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

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source code of linux/kernel/kcov.c