projects/linux·blob master · refs

1160 lines · 31.8 KiB

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 __guarded_by(&lock);
59 /* Size of arena (in long's). */
60 unsigned int size __guarded_by(&lock);
61 /* Coverage buffer shared with user space. */
62 void *area __guarded_by(&lock);
63 /* Task for which we collect coverage, or NULL. */
64 struct task_struct *t __guarded_by(&lock);
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[2] = {
90 LIST_HEAD_INIT(kcov_remote_areas[0]), LIST_HEAD_INIT(kcov_remote_areas[1])
91};
92
93struct kcov_percpu_data {
94 local_lock_t lock;
95};
96
97static DEFINE_PER_CPU(struct kcov_percpu_data, kcov_percpu_data) = {
98 .lock = INIT_LOCAL_LOCK(lock),
99};
100
101/* Must be called with kcov_remote_lock locked. */
102static struct kcov_remote *kcov_remote_find(u64 handle)
103{
104 struct kcov_remote *remote;
105
106 hash_for_each_possible(kcov_remote_map, remote, hnode, handle) {
107 if (remote->handle == handle)
108 return remote;
109 }
110 return NULL;
111}
112
113/* Must be called with kcov_remote_lock locked. */
114static struct kcov_remote *kcov_remote_add(struct kcov *kcov, u64 handle)
115{
116 struct kcov_remote *remote;
117
118 if (kcov_remote_find(handle))
119 return ERR_PTR(-EEXIST);
120 remote = kmalloc_obj(*remote, GFP_ATOMIC);
121 if (!remote)
122 return ERR_PTR(-ENOMEM);
123 remote->handle = handle;
124 remote->kcov = kcov;
125 hash_add(kcov_remote_map, &remote->hnode, handle);
126 return remote;
127}
128
129/* Must be called with kcov_remote_lock locked. */
130static struct kcov_remote_area *kcov_remote_area_get(unsigned int size, bool irq)
131{
132 struct kcov_remote_area *area;
133 struct list_head *pos;
134 struct list_head *list = &kcov_remote_areas[irq];
135
136 list_for_each(pos, list) {
137 area = list_entry(pos, struct kcov_remote_area, list);
138 if (area->size == size) {
139 list_del(&area->list);
140 return area;
141 }
142 }
143 return NULL;
144}
145
146/* Must be called with kcov_remote_lock locked. */
147static void kcov_remote_area_put(struct kcov_remote_area *area,
148 unsigned int size, bool irq)
149{
150 INIT_LIST_HEAD(&area->list);
151 area->size = size;
152 list_add(&area->list, &kcov_remote_areas[irq]);
153 /*
154 * KMSAN doesn't instrument this file, so it may not know area->list
155 * is initialized. Unpoison it explicitly to avoid reports in
156 * kcov_remote_area_get().
157 */
158 kmsan_unpoison_memory(&area->list, sizeof(area->list));
159}
160
161/*
162 * Unlike in_serving_softirq(), this function returns false when called during
163 * a hardirq or an NMI that happened in the softirq context.
164 */
165static __always_inline bool in_softirq_really(void)
166{
167 return in_serving_softirq() && !in_hardirq() && !in_nmi();
168}
169
170static notrace bool check_kcov_mode(enum kcov_mode needed_mode, struct task_struct *t)
171{
172 unsigned int mode;
173
174 /*
175 * We are interested in code coverage as a function of a syscall inputs,
176 * so we ignore code executed in interrupts, unless we are in a remote
177 * coverage collection section in a softirq.
178 */
179 if (!in_task() && !(in_softirq_really() && t->kcov_softirq))
180 return false;
181 mode = READ_ONCE(t->kcov_mode);
182 /*
183 * There is some code that runs in interrupts but for which
184 * in_interrupt() returns false (e.g. preempt_schedule_irq()).
185 * READ_ONCE()/barrier() effectively provides load-acquire wrt
186 * interrupts, there are paired barrier()/WRITE_ONCE() in
187 * kcov_start().
188 */
189 barrier();
190 return mode == needed_mode;
191}
192
193static notrace unsigned long canonicalize_ip(unsigned long ip)
194{
195#ifdef CONFIG_RANDOMIZE_BASE
196 ip -= kaslr_offset();
197#endif
198 return ip;
199}
200
201/*
202 * Entry point from instrumented code.
203 * This is called once per basic-block/edge.
204 */
205void notrace __sanitizer_cov_trace_pc(void)
206{
207 struct task_struct *t;
208 unsigned long *area;
209 unsigned long ip = canonicalize_ip(_RET_IP_);
210 unsigned long pos;
211
212 t = current;
213 if (!check_kcov_mode(KCOV_MODE_TRACE_PC, t))
214 return;
215
216 area = t->kcov_area;
217 /* The first 64-bit word is the number of subsequent PCs. */
218 pos = READ_ONCE(area[0]) + 1;
219 if (likely(pos < t->kcov_size)) {
220 /* Previously we write pc before updating pos. However, some
221 * early interrupt code could bypass check_kcov_mode() check
222 * and invoke __sanitizer_cov_trace_pc(). If such interrupt is
223 * raised between writing pc and updating pos, the pc could be
224 * overitten by the recursive __sanitizer_cov_trace_pc().
225 * Update pos before writing pc to avoid such interleaving.
226 */
227 WRITE_ONCE(area[0], pos);
228 barrier();
229 area[pos] = ip;
230 }
231}
232EXPORT_SYMBOL(__sanitizer_cov_trace_pc);
233
234#ifdef CONFIG_KCOV_ENABLE_COMPARISONS
235static void notrace write_comp_data(u64 type, u64 arg1, u64 arg2, u64 ip)
236{
237 struct task_struct *t;
238 u64 *area;
239 u64 count, start_index, end_pos, max_pos;
240
241 t = current;
242 if (!check_kcov_mode(KCOV_MODE_TRACE_CMP, t))
243 return;
244
245 ip = canonicalize_ip(ip);
246
247 /*
248 * We write all comparison arguments and types as u64.
249 * The buffer was allocated for t->kcov_size unsigned longs.
250 */
251 area = (u64 *)t->kcov_area;
252 max_pos = t->kcov_size * sizeof(unsigned long);
253
254 count = READ_ONCE(area[0]);
255
256 /* Every record is KCOV_WORDS_PER_CMP 64-bit words. */
257 start_index = 1 + count * KCOV_WORDS_PER_CMP;
258 end_pos = (start_index + KCOV_WORDS_PER_CMP) * sizeof(u64);
259 if (likely(end_pos <= max_pos)) {
260 /* See comment in __sanitizer_cov_trace_pc(). */
261 WRITE_ONCE(area[0], count + 1);
262 barrier();
263 area[start_index] = type;
264 area[start_index + 1] = arg1;
265 area[start_index + 2] = arg2;
266 area[start_index + 3] = ip;
267 }
268}
269
270void notrace __sanitizer_cov_trace_cmp1(u8 arg1, u8 arg2)
271{
272 write_comp_data(KCOV_CMP_SIZE(0), arg1, arg2, _RET_IP_);
273}
274EXPORT_SYMBOL(__sanitizer_cov_trace_cmp1);
275
276void notrace __sanitizer_cov_trace_cmp2(u16 arg1, u16 arg2)
277{
278 write_comp_data(KCOV_CMP_SIZE(1), arg1, arg2, _RET_IP_);
279}
280EXPORT_SYMBOL(__sanitizer_cov_trace_cmp2);
281
282void notrace __sanitizer_cov_trace_cmp4(u32 arg1, u32 arg2)
283{
284 write_comp_data(KCOV_CMP_SIZE(2), arg1, arg2, _RET_IP_);
285}
286EXPORT_SYMBOL(__sanitizer_cov_trace_cmp4);
287
288void notrace __sanitizer_cov_trace_cmp8(kcov_u64 arg1, kcov_u64 arg2)
289{
290 write_comp_data(KCOV_CMP_SIZE(3), arg1, arg2, _RET_IP_);
291}
292EXPORT_SYMBOL(__sanitizer_cov_trace_cmp8);
293
294void notrace __sanitizer_cov_trace_const_cmp1(u8 arg1, u8 arg2)
295{
296 write_comp_data(KCOV_CMP_SIZE(0) | KCOV_CMP_CONST, arg1, arg2,
297 _RET_IP_);
298}
299EXPORT_SYMBOL(__sanitizer_cov_trace_const_cmp1);
300
301void notrace __sanitizer_cov_trace_const_cmp2(u16 arg1, u16 arg2)
302{
303 write_comp_data(KCOV_CMP_SIZE(1) | KCOV_CMP_CONST, arg1, arg2,
304 _RET_IP_);
305}
306EXPORT_SYMBOL(__sanitizer_cov_trace_const_cmp2);
307
308void notrace __sanitizer_cov_trace_const_cmp4(u32 arg1, u32 arg2)
309{
310 write_comp_data(KCOV_CMP_SIZE(2) | KCOV_CMP_CONST, arg1, arg2,
311 _RET_IP_);
312}
313EXPORT_SYMBOL(__sanitizer_cov_trace_const_cmp4);
314
315void notrace __sanitizer_cov_trace_const_cmp8(kcov_u64 arg1, kcov_u64 arg2)
316{
317 write_comp_data(KCOV_CMP_SIZE(3) | KCOV_CMP_CONST, arg1, arg2,
318 _RET_IP_);
319}
320EXPORT_SYMBOL(__sanitizer_cov_trace_const_cmp8);
321
322void notrace __sanitizer_cov_trace_switch(kcov_u64 val, void *arg)
323{
324 u64 i;
325 u64 *cases = arg;
326 u64 count = cases[0];
327 u64 size = cases[1];
328 u64 type = KCOV_CMP_CONST;
329
330 switch (size) {
331 case 8:
332 type |= KCOV_CMP_SIZE(0);
333 break;
334 case 16:
335 type |= KCOV_CMP_SIZE(1);
336 break;
337 case 32:
338 type |= KCOV_CMP_SIZE(2);
339 break;
340 case 64:
341 type |= KCOV_CMP_SIZE(3);
342 break;
343 default:
344 return;
345 }
346 for (i = 0; i < count; i++)
347 write_comp_data(type, cases[i + 2], val, _RET_IP_);
348}
349EXPORT_SYMBOL(__sanitizer_cov_trace_switch);
350#endif /* ifdef CONFIG_KCOV_ENABLE_COMPARISONS */
351
352static void kcov_start(struct task_struct *t, struct kcov *kcov,
353 unsigned int size, void *area, enum kcov_mode mode,
354 int sequence)
355{
356 kcov_debug("t = %px, size = %u, area = %px\n", t, size, area);
357 t->kcov = kcov;
358 /* Cache in task struct for performance. */
359 t->kcov_size = size;
360 t->kcov_area = area;
361 t->kcov_sequence = sequence;
362 /* See comment in check_kcov_mode(). */
363 barrier();
364 WRITE_ONCE(t->kcov_mode, mode);
365}
366
367/* operates on coverage-generator-owned fields */
368static void kcov_stop(struct task_struct *t)
369{
370 WRITE_ONCE(t->kcov_mode, KCOV_MODE_DISABLED);
371 barrier();
372 t->kcov = NULL;
373 t->kcov_size = 0;
374 t->kcov_area = NULL;
375}
376
377/* operates on coverage-generator-owned fields */
378static void kcov_task_reset(struct task_struct *t)
379{
380 kcov_stop(t);
381 t->kcov_sequence = 0;
382}
383
384void kcov_task_init(struct task_struct *t)
385{
386 kcov_task_reset(t);
387 t->kcov_remote = NULL;
388 t->kcov_handle = current->kcov_handle;
389 t->kcov_softirq = 0;
390 t->kcov_saved_mode = 0;
391 t->kcov_saved_size = 0;
392 t->kcov_saved_area = NULL;
393 t->kcov_saved_kcov = NULL;
394 t->kcov_saved_sequence = 0;
395}
396
397static void kcov_reset(struct kcov *kcov)
398 __must_hold(&kcov->lock)
399{
400 kcov->t = NULL;
401 kcov->mode = KCOV_MODE_INIT;
402 kcov->remote = false;
403 kcov->remote_size = 0;
404 kcov->sequence++;
405}
406
407static void kcov_remote_reset(struct kcov *kcov)
408 __must_hold(&kcov->lock)
409{
410 int bkt;
411 struct kcov_remote *remote;
412 struct hlist_node *tmp;
413 unsigned long flags;
414
415 spin_lock_irqsave(&kcov_remote_lock, flags);
416 hash_for_each_safe(kcov_remote_map, bkt, tmp, remote, hnode) {
417 if (remote->kcov != kcov)
418 continue;
419 hash_del(&remote->hnode);
420 kfree(remote);
421 }
422 /* Do reset before unlock to prevent races with kcov_remote_start(). */
423 kcov_reset(kcov);
424 spin_unlock_irqrestore(&kcov_remote_lock, flags);
425}
426
427static void kcov_disable(struct task_struct *t, struct kcov *kcov)
428 __must_hold(&kcov->lock)
429{
430 if (kcov->remote) {
431 t->kcov_handle = 0;
432 t->kcov_remote = NULL;
433 kcov_remote_reset(kcov);
434 } else {
435 kcov_task_reset(t);
436 kcov_reset(kcov);
437 }
438}
439
440static void kcov_get(struct kcov *kcov)
441{
442 refcount_inc(&kcov->refcount);
443}
444
445static void kcov_put(struct kcov *kcov)
446{
447 if (refcount_dec_and_test(&kcov->refcount)) {
448 /* Context-safety: no references left, object being destroyed. */
449 context_unsafe(
450 kcov_remote_reset(kcov);
451 vfree(kcov->area);
452 );
453 kfree(kcov);
454 }
455}
456
457void kcov_task_exit(struct task_struct *t)
458{
459 struct kcov *kcov;
460 unsigned long flags;
461
462 kcov = t->kcov;
463 if (kcov) {
464 spin_lock_irqsave(&kcov->lock, flags);
465 kcov_debug("t = %px, kcov->t = %px\n", t, kcov->t);
466 /*
467 * This could be a remote task between kcov_remote_start() and
468 * kcov_remote_stop().
469 * In this case we should print a warning right away, since a
470 * task shouldn't be exiting when it's in a kcov coverage
471 * collection section.
472 *
473 * Otherwise, this should be a task that created a local
474 * kcov instance and hasn't called KCOV_DISABLE.
475 * Make sure that t->kcov->t is consistent.
476 */
477 if (WARN_ON(kcov->remote) || 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 kcov = t->kcov_remote;
487 if (kcov) {
488 spin_lock_irqsave(&kcov->lock, flags);
489 kcov_debug("t = %px, kcov->t = %px\n", t, kcov->t);
490 /*
491 * This is a KCOV_REMOTE_ENABLE device, and the task is the
492 * user task which has requested remote coverage collection.
493 * Make sure that t->kcov->t is consistent.
494 */
495 if (WARN_ON(!kcov->remote) || WARN_ON(kcov->t != t)) {
496 spin_unlock_irqrestore(&kcov->lock, flags);
497 return;
498 }
499 /* Just to not leave dangling references behind. */
500 kcov_disable(t, kcov);
501 spin_unlock_irqrestore(&kcov->lock, flags);
502 kcov_put(kcov);
503 }
504}
505
506static int kcov_mmap(struct file *filep, struct vm_area_struct *vma)
507{
508 int res = 0;
509 struct kcov *kcov = vma->vm_file->private_data;
510 unsigned long size, off;
511 struct page *page;
512 unsigned long flags;
513 void *area;
514
515 spin_lock_irqsave(&kcov->lock, flags);
516 size = kcov->size * sizeof(unsigned long);
517 if (kcov->area == NULL || vma_start_pgoff(vma) ||
518 vma->vm_end - vma->vm_start != size) {
519 res = -EINVAL;
520 goto exit;
521 }
522 area = kcov->area;
523 spin_unlock_irqrestore(&kcov->lock, flags);
524 vm_flags_set(vma, VM_DONTEXPAND);
525 for (off = 0; off < size; off += PAGE_SIZE) {
526 page = vmalloc_to_page(area + off);
527 res = vm_insert_page(vma, vma->vm_start + off, page);
528 if (res) {
529 pr_warn_once("kcov: vm_insert_page() failed\n");
530 return res;
531 }
532 }
533 return 0;
534exit:
535 spin_unlock_irqrestore(&kcov->lock, flags);
536 return res;
537}
538
539static int kcov_open(struct inode *inode, struct file *filep)
540{
541 struct kcov *kcov;
542
543 kcov = kzalloc_obj(*kcov);
544 if (!kcov)
545 return -ENOMEM;
546 guard(spinlock_init)(&kcov->lock);
547 kcov->mode = KCOV_MODE_DISABLED;
548 kcov->sequence = 1;
549 refcount_set(&kcov->refcount, 1);
550 filep->private_data = kcov;
551 return nonseekable_open(inode, filep);
552}
553
554static int kcov_close(struct inode *inode, struct file *filep)
555{
556 kcov_put(filep->private_data);
557 return 0;
558}
559
560static int kcov_get_mode(unsigned long arg)
561{
562 if (arg == KCOV_TRACE_PC)
563 return KCOV_MODE_TRACE_PC;
564 else if (arg == KCOV_TRACE_CMP)
565#ifdef CONFIG_KCOV_ENABLE_COMPARISONS
566 return KCOV_MODE_TRACE_CMP;
567#else
568 return -ENOTSUPP;
569#endif
570 else
571 return -EINVAL;
572}
573
574/*
575 * Fault in a lazily-faulted vmalloc area before it can be used by
576 * __sanitizer_cov_trace_pc(), to avoid recursion issues if any code on the
577 * vmalloc fault handling path is instrumented.
578 */
579static void kcov_fault_in_area(struct kcov *kcov)
580 __must_hold(&kcov->lock)
581{
582 unsigned long stride = PAGE_SIZE / sizeof(unsigned long);
583 unsigned long *area = kcov->area;
584 unsigned long offset;
585
586 for (offset = 0; offset < kcov->size; offset += stride)
587 READ_ONCE(area[offset]);
588}
589
590static inline bool kcov_check_handle(u64 handle, bool common_valid,
591 bool uncommon_valid, bool zero_valid)
592{
593 if (handle & ~(KCOV_SUBSYSTEM_MASK | KCOV_INSTANCE_MASK))
594 return false;
595 switch (handle & KCOV_SUBSYSTEM_MASK) {
596 case KCOV_SUBSYSTEM_COMMON:
597 return (handle & KCOV_INSTANCE_MASK) ?
598 common_valid : zero_valid;
599 case KCOV_SUBSYSTEM_USB:
600 return uncommon_valid;
601 default:
602 return false;
603 }
604 return false;
605}
606
607static int kcov_ioctl_locked(struct kcov *kcov, unsigned int cmd,
608 unsigned long arg)
609 __must_hold(&kcov->lock)
610{
611 struct task_struct *t;
612 unsigned long flags, unused;
613 int mode, i;
614 struct kcov_remote_arg *remote_arg;
615 struct kcov_remote *remote;
616
617 switch (cmd) {
618 case KCOV_ENABLE:
619 /*
620 * Enable coverage for the current task.
621 * At this point user must have been enabled trace mode,
622 * and mmapped the file. Coverage collection is disabled only
623 * at task exit or voluntary by KCOV_DISABLE. After that it can
624 * be enabled for another task.
625 */
626 if (kcov->mode != KCOV_MODE_INIT || !kcov->area)
627 return -EINVAL;
628 t = current;
629 if (kcov->t != NULL || t->kcov != NULL)
630 return -EBUSY;
631 mode = kcov_get_mode(arg);
632 if (mode < 0)
633 return mode;
634 kcov_fault_in_area(kcov);
635 kcov->mode = mode;
636 kcov_start(t, kcov, kcov->size, kcov->area, kcov->mode,
637 kcov->sequence);
638 kcov->t = t;
639 /* Put either in kcov_task_exit() or in KCOV_DISABLE. */
640 kcov_get(kcov);
641 return 0;
642 case KCOV_DISABLE:
643 /* Disable coverage for the current task. */
644 unused = arg;
645 t = current;
646 if (unused != 0 || (kcov != t->kcov && kcov != t->kcov_remote))
647 return -EINVAL;
648 if (WARN_ON(kcov->t != t))
649 return -EINVAL;
650 kcov_disable(t, kcov);
651 kcov_put(kcov);
652 return 0;
653 case KCOV_REMOTE_ENABLE:
654 if (kcov->mode != KCOV_MODE_INIT || !kcov->area)
655 return -EINVAL;
656 t = current;
657 if (kcov->t != NULL || t->kcov_remote != NULL)
658 return -EBUSY;
659 remote_arg = (struct kcov_remote_arg *)arg;
660 mode = kcov_get_mode(remote_arg->trace_mode);
661 if (mode < 0)
662 return mode;
663 if ((unsigned long)remote_arg->area_size >
664 LONG_MAX / sizeof(unsigned long))
665 return -EINVAL;
666 kcov->mode = mode;
667 t->kcov_remote = kcov;
668 kcov->t = t;
669 kcov->remote = true;
670 kcov->remote_size = remote_arg->area_size;
671 spin_lock_irqsave(&kcov_remote_lock, flags);
672 for (i = 0; i < remote_arg->num_handles; i++) {
673 if (!kcov_check_handle(remote_arg->handles[i],
674 false, true, false)) {
675 spin_unlock_irqrestore(&kcov_remote_lock,
676 flags);
677 kcov_disable(t, kcov);
678 return -EINVAL;
679 }
680 remote = kcov_remote_add(kcov, remote_arg->handles[i]);
681 if (IS_ERR(remote)) {
682 spin_unlock_irqrestore(&kcov_remote_lock,
683 flags);
684 kcov_disable(t, kcov);
685 return PTR_ERR(remote);
686 }
687 }
688 if (remote_arg->common_handle) {
689 if (!kcov_check_handle(remote_arg->common_handle,
690 true, false, false)) {
691 spin_unlock_irqrestore(&kcov_remote_lock,
692 flags);
693 kcov_disable(t, kcov);
694 return -EINVAL;
695 }
696 remote = kcov_remote_add(kcov,
697 remote_arg->common_handle);
698 if (IS_ERR(remote)) {
699 spin_unlock_irqrestore(&kcov_remote_lock,
700 flags);
701 kcov_disable(t, kcov);
702 return PTR_ERR(remote);
703 }
704 t->kcov_handle = remote_arg->common_handle;
705 }
706 spin_unlock_irqrestore(&kcov_remote_lock, flags);
707 /* Put either in kcov_task_exit() or in KCOV_DISABLE. */
708 kcov_get(kcov);
709 return 0;
710 default:
711 return -ENOTTY;
712 }
713}
714
715static long kcov_ioctl(struct file *filep, unsigned int cmd, unsigned long arg)
716{
717 struct kcov *kcov;
718 int res;
719 struct kcov_remote_arg *remote_arg = NULL;
720 unsigned int remote_num_handles;
721 unsigned long remote_arg_size;
722 unsigned long size, flags;
723 void *area;
724
725 kcov = filep->private_data;
726 switch (cmd) {
727 case KCOV_INIT_TRACE:
728 /*
729 * Enable kcov in trace mode and setup buffer size.
730 * Must happen before anything else.
731 *
732 * First check the size argument - it must be at least 2
733 * to hold the current position and one PC.
734 */
735 size = arg;
736 if (size < 2 || size > INT_MAX / sizeof(unsigned long))
737 return -EINVAL;
738 area = vmalloc_user(size * sizeof(unsigned long));
739 if (area == NULL)
740 return -ENOMEM;
741 spin_lock_irqsave(&kcov->lock, flags);
742 if (kcov->mode != KCOV_MODE_DISABLED) {
743 spin_unlock_irqrestore(&kcov->lock, flags);
744 vfree(area);
745 return -EBUSY;
746 }
747 kcov->area = area;
748 kcov->size = size;
749 kcov->mode = KCOV_MODE_INIT;
750 spin_unlock_irqrestore(&kcov->lock, flags);
751 return 0;
752 case KCOV_REMOTE_ENABLE:
753 if (get_user(remote_num_handles, (unsigned __user *)(arg +
754 offsetof(struct kcov_remote_arg, num_handles))))
755 return -EFAULT;
756 if (remote_num_handles > KCOV_REMOTE_MAX_HANDLES)
757 return -EINVAL;
758 remote_arg_size = struct_size(remote_arg, handles,
759 remote_num_handles);
760 remote_arg = memdup_user((void __user *)arg, remote_arg_size);
761 if (IS_ERR(remote_arg))
762 return PTR_ERR(remote_arg);
763 if (remote_arg->num_handles != remote_num_handles) {
764 kfree(remote_arg);
765 return -EINVAL;
766 }
767 arg = (unsigned long)remote_arg;
768 fallthrough;
769 default:
770 /*
771 * All other commands can be normally executed under a spin lock, so we
772 * obtain and release it here in order to simplify kcov_ioctl_locked().
773 */
774 spin_lock_irqsave(&kcov->lock, flags);
775 res = kcov_ioctl_locked(kcov, cmd, arg);
776 spin_unlock_irqrestore(&kcov->lock, flags);
777 kfree(remote_arg);
778 return res;
779 }
780}
781
782static const struct file_operations kcov_fops = {
783 .open = kcov_open,
784 .unlocked_ioctl = kcov_ioctl,
785 .compat_ioctl = kcov_ioctl,
786 .mmap = kcov_mmap,
787 .release = kcov_close,
788};
789
790/*
791 * kcov_remote_start() and kcov_remote_stop() can be used to annotate a section
792 * of code in a kernel background thread or in a softirq to allow kcov to be
793 * used to collect coverage from that part of code.
794 *
795 * The handle argument of kcov_remote_start() identifies a code section that is
796 * used for coverage collection. A userspace process passes this handle to
797 * KCOV_REMOTE_ENABLE ioctl to make the used kcov device start collecting
798 * coverage for the code section identified by this handle.
799 *
800 * The usage of these annotations in the kernel code is different depending on
801 * the type of the kernel thread whose code is being annotated.
802 *
803 * For global kernel threads that are spawned in a limited number of instances
804 * (e.g. one USB hub_event() worker thread is spawned per USB HCD) and for
805 * softirqs, each instance must be assigned a unique 4-byte instance id. The
806 * instance id is then combined with a 1-byte subsystem id to get a handle via
807 * kcov_remote_handle(subsystem_id, instance_id).
808 *
809 * For local kernel threads that are spawned from system calls handler when a
810 * user interacts with some kernel interface (e.g. vhost workers), a handle is
811 * passed from a userspace process as the common_handle field of the
812 * kcov_remote_arg struct (note, that the user must generate a handle by using
813 * kcov_remote_handle() with KCOV_SUBSYSTEM_COMMON as the subsystem id and an
814 * arbitrary 4-byte non-zero number as the instance id). This common handle
815 * then gets saved into the task_struct of the process that issued the
816 * KCOV_REMOTE_ENABLE ioctl. When this process issues system calls that spawn
817 * kernel threads, the common handle must be retrieved via kcov_common_handle()
818 * and passed to the spawned threads via custom annotations. Those kernel
819 * threads must in turn be annotated with kcov_remote_start(common_handle) and
820 * kcov_remote_stop(). All of the threads that are spawned by the same process
821 * obtain the same handle, hence the name "common".
822 *
823 * See Documentation/dev-tools/kcov.rst for more details.
824 *
825 * Internally, kcov_remote_start() looks up the kcov device associated with the
826 * provided handle, allocates an area for coverage collection, and saves the
827 * pointers to kcov and area into the current task_struct to allow coverage to
828 * be collected via __sanitizer_cov_trace_pc().
829 * In turns kcov_remote_stop() clears those pointers from task_struct to stop
830 * collecting coverage and copies all collected coverage into the kcov area.
831 */
832
833static inline bool kcov_mode_enabled(unsigned int mode)
834{
835 return (mode & ~KCOV_IN_CTXSW) != KCOV_MODE_DISABLED;
836}
837
838static void kcov_remote_softirq_start(struct task_struct *t)
839 __must_hold(&kcov_percpu_data.lock)
840{
841 unsigned int mode;
842
843 mode = READ_ONCE(t->kcov_mode);
844 barrier();
845 if (kcov_mode_enabled(mode)) {
846 t->kcov_saved_mode = mode;
847 t->kcov_saved_size = t->kcov_size;
848 t->kcov_saved_area = t->kcov_area;
849 t->kcov_saved_sequence = t->kcov_sequence;
850 t->kcov_saved_kcov = t->kcov;
851 kcov_stop(t);
852 }
853}
854
855static void kcov_remote_softirq_stop(struct task_struct *t)
856 __must_hold(&kcov_percpu_data.lock)
857{
858 if (t->kcov_saved_kcov) {
859 kcov_start(t, t->kcov_saved_kcov, t->kcov_saved_size,
860 t->kcov_saved_area, t->kcov_saved_mode,
861 t->kcov_saved_sequence);
862 t->kcov_saved_mode = 0;
863 t->kcov_saved_size = 0;
864 t->kcov_saved_area = NULL;
865 t->kcov_saved_sequence = 0;
866 t->kcov_saved_kcov = NULL;
867 }
868}
869
870void kcov_remote_start(u64 handle)
871{
872 struct task_struct *t = current;
873 struct kcov_remote *remote;
874 struct kcov *kcov;
875 unsigned int mode;
876 void *area;
877 unsigned int size;
878 int sequence;
879 unsigned long flags;
880
881 if (WARN_ON(!kcov_check_handle(handle, true, true, true)))
882 return;
883 if (!in_task() && !in_softirq_really())
884 return;
885
886 local_lock_irqsave(&kcov_percpu_data.lock, flags);
887
888 /*
889 * Check that kcov_remote_start() is not called twice in background
890 * threads nor called by user tasks (with enabled kcov).
891 */
892 mode = READ_ONCE(t->kcov_mode);
893 if (WARN_ON(in_task() && kcov_mode_enabled(mode))) {
894 local_unlock_irqrestore(&kcov_percpu_data.lock, flags);
895 return;
896 }
897 /*
898 * Check that kcov_remote_start() is not called twice in softirqs.
899 * Note, that kcov_remote_start() can be called from a softirq that
900 * happened while collecting coverage from a background thread.
901 */
902 if (WARN_ON(in_serving_softirq() && t->kcov_softirq)) {
903 local_unlock_irqrestore(&kcov_percpu_data.lock, flags);
904 return;
905 }
906
907 spin_lock(&kcov_remote_lock);
908 remote = kcov_remote_find(handle);
909 if (!remote) {
910 spin_unlock(&kcov_remote_lock);
911 local_unlock_irqrestore(&kcov_percpu_data.lock, flags);
912 return;
913 }
914 kcov_debug("handle = %llx, context: %s\n", handle,
915 in_task() ? "task" : "softirq");
916 kcov = remote->kcov;
917 /* Put in kcov_remote_stop(). */
918 kcov_get(kcov);
919 /*
920 * Read kcov fields before unlocking kcov_remote_lock to prevent races
921 * with KCOV_DISABLE and kcov_remote_reset(); cannot acquire kcov->lock
922 * here, because it might lead to deadlock given kcov_remote_lock is
923 * acquired _after_ kcov->lock elsewhere.
924 */
925 mode = context_unsafe(kcov->mode);
926 sequence = kcov->sequence;
927 if (in_task()) {
928 size = kcov->remote_size;
929 area = kcov_remote_area_get(size, false);
930 } else {
931 size = CONFIG_KCOV_IRQ_AREA_SIZE;
932 area = kcov_remote_area_get(size, true);
933 }
934 spin_unlock(&kcov_remote_lock);
935
936 /* Allocate new buffer if we can sleep. */
937 if (!area) {
938 local_unlock_irqrestore(&kcov_percpu_data.lock, flags);
939 area = in_task() ? vmalloc(size * sizeof(unsigned long)) : NULL;
940 if (!area) {
941 kcov_put(kcov);
942 return;
943 }
944 local_lock_irqsave(&kcov_percpu_data.lock, flags);
945 }
946
947 /* Reset coverage size. */
948 *(u64 *)area = 0;
949
950 if (in_serving_softirq()) {
951 kcov_remote_softirq_start(t);
952 t->kcov_softirq = 1;
953 }
954 kcov_start(t, kcov, size, area, mode, sequence);
955
956 local_unlock_irqrestore(&kcov_percpu_data.lock, flags);
957
958}
959EXPORT_SYMBOL(kcov_remote_start);
960
961static void kcov_move_area(enum kcov_mode mode, void *dst_area,
962 unsigned int dst_area_size, void *src_area)
963{
964 u64 word_size = sizeof(unsigned long);
965 u64 count_size, entry_size_log;
966 u64 dst_len, src_len;
967 void *dst_entries, *src_entries;
968 u64 dst_occupied, dst_free, bytes_to_move, entries_moved;
969
970 kcov_debug("%px %u <= %px %lu\n",
971 dst_area, dst_area_size, src_area, *(unsigned long *)src_area);
972
973 switch (mode) {
974 case KCOV_MODE_TRACE_PC:
975 dst_len = READ_ONCE(*(unsigned long *)dst_area);
976 src_len = *(unsigned long *)src_area;
977 count_size = sizeof(unsigned long);
978 entry_size_log = __ilog2_u64(sizeof(unsigned long));
979 break;
980 case KCOV_MODE_TRACE_CMP:
981 dst_len = READ_ONCE(*(u64 *)dst_area);
982 src_len = *(u64 *)src_area;
983 count_size = sizeof(u64);
984 BUILD_BUG_ON(!is_power_of_2(KCOV_WORDS_PER_CMP));
985 entry_size_log = __ilog2_u64(sizeof(u64) * KCOV_WORDS_PER_CMP);
986 break;
987 default:
988 WARN_ON(1);
989 return;
990 }
991
992 /* As arm can't divide u64 integers use log of entry size. */
993 if (dst_len > ((dst_area_size * word_size - count_size) >>
994 entry_size_log))
995 return;
996 dst_occupied = count_size + (dst_len << entry_size_log);
997 dst_free = dst_area_size * word_size - dst_occupied;
998 bytes_to_move = min(dst_free, src_len << entry_size_log);
999 dst_entries = dst_area + dst_occupied;
1000 src_entries = src_area + count_size;
1001 memcpy(dst_entries, src_entries, bytes_to_move);
1002 entries_moved = bytes_to_move >> entry_size_log;
1003
1004 /*
1005 * A write memory barrier is required here, to ensure
1006 * that the writes from the memcpy() are visible before
1007 * the count is updated. Without this, it is possible for
1008 * a user to observe a new count value but stale
1009 * coverage data.
1010 */
1011 smp_wmb();
1012
1013 switch (mode) {
1014 case KCOV_MODE_TRACE_PC:
1015 WRITE_ONCE(*(unsigned long *)dst_area, dst_len + entries_moved);
1016 break;
1017 case KCOV_MODE_TRACE_CMP:
1018 WRITE_ONCE(*(u64 *)dst_area, dst_len + entries_moved);
1019 break;
1020 default:
1021 break;
1022 }
1023}
1024
1025/* See the comment before kcov_remote_start() for usage details. */
1026void kcov_remote_stop(void)
1027{
1028 struct task_struct *t = current;
1029 struct kcov *kcov;
1030 unsigned int mode;
1031 void *area;
1032 unsigned int size;
1033 int sequence;
1034 unsigned long flags;
1035
1036 if (!in_task() && !in_softirq_really())
1037 return;
1038
1039 local_lock_irqsave(&kcov_percpu_data.lock, flags);
1040
1041 mode = READ_ONCE(t->kcov_mode);
1042 barrier();
1043 if (!kcov_mode_enabled(mode)) {
1044 local_unlock_irqrestore(&kcov_percpu_data.lock, flags);
1045 return;
1046 }
1047 /*
1048 * When in softirq, check if the corresponding kcov_remote_start()
1049 * actually found the remote handle and started collecting coverage.
1050 */
1051 if (in_serving_softirq() && !t->kcov_softirq) {
1052 local_unlock_irqrestore(&kcov_percpu_data.lock, flags);
1053 return;
1054 }
1055 /* Make sure that kcov_softirq is only set when in softirq. */
1056 if (WARN_ON(!in_serving_softirq() && t->kcov_softirq)) {
1057 local_unlock_irqrestore(&kcov_percpu_data.lock, flags);
1058 return;
1059 }
1060
1061 kcov = t->kcov;
1062 area = t->kcov_area;
1063 size = t->kcov_size;
1064 sequence = t->kcov_sequence;
1065
1066 kcov_stop(t);
1067 if (in_serving_softirq()) {
1068 t->kcov_softirq = 0;
1069 kcov_remote_softirq_stop(t);
1070 }
1071
1072 spin_lock(&kcov->lock);
1073 /*
1074 * KCOV_DISABLE could have been called between kcov_remote_start()
1075 * and kcov_remote_stop(), hence the sequence check.
1076 */
1077 if (sequence == kcov->sequence && kcov->remote)
1078 kcov_move_area(kcov->mode, kcov->area, kcov->size, area);
1079 spin_unlock(&kcov->lock);
1080
1081 spin_lock(&kcov_remote_lock);
1082 kcov_remote_area_put(area, size, !in_task());
1083 spin_unlock(&kcov_remote_lock);
1084
1085 local_unlock_irqrestore(&kcov_percpu_data.lock, flags);
1086
1087 /* Get in kcov_remote_start(). */
1088 kcov_put(kcov);
1089}
1090EXPORT_SYMBOL(kcov_remote_stop);
1091
1092/* See the comment before kcov_remote_start() for usage details. */
1093struct kcov_common_handle_id kcov_common_handle(void)
1094{
1095 if (!in_task())
1096 return (struct kcov_common_handle_id){ .val = 0 };
1097 return (struct kcov_common_handle_id){ .val = current->kcov_handle };
1098}
1099EXPORT_SYMBOL(kcov_common_handle);
1100
1101#ifdef CONFIG_KCOV_SELFTEST
1102static void __init selftest(void)
1103{
1104 unsigned long start;
1105
1106 pr_err("running self test\n");
1107 /*
1108 * Test that interrupts don't produce spurious coverage.
1109 * The coverage callback filters out interrupt code, but only
1110 * after the handler updates preempt count. Some code periodically
1111 * leaks out of that section and leads to spurious coverage.
1112 * It's hard to call the actual interrupt handler directly,
1113 * so we just loop here for a bit waiting for a timer interrupt.
1114 * We set kcov_mode to enable tracing, but don't setup the area,
1115 * so any attempt to trace will crash. Note: we must not call any
1116 * potentially traced functions in this region.
1117 */
1118 start = jiffies;
1119 WRITE_ONCE(current->kcov_mode, KCOV_MODE_TRACE_PC);
1120 while ((jiffies - start) * MSEC_PER_SEC / HZ < 300)
1121 ;
1122 WRITE_ONCE(current->kcov_mode, 0);
1123 pr_err("done running self test\n");
1124}
1125#endif
1126
1127static int __init kcov_init(void)
1128{
1129 int cpu = num_possible_cpus();
1130
1131#ifdef CONFIG_PREEMPT_RT
1132 /* Allocate some extra buffers in order to prepare for softirq preemption. */
1133 cpu = cpu >= 4 ? cpu * 2 : cpu + 4;
1134#endif
1135 while (cpu--) {
1136 void *area = vmalloc(CONFIG_KCOV_IRQ_AREA_SIZE * sizeof(unsigned long));
1137 unsigned long flags;
1138
1139 if (!area)
1140 return -ENOMEM;
1141 spin_lock_irqsave(&kcov_remote_lock, flags);
1142 kcov_remote_area_put(area, CONFIG_KCOV_IRQ_AREA_SIZE, true);
1143 spin_unlock_irqrestore(&kcov_remote_lock, flags);
1144 }
1145
1146 /*
1147 * The kcov debugfs file won't ever get removed and thus,
1148 * there is no need to protect it against removal races. The
1149 * use of debugfs_create_file_unsafe() is actually safe here.
1150 */
1151 debugfs_create_file_unsafe("kcov", 0600, NULL, NULL, &kcov_fops);
1152
1153#ifdef CONFIG_KCOV_SELFTEST
1154 selftest();
1155#endif
1156
1157 return 0;
1158}
1159
1160device_initcall(kcov_init);