067 if (ret)
1068 goto out;
1069
1070 range.start = uffdio_wake.start;
1071 range.len = uffdio_wake.len;
1072
1073 /*
1074 * len == 0 means wake all and we don't want to wake all here,
1075 * so check it again to be sure.
1076 */
1077 VM_BUG_ON(!range.len);
1078
1079 wake_userfault(ctx, &range);
1080 ret = 0;
1081
1082out:
1083 return ret;
1084}
1085
1086static int userfaultfd_copy(struct userfaultfd_ctx *ctx,
1087 unsigned long arg)
1088{
1089 __s64 ret;
1090 struct uffdio_copy uffdio_copy;
1091 struct uffdio_copy __user *user_uffdio_copy;
1092 struct userfaultfd_wake_range range;
1093
1094 user_uffdio_copy = (struct uffdio_copy __user *) arg;
1095
1096 ret = -EFAULT;
1097 if (copy_from_user(&uffdio_copy, user_uffdio_copy,
1098 /* don't copy "copy" last field */
1099 sizeof(uffdio_copy)-sizeof(__s64)))
1100 goto out;
1101
1102 ret = validate_range(ctx->mm, uffdio_copy.dst, uffdio_copy.len);
1103 if (ret)
1104 goto out;
1105 /*
1106 * double check for wraparound just in case. copy_from_user()
1107 * will later check uffdio_copy.src + uffdio_copy.len to fit
1108 * in the userland range.
1109 */
1110 ret = -EINVAL;
1111 if (uffdio_copy.src + uffdio_copy.len <= uffdio_copy.src)
1112 goto out;
1113 if (uffdio_copy.mode & ~UFFDIO_COPY_MODE_DONTWAKE)
1114 goto out;
1115 if (mmget_not_zero(ctx->mm)) {
1116 ret = mcopy_atomic(ctx->mm, uffdio_copy.dst, uffdio_copy.src,
1117 uffdio_copy.len);
1118 mmput(ctx->mm);
1119 }
1120 if (unlikely(put_user(ret, &user_uffdio_copy->copy)))
1121 return -EFAULT;
1122 if (ret < 0)
1123 goto out;
1124 BUG_ON(!ret);
1125 /* len == 0 would wake all */
1126 range.len = ret;
1127 if (!(uffdio_copy.mode & UFFDIO_COPY_MODE_DONTWAKE)) {
1128 range.start = uffdio_copy.dst;
1129 wake_userfault(ctx, &range);
1130 }
1131 ret = range.len == uffdio_copy.len ? 0 : -EAGAIN;
1132out:
1133 return ret;
1134}
1135
1136static int userfaultfd_zeropage(struct userfaultfd_ctx *ctx,
1137 unsigned long arg)
1138{
1139 __s64 ret;
1140 struct uffdio_zeropage uffdio_zeropage;
1141 struct uffdio_zeropage __user *user_uffdio_zeropage;
1142 struct userfaultfd_wake_range range;
1143
1144 user_uffdio_zeropage = (struct uffdio_zeropage __user *) arg;
1145
1146 ret = -EFAULT;
1147 if (copy_from_user(&uffdio_zeropage, user_uffdio_zeropage,
1148 /* don't copy "zeropage" last field */
1149 sizeof(uffdio_zeropage)-sizeof(__s64)))
1150 goto out;
1151
1152 ret = validate_range(ctx->mm, uffdio_zeropage.range.start,
1153 uffdio_zeropage.range.len);
1154 if (ret)
1155 goto out;
1156 ret = -EINVAL;
1157 if (uffdio_zeropage.mode & ~UFFDIO_ZEROPAGE_MODE_DONTWAKE)
1158 goto out;
1159
1160 if (mmget_not_zero(ctx->mm)) {
1161 ret = mfill_zeropage(ctx->mm, uffdio_zeropage.range.start,
1162 uffdio_zeropage.range.len);
1163 mmput(ctx->mm);
1164 }
1165 if (unlikely(put_user(ret, &user_uffdio_zeropage->zeropage)))
1166 return -EFAULT;
1167 if (ret < 0)
1168 goto out;
1169 /* len == 0 would wake all */
1170 BUG_ON(!ret);
1171 range.len = ret;
1172 if (!(uffdio_zeropage.mode & UFFDIO_ZEROPAGE_MODE_DONTWAKE)) {
1173 range.start = uffdio_zeropage.range.start;
1174 wake_userfault(ctx, &range);
1175 }
1176 ret = range.len == uffdio_zeropage.range.len ? 0 : -EAGAIN;
1177out:
1178 return ret;
1179}
1180
1181/*
1182 * userland asks for a certain API version and we return which bits
1183 * and ioctl commands are implemented in this kernel for such API
1184 * version or -EINVAL if unknown.
1185 */
1186static int userfaultfd_api(struct userfaultfd_ctx *ctx,
1187 unsigned long arg)
1188{
1189 struct uffdio_api uffdio_api;
1190 void __user *buf = (void __user *)arg;
1191 int ret;
1192
1193 ret = -EINVAL;
1194 if (ctx->state != UFFD_STATE_WAIT_API)
1195 goto out;
1196 ret = -EFAULT;
1197 if (copy_from_user(&uffdio_api, buf, sizeof(uffdio_api)))
1198 goto out;
1199 if (uffdio_api.api != UFFD_API || uffdio_api.features) {
1200 memset(&uffdio_api, 0, sizeof(uffdio_api));
1201 if (copy_to_user(buf, &uffdio_api, sizeof(uffdio_api)))
1202 goto out;
1203 ret = -EINVAL;
1204 goto out;
1205 }
1206 uffdio_api.features = UFFD_API_FEATURES;
1207 uffdio_api.ioctls = UFFD_API_IOCTLS;
1208 ret = -EFAULT;
1209 if (copy_to_user(buf, &uffdio_api, sizeof(uffdio_api)))
1210 goto out;
1211 ctx->state = UFFD_STATE_RUNNING;
1212 ret = 0;
1213out:
1214 return ret;
1215}
1216
1217static long userfaultfd_ioctl(struct file *file, unsigned cmd,
1218 unsigned long arg)
1219{
1220 int ret = -EINVAL;
1221 struct userfaultfd_ctx *ctx = file->private_data;
1222
1223 if (cmd != UFFDIO_API && ctx->state == UFFD_STATE_WAIT_API)
1224 return -EINVAL;
1225
1226 switch(cmd) {
1227 case UFFDIO_API:
1228 ret = userfaultfd_api(ctx, arg);
1229 break;
1230 case UFFDIO_REGISTER:
1231 ret = userfaultfd_register(ctx, arg);
1232 break;
1233 case UFFDIO_UNREGISTER:
1234 ret = userfaultfd_unregister(ctx, arg);
1235 break;
1236 case UFFDIO_WAKE:
1237 ret = userfaultfd_wake(ctx, arg);
1238 break;
1239 case UFFDIO_COPY:
1240 ret = userfaultfd_copy(ctx, arg);
1241 break;
1242 case UFFDIO_ZEROPAGE:
1243 ret = userfaultfd_zeropage(ctx, arg);
1244 break;
1245 }
1246 return ret;
1247}
1248
1249#ifdef CONFIG_PROC_FS
1250static void userfaultfd_show_fdinfo(struct seq_file *m, struct file *f)
1251{
1252 struct userfaultfd_ctx *ctx = f->private_data;
1253 wait_queue_t *wq;
1254 struct userfaultfd_wait_queue *uwq;
1255 unsigned long pending = 0, total = 0;
1256
1257 spin_lock(&ctx->fault_pending_wqh.lock);
1258 list_for_each_entry(wq, &ctx->fault_pending_wqh.task_list, task_list) {
1259 uwq = container_of(wq, struct userfaultfd_wait_queue, wq);
1260 pending++;
1261 total++;
1262 }
1263 list_for_each_entry(wq, &ctx->fault_wqh.task_list, task_list) {
1264 uwq = container_of(wq, struct userfaultfd_wait_queue, wq);
1265 total++;
1266 }
1267 spin_unlock(&ctx->fault_pending_wqh.lock);
1268
1269 /*
1270 * If more protocols will be added, there will be all shown
1271 * separated by a space. Like this:
1272 * protocols: aa:... bb:...
1273 */
1274 seq_printf(m, "pending:\t%lu\ntotal:\t%lu\nAPI:\t%Lx:%x:%Lx\n",
1275 pending, total, UFFD_API, UFFD_API_FEATURES,
1276 UFFD_API_IOCTLS|UFFD_API_RANGE_IOCTLS);
1277}
1278#endif
1279
1280static const struct file_operations userfaultfd_fops = {
1281#ifdef CONFIG_PROC_FS
1282 .show_fdinfo = userfaultfd_show_fdinfo,
1283#endif
1284 .release = userfaultfd_release,
1285 .poll = userfaultfd_poll,
1286 .read = userfaultfd_read,
1287 .unlocked_ioctl = userfaultfd_ioctl,
1288 .compat_ioctl = userfaultfd_ioctl,
1289 .llseek = noop_llseek,
1290};
1291
1292static void init_once_userfaultfd_ctx(void *mem)
1293{
1294 struct userfaultfd_ctx *ctx = (struct userfaultfd_ctx *) mem;
1295
1296 init_waitqueue_head(&ctx->fault_pending_wqh);
1297 init_waitqueue_head(&ctx->fault_wqh);
1298 init_waitqueue_head(&ctx->fd_wqh);
1299 seqcount_init(&ctx->refile_seq);
1300}
1301
1302/**
1303 * userfaultfd_file_create - Creates an userfaultfd file pointer.
1304 * @flags: Flags for the userfaultfd file.
1305 *
1306 * This function creates an userfaultfd file pointer, w/out installing
1307 * it into the fd table. This is useful when the userfaultfd file is
1308 * used during the initialization of data structures that require
1309 * extra setup after the userfaultfd creation. So the userfaultfd
1310 * creation is split into the file pointer creation phase, and the
1311 * file descriptor installation phase. In this way races with
1312 * userspace closing the newly installed file descriptor can be
1313 * avoided. Returns an userfaultfd file pointer, or a proper error
1314 * pointer.
1315 */
1316static struct file *userfaultfd_file_create(int flags)
1317{
1318 struct file *file;
1319 struct userfaultfd_ctx *ctx;
1320
1321 BUG_ON(!current->mm);
1322
1323 /* Check the UFFD_* constants for consistency. */
1324 BUILD_BUG_ON(UFFD_CLOEXEC != O_CLOEXEC);
1325 BUILD_BUG_ON(UFFD_NONBLOCK != O_NONBLOCK);
1326
1327 file = ERR_PTR(-EINVAL);
1328 if (flags & ~UFFD_SHARED_FCNTL_FLAGS)
1329 goto out;
1330
1331 file = ERR_PTR(-ENOMEM);
1332 ctx = kmem_cache_alloc(userfaultfd_ctx_cachep, GFP_KERNEL);
1333 if (!ctx)
1334 goto out;
1335
1336 atomic_set(&ctx->refcount, 1);
1337 ctx->flags = flags;
1338 ctx->state = UFFD_STATE_WAIT_API;
1339 ctx->released = false;
1340 ctx->mm = current->mm;
1341 /* prevent the mm struct to be freed */
1342 atomic_inc(&ctx->mm->mm_count);
1343
1344 file = anon_inode_getfile("[userfaultfd]", &userfaultfd_fops, ctx,
1345 O_RDWR | (flags & UFFD_SHARED_FCNTL_FLAGS));
1346 if (IS_ERR(file)) {
1347 mmdrop(ctx->mm);
1348 kmem_cache_free(userfaultfd_ctx_cachep, ctx);
1349 }
1350out:
1351 return file;
1352}
1353
1354SYSCALL_DEFINE1(userfaultfd, int, flags)
1355{
1356 int fd, error;
1357 struct file *file;
1358
1359 error = get_unused_fd_flags(flags & UFFD_SHARED_FCNTL_FLAGS);
1360 if (error < 0)
1361 return error;
1362 fd = error;
1363
1364 file = userfaultfd_file_create(flags);
1365 if (IS_ERR(file)) {
1366 error = PTR_ERR(file);
1367 goto err_put_unused_fd;
1368 }
1369 fd_install(fd, file);
1370
1371 return fd;
1372
1373err_put_unused_fd:
1374 put_unused_fd(fd);
1375
1376 return error;
1377}
1378
1379static int __init userfaultfd_init(void)
1380{
1381 userfaultfd_ctx_cachep = kmem_cache_create("userfaultfd_ctx_cache",
1382 sizeof(struct userfaultfd_ctx),
1383 0,
1384 SLAB_HWCACHE_ALIGN|SLAB_PANIC,
1385 init_once_userfaultfd_ctx);
1386 return 0;
1387}
1388__initcall(userfaultfd_init);
1// SPDX-License-Identifier: GPL-2.0-only
2/*
3 * fs/userfaultfd.c
4 *
5 * Copyright (C) 2007 Davide Libenzi <davidel@xmailserver.org>
6 * Copyright (C) 2008-2009 Red Hat, Inc.
7 * Copyright (C) 2015 Red Hat, Inc.
8 *
9 * Some part derived from fs/eventfd.c (anon inode setup) and
10 * mm/ksm.c (mm hashing).
11 */
12
13#include <linux/list.h>
14#include <linux/hashtable.h>
15#include <linux/sched/signal.h>
16#include <linux/sched/mm.h>
17#include <linux/mm.h>
18#include <linux/mm_inline.h>
19#include <linux/mmu_notifier.h>
20#include <linux/poll.h>
21#include <linux/slab.h>
22#include <linux/seq_file.h>
23#include <linux/file.h>
24#include <linux/bug.h>
25#include <linux/anon_inodes.h>
26#include <linux/syscalls.h>
27#include <linux/userfaultfd_k.h>
28#include <linux/mempolicy.h>
29#include <linux/ioctl.h>
30#include <linux/security.h>
31#include <linux/hugetlb.h>
32#include <linux/swapops.h>
33#include <linux/miscdevice.h>
34
35static int sysctl_unprivileged_userfaultfd __read_mostly;
36
37#ifdef CONFIG_SYSCTL
38static struct ctl_table vm_userfaultfd_table[] = {
39 {
40 .procname = "unprivileged_userfaultfd",
41 .data = &sysctl_unprivileged_userfaultfd,
42 .maxlen = sizeof(sysctl_unprivileged_userfaultfd),
43 .mode = 0644,
44 .proc_handler = proc_dointvec_minmax,
45 .extra1 = SYSCTL_ZERO,
46 .extra2 = SYSCTL_ONE,
47 },
48};
49#endif
50
51static struct kmem_cache *userfaultfd_ctx_cachep __ro_after_init;
52
53/*
54 * Start with fault_pending_wqh and fault_wqh so they're more likely
55 * to be in the same cacheline.
56 *
57 * Locking order:
58 * fd_wqh.lock
59 * fault_pending_wqh.lock
60 * fault_wqh.lock
61 * event_wqh.lock
62 *
63 * To avoid deadlocks, IRQs must be disabled when taking any of the above locks,
64 * since fd_wqh.lock is taken by aio_poll() while it's holding a lock that's
65 * also taken in IRQ context.
66 */
67struct userfaultfd_ctx {
68 /* waitqueue head for the pending (i.e. not read) userfaults */
69 wait_queue_head_t fault_pending_wqh;
70 /* waitqueue head for the userfaults */
71 wait_queue_head_t fault_wqh;
72 /* waitqueue head for the pseudo fd to wakeup poll/read */
73 wait_queue_head_t fd_wqh;
74 /* waitqueue head for events */
75 wait_queue_head_t event_wqh;
76 /* a refile sequence protected by fault_pending_wqh lock */
77 seqcount_spinlock_t refile_seq;
78 /* pseudo fd refcounting */
79 refcount_t refcount;
80 /* userfaultfd syscall flags */
81 unsigned int flags;
82 /* features requested from the userspace */
83 unsigned int features;
84 /* released */
85 bool released;
86 /* memory mappings are changing because of non-cooperative event */
87 atomic_t mmap_changing;
88 /* mm with one ore more vmas attached to this userfaultfd_ctx */
89 struct mm_struct *mm;
90};
91
92struct userfaultfd_fork_ctx {
93 struct userfaultfd_ctx *orig;
94 struct userfaultfd_ctx *new;
95 struct list_head list;
96};
97
98struct userfaultfd_unmap_ctx {
99 struct userfaultfd_ctx *ctx;
100 unsigned long start;
101 unsigned long end;
102 struct list_head list;
103};
104
105struct userfaultfd_wait_queue {
106 struct uffd_msg msg;
107 wait_queue_entry_t wq;
108 struct userfaultfd_ctx *ctx;
109 bool waken;
110};
111
112struct userfaultfd_wake_range {
113 unsigned long start;
114 unsigned long len;
115};
116
117/* internal indication that UFFD_API ioctl was successfully executed */
118#define UFFD_FEATURE_INITIALIZED (1u << 31)
119
120static bool userfaultfd_is_initialized(struct userfaultfd_ctx *ctx)
121{
122 return ctx->features & UFFD_FEATURE_INITIALIZED;
123}
124
125static bool userfaultfd_wp_async_ctx(struct userfaultfd_ctx *ctx)
126{
127 return ctx && (ctx->features & UFFD_FEATURE_WP_ASYNC);
128}
129
130/*
131 * Whether WP_UNPOPULATED is enabled on the uffd context. It is only
132 * meaningful when userfaultfd_wp()==true on the vma and when it's
133 * anonymous.
134 */
135bool userfaultfd_wp_unpopulated(struct vm_area_struct *vma)
136{
137 struct userfaultfd_ctx *ctx = vma->vm_userfaultfd_ctx.ctx;
138
139 if (!ctx)
140 return false;
141
142 return ctx->features & UFFD_FEATURE_WP_UNPOPULATED;
143}
144
145static void userfaultfd_set_vm_flags(struct vm_area_struct *vma,
146 vm_flags_t flags)
147{
148 const bool uffd_wp_changed = (vma->vm_flags ^ flags) & VM_UFFD_WP;
149
150 vm_flags_reset(vma, flags);
151 /*
152 * For shared mappings, we want to enable writenotify while
153 * userfaultfd-wp is enabled (see vma_wants_writenotify()). We'll simply
154 * recalculate vma->vm_page_prot whenever userfaultfd-wp changes.
155 */
156 if ((vma->vm_flags & VM_SHARED) && uffd_wp_changed)
157 vma_set_page_prot(vma);
158}
159
160static int userfaultfd_wake_function(wait_queue_entry_t *wq, unsigned mode,
161 int wake_flags, void *key)
162{
163 struct userfaultfd_wake_range *range = key;
164 int ret;
165 struct userfaultfd_wait_queue *uwq;
166 unsigned long start, len;
167
168 uwq = container_of(wq, struct userfaultfd_wait_queue, wq);
169 ret = 0;
170 /* len == 0 means wake all */
171 start = range->start;
172 len = range->len;
173 if (len && (start > uwq->msg.arg.pagefault.address ||
174 start + len <= uwq->msg.arg.pagefault.address))
175 goto out;
176 WRITE_ONCE(uwq->waken, true);
177 /*
178 * The Program-Order guarantees provided by the scheduler
179 * ensure uwq->waken is visible before the task is woken.
180 */
181 ret = wake_up_state(wq->private, mode);
182 if (ret) {
183 /*
184 * Wake only once, autoremove behavior.
185 *
186 * After the effect of list_del_init is visible to the other
187 * CPUs, the waitqueue may disappear from under us, see the
188 * !list_empty_careful() in handle_userfault().
189 *
190 * try_to_wake_up() has an implicit smp_mb(), and the
191 * wq->private is read before calling the extern function
192 * "wake_up_state" (which in turns calls try_to_wake_up).
193 */
194 list_del_init(&wq->entry);
195 }
196out:
197 return ret;
198}
199
200/**
201 * userfaultfd_ctx_get - Acquires a reference to the internal userfaultfd
202 * context.
203 * @ctx: [in] Pointer to the userfaultfd context.
204 */
205static void userfaultfd_ctx_get(struct userfaultfd_ctx *ctx)
206{
207 refcount_inc(&ctx->refcount);
208}
209
210/**
211 * userfaultfd_ctx_put - Releases a reference to the internal userfaultfd
212 * context.
213 * @ctx: [in] Pointer to userfaultfd context.
214 *
215 * The userfaultfd context reference must have been previously acquired either
216 * with userfaultfd_ctx_get() or userfaultfd_ctx_fdget().
217 */
218static void userfaultfd_ctx_put(struct userfaultfd_ctx *ctx)
219{
220 if (refcount_dec_and_test(&ctx->refcount)) {
221 VM_BUG_ON(spin_is_locked(&ctx->fault_pending_wqh.lock));
222 VM_BUG_ON(waitqueue_active(&ctx->fault_pending_wqh));
223 VM_BUG_ON(spin_is_locked(&ctx->fault_wqh.lock));
224 VM_BUG_ON(waitqueue_active(&ctx->fault_wqh));
225 VM_BUG_ON(spin_is_locked(&ctx->event_wqh.lock));
226 VM_BUG_ON(waitqueue_active(&ctx->event_wqh));
227 VM_BUG_ON(spin_is_locked(&ctx->fd_wqh.lock));
228 VM_BUG_ON(waitqueue_active(&ctx->fd_wqh));
229 mmdrop(ctx->mm);
230 kmem_cache_free(userfaultfd_ctx_cachep, ctx);
231 }
232}
233
234static inline void msg_init(struct uffd_msg *msg)
235{
236 BUILD_BUG_ON(sizeof(struct uffd_msg) != 32);
237 /*
238 * Must use memset to zero out the paddings or kernel data is
239 * leaked to userland.
240 */
241 memset(msg, 0, sizeof(struct uffd_msg));
242}
243
244static inline struct uffd_msg userfault_msg(unsigned long address,
245 unsigned long real_address,
246 unsigned int flags,
247 unsigned long reason,
248 unsigned int features)
249{
250 struct uffd_msg msg;
251
252 msg_init(&msg);
253 msg.event = UFFD_EVENT_PAGEFAULT;
254
255 msg.arg.pagefault.address = (features & UFFD_FEATURE_EXACT_ADDRESS) ?
256 real_address : address;
257
258 /*
259 * These flags indicate why the userfault occurred:
260 * - UFFD_PAGEFAULT_FLAG_WP indicates a write protect fault.
261 * - UFFD_PAGEFAULT_FLAG_MINOR indicates a minor fault.
262 * - Neither of these flags being set indicates a MISSING fault.
263 *
264 * Separately, UFFD_PAGEFAULT_FLAG_WRITE indicates it was a write
265 * fault. Otherwise, it was a read fault.
266 */
267 if (flags & FAULT_FLAG_WRITE)
268 msg.arg.pagefault.flags |= UFFD_PAGEFAULT_FLAG_WRITE;
269 if (reason & VM_UFFD_WP)
270 msg.arg.pagefault.flags |= UFFD_PAGEFAULT_FLAG_WP;
271 if (reason & VM_UFFD_MINOR)
272 msg.arg.pagefault.flags |= UFFD_PAGEFAULT_FLAG_MINOR;
273 if (features & UFFD_FEATURE_THREAD_ID)
274 msg.arg.pagefault.feat.ptid = task_pid_vnr(current);
275 return msg;
276}
277
278#ifdef CONFIG_HUGETLB_PAGE
279/*
280 * Same functionality as userfaultfd_must_wait below with modifications for
281 * hugepmd ranges.
282 */
283static inline bool userfaultfd_huge_must_wait(struct userfaultfd_ctx *ctx,
284 struct vm_fault *vmf,
285 unsigned long reason)
286{
287 struct vm_area_struct *vma = vmf->vma;
288 pte_t *ptep, pte;
289 bool ret = true;
290
291 assert_fault_locked(vmf);
292
293 ptep = hugetlb_walk(vma, vmf->address, vma_mmu_pagesize(vma));
294 if (!ptep)
295 goto out;
296
297 ret = false;
298 pte = huge_ptep_get(ptep);
299
300 /*
301 * Lockless access: we're in a wait_event so it's ok if it
302 * changes under us. PTE markers should be handled the same as none
303 * ptes here.
304 */
305 if (huge_pte_none_mostly(pte))
306 ret = true;
307 if (!huge_pte_write(pte) && (reason & VM_UFFD_WP))
308 ret = true;
309out:
310 return ret;
311}
312#else
313static inline bool userfaultfd_huge_must_wait(struct userfaultfd_ctx *ctx,
314 struct vm_fault *vmf,
315 unsigned long reason)
316{
317 return false; /* should never get here */
318}
319#endif /* CONFIG_HUGETLB_PAGE */
320
321/*
322 * Verify the pagetables are still not ok after having reigstered into
323 * the fault_pending_wqh to avoid userland having to UFFDIO_WAKE any
324 * userfault that has already been resolved, if userfaultfd_read and
325 * UFFDIO_COPY|ZEROPAGE are being run simultaneously on two different
326 * threads.
327 */
328static inline bool userfaultfd_must_wait(struct userfaultfd_ctx *ctx,
329 struct vm_fault *vmf,
330 unsigned long reason)
331{
332 struct mm_struct *mm = ctx->mm;
333 unsigned long address = vmf->address;
334 pgd_t *pgd;
335 p4d_t *p4d;
336 pud_t *pud;
337 pmd_t *pmd, _pmd;
338 pte_t *pte;
339 pte_t ptent;
340 bool ret = true;
341
342 assert_fault_locked(vmf);
343
344 pgd = pgd_offset(mm, address);
345 if (!pgd_present(*pgd))
346 goto out;
347 p4d = p4d_offset(pgd, address);
348 if (!p4d_present(*p4d))
349 goto out;
350 pud = pud_offset(p4d, address);
351 if (!pud_present(*pud))
352 goto out;
353 pmd = pmd_offset(pud, address);
354again:
355 _pmd = pmdp_get_lockless(pmd);
356 if (pmd_none(_pmd))
357 goto out;
358
359 ret = false;
360 if (!pmd_present(_pmd) || pmd_devmap(_pmd))
361 goto out;
362
363 if (pmd_trans_huge(_pmd)) {
364 if (!pmd_write(_pmd) && (reason & VM_UFFD_WP))
365 ret = true;
366 goto out;
367 }
368
369 pte = pte_offset_map(pmd, address);
370 if (!pte) {
371 ret = true;
372 goto again;
373 }
374 /*
375 * Lockless access: we're in a wait_event so it's ok if it
376 * changes under us. PTE markers should be handled the same as none
377 * ptes here.
378 */
379 ptent = ptep_get(pte);
380 if (pte_none_mostly(ptent))
381 ret = true;
382 if (!pte_write(ptent) && (reason & VM_UFFD_WP))
383 ret = true;
384 pte_unmap(pte);
385
386out:
387 return ret;
388}
389
390static inline unsigned int userfaultfd_get_blocking_state(unsigned int flags)
391{
392 if (flags & FAULT_FLAG_INTERRUPTIBLE)
393 return TASK_INTERRUPTIBLE;
394
395 if (flags & FAULT_FLAG_KILLABLE)
396 return TASK_KILLABLE;
397
398 return TASK_UNINTERRUPTIBLE;
399}
400
401/*
402 * The locking rules involved in returning VM_FAULT_RETRY depending on
403 * FAULT_FLAG_ALLOW_RETRY, FAULT_FLAG_RETRY_NOWAIT and
404 * FAULT_FLAG_KILLABLE are not straightforward. The "Caution"
405 * recommendation in __lock_page_or_retry is not an understatement.
406 *
407 * If FAULT_FLAG_ALLOW_RETRY is set, the mmap_lock must be released
408 * before returning VM_FAULT_RETRY only if FAULT_FLAG_RETRY_NOWAIT is
409 * not set.
410 *
411 * If FAULT_FLAG_ALLOW_RETRY is set but FAULT_FLAG_KILLABLE is not
412 * set, VM_FAULT_RETRY can still be returned if and only if there are
413 * fatal_signal_pending()s, and the mmap_lock must be released before
414 * returning it.
415 */
416vm_fault_t handle_userfault(struct vm_fault *vmf, unsigned long reason)
417{
418 struct vm_area_struct *vma = vmf->vma;
419 struct mm_struct *mm = vma->vm_mm;
420 struct userfaultfd_ctx *ctx;
421 struct userfaultfd_wait_queue uwq;
422 vm_fault_t ret = VM_FAULT_SIGBUS;
423 bool must_wait;
424 unsigned int blocking_state;
425
426 /*
427 * We don't do userfault handling for the final child pid update.
428 *
429 * We also don't do userfault handling during
430 * coredumping. hugetlbfs has the special
431 * hugetlb_follow_page_mask() to skip missing pages in the
432 * FOLL_DUMP case, anon memory also checks for FOLL_DUMP with
433 * the no_page_table() helper in follow_page_mask(), but the
434 * shmem_vm_ops->fault method is invoked even during
435 * coredumping and it ends up here.
436 */
437 if (current->flags & (PF_EXITING|PF_DUMPCORE))
438 goto out;
439
440 assert_fault_locked(vmf);
441
442 ctx = vma->vm_userfaultfd_ctx.ctx;
443 if (!ctx)
444 goto out;
445
446 BUG_ON(ctx->mm != mm);
447
448 /* Any unrecognized flag is a bug. */
449 VM_BUG_ON(reason & ~__VM_UFFD_FLAGS);
450 /* 0 or > 1 flags set is a bug; we expect exactly 1. */
451 VM_BUG_ON(!reason || (reason & (reason - 1)));
452
453 if (ctx->features & UFFD_FEATURE_SIGBUS)
454 goto out;
455 if (!(vmf->flags & FAULT_FLAG_USER) && (ctx->flags & UFFD_USER_MODE_ONLY))
456 goto out;
457
458 /*
459 * If it's already released don't get it. This avoids to loop
460 * in __get_user_pages if userfaultfd_release waits on the
461 * caller of handle_userfault to release the mmap_lock.
462 */
463 if (unlikely(READ_ONCE(ctx->released))) {
464 /*
465 * Don't return VM_FAULT_SIGBUS in this case, so a non
466 * cooperative manager can close the uffd after the
467 * last UFFDIO_COPY, without risking to trigger an
468 * involuntary SIGBUS if the process was starting the
469 * userfaultfd while the userfaultfd was still armed
470 * (but after the last UFFDIO_COPY). If the uffd
471 * wasn't already closed when the userfault reached
472 * this point, that would normally be solved by
473 * userfaultfd_must_wait returning 'false'.
474 *
475 * If we were to return VM_FAULT_SIGBUS here, the non
476 * cooperative manager would be instead forced to
477 * always call UFFDIO_UNREGISTER before it can safely
478 * close the uffd.
479 */
480 ret = VM_FAULT_NOPAGE;
481 goto out;
482 }
483
484 /*
485 * Check that we can return VM_FAULT_RETRY.
486 *
487 * NOTE: it should become possible to return VM_FAULT_RETRY
488 * even if FAULT_FLAG_TRIED is set without leading to gup()
489 * -EBUSY failures, if the userfaultfd is to be extended for
490 * VM_UFFD_WP tracking and we intend to arm the userfault
491 * without first stopping userland access to the memory. For
492 * VM_UFFD_MISSING userfaults this is enough for now.
493 */
494 if (unlikely(!(vmf->flags & FAULT_FLAG_ALLOW_RETRY))) {
495 /*
496 * Validate the invariant that nowait must allow retry
497 * to be sure not to return SIGBUS erroneously on
498 * nowait invocations.
499 */
500 BUG_ON(vmf->flags & FAULT_FLAG_RETRY_NOWAIT);
501#ifdef CONFIG_DEBUG_VM
502 if (printk_ratelimit()) {
503 printk(KERN_WARNING
504 "FAULT_FLAG_ALLOW_RETRY missing %x\n",
505 vmf->flags);
506 dump_stack();
507 }
508#endif
509 goto out;
510 }
511
512 /*
513 * Handle nowait, not much to do other than tell it to retry
514 * and wait.
515 */
516 ret = VM_FAULT_RETRY;
517 if (vmf->flags & FAULT_FLAG_RETRY_NOWAIT)
518 goto out;
519
520 /* take the reference before dropping the mmap_lock */
521 userfaultfd_ctx_get(ctx);
522
523 init_waitqueue_func_entry(&uwq.wq, userfaultfd_wake_function);
524 uwq.wq.private = current;
525 uwq.msg = userfault_msg(vmf->address, vmf->real_address, vmf->flags,
526 reason, ctx->features);
527 uwq.ctx = ctx;
528 uwq.waken = false;
529
530 blocking_state = userfaultfd_get_blocking_state(vmf->flags);
531
532 /*
533 * Take the vma lock now, in order to safely call
534 * userfaultfd_huge_must_wait() later. Since acquiring the
535 * (sleepable) vma lock can modify the current task state, that
536 * must be before explicitly calling set_current_state().
537 */
538 if (is_vm_hugetlb_page(vma))
539 hugetlb_vma_lock_read(vma);
540
541 spin_lock_irq(&ctx->fault_pending_wqh.lock);
542 /*
543 * After the __add_wait_queue the uwq is visible to userland
544 * through poll/read().
545 */
546 __add_wait_queue(&ctx->fault_pending_wqh, &uwq.wq);
547 /*
548 * The smp_mb() after __set_current_state prevents the reads
549 * following the spin_unlock to happen before the list_add in
550 * __add_wait_queue.
551 */
552 set_current_state(blocking_state);
553 spin_unlock_irq(&ctx->fault_pending_wqh.lock);
554
555 if (!is_vm_hugetlb_page(vma))
556 must_wait = userfaultfd_must_wait(ctx, vmf, reason);
557 else
558 must_wait = userfaultfd_huge_must_wait(ctx, vmf, reason);
559 if (is_vm_hugetlb_page(vma))
560 hugetlb_vma_unlock_read(vma);
561 release_fault_lock(vmf);
562
563 if (likely(must_wait && !READ_ONCE(ctx->released))) {
564 wake_up_poll(&ctx->fd_wqh, EPOLLIN);
565 schedule();
566 }
567
568 __set_current_state(TASK_RUNNING);
569
570 /*
571 * Here we race with the list_del; list_add in
572 * userfaultfd_ctx_read(), however because we don't ever run
573 * list_del_init() to refile across the two lists, the prev
574 * and next pointers will never point to self. list_add also
575 * would never let any of the two pointers to point to
576 * self. So list_empty_careful won't risk to see both pointers
577 * pointing to self at any time during the list refile. The
578 * only case where list_del_init() is called is the full
579 * removal in the wake function and there we don't re-list_add
580 * and it's fine not to block on the spinlock. The uwq on this
581 * kernel stack can be released after the list_del_init.
582 */
583 if (!list_empty_careful(&uwq.wq.entry)) {
584 spin_lock_irq(&ctx->fault_pending_wqh.lock);
585 /*
586 * No need of list_del_init(), the uwq on the stack
587 * will be freed shortly anyway.
588 */
589 list_del(&uwq.wq.entry);
590 spin_unlock_irq(&ctx->fault_pending_wqh.lock);
591 }
592
593 /*
594 * ctx may go away after this if the userfault pseudo fd is
595 * already released.
596 */
597 userfaultfd_ctx_put(ctx);
598
599out:
600 return ret;
601}
602
603static void userfaultfd_event_wait_completion(struct userfaultfd_ctx *ctx,
604 struct userfaultfd_wait_queue *ewq)
605{
606 struct userfaultfd_ctx *release_new_ctx;
607
608 if (WARN_ON_ONCE(current->flags & PF_EXITING))
609 goto out;
610
611 ewq->ctx = ctx;
612 init_waitqueue_entry(&ewq->wq, current);
613 release_new_ctx = NULL;
614
615 spin_lock_irq(&ctx->event_wqh.lock);
616 /*
617 * After the __add_wait_queue the uwq is visible to userland
618 * through poll/read().
619 */
620 __add_wait_queue(&ctx->event_wqh, &ewq->wq);
621 for (;;) {
622 set_current_state(TASK_KILLABLE);
623 if (ewq->msg.event == 0)
624 break;
625 if (READ_ONCE(ctx->released) ||
626 fatal_signal_pending(current)) {
627 /*
628 * &ewq->wq may be queued in fork_event, but
629 * __remove_wait_queue ignores the head
630 * parameter. It would be a problem if it
631 * didn't.
632 */
633 __remove_wait_queue(&ctx->event_wqh, &ewq->wq);
634 if (ewq->msg.event == UFFD_EVENT_FORK) {
635 struct userfaultfd_ctx *new;
636
637 new = (struct userfaultfd_ctx *)
638 (unsigned long)
639 ewq->msg.arg.reserved.reserved1;
640 release_new_ctx = new;
641 }
642 break;
643 }
644
645 spin_unlock_irq(&ctx->event_wqh.lock);
646
647 wake_up_poll(&ctx->fd_wqh, EPOLLIN);
648 schedule();
649
650 spin_lock_irq(&ctx->event_wqh.lock);
651 }
652 __set_current_state(TASK_RUNNING);
653 spin_unlock_irq(&ctx->event_wqh.lock);
654
655 if (release_new_ctx) {
656 struct vm_area_struct *vma;
657 struct mm_struct *mm = release_new_ctx->mm;
658 VMA_ITERATOR(vmi, mm, 0);
659
660 /* the various vma->vm_userfaultfd_ctx still points to it */
661 mmap_write_lock(mm);
662 for_each_vma(vmi, vma) {
663 if (vma->vm_userfaultfd_ctx.ctx == release_new_ctx) {
664 vma_start_write(vma);
665 vma->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX;
666 userfaultfd_set_vm_flags(vma,
667 vma->vm_flags & ~__VM_UFFD_FLAGS);
668 }
669 }
670 mmap_write_unlock(mm);
671
672 userfaultfd_ctx_put(release_new_ctx);
673 }
674
675 /*
676 * ctx may go away after this if the userfault pseudo fd is
677 * already released.
678 */
679out:
680 atomic_dec(&ctx->mmap_changing);
681 VM_BUG_ON(atomic_read(&ctx->mmap_changing) < 0);
682 userfaultfd_ctx_put(ctx);
683}
684
685static void userfaultfd_event_complete(struct userfaultfd_ctx *ctx,
686 struct userfaultfd_wait_queue *ewq)
687{
688 ewq->msg.event = 0;
689 wake_up_locked(&ctx->event_wqh);
690 __remove_wait_queue(&ctx->event_wqh, &ewq->wq);
691}
692
693int dup_userfaultfd(struct vm_area_struct *vma, struct list_head *fcs)
694{
695 struct userfaultfd_ctx *ctx = NULL, *octx;
696 struct userfaultfd_fork_ctx *fctx;
697
698 octx = vma->vm_userfaultfd_ctx.ctx;
699 if (!octx || !(octx->features & UFFD_FEATURE_EVENT_FORK)) {
700 vma_start_write(vma);
701 vma->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX;
702 userfaultfd_set_vm_flags(vma, vma->vm_flags & ~__VM_UFFD_FLAGS);
703 return 0;
704 }
705
706 list_for_each_entry(fctx, fcs, list)
707 if (fctx->orig == octx) {
708 ctx = fctx->new;
709 break;
710 }
711
712 if (!ctx) {
713 fctx = kmalloc(sizeof(*fctx), GFP_KERNEL);
714 if (!fctx)
715 return -ENOMEM;
716
717 ctx = kmem_cache_alloc(userfaultfd_ctx_cachep, GFP_KERNEL);
718 if (!ctx) {
719 kfree(fctx);
720 return -ENOMEM;
721 }
722
723 refcount_set(&ctx->refcount, 1);
724 ctx->flags = octx->flags;
725 ctx->features = octx->features;
726 ctx->released = false;
727 atomic_set(&ctx->mmap_changing, 0);
728 ctx->mm = vma->vm_mm;
729 mmgrab(ctx->mm);
730
731 userfaultfd_ctx_get(octx);
732 atomic_inc(&octx->mmap_changing);
733 fctx->orig = octx;
734 fctx->new = ctx;
735 list_add_tail(&fctx->list, fcs);
736 }
737
738 vma->vm_userfaultfd_ctx.ctx = ctx;
739 return 0;
740}
741
742static void dup_fctx(struct userfaultfd_fork_ctx *fctx)
743{
744 struct userfaultfd_ctx *ctx = fctx->orig;
745 struct userfaultfd_wait_queue ewq;
746
747 msg_init(&ewq.msg);
748
749 ewq.msg.event = UFFD_EVENT_FORK;
750 ewq.msg.arg.reserved.reserved1 = (unsigned long)fctx->new;
751
752 userfaultfd_event_wait_completion(ctx, &ewq);
753}
754
755void dup_userfaultfd_complete(struct list_head *fcs)
756{
757 struct userfaultfd_fork_ctx *fctx, *n;
758
759 list_for_each_entry_safe(fctx, n, fcs, list) {
760 dup_fctx(fctx);
761 list_del(&fctx->list);
762 kfree(fctx);
763 }
764}
765
766void mremap_userfaultfd_prep(struct vm_area_struct *vma,
767 struct vm_userfaultfd_ctx *vm_ctx)
768{
769 struct userfaultfd_ctx *ctx;
770
771 ctx = vma->vm_userfaultfd_ctx.ctx;
772
773 if (!ctx)
774 return;
775
776 if (ctx->features & UFFD_FEATURE_EVENT_REMAP) {
777 vm_ctx->ctx = ctx;
778 userfaultfd_ctx_get(ctx);
779 atomic_inc(&ctx->mmap_changing);
780 } else {
781 /* Drop uffd context if remap feature not enabled */
782 vma_start_write(vma);
783 vma->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX;
784 userfaultfd_set_vm_flags(vma, vma->vm_flags & ~__VM_UFFD_FLAGS);
785 }
786}
787
788void mremap_userfaultfd_complete(struct vm_userfaultfd_ctx *vm_ctx,
789 unsigned long from, unsigned long to,
790 unsigned long len)
791{
792 struct userfaultfd_ctx *ctx = vm_ctx->ctx;
793 struct userfaultfd_wait_queue ewq;
794
795 if (!ctx)
796 return;
797
798 if (to & ~PAGE_MASK) {
799 userfaultfd_ctx_put(ctx);
800 return;
801 }
802
803 msg_init(&ewq.msg);
804
805 ewq.msg.event = UFFD_EVENT_REMAP;
806 ewq.msg.arg.remap.from = from;
807 ewq.msg.arg.remap.to = to;
808 ewq.msg.arg.remap.len = len;
809
810 userfaultfd_event_wait_completion(ctx, &ewq);
811}
812
813bool userfaultfd_remove(struct vm_area_struct *vma,
814 unsigned long start, unsigned long end)
815{
816 struct mm_struct *mm = vma->vm_mm;
817 struct userfaultfd_ctx *ctx;
818 struct userfaultfd_wait_queue ewq;
819
820 ctx = vma->vm_userfaultfd_ctx.ctx;
821 if (!ctx || !(ctx->features & UFFD_FEATURE_EVENT_REMOVE))
822 return true;
823
824 userfaultfd_ctx_get(ctx);
825 atomic_inc(&ctx->mmap_changing);
826 mmap_read_unlock(mm);
827
828 msg_init(&ewq.msg);
829
830 ewq.msg.event = UFFD_EVENT_REMOVE;
831 ewq.msg.arg.remove.start = start;
832 ewq.msg.arg.remove.end = end;
833
834 userfaultfd_event_wait_completion(ctx, &ewq);
835
836 return false;
837}
838
839static bool has_unmap_ctx(struct userfaultfd_ctx *ctx, struct list_head *unmaps,
840 unsigned long start, unsigned long end)
841{
842 struct userfaultfd_unmap_ctx *unmap_ctx;
843
844 list_for_each_entry(unmap_ctx, unmaps, list)
845 if (unmap_ctx->ctx == ctx && unmap_ctx->start == start &&
846 unmap_ctx->end == end)
847 return true;
848
849 return false;
850}
851
852int userfaultfd_unmap_prep(struct vm_area_struct *vma, unsigned long start,
853 unsigned long end, struct list_head *unmaps)
854{
855 struct userfaultfd_unmap_ctx *unmap_ctx;
856 struct userfaultfd_ctx *ctx = vma->vm_userfaultfd_ctx.ctx;
857
858 if (!ctx || !(ctx->features & UFFD_FEATURE_EVENT_UNMAP) ||
859 has_unmap_ctx(ctx, unmaps, start, end))
860 return 0;
861
862 unmap_ctx = kzalloc(sizeof(*unmap_ctx), GFP_KERNEL);
863 if (!unmap_ctx)
864 return -ENOMEM;
865
866 userfaultfd_ctx_get(ctx);
867 atomic_inc(&ctx->mmap_changing);
868 unmap_ctx->ctx = ctx;
869 unmap_ctx->start = start;
870 unmap_ctx->end = end;
871 list_add_tail(&unmap_ctx->list, unmaps);
872
873 return 0;
874}
875
876void userfaultfd_unmap_complete(struct mm_struct *mm, struct list_head *uf)
877{
878 struct userfaultfd_unmap_ctx *ctx, *n;
879 struct userfaultfd_wait_queue ewq;
880
881 list_for_each_entry_safe(ctx, n, uf, list) {
882 msg_init(&ewq.msg);
883
884 ewq.msg.event = UFFD_EVENT_UNMAP;
885 ewq.msg.arg.remove.start = ctx->start;
886 ewq.msg.arg.remove.end = ctx->end;
887
888 userfaultfd_event_wait_completion(ctx->ctx, &ewq);
889
890 list_del(&ctx->list);
891 kfree(ctx);
892 }
893}
894
895static int userfaultfd_release(struct inode *inode, struct file *file)
896{
897 struct userfaultfd_ctx *ctx = file->private_data;
898 struct mm_struct *mm = ctx->mm;
899 struct vm_area_struct *vma, *prev;
900 /* len == 0 means wake all */
901 struct userfaultfd_wake_range range = { .len = 0, };
902 unsigned long new_flags;
903 VMA_ITERATOR(vmi, mm, 0);
904
905 WRITE_ONCE(ctx->released, true);
906
907 if (!mmget_not_zero(mm))
908 goto wakeup;
909
910 /*
911 * Flush page faults out of all CPUs. NOTE: all page faults
912 * must be retried without returning VM_FAULT_SIGBUS if
913 * userfaultfd_ctx_get() succeeds but vma->vma_userfault_ctx
914 * changes while handle_userfault released the mmap_lock. So
915 * it's critical that released is set to true (above), before
916 * taking the mmap_lock for writing.
917 */
918 mmap_write_lock(mm);
919 prev = NULL;
920 for_each_vma(vmi, vma) {
921 cond_resched();
922 BUG_ON(!!vma->vm_userfaultfd_ctx.ctx ^
923 !!(vma->vm_flags & __VM_UFFD_FLAGS));
924 if (vma->vm_userfaultfd_ctx.ctx != ctx) {
925 prev = vma;
926 continue;
927 }
928 new_flags = vma->vm_flags & ~__VM_UFFD_FLAGS;
929 vma = vma_modify_flags_uffd(&vmi, prev, vma, vma->vm_start,
930 vma->vm_end, new_flags,
931 NULL_VM_UFFD_CTX);
932
933 vma_start_write(vma);
934 userfaultfd_set_vm_flags(vma, new_flags);
935 vma->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX;
936
937 prev = vma;
938 }
939 mmap_write_unlock(mm);
940 mmput(mm);
941wakeup:
942 /*
943 * After no new page faults can wait on this fault_*wqh, flush
944 * the last page faults that may have been already waiting on
945 * the fault_*wqh.
946 */
947 spin_lock_irq(&ctx->fault_pending_wqh.lock);
948 __wake_up_locked_key(&ctx->fault_pending_wqh, TASK_NORMAL, &range);
949 __wake_up(&ctx->fault_wqh, TASK_NORMAL, 1, &range);
950 spin_unlock_irq(&ctx->fault_pending_wqh.lock);
951
952 /* Flush pending events that may still wait on event_wqh */
953 wake_up_all(&ctx->event_wqh);
954
955 wake_up_poll(&ctx->fd_wqh, EPOLLHUP);
956 userfaultfd_ctx_put(ctx);
957 return 0;
958}
959
960/* fault_pending_wqh.lock must be hold by the caller */
961static inline struct userfaultfd_wait_queue *find_userfault_in(
962 wait_queue_head_t *wqh)
963{
964 wait_queue_entry_t *wq;
965 struct userfaultfd_wait_queue *uwq;
966
967 lockdep_assert_held(&wqh->lock);
968
969 uwq = NULL;
970 if (!waitqueue_active(wqh))
971 goto out;
972 /* walk in reverse to provide FIFO behavior to read userfaults */
973 wq = list_last_entry(&wqh->head, typeof(*wq), entry);
974 uwq = container_of(wq, struct userfaultfd_wait_queue, wq);
975out:
976 return uwq;
977}
978
979static inline struct userfaultfd_wait_queue *find_userfault(
980 struct userfaultfd_ctx *ctx)
981{
982 return find_userfault_in(&ctx->fault_pending_wqh);
983}
984
985static inline struct userfaultfd_wait_queue *find_userfault_evt(
986 struct userfaultfd_ctx *ctx)
987{
988 return find_userfault_in(&ctx->event_wqh);
989}
990
991static __poll_t userfaultfd_poll(struct file *file, poll_table *wait)
992{
993 struct userfaultfd_ctx *ctx = file->private_data;
994 __poll_t ret;
995
996 poll_wait(file, &ctx->fd_wqh, wait);
997
998 if (!userfaultfd_is_initialized(ctx))
999 return EPOLLERR;
1000
1001 /*
1002 * poll() never guarantees that read won't block.
1003 * userfaults can be waken before they're read().
1004 */
1005 if (unlikely(!(file->f_flags & O_NONBLOCK)))
1006 return EPOLLERR;
1007 /*
1008 * lockless access to see if there are pending faults
1009 * __pollwait last action is the add_wait_queue but
1010 * the spin_unlock would allow the waitqueue_active to
1011 * pass above the actual list_add inside
1012 * add_wait_queue critical section. So use a full
1013 * memory barrier to serialize the list_add write of
1014 * add_wait_queue() with the waitqueue_active read
1015 * below.
1016 */
1017 ret = 0;
1018 smp_mb();
1019 if (waitqueue_active(&ctx->fault_pending_wqh))
1020 ret = EPOLLIN;
1021 else if (waitqueue_active(&ctx->event_wqh))
1022 ret = EPOLLIN;
1023
1024 return ret;
1025}
1026
1027static const struct file_operations userfaultfd_fops;
1028
1029static int resolve_userfault_fork(struct userfaultfd_ctx *new,
1030 struct inode *inode,
1031 struct uffd_msg *msg)
1032{
1033 int fd;
1034
1035 fd = anon_inode_create_getfd("[userfaultfd]", &userfaultfd_fops, new,
1036 O_RDONLY | (new->flags & UFFD_SHARED_FCNTL_FLAGS), inode);
1037 if (fd < 0)
1038 return fd;
1039
1040 msg->arg.reserved.reserved1 = 0;
1041 msg->arg.fork.ufd = fd;
1042 return 0;
1043}
1044
1045static ssize_t userfaultfd_ctx_read(struct userfaultfd_ctx *ctx, int no_wait,
1046 struct uffd_msg *msg, struct inode *inode)
1047{
1048 ssize_t ret;
1049 DECLARE_WAITQUEUE(wait, current);
1050 struct userfaultfd_wait_queue *uwq;
1051 /*
1052 * Handling fork event requires sleeping operations, so
1053 * we drop the event_wqh lock, then do these ops, then
1054 * lock it back and wake up the waiter. While the lock is
1055 * dropped the ewq may go away so we keep track of it
1056 * carefully.
1057 */
1058 LIST_HEAD(fork_event);
1059 struct userfaultfd_ctx *fork_nctx = NULL;
1060
1061 /* always take the fd_wqh lock before the fault_pending_wqh lock */
1062 spin_lock_irq(&ctx->fd_wqh.lock);
1063 __add_wait_queue(&ctx->fd_wqh, &wait);
1064 for (;;) {
1065 set_current_state(TASK_INTERRUPTIBLE);
1066 spin_lock(&ctx->fault_pending_wqh.lock);
1067 uwq = find_userfault(ctx);
1068 if (uwq) {
1069 /*
1070 * Use a seqcount to repeat the lockless check
1071 * in wake_userfault() to avoid missing
1072 * wakeups because during the refile both
1073 * waitqueue could become empty if this is the
1074 * only userfault.
1075 */
1076 write_seqcount_begin(&ctx->refile_seq);
1077
1078 /*
1079 * The fault_pending_wqh.lock prevents the uwq
1080 * to disappear from under us.
1081 *
1082 * Refile this userfault from
1083 * fault_pending_wqh to fault_wqh, it's not
1084 * pending anymore after we read it.
1085 *
1086 * Use list_del() by hand (as
1087 * userfaultfd_wake_function also uses
1088 * list_del_init() by hand) to be sure nobody
1089 * changes __remove_wait_queue() to use
1090 * list_del_init() in turn breaking the
1091 * !list_empty_careful() check in
1092 * handle_userfault(). The uwq->wq.head list
1093 * must never be empty at any time during the
1094 * refile, or the waitqueue could disappear
1095 * from under us. The "wait_queue_head_t"
1096 * parameter of __remove_wait_queue() is unused
1097 * anyway.
1098 */
1099 list_del(&uwq->wq.entry);
1100 add_wait_queue(&ctx->fault_wqh, &uwq->wq);
1101
1102 write_seqcount_end(&ctx->refile_seq);
1103
1104 /* careful to always initialize msg if ret == 0 */
1105 *msg = uwq->msg;
1106 spin_unlock(&ctx->fault_pending_wqh.lock);
1107 ret = 0;
1108 break;
1109 }
1110 spin_unlock(&ctx->fault_pending_wqh.lock);
1111
1112 spin_lock(&ctx->event_wqh.lock);
1113 uwq = find_userfault_evt(ctx);
1114 if (uwq) {
1115 *msg = uwq->msg;
1116
1117 if (uwq->msg.event == UFFD_EVENT_FORK) {
1118 fork_nctx = (struct userfaultfd_ctx *)
1119 (unsigned long)
1120 uwq->msg.arg.reserved.reserved1;
1121 list_move(&uwq->wq.entry, &fork_event);
1122 /*
1123 * fork_nctx can be freed as soon as
1124 * we drop the lock, unless we take a
1125 * reference on it.
1126 */
1127 userfaultfd_ctx_get(fork_nctx);
1128 spin_unlock(&ctx->event_wqh.lock);
1129 ret = 0;
1130 break;
1131 }
1132
1133 userfaultfd_event_complete(ctx, uwq);
1134 spin_unlock(&ctx->event_wqh.lock);
1135 ret = 0;
1136 break;
1137 }
1138 spin_unlock(&ctx->event_wqh.lock);
1139
1140 if (signal_pending(current)) {
1141 ret = -ERESTARTSYS;
1142 break;
1143 }
1144 if (no_wait) {
1145 ret = -EAGAIN;
1146 break;
1147 }
1148 spin_unlock_irq(&ctx->fd_wqh.lock);
1149 schedule();
1150 spin_lock_irq(&ctx->fd_wqh.lock);
1151 }
1152 __remove_wait_queue(&ctx->fd_wqh, &wait);
1153 __set_current_state(TASK_RUNNING);
1154 spin_unlock_irq(&ctx->fd_wqh.lock);
1155
1156 if (!ret && msg->event == UFFD_EVENT_FORK) {
1157 ret = resolve_userfault_fork(fork_nctx, inode, msg);
1158 spin_lock_irq(&ctx->event_wqh.lock);
1159 if (!list_empty(&fork_event)) {
1160 /*
1161 * The fork thread didn't abort, so we can
1162 * drop the temporary refcount.
1163 */
1164 userfaultfd_ctx_put(fork_nctx);
1165
1166 uwq = list_first_entry(&fork_event,
1167 typeof(*uwq),
1168 wq.entry);
1169 /*
1170 * If fork_event list wasn't empty and in turn
1171 * the event wasn't already released by fork
1172 * (the event is allocated on fork kernel
1173 * stack), put the event back to its place in
1174 * the event_wq. fork_event head will be freed
1175 * as soon as we return so the event cannot
1176 * stay queued there no matter the current
1177 * "ret" value.
1178 */
1179 list_del(&uwq->wq.entry);
1180 __add_wait_queue(&ctx->event_wqh, &uwq->wq);
1181
1182 /*
1183 * Leave the event in the waitqueue and report
1184 * error to userland if we failed to resolve
1185 * the userfault fork.
1186 */
1187 if (likely(!ret))
1188 userfaultfd_event_complete(ctx, uwq);
1189 } else {
1190 /*
1191 * Here the fork thread aborted and the
1192 * refcount from the fork thread on fork_nctx
1193 * has already been released. We still hold
1194 * the reference we took before releasing the
1195 * lock above. If resolve_userfault_fork
1196 * failed we've to drop it because the
1197 * fork_nctx has to be freed in such case. If
1198 * it succeeded we'll hold it because the new
1199 * uffd references it.
1200 */
1201 if (ret)
1202 userfaultfd_ctx_put(fork_nctx);
1203 }
1204 spin_unlock_irq(&ctx->event_wqh.lock);
1205 }
1206
1207 return ret;
1208}
1209
1210static ssize_t userfaultfd_read(struct file *file, char __user *buf,
1211 size_t count, loff_t *ppos)
1212{
1213 struct userfaultfd_ctx *ctx = file->private_data;
1214 ssize_t _ret, ret = 0;
1215 struct uffd_msg msg;
1216 int no_wait = file->f_flags & O_NONBLOCK;
1217 struct inode *inode = file_inode(file);
1218
1219 if (!userfaultfd_is_initialized(ctx))
1220 return -EINVAL;
1221
1222 for (;;) {
1223 if (count < sizeof(msg))
1224 return ret ? ret : -EINVAL;
1225 _ret = userfaultfd_ctx_read(ctx, no_wait, &msg, inode);
1226 if (_ret < 0)
1227 return ret ? ret : _ret;
1228 if (copy_to_user((__u64 __user *) buf, &msg, sizeof(msg)))
1229 return ret ? ret : -EFAULT;
1230 ret += sizeof(msg);
1231 buf += sizeof(msg);
1232 count -= sizeof(msg);
1233 /*
1234 * Allow to read more than one fault at time but only
1235 * block if waiting for the very first one.
1236 */
1237 no_wait = O_NONBLOCK;
1238 }
1239}
1240
1241static void __wake_userfault(struct userfaultfd_ctx *ctx,
1242 struct userfaultfd_wake_range *range)
1243{
1244 spin_lock_irq(&ctx->fault_pending_wqh.lock);
1245 /* wake all in the range and autoremove */
1246 if (waitqueue_active(&ctx->fault_pending_wqh))
1247 __wake_up_locked_key(&ctx->fault_pending_wqh, TASK_NORMAL,
1248 range);
1249 if (waitqueue_active(&ctx->fault_wqh))
1250 __wake_up(&ctx->fault_wqh, TASK_NORMAL, 1, range);
1251 spin_unlock_irq(&ctx->fault_pending_wqh.lock);
1252}
1253
1254static __always_inline void wake_userfault(struct userfaultfd_ctx *ctx,
1255 struct userfaultfd_wake_range *range)
1256{
1257 unsigned seq;
1258 bool need_wakeup;
1259
1260 /*
1261 * To be sure waitqueue_active() is not reordered by the CPU
1262 * before the pagetable update, use an explicit SMP memory
1263 * barrier here. PT lock release or mmap_read_unlock(mm) still
1264 * have release semantics that can allow the
1265 * waitqueue_active() to be reordered before the pte update.
1266 */
1267 smp_mb();
1268
1269 /*
1270 * Use waitqueue_active because it's very frequent to
1271 * change the address space atomically even if there are no
1272 * userfaults yet. So we take the spinlock only when we're
1273 * sure we've userfaults to wake.
1274 */
1275 do {
1276 seq = read_seqcount_begin(&ctx->refile_seq);
1277 need_wakeup = waitqueue_active(&ctx->fault_pending_wqh) ||
1278 waitqueue_active(&ctx->fault_wqh);
1279 cond_resched();
1280 } while (read_seqcount_retry(&ctx->refile_seq, seq));
1281 if (need_wakeup)
1282 __wake_userfault(ctx, range);
1283}
1284
1285static __always_inline int validate_unaligned_range(
1286 struct mm_struct *mm, __u64 start, __u64 len)
1287{
1288 __u64 task_size = mm->task_size;
1289
1290 if (len & ~PAGE_MASK)
1291 return -EINVAL;
1292 if (!len)
1293 return -EINVAL;
1294 if (start < mmap_min_addr)
1295 return -EINVAL;
1296 if (start >= task_size)
1297 return -EINVAL;
1298 if (len > task_size - start)
1299 return -EINVAL;
1300 if (start + len <= start)
1301 return -EINVAL;
1302 return 0;
1303}
1304
1305static __always_inline int validate_range(struct mm_struct *mm,
1306 __u64 start, __u64 len)
1307{
1308 if (start & ~PAGE_MASK)
1309 return -EINVAL;
1310
1311 return validate_unaligned_range(mm, start, len);
1312}
1313
1314static int userfaultfd_register(struct userfaultfd_ctx *ctx,
1315 unsigned long arg)
1316{
1317 struct mm_struct *mm = ctx->mm;
1318 struct vm_area_struct *vma, *prev, *cur;
1319 int ret;
1320 struct uffdio_register uffdio_register;
1321 struct uffdio_register __user *user_uffdio_register;
1322 unsigned long vm_flags, new_flags;
1323 bool found;
1324 bool basic_ioctls;
1325 unsigned long start, end, vma_end;
1326 struct vma_iterator vmi;
1327 bool wp_async = userfaultfd_wp_async_ctx(ctx);
1328
1329 user_uffdio_register = (struct uffdio_register __user *) arg;
1330
1331 ret = -EFAULT;
1332 if (copy_from_user(&uffdio_register, user_uffdio_register,
1333 sizeof(uffdio_register)-sizeof(__u64)))
1334 goto out;
1335
1336 ret = -EINVAL;
1337 if (!uffdio_register.mode)
1338 goto out;
1339 if (uffdio_register.mode & ~UFFD_API_REGISTER_MODES)
1340 goto out;
1341 vm_flags = 0;
1342 if (uffdio_register.mode & UFFDIO_REGISTER_MODE_MISSING)
1343 vm_flags |= VM_UFFD_MISSING;
1344 if (uffdio_register.mode & UFFDIO_REGISTER_MODE_WP) {
1345#ifndef CONFIG_HAVE_ARCH_USERFAULTFD_WP
1346 goto out;
1347#endif
1348 vm_flags |= VM_UFFD_WP;
1349 }
1350 if (uffdio_register.mode & UFFDIO_REGISTER_MODE_MINOR) {
1351#ifndef CONFIG_HAVE_ARCH_USERFAULTFD_MINOR
1352 goto out;
1353#endif
1354 vm_flags |= VM_UFFD_MINOR;
1355 }
1356
1357 ret = validate_range(mm, uffdio_register.range.start,
1358 uffdio_register.range.len);
1359 if (ret)
1360 goto out;
1361
1362 start = uffdio_register.range.start;
1363 end = start + uffdio_register.range.len;
1364
1365 ret = -ENOMEM;
1366 if (!mmget_not_zero(mm))
1367 goto out;
1368
1369 ret = -EINVAL;
1370 mmap_write_lock(mm);
1371 vma_iter_init(&vmi, mm, start);
1372 vma = vma_find(&vmi, end);
1373 if (!vma)
1374 goto out_unlock;
1375
1376 /*
1377 * If the first vma contains huge pages, make sure start address
1378 * is aligned to huge page size.
1379 */
1380 if (is_vm_hugetlb_page(vma)) {
1381 unsigned long vma_hpagesize = vma_kernel_pagesize(vma);
1382
1383 if (start & (vma_hpagesize - 1))
1384 goto out_unlock;
1385 }
1386
1387 /*
1388 * Search for not compatible vmas.
1389 */
1390 found = false;
1391 basic_ioctls = false;
1392 cur = vma;
1393 do {
1394 cond_resched();
1395
1396 BUG_ON(!!cur->vm_userfaultfd_ctx.ctx ^
1397 !!(cur->vm_flags & __VM_UFFD_FLAGS));
1398
1399 /* check not compatible vmas */
1400 ret = -EINVAL;
1401 if (!vma_can_userfault(cur, vm_flags, wp_async))
1402 goto out_unlock;
1403
1404 /*
1405 * UFFDIO_COPY will fill file holes even without
1406 * PROT_WRITE. This check enforces that if this is a
1407 * MAP_SHARED, the process has write permission to the backing
1408 * file. If VM_MAYWRITE is set it also enforces that on a
1409 * MAP_SHARED vma: there is no F_WRITE_SEAL and no further
1410 * F_WRITE_SEAL can be taken until the vma is destroyed.
1411 */
1412 ret = -EPERM;
1413 if (unlikely(!(cur->vm_flags & VM_MAYWRITE)))
1414 goto out_unlock;
1415
1416 /*
1417 * If this vma contains ending address, and huge pages
1418 * check alignment.
1419 */
1420 if (is_vm_hugetlb_page(cur) && end <= cur->vm_end &&
1421 end > cur->vm_start) {
1422 unsigned long vma_hpagesize = vma_kernel_pagesize(cur);
1423
1424 ret = -EINVAL;
1425
1426 if (end & (vma_hpagesize - 1))
1427 goto out_unlock;
1428 }
1429 if ((vm_flags & VM_UFFD_WP) && !(cur->vm_flags & VM_MAYWRITE))
1430 goto out_unlock;
1431
1432 /*
1433 * Check that this vma isn't already owned by a
1434 * different userfaultfd. We can't allow more than one
1435 * userfaultfd to own a single vma simultaneously or we
1436 * wouldn't know which one to deliver the userfaults to.
1437 */
1438 ret = -EBUSY;
1439 if (cur->vm_userfaultfd_ctx.ctx &&
1440 cur->vm_userfaultfd_ctx.ctx != ctx)
1441 goto out_unlock;
1442
1443 /*
1444 * Note vmas containing huge pages
1445 */
1446 if (is_vm_hugetlb_page(cur))
1447 basic_ioctls = true;
1448
1449 found = true;
1450 } for_each_vma_range(vmi, cur, end);
1451 BUG_ON(!found);
1452
1453 vma_iter_set(&vmi, start);
1454 prev = vma_prev(&vmi);
1455 if (vma->vm_start < start)
1456 prev = vma;
1457
1458 ret = 0;
1459 for_each_vma_range(vmi, vma, end) {
1460 cond_resched();
1461
1462 BUG_ON(!vma_can_userfault(vma, vm_flags, wp_async));
1463 BUG_ON(vma->vm_userfaultfd_ctx.ctx &&
1464 vma->vm_userfaultfd_ctx.ctx != ctx);
1465 WARN_ON(!(vma->vm_flags & VM_MAYWRITE));
1466
1467 /*
1468 * Nothing to do: this vma is already registered into this
1469 * userfaultfd and with the right tracking mode too.
1470 */
1471 if (vma->vm_userfaultfd_ctx.ctx == ctx &&
1472 (vma->vm_flags & vm_flags) == vm_flags)
1473 goto skip;
1474
1475 if (vma->vm_start > start)
1476 start = vma->vm_start;
1477 vma_end = min(end, vma->vm_end);
1478
1479 new_flags = (vma->vm_flags & ~__VM_UFFD_FLAGS) | vm_flags;
1480 vma = vma_modify_flags_uffd(&vmi, prev, vma, start, vma_end,
1481 new_flags,
1482 (struct vm_userfaultfd_ctx){ctx});
1483 if (IS_ERR(vma)) {
1484 ret = PTR_ERR(vma);
1485 break;
1486 }
1487
1488 /*
1489 * In the vma_merge() successful mprotect-like case 8:
1490 * the next vma was merged into the current one and
1491 * the current one has not been updated yet.
1492 */
1493 vma_start_write(vma);
1494 userfaultfd_set_vm_flags(vma, new_flags);
1495 vma->vm_userfaultfd_ctx.ctx = ctx;
1496
1497 if (is_vm_hugetlb_page(vma) && uffd_disable_huge_pmd_share(vma))
1498 hugetlb_unshare_all_pmds(vma);
1499
1500 skip:
1501 prev = vma;
1502 start = vma->vm_end;
1503 }
1504
1505out_unlock:
1506 mmap_write_unlock(mm);
1507 mmput(mm);
1508 if (!ret) {
1509 __u64 ioctls_out;
1510
1511 ioctls_out = basic_ioctls ? UFFD_API_RANGE_IOCTLS_BASIC :
1512 UFFD_API_RANGE_IOCTLS;
1513
1514 /*
1515 * Declare the WP ioctl only if the WP mode is
1516 * specified and all checks passed with the range
1517 */
1518 if (!(uffdio_register.mode & UFFDIO_REGISTER_MODE_WP))
1519 ioctls_out &= ~((__u64)1 << _UFFDIO_WRITEPROTECT);
1520
1521 /* CONTINUE ioctl is only supported for MINOR ranges. */
1522 if (!(uffdio_register.mode & UFFDIO_REGISTER_MODE_MINOR))
1523 ioctls_out &= ~((__u64)1 << _UFFDIO_CONTINUE);
1524
1525 /*
1526 * Now that we scanned all vmas we can already tell
1527 * userland which ioctls methods are guaranteed to
1528 * succeed on this range.
1529 */
1530 if (put_user(ioctls_out, &user_uffdio_register->ioctls))
1531 ret = -EFAULT;
1532 }
1533out:
1534 return ret;
1535}
1536
1537static int userfaultfd_unregister(struct userfaultfd_ctx *ctx,
1538 unsigned long arg)
1539{
1540 struct mm_struct *mm = ctx->mm;
1541 struct vm_area_struct *vma, *prev, *cur;
1542 int ret;
1543 struct uffdio_range uffdio_unregister;
1544 unsigned long new_flags;
1545 bool found;
1546 unsigned long start, end, vma_end;
1547 const void __user *buf = (void __user *)arg;
1548 struct vma_iterator vmi;
1549 bool wp_async = userfaultfd_wp_async_ctx(ctx);
1550
1551 ret = -EFAULT;
1552 if (copy_from_user(&uffdio_unregister, buf, sizeof(uffdio_unregister)))
1553 goto out;
1554
1555 ret = validate_range(mm, uffdio_unregister.start,
1556 uffdio_unregister.len);
1557 if (ret)
1558 goto out;
1559
1560 start = uffdio_unregister.start;
1561 end = start + uffdio_unregister.len;
1562
1563 ret = -ENOMEM;
1564 if (!mmget_not_zero(mm))
1565 goto out;
1566
1567 mmap_write_lock(mm);
1568 ret = -EINVAL;
1569 vma_iter_init(&vmi, mm, start);
1570 vma = vma_find(&vmi, end);
1571 if (!vma)
1572 goto out_unlock;
1573
1574 /*
1575 * If the first vma contains huge pages, make sure start address
1576 * is aligned to huge page size.
1577 */
1578 if (is_vm_hugetlb_page(vma)) {
1579 unsigned long vma_hpagesize = vma_kernel_pagesize(vma);
1580
1581 if (start & (vma_hpagesize - 1))
1582 goto out_unlock;
1583 }
1584
1585 /*
1586 * Search for not compatible vmas.
1587 */
1588 found = false;
1589 cur = vma;
1590 do {
1591 cond_resched();
1592
1593 BUG_ON(!!cur->vm_userfaultfd_ctx.ctx ^
1594 !!(cur->vm_flags & __VM_UFFD_FLAGS));
1595
1596 /*
1597 * Check not compatible vmas, not strictly required
1598 * here as not compatible vmas cannot have an
1599 * userfaultfd_ctx registered on them, but this
1600 * provides for more strict behavior to notice
1601 * unregistration errors.
1602 */
1603 if (!vma_can_userfault(cur, cur->vm_flags, wp_async))
1604 goto out_unlock;
1605
1606 found = true;
1607 } for_each_vma_range(vmi, cur, end);
1608 BUG_ON(!found);
1609
1610 vma_iter_set(&vmi, start);
1611 prev = vma_prev(&vmi);
1612 if (vma->vm_start < start)
1613 prev = vma;
1614
1615 ret = 0;
1616 for_each_vma_range(vmi, vma, end) {
1617 cond_resched();
1618
1619 BUG_ON(!vma_can_userfault(vma, vma->vm_flags, wp_async));
1620
1621 /*
1622 * Nothing to do: this vma is already registered into this
1623 * userfaultfd and with the right tracking mode too.
1624 */
1625 if (!vma->vm_userfaultfd_ctx.ctx)
1626 goto skip;
1627
1628 WARN_ON(!(vma->vm_flags & VM_MAYWRITE));
1629
1630 if (vma->vm_start > start)
1631 start = vma->vm_start;
1632 vma_end = min(end, vma->vm_end);
1633
1634 if (userfaultfd_missing(vma)) {
1635 /*
1636 * Wake any concurrent pending userfault while
1637 * we unregister, so they will not hang
1638 * permanently and it avoids userland to call
1639 * UFFDIO_WAKE explicitly.
1640 */
1641 struct userfaultfd_wake_range range;
1642 range.start = start;
1643 range.len = vma_end - start;
1644 wake_userfault(vma->vm_userfaultfd_ctx.ctx, &range);
1645 }
1646
1647 /* Reset ptes for the whole vma range if wr-protected */
1648 if (userfaultfd_wp(vma))
1649 uffd_wp_range(vma, start, vma_end - start, false);
1650
1651 new_flags = vma->vm_flags & ~__VM_UFFD_FLAGS;
1652 vma = vma_modify_flags_uffd(&vmi, prev, vma, start, vma_end,
1653 new_flags, NULL_VM_UFFD_CTX);
1654 if (IS_ERR(vma)) {
1655 ret = PTR_ERR(vma);
1656 break;
1657 }
1658
1659 /*
1660 * In the vma_merge() successful mprotect-like case 8:
1661 * the next vma was merged into the current one and
1662 * the current one has not been updated yet.
1663 */
1664 vma_start_write(vma);
1665 userfaultfd_set_vm_flags(vma, new_flags);
1666 vma->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX;
1667
1668 skip:
1669 prev = vma;
1670 start = vma->vm_end;
1671 }
1672
1673out_unlock:
1674 mmap_write_unlock(mm);
1675 mmput(mm);
1676out:
1677 return ret;
1678}
1679
1680/*
1681 * userfaultfd_wake may be used in combination with the
1682 * UFFDIO_*_MODE_DONTWAKE to wakeup userfaults in batches.
1683 */
1684static int userfaultfd_wake(struct userfaultfd_ctx *ctx,
1685 unsigned long arg)
1686{
1687 int ret;
1688 struct uffdio_range uffdio_wake;
1689 struct userfaultfd_wake_range range;
1690 const void __user *buf = (void __user *)arg;
1691
1692 ret = -EFAULT;
1693 if (copy_from_user(&uffdio_wake, buf, sizeof(uffdio_wake)))
1694 goto out;
1695
1696 ret = validate_range(ctx->mm, uffdio_wake.start, uffdio_wake.len);
1697 if (ret)
1698 goto out;
1699
1700 range.start = uffdio_wake.start;
1701 range.len = uffdio_wake.len;
1702
1703 /*
1704 * len == 0 means wake all and we don't want to wake all here,
1705 * so check it again to be sure.
1706 */
1707 VM_BUG_ON(!range.len);
1708
1709 wake_userfault(ctx, &range);
1710 ret = 0;
1711
1712out:
1713 return ret;
1714}
1715
1716static int userfaultfd_copy(struct userfaultfd_ctx *ctx,
1717 unsigned long arg)
1718{
1719 __s64 ret;
1720 struct uffdio_copy uffdio_copy;
1721 struct uffdio_copy __user *user_uffdio_copy;
1722 struct userfaultfd_wake_range range;
1723 uffd_flags_t flags = 0;
1724
1725 user_uffdio_copy = (struct uffdio_copy __user *) arg;
1726
1727 ret = -EAGAIN;
1728 if (atomic_read(&ctx->mmap_changing))
1729 goto out;
1730
1731 ret = -EFAULT;
1732 if (copy_from_user(&uffdio_copy, user_uffdio_copy,
1733 /* don't copy "copy" last field */
1734 sizeof(uffdio_copy)-sizeof(__s64)))
1735 goto out;
1736
1737 ret = validate_unaligned_range(ctx->mm, uffdio_copy.src,
1738 uffdio_copy.len);
1739 if (ret)
1740 goto out;
1741 ret = validate_range(ctx->mm, uffdio_copy.dst, uffdio_copy.len);
1742 if (ret)
1743 goto out;
1744
1745 ret = -EINVAL;
1746 if (uffdio_copy.mode & ~(UFFDIO_COPY_MODE_DONTWAKE|UFFDIO_COPY_MODE_WP))
1747 goto out;
1748 if (uffdio_copy.mode & UFFDIO_COPY_MODE_WP)
1749 flags |= MFILL_ATOMIC_WP;
1750 if (mmget_not_zero(ctx->mm)) {
1751 ret = mfill_atomic_copy(ctx->mm, uffdio_copy.dst, uffdio_copy.src,
1752 uffdio_copy.len, &ctx->mmap_changing,
1753 flags);
1754 mmput(ctx->mm);
1755 } else {
1756 return -ESRCH;
1757 }
1758 if (unlikely(put_user(ret, &user_uffdio_copy->copy)))
1759 return -EFAULT;
1760 if (ret < 0)
1761 goto out;
1762 BUG_ON(!ret);
1763 /* len == 0 would wake all */
1764 range.len = ret;
1765 if (!(uffdio_copy.mode & UFFDIO_COPY_MODE_DONTWAKE)) {
1766 range.start = uffdio_copy.dst;
1767 wake_userfault(ctx, &range);
1768 }
1769 ret = range.len == uffdio_copy.len ? 0 : -EAGAIN;
1770out:
1771 return ret;
1772}
1773
1774static int userfaultfd_zeropage(struct userfaultfd_ctx *ctx,
1775 unsigned long arg)
1776{
1777 __s64 ret;
1778 struct uffdio_zeropage uffdio_zeropage;
1779 struct uffdio_zeropage __user *user_uffdio_zeropage;
1780 struct userfaultfd_wake_range range;
1781
1782 user_uffdio_zeropage = (struct uffdio_zeropage __user *) arg;
1783
1784 ret = -EAGAIN;
1785 if (atomic_read(&ctx->mmap_changing))
1786 goto out;
1787
1788 ret = -EFAULT;
1789 if (copy_from_user(&uffdio_zeropage, user_uffdio_zeropage,
1790 /* don't copy "zeropage" last field */
1791 sizeof(uffdio_zeropage)-sizeof(__s64)))
1792 goto out;
1793
1794 ret = validate_range(ctx->mm, uffdio_zeropage.range.start,
1795 uffdio_zeropage.range.len);
1796 if (ret)
1797 goto out;
1798 ret = -EINVAL;
1799 if (uffdio_zeropage.mode & ~UFFDIO_ZEROPAGE_MODE_DONTWAKE)
1800 goto out;
1801
1802 if (mmget_not_zero(ctx->mm)) {
1803 ret = mfill_atomic_zeropage(ctx->mm, uffdio_zeropage.range.start,
1804 uffdio_zeropage.range.len,
1805 &ctx->mmap_changing);
1806 mmput(ctx->mm);
1807 } else {
1808 return -ESRCH;
1809 }
1810 if (unlikely(put_user(ret, &user_uffdio_zeropage->zeropage)))
1811 return -EFAULT;
1812 if (ret < 0)
1813 goto out;
1814 /* len == 0 would wake all */
1815 BUG_ON(!ret);
1816 range.len = ret;
1817 if (!(uffdio_zeropage.mode & UFFDIO_ZEROPAGE_MODE_DONTWAKE)) {
1818 range.start = uffdio_zeropage.range.start;
1819 wake_userfault(ctx, &range);
1820 }
1821 ret = range.len == uffdio_zeropage.range.len ? 0 : -EAGAIN;
1822out:
1823 return ret;
1824}
1825
1826static int userfaultfd_writeprotect(struct userfaultfd_ctx *ctx,
1827 unsigned long arg)
1828{
1829 int ret;
1830 struct uffdio_writeprotect uffdio_wp;
1831 struct uffdio_writeprotect __user *user_uffdio_wp;
1832 struct userfaultfd_wake_range range;
1833 bool mode_wp, mode_dontwake;
1834
1835 if (atomic_read(&ctx->mmap_changing))
1836 return -EAGAIN;
1837
1838 user_uffdio_wp = (struct uffdio_writeprotect __user *) arg;
1839
1840 if (copy_from_user(&uffdio_wp, user_uffdio_wp,
1841 sizeof(struct uffdio_writeprotect)))
1842 return -EFAULT;
1843
1844 ret = validate_range(ctx->mm, uffdio_wp.range.start,
1845 uffdio_wp.range.len);
1846 if (ret)
1847 return ret;
1848
1849 if (uffdio_wp.mode & ~(UFFDIO_WRITEPROTECT_MODE_DONTWAKE |
1850 UFFDIO_WRITEPROTECT_MODE_WP))
1851 return -EINVAL;
1852
1853 mode_wp = uffdio_wp.mode & UFFDIO_WRITEPROTECT_MODE_WP;
1854 mode_dontwake = uffdio_wp.mode & UFFDIO_WRITEPROTECT_MODE_DONTWAKE;
1855
1856 if (mode_wp && mode_dontwake)
1857 return -EINVAL;
1858
1859 if (mmget_not_zero(ctx->mm)) {
1860 ret = mwriteprotect_range(ctx->mm, uffdio_wp.range.start,
1861 uffdio_wp.range.len, mode_wp,
1862 &ctx->mmap_changing);
1863 mmput(ctx->mm);
1864 } else {
1865 return -ESRCH;
1866 }
1867
1868 if (ret)
1869 return ret;
1870
1871 if (!mode_wp && !mode_dontwake) {
1872 range.start = uffdio_wp.range.start;
1873 range.len = uffdio_wp.range.len;
1874 wake_userfault(ctx, &range);
1875 }
1876 return ret;
1877}
1878
1879static int userfaultfd_continue(struct userfaultfd_ctx *ctx, unsigned long arg)
1880{
1881 __s64 ret;
1882 struct uffdio_continue uffdio_continue;
1883 struct uffdio_continue __user *user_uffdio_continue;
1884 struct userfaultfd_wake_range range;
1885 uffd_flags_t flags = 0;
1886
1887 user_uffdio_continue = (struct uffdio_continue __user *)arg;
1888
1889 ret = -EAGAIN;
1890 if (atomic_read(&ctx->mmap_changing))
1891 goto out;
1892
1893 ret = -EFAULT;
1894 if (copy_from_user(&uffdio_continue, user_uffdio_continue,
1895 /* don't copy the output fields */
1896 sizeof(uffdio_continue) - (sizeof(__s64))))
1897 goto out;
1898
1899 ret = validate_range(ctx->mm, uffdio_continue.range.start,
1900 uffdio_continue.range.len);
1901 if (ret)
1902 goto out;
1903
1904 ret = -EINVAL;
1905 if (uffdio_continue.mode & ~(UFFDIO_CONTINUE_MODE_DONTWAKE |
1906 UFFDIO_CONTINUE_MODE_WP))
1907 goto out;
1908 if (uffdio_continue.mode & UFFDIO_CONTINUE_MODE_WP)
1909 flags |= MFILL_ATOMIC_WP;
1910
1911 if (mmget_not_zero(ctx->mm)) {
1912 ret = mfill_atomic_continue(ctx->mm, uffdio_continue.range.start,
1913 uffdio_continue.range.len,
1914 &ctx->mmap_changing, flags);
1915 mmput(ctx->mm);
1916 } else {
1917 return -ESRCH;
1918 }
1919
1920 if (unlikely(put_user(ret, &user_uffdio_continue->mapped)))
1921 return -EFAULT;
1922 if (ret < 0)
1923 goto out;
1924
1925 /* len == 0 would wake all */
1926 BUG_ON(!ret);
1927 range.len = ret;
1928 if (!(uffdio_continue.mode & UFFDIO_CONTINUE_MODE_DONTWAKE)) {
1929 range.start = uffdio_continue.range.start;
1930 wake_userfault(ctx, &range);
1931 }
1932 ret = range.len == uffdio_continue.range.len ? 0 : -EAGAIN;
1933
1934out:
1935 return ret;
1936}
1937
1938static inline int userfaultfd_poison(struct userfaultfd_ctx *ctx, unsigned long arg)
1939{
1940 __s64 ret;
1941 struct uffdio_poison uffdio_poison;
1942 struct uffdio_poison __user *user_uffdio_poison;
1943 struct userfaultfd_wake_range range;
1944
1945 user_uffdio_poison = (struct uffdio_poison __user *)arg;
1946
1947 ret = -EAGAIN;
1948 if (atomic_read(&ctx->mmap_changing))
1949 goto out;
1950
1951 ret = -EFAULT;
1952 if (copy_from_user(&uffdio_poison, user_uffdio_poison,
1953 /* don't copy the output fields */
1954 sizeof(uffdio_poison) - (sizeof(__s64))))
1955 goto out;
1956
1957 ret = validate_range(ctx->mm, uffdio_poison.range.start,
1958 uffdio_poison.range.len);
1959 if (ret)
1960 goto out;
1961
1962 ret = -EINVAL;
1963 if (uffdio_poison.mode & ~UFFDIO_POISON_MODE_DONTWAKE)
1964 goto out;
1965
1966 if (mmget_not_zero(ctx->mm)) {
1967 ret = mfill_atomic_poison(ctx->mm, uffdio_poison.range.start,
1968 uffdio_poison.range.len,
1969 &ctx->mmap_changing, 0);
1970 mmput(ctx->mm);
1971 } else {
1972 return -ESRCH;
1973 }
1974
1975 if (unlikely(put_user(ret, &user_uffdio_poison->updated)))
1976 return -EFAULT;
1977 if (ret < 0)
1978 goto out;
1979
1980 /* len == 0 would wake all */
1981 BUG_ON(!ret);
1982 range.len = ret;
1983 if (!(uffdio_poison.mode & UFFDIO_POISON_MODE_DONTWAKE)) {
1984 range.start = uffdio_poison.range.start;
1985 wake_userfault(ctx, &range);
1986 }
1987 ret = range.len == uffdio_poison.range.len ? 0 : -EAGAIN;
1988
1989out:
1990 return ret;
1991}
1992
1993bool userfaultfd_wp_async(struct vm_area_struct *vma)
1994{
1995 return userfaultfd_wp_async_ctx(vma->vm_userfaultfd_ctx.ctx);
1996}
1997
1998static inline unsigned int uffd_ctx_features(__u64 user_features)
1999{
2000 /*
2001 * For the current set of features the bits just coincide. Set
2002 * UFFD_FEATURE_INITIALIZED to mark the features as enabled.
2003 */
2004 return (unsigned int)user_features | UFFD_FEATURE_INITIALIZED;
2005}
2006
2007static int userfaultfd_move(struct userfaultfd_ctx *ctx,
2008 unsigned long arg)
2009{
2010 __s64 ret;
2011 struct uffdio_move uffdio_move;
2012 struct uffdio_move __user *user_uffdio_move;
2013 struct userfaultfd_wake_range range;
2014 struct mm_struct *mm = ctx->mm;
2015
2016 user_uffdio_move = (struct uffdio_move __user *) arg;
2017
2018 if (atomic_read(&ctx->mmap_changing))
2019 return -EAGAIN;
2020
2021 if (copy_from_user(&uffdio_move, user_uffdio_move,
2022 /* don't copy "move" last field */
2023 sizeof(uffdio_move)-sizeof(__s64)))
2024 return -EFAULT;
2025
2026 /* Do not allow cross-mm moves. */
2027 if (mm != current->mm)
2028 return -EINVAL;
2029
2030 ret = validate_range(mm, uffdio_move.dst, uffdio_move.len);
2031 if (ret)
2032 return ret;
2033
2034 ret = validate_range(mm, uffdio_move.src, uffdio_move.len);
2035 if (ret)
2036 return ret;
2037
2038 if (uffdio_move.mode & ~(UFFDIO_MOVE_MODE_ALLOW_SRC_HOLES|
2039 UFFDIO_MOVE_MODE_DONTWAKE))
2040 return -EINVAL;
2041
2042 if (mmget_not_zero(mm)) {
2043 mmap_read_lock(mm);
2044
2045 /* Re-check after taking mmap_lock */
2046 if (likely(!atomic_read(&ctx->mmap_changing)))
2047 ret = move_pages(ctx, mm, uffdio_move.dst, uffdio_move.src,
2048 uffdio_move.len, uffdio_move.mode);
2049 else
2050 ret = -EINVAL;
2051
2052 mmap_read_unlock(mm);
2053 mmput(mm);
2054 } else {
2055 return -ESRCH;
2056 }
2057
2058 if (unlikely(put_user(ret, &user_uffdio_move->move)))
2059 return -EFAULT;
2060 if (ret < 0)
2061 goto out;
2062
2063 /* len == 0 would wake all */
2064 VM_WARN_ON(!ret);
2065 range.len = ret;
2066 if (!(uffdio_move.mode & UFFDIO_MOVE_MODE_DONTWAKE)) {
2067 range.start = uffdio_move.dst;
2068 wake_userfault(ctx, &range);
2069 }
2070 ret = range.len == uffdio_move.len ? 0 : -EAGAIN;
2071
2072out:
2073 return ret;
2074}
2075
2076/*
2077 * userland asks for a certain API version and we return which bits
2078 * and ioctl commands are implemented in this kernel for such API
2079 * version or -EINVAL if unknown.
2080 */
2081static int userfaultfd_api(struct userfaultfd_ctx *ctx,
2082 unsigned long arg)
2083{
2084 struct uffdio_api uffdio_api;
2085 void __user *buf = (void __user *)arg;
2086 unsigned int ctx_features;
2087 int ret;
2088 __u64 features;
2089
2090 ret = -EFAULT;
2091 if (copy_from_user(&uffdio_api, buf, sizeof(uffdio_api)))
2092 goto out;
2093 features = uffdio_api.features;
2094 ret = -EINVAL;
2095 if (uffdio_api.api != UFFD_API || (features & ~UFFD_API_FEATURES))
2096 goto err_out;
2097 ret = -EPERM;
2098 if ((features & UFFD_FEATURE_EVENT_FORK) && !capable(CAP_SYS_PTRACE))
2099 goto err_out;
2100
2101 /* WP_ASYNC relies on WP_UNPOPULATED, choose it unconditionally */
2102 if (features & UFFD_FEATURE_WP_ASYNC)
2103 features |= UFFD_FEATURE_WP_UNPOPULATED;
2104
2105 /* report all available features and ioctls to userland */
2106 uffdio_api.features = UFFD_API_FEATURES;
2107#ifndef CONFIG_HAVE_ARCH_USERFAULTFD_MINOR
2108 uffdio_api.features &=
2109 ~(UFFD_FEATURE_MINOR_HUGETLBFS | UFFD_FEATURE_MINOR_SHMEM);
2110#endif
2111#ifndef CONFIG_HAVE_ARCH_USERFAULTFD_WP
2112 uffdio_api.features &= ~UFFD_FEATURE_PAGEFAULT_FLAG_WP;
2113#endif
2114#ifndef CONFIG_PTE_MARKER_UFFD_WP
2115 uffdio_api.features &= ~UFFD_FEATURE_WP_HUGETLBFS_SHMEM;
2116 uffdio_api.features &= ~UFFD_FEATURE_WP_UNPOPULATED;
2117 uffdio_api.features &= ~UFFD_FEATURE_WP_ASYNC;
2118#endif
2119 uffdio_api.ioctls = UFFD_API_IOCTLS;
2120 ret = -EFAULT;
2121 if (copy_to_user(buf, &uffdio_api, sizeof(uffdio_api)))
2122 goto out;
2123
2124 /* only enable the requested features for this uffd context */
2125 ctx_features = uffd_ctx_features(features);
2126 ret = -EINVAL;
2127 if (cmpxchg(&ctx->features, 0, ctx_features) != 0)
2128 goto err_out;
2129
2130 ret = 0;
2131out:
2132 return ret;
2133err_out:
2134 memset(&uffdio_api, 0, sizeof(uffdio_api));
2135 if (copy_to_user(buf, &uffdio_api, sizeof(uffdio_api)))
2136 ret = -EFAULT;
2137 goto out;
2138}
2139
2140static long userfaultfd_ioctl(struct file *file, unsigned cmd,
2141 unsigned long arg)
2142{
2143 int ret = -EINVAL;
2144 struct userfaultfd_ctx *ctx = file->private_data;
2145
2146 if (cmd != UFFDIO_API && !userfaultfd_is_initialized(ctx))
2147 return -EINVAL;
2148
2149 switch(cmd) {
2150 case UFFDIO_API:
2151 ret = userfaultfd_api(ctx, arg);
2152 break;
2153 case UFFDIO_REGISTER:
2154 ret = userfaultfd_register(ctx, arg);
2155 break;
2156 case UFFDIO_UNREGISTER:
2157 ret = userfaultfd_unregister(ctx, arg);
2158 break;
2159 case UFFDIO_WAKE:
2160 ret = userfaultfd_wake(ctx, arg);
2161 break;
2162 case UFFDIO_COPY:
2163 ret = userfaultfd_copy(ctx, arg);
2164 break;
2165 case UFFDIO_ZEROPAGE:
2166 ret = userfaultfd_zeropage(ctx, arg);
2167 break;
2168 case UFFDIO_MOVE:
2169 ret = userfaultfd_move(ctx, arg);
2170 break;
2171 case UFFDIO_WRITEPROTECT:
2172 ret = userfaultfd_writeprotect(ctx, arg);
2173 break;
2174 case UFFDIO_CONTINUE:
2175 ret = userfaultfd_continue(ctx, arg);
2176 break;
2177 case UFFDIO_POISON:
2178 ret = userfaultfd_poison(ctx, arg);
2179 break;
2180 }
2181 return ret;
2182}
2183
2184#ifdef CONFIG_PROC_FS
2185static void userfaultfd_show_fdinfo(struct seq_file *m, struct file *f)
2186{
2187 struct userfaultfd_ctx *ctx = f->private_data;
2188 wait_queue_entry_t *wq;
2189 unsigned long pending = 0, total = 0;
2190
2191 spin_lock_irq(&ctx->fault_pending_wqh.lock);
2192 list_for_each_entry(wq, &ctx->fault_pending_wqh.head, entry) {
2193 pending++;
2194 total++;
2195 }
2196 list_for_each_entry(wq, &ctx->fault_wqh.head, entry) {
2197 total++;
2198 }
2199 spin_unlock_irq(&ctx->fault_pending_wqh.lock);
2200
2201 /*
2202 * If more protocols will be added, there will be all shown
2203 * separated by a space. Like this:
2204 * protocols: aa:... bb:...
2205 */
2206 seq_printf(m, "pending:\t%lu\ntotal:\t%lu\nAPI:\t%Lx:%x:%Lx\n",
2207 pending, total, UFFD_API, ctx->features,
2208 UFFD_API_IOCTLS|UFFD_API_RANGE_IOCTLS);
2209}
2210#endif
2211
2212static const struct file_operations userfaultfd_fops = {
2213#ifdef CONFIG_PROC_FS
2214 .show_fdinfo = userfaultfd_show_fdinfo,
2215#endif
2216 .release = userfaultfd_release,
2217 .poll = userfaultfd_poll,
2218 .read = userfaultfd_read,
2219 .unlocked_ioctl = userfaultfd_ioctl,
2220 .compat_ioctl = compat_ptr_ioctl,
2221 .llseek = noop_llseek,
2222};
2223
2224static void init_once_userfaultfd_ctx(void *mem)
2225{
2226 struct userfaultfd_ctx *ctx = (struct userfaultfd_ctx *) mem;
2227
2228 init_waitqueue_head(&ctx->fault_pending_wqh);
2229 init_waitqueue_head(&ctx->fault_wqh);
2230 init_waitqueue_head(&ctx->event_wqh);
2231 init_waitqueue_head(&ctx->fd_wqh);
2232 seqcount_spinlock_init(&ctx->refile_seq, &ctx->fault_pending_wqh.lock);
2233}
2234
2235static int new_userfaultfd(int flags)
2236{
2237 struct userfaultfd_ctx *ctx;
2238 int fd;
2239
2240 BUG_ON(!current->mm);
2241
2242 /* Check the UFFD_* constants for consistency. */
2243 BUILD_BUG_ON(UFFD_USER_MODE_ONLY & UFFD_SHARED_FCNTL_FLAGS);
2244 BUILD_BUG_ON(UFFD_CLOEXEC != O_CLOEXEC);
2245 BUILD_BUG_ON(UFFD_NONBLOCK != O_NONBLOCK);
2246
2247 if (flags & ~(UFFD_SHARED_FCNTL_FLAGS | UFFD_USER_MODE_ONLY))
2248 return -EINVAL;
2249
2250 ctx = kmem_cache_alloc(userfaultfd_ctx_cachep, GFP_KERNEL);
2251 if (!ctx)
2252 return -ENOMEM;
2253
2254 refcount_set(&ctx->refcount, 1);
2255 ctx->flags = flags;
2256 ctx->features = 0;
2257 ctx->released = false;
2258 atomic_set(&ctx->mmap_changing, 0);
2259 ctx->mm = current->mm;
2260 /* prevent the mm struct to be freed */
2261 mmgrab(ctx->mm);
2262
2263 /* Create a new inode so that the LSM can block the creation. */
2264 fd = anon_inode_create_getfd("[userfaultfd]", &userfaultfd_fops, ctx,
2265 O_RDONLY | (flags & UFFD_SHARED_FCNTL_FLAGS), NULL);
2266 if (fd < 0) {
2267 mmdrop(ctx->mm);
2268 kmem_cache_free(userfaultfd_ctx_cachep, ctx);
2269 }
2270 return fd;
2271}
2272
2273static inline bool userfaultfd_syscall_allowed(int flags)
2274{
2275 /* Userspace-only page faults are always allowed */
2276 if (flags & UFFD_USER_MODE_ONLY)
2277 return true;
2278
2279 /*
2280 * The user is requesting a userfaultfd which can handle kernel faults.
2281 * Privileged users are always allowed to do this.
2282 */
2283 if (capable(CAP_SYS_PTRACE))
2284 return true;
2285
2286 /* Otherwise, access to kernel fault handling is sysctl controlled. */
2287 return sysctl_unprivileged_userfaultfd;
2288}
2289
2290SYSCALL_DEFINE1(userfaultfd, int, flags)
2291{
2292 if (!userfaultfd_syscall_allowed(flags))
2293 return -EPERM;
2294
2295 return new_userfaultfd(flags);
2296}
2297
2298static long userfaultfd_dev_ioctl(struct file *file, unsigned int cmd, unsigned long flags)
2299{
2300 if (cmd != USERFAULTFD_IOC_NEW)
2301 return -EINVAL;
2302
2303 return new_userfaultfd(flags);
2304}
2305
2306static const struct file_operations userfaultfd_dev_fops = {
2307 .unlocked_ioctl = userfaultfd_dev_ioctl,
2308 .compat_ioctl = userfaultfd_dev_ioctl,
2309 .owner = THIS_MODULE,
2310 .llseek = noop_llseek,
2311};
2312
2313static struct miscdevice userfaultfd_misc = {
2314 .minor = MISC_DYNAMIC_MINOR,
2315 .name = "userfaultfd",
2316 .fops = &userfaultfd_dev_fops
2317};
2318
2319static int __init userfaultfd_init(void)
2320{
2321 int ret;
2322
2323 ret = misc_register(&userfaultfd_misc);
2324 if (ret)
2325 return ret;
2326
2327 userfaultfd_ctx_cachep = kmem_cache_create("userfaultfd_ctx_cache",
2328 sizeof(struct userfaultfd_ctx),
2329 0,
2330 SLAB_HWCACHE_ALIGN|SLAB_PANIC,
2331 init_once_userfaultfd_ctx);
2332#ifdef CONFIG_SYSCTL
2333 register_sysctl_init("vm", vm_userfaultfd_table);
2334#endif
2335 return 0;
2336}
2337__initcall(userfaultfd_init);