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