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1// SPDX-License-Identifier: GPL-2.0
2#define pr_fmt(fmt) "kcov: " fmt
3
4#define DISABLE_BRANCH_PROFILING
5#include <linux/atomic.h>
6#include <linux/compiler.h>
7#include <linux/errno.h>
8#include <linux/export.h>
9#include <linux/types.h>
10#include <linux/file.h>
11#include <linux/fs.h>
12#include <linux/hashtable.h>
13#include <linux/init.h>
14#include <linux/jiffies.h>
15#include <linux/kmsan-checks.h>
16#include <linux/mm.h>
17#include <linux/preempt.h>
18#include <linux/printk.h>
19#include <linux/sched.h>
20#include <linux/slab.h>
21#include <linux/spinlock.h>
22#include <linux/vmalloc.h>
23#include <linux/debugfs.h>
24#include <linux/uaccess.h>
25#include <linux/kcov.h>
26#include <linux/refcount.h>
27#include <linux/log2.h>
28#include <asm/setup.h>
29
30#define kcov_debug(fmt, ...) pr_debug("%s: " fmt, __func__, ##__VA_ARGS__)
31
32/* Number of 64-bit words written per one comparison: */
33#define KCOV_WORDS_PER_CMP 4
34
35/*
36 * kcov descriptor (one per opened debugfs file).
37 * State transitions of the descriptor:
38 * - initial state after open()
39 * - then there must be a single ioctl(KCOV_INIT_TRACE) call
40 * - then, mmap() call (several calls are allowed but not useful)
41 * - then, ioctl(KCOV_ENABLE, arg), where arg is
42 * KCOV_TRACE_PC - to trace only the PCs
43 * or
44 * KCOV_TRACE_CMP - to trace only the comparison operands
45 * - then, ioctl(KCOV_DISABLE) to disable the task.
46 * Enabling/disabling ioctls can be repeated (only one task a time allowed).
47 */
48struct kcov {
49 /*
50 * Reference counter. We keep one for:
51 * - opened file descriptor
52 * - task with enabled coverage (we can't unwire it from another task)
53 * - each code section for remote coverage collection
54 */
55 refcount_t refcount;
56 /* The lock protects mode, size, area and t. */
57 spinlock_t lock;
58 enum kcov_mode mode;
59 /* Size of arena (in long's). */
60 unsigned int size;
61 /* Coverage buffer shared with user space. */
62 void *area;
63 /* Task for which we collect coverage, or NULL. */
64 struct task_struct *t;
65 /* Collecting coverage from remote (background) threads. */
66 bool remote;
67 /* Size of remote area (in long's). */
68 unsigned int remote_size;
69 /*
70 * Sequence is incremented each time kcov is reenabled, used by
71 * kcov_remote_stop(), see the comment there.
72 */
73 int sequence;
74};
75
76struct kcov_remote_area {
77 struct list_head list;
78 unsigned int size;
79};
80
81struct kcov_remote {
82 u64 handle;
83 struct kcov *kcov;
84 struct hlist_node hnode;
85};
86
87static DEFINE_SPINLOCK(kcov_remote_lock);
88static DEFINE_HASHTABLE(kcov_remote_map, 4);
89static struct list_head kcov_remote_areas = LIST_HEAD_INIT(kcov_remote_areas);
90
91struct kcov_percpu_data {
92 void *irq_area;
93 local_lock_t lock;
94
95 unsigned int saved_mode;
96 unsigned int saved_size;
97 void *saved_area;
98 struct kcov *saved_kcov;
99 int saved_sequence;
100};
101
102static DEFINE_PER_CPU(struct kcov_percpu_data, kcov_percpu_data) = {
103 .lock = INIT_LOCAL_LOCK(lock),
104};
105
106/* Must be called with kcov_remote_lock locked. */
107static struct kcov_remote *kcov_remote_find(u64 handle)
108{
109 struct kcov_remote *remote;
110
111 hash_for_each_possible(kcov_remote_map, remote, hnode, handle) {
112 if (remote->handle == handle)
113 return remote;
114 }
115 return NULL;
116}
117
118/* Must be called with kcov_remote_lock locked. */
119static struct kcov_remote *kcov_remote_add(struct kcov *kcov, u64 handle)
120{
121 struct kcov_remote *remote;
122
123 if (kcov_remote_find(handle))
124 return ERR_PTR(-EEXIST);
125 remote = kmalloc(sizeof(*remote), GFP_ATOMIC);
126 if (!remote)
127 return ERR_PTR(-ENOMEM);
128 remote->handle = handle;
129 remote->kcov = kcov;
130 hash_add(kcov_remote_map, &remote->hnode, handle);
131 return remote;
132}
133
134/* Must be called with kcov_remote_lock locked. */
135static struct kcov_remote_area *kcov_remote_area_get(unsigned int size)
136{
137 struct kcov_remote_area *area;
138 struct list_head *pos;
139
140 list_for_each(pos, &kcov_remote_areas) {
141 area = list_entry(pos, struct kcov_remote_area, list);
142 if (area->size == size) {
143 list_del(&area->list);
144 return area;
145 }
146 }
147 return NULL;
148}
149
150/* Must be called with kcov_remote_lock locked. */
151static void kcov_remote_area_put(struct kcov_remote_area *area,
152 unsigned int size)
153{
154 INIT_LIST_HEAD(&area->list);
155 area->size = size;
156 list_add(&area->list, &kcov_remote_areas);
157 /*
158 * KMSAN doesn't instrument this file, so it may not know area->list
159 * is initialized. Unpoison it explicitly to avoid reports in
160 * kcov_remote_area_get().
161 */
162 kmsan_unpoison_memory(&area->list, sizeof(area->list));
163}
164
165/*
166 * Unlike in_serving_softirq(), this function returns false when called during
167 * a hardirq or an NMI that happened in the softirq context.
168 */
169static __always_inline bool in_softirq_really(void)
170{
171 return in_serving_softirq() && !in_hardirq() && !in_nmi();
172}
173
174static notrace bool check_kcov_mode(enum kcov_mode needed_mode, struct task_struct *t)
175{
176 unsigned int mode;
177
178 /*
179 * We are interested in code coverage as a function of a syscall inputs,
180 * so we ignore code executed in interrupts, unless we are in a remote
181 * coverage collection section in a softirq.
182 */
183 if (!in_task() && !(in_softirq_really() && t->kcov_softirq))
184 return false;
185 mode = READ_ONCE(t->kcov_mode);
186 /*
187 * There is some code that runs in interrupts but for which
188 * in_interrupt() returns false (e.g. preempt_schedule_irq()).
189 * READ_ONCE()/barrier() effectively provides load-acquire wrt
190 * interrupts, there are paired barrier()/WRITE_ONCE() in
191 * kcov_start().
192 */
193 barrier();
194 return mode == needed_mode;
195}
196
197static notrace unsigned long canonicalize_ip(unsigned long ip)
198{
199#ifdef CONFIG_RANDOMIZE_BASE
200 ip -= kaslr_offset();
201#endif
202 return ip;
203}
204
205/*
206 * Entry point from instrumented code.
207 * This is called once per basic-block/edge.
208 */
209void notrace __sanitizer_cov_trace_pc(void)
210{
211 struct task_struct *t;
212 unsigned long *area;
213 unsigned long ip = canonicalize_ip(_RET_IP_);
214 unsigned long pos;
215
216 t = current;
217 if (!check_kcov_mode(KCOV_MODE_TRACE_PC, t))
218 return;
219
220 area = t->kcov_area;
221 /* The first 64-bit word is the number of subsequent PCs. */
222 pos = READ_ONCE(area[0]) + 1;
223 if (likely(pos < t->kcov_size)) {
224 /* Previously we write pc before updating pos. However, some
225 * early interrupt code could bypass check_kcov_mode() check
226 * and invoke __sanitizer_cov_trace_pc(). If such interrupt is
227 * raised between writing pc and updating pos, the pc could be
228 * overitten by the recursive __sanitizer_cov_trace_pc().
229 * Update pos before writing pc to avoid such interleaving.
230 */
231 WRITE_ONCE(area[0], pos);
232 barrier();
233 area[pos] = ip;
234 }
235}
236EXPORT_SYMBOL(__sanitizer_cov_trace_pc);
237
238#ifdef CONFIG_KCOV_ENABLE_COMPARISONS
239static void notrace write_comp_data(u64 type, u64 arg1, u64 arg2, u64 ip)
240{
241 struct task_struct *t;
242 u64 *area;
243 u64 count, start_index, end_pos, max_pos;
244
245 t = current;
246 if (!check_kcov_mode(KCOV_MODE_TRACE_CMP, t))
247 return;
248
249 ip = canonicalize_ip(ip);
250
251 /*
252 * We write all comparison arguments and types as u64.
253 * The buffer was allocated for t->kcov_size unsigned longs.
254 */
255 area = (u64 *)t->kcov_area;
256 max_pos = t->kcov_size * sizeof(unsigned long);
257
258 count = READ_ONCE(area[0]);
259
260 /* Every record is KCOV_WORDS_PER_CMP 64-bit words. */
261 start_index = 1 + count * KCOV_WORDS_PER_CMP;
262 end_pos = (start_index + KCOV_WORDS_PER_CMP) * sizeof(u64);
263 if (likely(end_pos <= max_pos)) {
264 /* See comment in __sanitizer_cov_trace_pc(). */
265 WRITE_ONCE(area[0], count + 1);
266 barrier();
267 area[start_index] = type;
268 area[start_index + 1] = arg1;
269 area[start_index + 2] = arg2;
270 area[start_index + 3] = ip;
271 }
272}
273
274void notrace __sanitizer_cov_trace_cmp1(u8 arg1, u8 arg2)
275{
276 write_comp_data(KCOV_CMP_SIZE(0), arg1, arg2, _RET_IP_);
277}
278EXPORT_SYMBOL(__sanitizer_cov_trace_cmp1);
279
280void notrace __sanitizer_cov_trace_cmp2(u16 arg1, u16 arg2)
281{
282 write_comp_data(KCOV_CMP_SIZE(1), arg1, arg2, _RET_IP_);
283}
284EXPORT_SYMBOL(__sanitizer_cov_trace_cmp2);
285
286void notrace __sanitizer_cov_trace_cmp4(u32 arg1, u32 arg2)
287{
288 write_comp_data(KCOV_CMP_SIZE(2), arg1, arg2, _RET_IP_);
289}
290EXPORT_SYMBOL(__sanitizer_cov_trace_cmp4);
291
292void notrace __sanitizer_cov_trace_cmp8(kcov_u64 arg1, kcov_u64 arg2)
293{
294 write_comp_data(KCOV_CMP_SIZE(3), arg1, arg2, _RET_IP_);
295}
296EXPORT_SYMBOL(__sanitizer_cov_trace_cmp8);
297
298void notrace __sanitizer_cov_trace_const_cmp1(u8 arg1, u8 arg2)
299{
300 write_comp_data(KCOV_CMP_SIZE(0) | KCOV_CMP_CONST, arg1, arg2,
301 _RET_IP_);
302}
303EXPORT_SYMBOL(__sanitizer_cov_trace_const_cmp1);
304
305void notrace __sanitizer_cov_trace_const_cmp2(u16 arg1, u16 arg2)
306{
307 write_comp_data(KCOV_CMP_SIZE(1) | KCOV_CMP_CONST, arg1, arg2,
308 _RET_IP_);
309}
310EXPORT_SYMBOL(__sanitizer_cov_trace_const_cmp2);
311
312void notrace __sanitizer_cov_trace_const_cmp4(u32 arg1, u32 arg2)
313{
314 write_comp_data(KCOV_CMP_SIZE(2) | KCOV_CMP_CONST, arg1, arg2,
315 _RET_IP_);
316}
317EXPORT_SYMBOL(__sanitizer_cov_trace_const_cmp4);
318
319void notrace __sanitizer_cov_trace_const_cmp8(kcov_u64 arg1, kcov_u64 arg2)
320{
321 write_comp_data(KCOV_CMP_SIZE(3) | KCOV_CMP_CONST, arg1, arg2,
322 _RET_IP_);
323}
324EXPORT_SYMBOL(__sanitizer_cov_trace_const_cmp8);
325
326void notrace __sanitizer_cov_trace_switch(kcov_u64 val, void *arg)
327{
328 u64 i;
329 u64 *cases = arg;
330 u64 count = cases[0];
331 u64 size = cases[1];
332 u64 type = KCOV_CMP_CONST;
333
334 switch (size) {
335 case 8:
336 type |= KCOV_CMP_SIZE(0);
337 break;
338 case 16:
339 type |= KCOV_CMP_SIZE(1);
340 break;
341 case 32:
342 type |= KCOV_CMP_SIZE(2);
343 break;
344 case 64:
345 type |= KCOV_CMP_SIZE(3);
346 break;
347 default:
348 return;
349 }
350 for (i = 0; i < count; i++)
351 write_comp_data(type, cases[i + 2], val, _RET_IP_);
352}
353EXPORT_SYMBOL(__sanitizer_cov_trace_switch);
354#endif /* ifdef CONFIG_KCOV_ENABLE_COMPARISONS */
355
356static void kcov_start(struct task_struct *t, struct kcov *kcov,
357 unsigned int size, void *area, enum kcov_mode mode,
358 int sequence)
359{
360 kcov_debug("t = %px, size = %u, area = %px\n", t, size, area);
361 t->kcov = kcov;
362 /* Cache in task struct for performance. */
363 t->kcov_size = size;
364 t->kcov_area = area;
365 t->kcov_sequence = sequence;
366 /* See comment in check_kcov_mode(). */
367 barrier();
368 WRITE_ONCE(t->kcov_mode, mode);
369}
370
371static void kcov_stop(struct task_struct *t)
372{
373 WRITE_ONCE(t->kcov_mode, KCOV_MODE_DISABLED);
374 barrier();
375 t->kcov = NULL;
376 t->kcov_size = 0;
377 t->kcov_area = NULL;
378}
379
380static void kcov_task_reset(struct task_struct *t)
381{
382 kcov_stop(t);
383 t->kcov_sequence = 0;
384 t->kcov_handle = 0;
385}
386
387void kcov_task_init(struct task_struct *t)
388{
389 kcov_task_reset(t);
390 t->kcov_handle = current->kcov_handle;
391}
392
393static void kcov_reset(struct kcov *kcov)
394{
395 kcov->t = NULL;
396 kcov->mode = KCOV_MODE_INIT;
397 kcov->remote = false;
398 kcov->remote_size = 0;
399 kcov->sequence++;
400}
401
402static void kcov_remote_reset(struct kcov *kcov)
403{
404 int bkt;
405 struct kcov_remote *remote;
406 struct hlist_node *tmp;
407 unsigned long flags;
408
409 spin_lock_irqsave(&kcov_remote_lock, flags);
410 hash_for_each_safe(kcov_remote_map, bkt, tmp, remote, hnode) {
411 if (remote->kcov != kcov)
412 continue;
413 hash_del(&remote->hnode);
414 kfree(remote);
415 }
416 /* Do reset before unlock to prevent races with kcov_remote_start(). */
417 kcov_reset(kcov);
418 spin_unlock_irqrestore(&kcov_remote_lock, flags);
419}
420
421static void kcov_disable(struct task_struct *t, struct kcov *kcov)
422{
423 kcov_task_reset(t);
424 if (kcov->remote)
425 kcov_remote_reset(kcov);
426 else
427 kcov_reset(kcov);
428}
429
430static void kcov_get(struct kcov *kcov)
431{
432 refcount_inc(&kcov->refcount);
433}
434
435static void kcov_put(struct kcov *kcov)
436{
437 if (refcount_dec_and_test(&kcov->refcount)) {
438 kcov_remote_reset(kcov);
439 vfree(kcov->area);
440 kfree(kcov);
441 }
442}
443
444void kcov_task_exit(struct task_struct *t)
445{
446 struct kcov *kcov;
447 unsigned long flags;
448
449 kcov = t->kcov;
450 if (kcov == NULL)
451 return;
452
453 spin_lock_irqsave(&kcov->lock, flags);
454 kcov_debug("t = %px, kcov->t = %px\n", t, kcov->t);
455 /*
456 * For KCOV_ENABLE devices we want to make sure that t->kcov->t == t,
457 * which comes down to:
458 * WARN_ON(!kcov->remote && kcov->t != t);
459 *
460 * For KCOV_REMOTE_ENABLE devices, the exiting task is either:
461 *
462 * 1. A remote task between kcov_remote_start() and kcov_remote_stop().
463 * In this case we should print a warning right away, since a task
464 * shouldn't be exiting when it's in a kcov coverage collection
465 * section. Here t points to the task that is collecting remote
466 * coverage, and t->kcov->t points to the thread that created the
467 * kcov device. Which means that to detect this case we need to
468 * check that t != t->kcov->t, and this gives us the following:
469 * WARN_ON(kcov->remote && kcov->t != t);
470 *
471 * 2. The task that created kcov exiting without calling KCOV_DISABLE,
472 * and then again we make sure that t->kcov->t == t:
473 * WARN_ON(kcov->remote && kcov->t != t);
474 *
475 * By combining all three checks into one we get:
476 */
477 if (WARN_ON(kcov->t != t)) {
478 spin_unlock_irqrestore(&kcov->lock, flags);
479 return;
480 }
481 /* Just to not leave dangling references behind. */
482 kcov_disable(t, kcov);
483 spin_unlock_irqrestore(&kcov->lock, flags);
484 kcov_put(kcov);
485}
486
487static int kcov_mmap(struct file *filep, struct vm_area_struct *vma)
488{
489 int res = 0;
490 struct kcov *kcov = vma->vm_file->private_data;
491 unsigned long size, off;
492 struct page *page;
493 unsigned long flags;
494
495 spin_lock_irqsave(&kcov->lock, flags);
496 size = kcov->size * sizeof(unsigned long);
497 if (kcov->area == NULL || vma->vm_pgoff != 0 ||
498 vma->vm_end - vma->vm_start != size) {
499 res = -EINVAL;
500 goto exit;
501 }
502 spin_unlock_irqrestore(&kcov->lock, flags);
503 vm_flags_set(vma, VM_DONTEXPAND);
504 for (off = 0; off < size; off += PAGE_SIZE) {
505 page = vmalloc_to_page(kcov->area + off);
506 res = vm_insert_page(vma, vma->vm_start + off, page);
507 if (res) {
508 pr_warn_once("kcov: vm_insert_page() failed\n");
509 return res;
510 }
511 }
512 return 0;
513exit:
514 spin_unlock_irqrestore(&kcov->lock, flags);
515 return res;
516}
517
518static int kcov_open(struct inode *inode, struct file *filep)
519{
520 struct kcov *kcov;
521
522 kcov = kzalloc(sizeof(*kcov), GFP_KERNEL);
523 if (!kcov)
524 return -ENOMEM;
525 kcov->mode = KCOV_MODE_DISABLED;
526 kcov->sequence = 1;
527 refcount_set(&kcov->refcount, 1);
528 spin_lock_init(&kcov->lock);
529 filep->private_data = kcov;
530 return nonseekable_open(inode, filep);
531}
532
533static int kcov_close(struct inode *inode, struct file *filep)
534{
535 kcov_put(filep->private_data);
536 return 0;
537}
538
539static int kcov_get_mode(unsigned long arg)
540{
541 if (arg == KCOV_TRACE_PC)
542 return KCOV_MODE_TRACE_PC;
543 else if (arg == KCOV_TRACE_CMP)
544#ifdef CONFIG_KCOV_ENABLE_COMPARISONS
545 return KCOV_MODE_TRACE_CMP;
546#else
547 return -ENOTSUPP;
548#endif
549 else
550 return -EINVAL;
551}
552
553/*
554 * Fault in a lazily-faulted vmalloc area before it can be used by
555 * __santizer_cov_trace_pc(), to avoid recursion issues if any code on the
556 * vmalloc fault handling path is instrumented.
557 */
558static void kcov_fault_in_area(struct kcov *kcov)
559{
560 unsigned long stride = PAGE_SIZE / sizeof(unsigned long);
561 unsigned long *area = kcov->area;
562 unsigned long offset;
563
564 for (offset = 0; offset < kcov->size; offset += stride)
565 READ_ONCE(area[offset]);
566}
567
568static inline bool kcov_check_handle(u64 handle, bool common_valid,
569 bool uncommon_valid, bool zero_valid)
570{
571 if (handle & ~(KCOV_SUBSYSTEM_MASK | KCOV_INSTANCE_MASK))
572 return false;
573 switch (handle & KCOV_SUBSYSTEM_MASK) {
574 case KCOV_SUBSYSTEM_COMMON:
575 return (handle & KCOV_INSTANCE_MASK) ?
576 common_valid : zero_valid;
577 case KCOV_SUBSYSTEM_USB:
578 return uncommon_valid;
579 default:
580 return false;
581 }
582 return false;
583}
584
585static int kcov_ioctl_locked(struct kcov *kcov, unsigned int cmd,
586 unsigned long arg)
587{
588 struct task_struct *t;
589 unsigned long flags, unused;
590 int mode, i;
591 struct kcov_remote_arg *remote_arg;
592 struct kcov_remote *remote;
593
594 switch (cmd) {
595 case KCOV_ENABLE:
596 /*
597 * Enable coverage for the current task.
598 * At this point user must have been enabled trace mode,
599 * and mmapped the file. Coverage collection is disabled only
600 * at task exit or voluntary by KCOV_DISABLE. After that it can
601 * be enabled for another task.
602 */
603 if (kcov->mode != KCOV_MODE_INIT || !kcov->area)
604 return -EINVAL;
605 t = current;
606 if (kcov->t != NULL || t->kcov != NULL)
607 return -EBUSY;
608 mode = kcov_get_mode(arg);
609 if (mode < 0)
610 return mode;
611 kcov_fault_in_area(kcov);
612 kcov->mode = mode;
613 kcov_start(t, kcov, kcov->size, kcov->area, kcov->mode,
614 kcov->sequence);
615 kcov->t = t;
616 /* Put either in kcov_task_exit() or in KCOV_DISABLE. */
617 kcov_get(kcov);
618 return 0;
619 case KCOV_DISABLE:
620 /* Disable coverage for the current task. */
621 unused = arg;
622 if (unused != 0 || current->kcov != kcov)
623 return -EINVAL;
624 t = current;
625 if (WARN_ON(kcov->t != t))
626 return -EINVAL;
627 kcov_disable(t, kcov);
628 kcov_put(kcov);
629 return 0;
630 case KCOV_REMOTE_ENABLE:
631 if (kcov->mode != KCOV_MODE_INIT || !kcov->area)
632 return -EINVAL;
633 t = current;
634 if (kcov->t != NULL || t->kcov != NULL)
635 return -EBUSY;
636 remote_arg = (struct kcov_remote_arg *)arg;
637 mode = kcov_get_mode(remote_arg->trace_mode);
638 if (mode < 0)
639 return mode;
640 if ((unsigned long)remote_arg->area_size >
641 LONG_MAX / sizeof(unsigned long))
642 return -EINVAL;
643 kcov->mode = mode;
644 t->kcov = kcov;
645 t->kcov_mode = KCOV_MODE_REMOTE;
646 kcov->t = t;
647 kcov->remote = true;
648 kcov->remote_size = remote_arg->area_size;
649 spin_lock_irqsave(&kcov_remote_lock, flags);
650 for (i = 0; i < remote_arg->num_handles; i++) {
651 if (!kcov_check_handle(remote_arg->handles[i],
652 false, true, false)) {
653 spin_unlock_irqrestore(&kcov_remote_lock,
654 flags);
655 kcov_disable(t, kcov);
656 return -EINVAL;
657 }
658 remote = kcov_remote_add(kcov, remote_arg->handles[i]);
659 if (IS_ERR(remote)) {
660 spin_unlock_irqrestore(&kcov_remote_lock,
661 flags);
662 kcov_disable(t, kcov);
663 return PTR_ERR(remote);
664 }
665 }
666 if (remote_arg->common_handle) {
667 if (!kcov_check_handle(remote_arg->common_handle,
668 true, false, false)) {
669 spin_unlock_irqrestore(&kcov_remote_lock,
670 flags);
671 kcov_disable(t, kcov);
672 return -EINVAL;
673 }
674 remote = kcov_remote_add(kcov,
675 remote_arg->common_handle);
676 if (IS_ERR(remote)) {
677 spin_unlock_irqrestore(&kcov_remote_lock,
678 flags);
679 kcov_disable(t, kcov);
680 return PTR_ERR(remote);
681 }
682 t->kcov_handle = remote_arg->common_handle;
683 }
684 spin_unlock_irqrestore(&kcov_remote_lock, flags);
685 /* Put either in kcov_task_exit() or in KCOV_DISABLE. */
686 kcov_get(kcov);
687 return 0;
688 default:
689 return -ENOTTY;
690 }
691}
692
693static long kcov_ioctl(struct file *filep, unsigned int cmd, unsigned long arg)
694{
695 struct kcov *kcov;
696 int res;
697 struct kcov_remote_arg *remote_arg = NULL;
698 unsigned int remote_num_handles;
699 unsigned long remote_arg_size;
700 unsigned long size, flags;
701 void *area;
702
703 kcov = filep->private_data;
704 switch (cmd) {
705 case KCOV_INIT_TRACE:
706 /*
707 * Enable kcov in trace mode and setup buffer size.
708 * Must happen before anything else.
709 *
710 * First check the size argument - it must be at least 2
711 * to hold the current position and one PC.
712 */
713 size = arg;
714 if (size < 2 || size > INT_MAX / sizeof(unsigned long))
715 return -EINVAL;
716 area = vmalloc_user(size * sizeof(unsigned long));
717 if (area == NULL)
718 return -ENOMEM;
719 spin_lock_irqsave(&kcov->lock, flags);
720 if (kcov->mode != KCOV_MODE_DISABLED) {
721 spin_unlock_irqrestore(&kcov->lock, flags);
722 vfree(area);
723 return -EBUSY;
724 }
725 kcov->area = area;
726 kcov->size = size;
727 kcov->mode = KCOV_MODE_INIT;
728 spin_unlock_irqrestore(&kcov->lock, flags);
729 return 0;
730 case KCOV_REMOTE_ENABLE:
731 if (get_user(remote_num_handles, (unsigned __user *)(arg +
732 offsetof(struct kcov_remote_arg, num_handles))))
733 return -EFAULT;
734 if (remote_num_handles > KCOV_REMOTE_MAX_HANDLES)
735 return -EINVAL;
736 remote_arg_size = struct_size(remote_arg, handles,
737 remote_num_handles);
738 remote_arg = memdup_user((void __user *)arg, remote_arg_size);
739 if (IS_ERR(remote_arg))
740 return PTR_ERR(remote_arg);
741 if (remote_arg->num_handles != remote_num_handles) {
742 kfree(remote_arg);
743 return -EINVAL;
744 }
745 arg = (unsigned long)remote_arg;
746 fallthrough;
747 default:
748 /*
749 * All other commands can be normally executed under a spin lock, so we
750 * obtain and release it here in order to simplify kcov_ioctl_locked().
751 */
752 spin_lock_irqsave(&kcov->lock, flags);
753 res = kcov_ioctl_locked(kcov, cmd, arg);
754 spin_unlock_irqrestore(&kcov->lock, flags);
755 kfree(remote_arg);
756 return res;
757 }
758}
759
760static const struct file_operations kcov_fops = {
761 .open = kcov_open,
762 .unlocked_ioctl = kcov_ioctl,
763 .compat_ioctl = kcov_ioctl,
764 .mmap = kcov_mmap,
765 .release = kcov_close,
766};
767
768/*
769 * kcov_remote_start() and kcov_remote_stop() can be used to annotate a section
770 * of code in a kernel background thread or in a softirq to allow kcov to be
771 * used to collect coverage from that part of code.
772 *
773 * The handle argument of kcov_remote_start() identifies a code section that is
774 * used for coverage collection. A userspace process passes this handle to
775 * KCOV_REMOTE_ENABLE ioctl to make the used kcov device start collecting
776 * coverage for the code section identified by this handle.
777 *
778 * The usage of these annotations in the kernel code is different depending on
779 * the type of the kernel thread whose code is being annotated.
780 *
781 * For global kernel threads that are spawned in a limited number of instances
782 * (e.g. one USB hub_event() worker thread is spawned per USB HCD) and for
783 * softirqs, each instance must be assigned a unique 4-byte instance id. The
784 * instance id is then combined with a 1-byte subsystem id to get a handle via
785 * kcov_remote_handle(subsystem_id, instance_id).
786 *
787 * For local kernel threads that are spawned from system calls handler when a
788 * user interacts with some kernel interface (e.g. vhost workers), a handle is
789 * passed from a userspace process as the common_handle field of the
790 * kcov_remote_arg struct (note, that the user must generate a handle by using
791 * kcov_remote_handle() with KCOV_SUBSYSTEM_COMMON as the subsystem id and an
792 * arbitrary 4-byte non-zero number as the instance id). This common handle
793 * then gets saved into the task_struct of the process that issued the
794 * KCOV_REMOTE_ENABLE ioctl. When this process issues system calls that spawn
795 * kernel threads, the common handle must be retrieved via kcov_common_handle()
796 * and passed to the spawned threads via custom annotations. Those kernel
797 * threads must in turn be annotated with kcov_remote_start(common_handle) and
798 * kcov_remote_stop(). All of the threads that are spawned by the same process
799 * obtain the same handle, hence the name "common".
800 *
801 * See Documentation/dev-tools/kcov.rst for more details.
802 *
803 * Internally, kcov_remote_start() looks up the kcov device associated with the
804 * provided handle, allocates an area for coverage collection, and saves the
805 * pointers to kcov and area into the current task_struct to allow coverage to
806 * be collected via __sanitizer_cov_trace_pc().
807 * In turns kcov_remote_stop() clears those pointers from task_struct to stop
808 * collecting coverage and copies all collected coverage into the kcov area.
809 */
810
811static inline bool kcov_mode_enabled(unsigned int mode)
812{
813 return (mode & ~KCOV_IN_CTXSW) != KCOV_MODE_DISABLED;
814}
815
816static void kcov_remote_softirq_start(struct task_struct *t)
817{
818 struct kcov_percpu_data *data = this_cpu_ptr(&kcov_percpu_data);
819 unsigned int mode;
820
821 mode = READ_ONCE(t->kcov_mode);
822 barrier();
823 if (kcov_mode_enabled(mode)) {
824 data->saved_mode = mode;
825 data->saved_size = t->kcov_size;
826 data->saved_area = t->kcov_area;
827 data->saved_sequence = t->kcov_sequence;
828 data->saved_kcov = t->kcov;
829 kcov_stop(t);
830 }
831}
832
833static void kcov_remote_softirq_stop(struct task_struct *t)
834{
835 struct kcov_percpu_data *data = this_cpu_ptr(&kcov_percpu_data);
836
837 if (data->saved_kcov) {
838 kcov_start(t, data->saved_kcov, data->saved_size,
839 data->saved_area, data->saved_mode,
840 data->saved_sequence);
841 data->saved_mode = 0;
842 data->saved_size = 0;
843 data->saved_area = NULL;
844 data->saved_sequence = 0;
845 data->saved_kcov = NULL;
846 }
847}
848
849void kcov_remote_start(u64 handle)
850{
851 struct task_struct *t = current;
852 struct kcov_remote *remote;
853 struct kcov *kcov;
854 unsigned int mode;
855 void *area;
856 unsigned int size;
857 int sequence;
858 unsigned long flags;
859
860 if (WARN_ON(!kcov_check_handle(handle, true, true, true)))
861 return;
862 if (!in_task() && !in_softirq_really())
863 return;
864
865 local_lock_irqsave(&kcov_percpu_data.lock, flags);
866
867 /*
868 * Check that kcov_remote_start() is not called twice in background
869 * threads nor called by user tasks (with enabled kcov).
870 */
871 mode = READ_ONCE(t->kcov_mode);
872 if (WARN_ON(in_task() && kcov_mode_enabled(mode))) {
873 local_unlock_irqrestore(&kcov_percpu_data.lock, flags);
874 return;
875 }
876 /*
877 * Check that kcov_remote_start() is not called twice in softirqs.
878 * Note, that kcov_remote_start() can be called from a softirq that
879 * happened while collecting coverage from a background thread.
880 */
881 if (WARN_ON(in_serving_softirq() && t->kcov_softirq)) {
882 local_unlock_irqrestore(&kcov_percpu_data.lock, flags);
883 return;
884 }
885
886 spin_lock(&kcov_remote_lock);
887 remote = kcov_remote_find(handle);
888 if (!remote) {
889 spin_unlock(&kcov_remote_lock);
890 local_unlock_irqrestore(&kcov_percpu_data.lock, flags);
891 return;
892 }
893 kcov_debug("handle = %llx, context: %s\n", handle,
894 in_task() ? "task" : "softirq");
895 kcov = remote->kcov;
896 /* Put in kcov_remote_stop(). */
897 kcov_get(kcov);
898 /*
899 * Read kcov fields before unlock to prevent races with
900 * KCOV_DISABLE / kcov_remote_reset().
901 */
902 mode = kcov->mode;
903 sequence = kcov->sequence;
904 if (in_task()) {
905 size = kcov->remote_size;
906 area = kcov_remote_area_get(size);
907 } else {
908 size = CONFIG_KCOV_IRQ_AREA_SIZE;
909 area = this_cpu_ptr(&kcov_percpu_data)->irq_area;
910 }
911 spin_unlock(&kcov_remote_lock);
912
913 /* Can only happen when in_task(). */
914 if (!area) {
915 local_unlock_irqrestore(&kcov_percpu_data.lock, flags);
916 area = vmalloc(size * sizeof(unsigned long));
917 if (!area) {
918 kcov_put(kcov);
919 return;
920 }
921 local_lock_irqsave(&kcov_percpu_data.lock, flags);
922 }
923
924 /* Reset coverage size. */
925 *(u64 *)area = 0;
926
927 if (in_serving_softirq()) {
928 kcov_remote_softirq_start(t);
929 t->kcov_softirq = 1;
930 }
931 kcov_start(t, kcov, size, area, mode, sequence);
932
933 local_unlock_irqrestore(&kcov_percpu_data.lock, flags);
934
935}
936EXPORT_SYMBOL(kcov_remote_start);
937
938static void kcov_move_area(enum kcov_mode mode, void *dst_area,
939 unsigned int dst_area_size, void *src_area)
940{
941 u64 word_size = sizeof(unsigned long);
942 u64 count_size, entry_size_log;
943 u64 dst_len, src_len;
944 void *dst_entries, *src_entries;
945 u64 dst_occupied, dst_free, bytes_to_move, entries_moved;
946
947 kcov_debug("%px %u <= %px %lu\n",
948 dst_area, dst_area_size, src_area, *(unsigned long *)src_area);
949
950 switch (mode) {
951 case KCOV_MODE_TRACE_PC:
952 dst_len = READ_ONCE(*(unsigned long *)dst_area);
953 src_len = *(unsigned long *)src_area;
954 count_size = sizeof(unsigned long);
955 entry_size_log = __ilog2_u64(sizeof(unsigned long));
956 break;
957 case KCOV_MODE_TRACE_CMP:
958 dst_len = READ_ONCE(*(u64 *)dst_area);
959 src_len = *(u64 *)src_area;
960 count_size = sizeof(u64);
961 BUILD_BUG_ON(!is_power_of_2(KCOV_WORDS_PER_CMP));
962 entry_size_log = __ilog2_u64(sizeof(u64) * KCOV_WORDS_PER_CMP);
963 break;
964 default:
965 WARN_ON(1);
966 return;
967 }
968
969 /* As arm can't divide u64 integers use log of entry size. */
970 if (dst_len > ((dst_area_size * word_size - count_size) >>
971 entry_size_log))
972 return;
973 dst_occupied = count_size + (dst_len << entry_size_log);
974 dst_free = dst_area_size * word_size - dst_occupied;
975 bytes_to_move = min(dst_free, src_len << entry_size_log);
976 dst_entries = dst_area + dst_occupied;
977 src_entries = src_area + count_size;
978 memcpy(dst_entries, src_entries, bytes_to_move);
979 entries_moved = bytes_to_move >> entry_size_log;
980
981 switch (mode) {
982 case KCOV_MODE_TRACE_PC:
983 WRITE_ONCE(*(unsigned long *)dst_area, dst_len + entries_moved);
984 break;
985 case KCOV_MODE_TRACE_CMP:
986 WRITE_ONCE(*(u64 *)dst_area, dst_len + entries_moved);
987 break;
988 default:
989 break;
990 }
991}
992
993/* See the comment before kcov_remote_start() for usage details. */
994void kcov_remote_stop(void)
995{
996 struct task_struct *t = current;
997 struct kcov *kcov;
998 unsigned int mode;
999 void *area;
1000 unsigned int size;
1001 int sequence;
1002 unsigned long flags;
1003
1004 if (!in_task() && !in_softirq_really())
1005 return;
1006
1007 local_lock_irqsave(&kcov_percpu_data.lock, flags);
1008
1009 mode = READ_ONCE(t->kcov_mode);
1010 barrier();
1011 if (!kcov_mode_enabled(mode)) {
1012 local_unlock_irqrestore(&kcov_percpu_data.lock, flags);
1013 return;
1014 }
1015 /*
1016 * When in softirq, check if the corresponding kcov_remote_start()
1017 * actually found the remote handle and started collecting coverage.
1018 */
1019 if (in_serving_softirq() && !t->kcov_softirq) {
1020 local_unlock_irqrestore(&kcov_percpu_data.lock, flags);
1021 return;
1022 }
1023 /* Make sure that kcov_softirq is only set when in softirq. */
1024 if (WARN_ON(!in_serving_softirq() && t->kcov_softirq)) {
1025 local_unlock_irqrestore(&kcov_percpu_data.lock, flags);
1026 return;
1027 }
1028
1029 kcov = t->kcov;
1030 area = t->kcov_area;
1031 size = t->kcov_size;
1032 sequence = t->kcov_sequence;
1033
1034 kcov_stop(t);
1035 if (in_serving_softirq()) {
1036 t->kcov_softirq = 0;
1037 kcov_remote_softirq_stop(t);
1038 }
1039
1040 spin_lock(&kcov->lock);
1041 /*
1042 * KCOV_DISABLE could have been called between kcov_remote_start()
1043 * and kcov_remote_stop(), hence the sequence check.
1044 */
1045 if (sequence == kcov->sequence && kcov->remote)
1046 kcov_move_area(kcov->mode, kcov->area, kcov->size, area);
1047 spin_unlock(&kcov->lock);
1048
1049 if (in_task()) {
1050 spin_lock(&kcov_remote_lock);
1051 kcov_remote_area_put(area, size);
1052 spin_unlock(&kcov_remote_lock);
1053 }
1054
1055 local_unlock_irqrestore(&kcov_percpu_data.lock, flags);
1056
1057 /* Get in kcov_remote_start(). */
1058 kcov_put(kcov);
1059}
1060EXPORT_SYMBOL(kcov_remote_stop);
1061
1062/* See the comment before kcov_remote_start() for usage details. */
1063u64 kcov_common_handle(void)
1064{
1065 if (!in_task())
1066 return 0;
1067 return current->kcov_handle;
1068}
1069EXPORT_SYMBOL(kcov_common_handle);
1070
1071#ifdef CONFIG_KCOV_SELFTEST
1072static void __init selftest(void)
1073{
1074 unsigned long start;
1075
1076 pr_err("running self test\n");
1077 /*
1078 * Test that interrupts don't produce spurious coverage.
1079 * The coverage callback filters out interrupt code, but only
1080 * after the handler updates preempt count. Some code periodically
1081 * leaks out of that section and leads to spurious coverage.
1082 * It's hard to call the actual interrupt handler directly,
1083 * so we just loop here for a bit waiting for a timer interrupt.
1084 * We set kcov_mode to enable tracing, but don't setup the area,
1085 * so any attempt to trace will crash. Note: we must not call any
1086 * potentially traced functions in this region.
1087 */
1088 start = jiffies;
1089 current->kcov_mode = KCOV_MODE_TRACE_PC;
1090 while ((jiffies - start) * MSEC_PER_SEC / HZ < 300)
1091 ;
1092 current->kcov_mode = 0;
1093 pr_err("done running self test\n");
1094}
1095#endif
1096
1097static int __init kcov_init(void)
1098{
1099 int cpu;
1100
1101 for_each_possible_cpu(cpu) {
1102 void *area = vmalloc_node(CONFIG_KCOV_IRQ_AREA_SIZE *
1103 sizeof(unsigned long), cpu_to_node(cpu));
1104 if (!area)
1105 return -ENOMEM;
1106 per_cpu_ptr(&kcov_percpu_data, cpu)->irq_area = area;
1107 }
1108
1109 /*
1110 * The kcov debugfs file won't ever get removed and thus,
1111 * there is no need to protect it against removal races. The
1112 * use of debugfs_create_file_unsafe() is actually safe here.
1113 */
1114 debugfs_create_file_unsafe("kcov", 0600, NULL, NULL, &kcov_fops);
1115
1116#ifdef CONFIG_KCOV_SELFTEST
1117 selftest();
1118#endif
1119
1120 return 0;
1121}
1122
1123device_initcall(kcov_init);