xref: /linux/kernel/kcov.c (revision ff30564411ffdcee49d579cb15eb13185a36e253)
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  */
47 struct 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 
75 struct kcov_remote_area {
76 	struct list_head	list;
77 	unsigned int		size;
78 };
79 
80 struct kcov_remote {
81 	u64			handle;
82 	struct kcov		*kcov;
83 	struct hlist_node	hnode;
84 };
85 
86 static DEFINE_SPINLOCK(kcov_remote_lock);
87 static DEFINE_HASHTABLE(kcov_remote_map, 4);
88 static struct list_head kcov_remote_areas = LIST_HEAD_INIT(kcov_remote_areas);
89 
90 struct 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 
101 static 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. */
106 static 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. */
118 static 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(-EEXIST);
124 	remote = kmalloc(sizeof(*remote), GFP_ATOMIC);
125 	if (!remote)
126 		return ERR_PTR(-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. */
134 static 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(&area->list);
143 			return area;
144 		}
145 	}
146 	return NULL;
147 }
148 
149 /* Must be called with kcov_remote_lock locked. */
150 static void kcov_remote_area_put(struct kcov_remote_area *area,
151 					unsigned int size)
152 {
153 	INIT_LIST_HEAD(&area->list);
154 	area->size = size;
155 	list_add(&area->list, &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(&area->list, sizeof(area->list));
162 }
163 
164 static 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 
187 static 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  */
199 void 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(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 }
226 EXPORT_SYMBOL(__sanitizer_cov_trace_pc);
227 
228 #ifdef CONFIG_KCOV_ENABLE_COMPARISONS
229 static 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(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 
264 void notrace __sanitizer_cov_trace_cmp1(u8 arg1, u8 arg2)
265 {
266 	write_comp_data(KCOV_CMP_SIZE(0), arg1, arg2, _RET_IP_);
267 }
268 EXPORT_SYMBOL(__sanitizer_cov_trace_cmp1);
269 
270 void notrace __sanitizer_cov_trace_cmp2(u16 arg1, u16 arg2)
271 {
272 	write_comp_data(KCOV_CMP_SIZE(1), arg1, arg2, _RET_IP_);
273 }
274 EXPORT_SYMBOL(__sanitizer_cov_trace_cmp2);
275 
276 void notrace __sanitizer_cov_trace_cmp4(u32 arg1, u32 arg2)
277 {
278 	write_comp_data(KCOV_CMP_SIZE(2), arg1, arg2, _RET_IP_);
279 }
280 EXPORT_SYMBOL(__sanitizer_cov_trace_cmp4);
281 
282 void 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 }
286 EXPORT_SYMBOL(__sanitizer_cov_trace_cmp8);
287 
288 void 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 }
293 EXPORT_SYMBOL(__sanitizer_cov_trace_const_cmp1);
294 
295 void 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 }
300 EXPORT_SYMBOL(__sanitizer_cov_trace_const_cmp2);
301 
302 void 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 }
307 EXPORT_SYMBOL(__sanitizer_cov_trace_const_cmp4);
308 
309 void 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 }
314 EXPORT_SYMBOL(__sanitizer_cov_trace_const_cmp8);
315 
316 void 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, cases[i + 2], val, _RET_IP_);
342 }
343 EXPORT_SYMBOL(__sanitizer_cov_trace_switch);
344 #endif /* ifdef CONFIG_KCOV_ENABLE_COMPARISONS */
345 
346 static 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 
361 static 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 
370 static 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 
377 void kcov_task_init(struct task_struct *t)
378 {
379 	kcov_task_reset(t);
380 	t->kcov_handle = current->kcov_handle;
381 }
382 
383 static 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 
392 static 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(&remote->hnode);
404 		kfree(remote);
405 	}
406 	/* Do reset before unlock to prevent races with kcov_remote_start(). */
407 	kcov_reset(kcov);
408 	spin_unlock_irqrestore(&kcov_remote_lock, flags);
409 }
410 
411 static 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 
420 static void kcov_get(struct kcov *kcov)
421 {
422 	refcount_inc(&kcov->refcount);
423 }
424 
425 static void kcov_put(struct kcov *kcov)
426 {
427 	if (refcount_dec_and_test(&kcov->refcount)) {
428 		kcov_remote_reset(kcov);
429 		vfree(kcov->area);
430 		kfree(kcov);
431 	}
432 }
433 
434 void 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(&kcov->lock, flags);
469 		return;
470 	}
471 	/* Just to not leave dangling references behind. */
472 	kcov_disable(t, kcov);
473 	spin_unlock_irqrestore(&kcov->lock, flags);
474 	kcov_put(kcov);
475 }
476 
477 static 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(&kcov->lock, flags);
493 	vm_flags_set(vma, VM_DONTEXPAND);
494 	for (off = 0; off < size; off += PAGE_SIZE) {
495 		page = vmalloc_to_page(kcov->area + off);
496 		res = vm_insert_page(vma, 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;
503 exit:
504 	spin_unlock_irqrestore(&kcov->lock, flags);
505 	return res;
506 }
507 
508 static int kcov_open(struct inode *inode, struct file *filep)
509 {
510 	struct kcov *kcov;
511 
512 	kcov = kzalloc(sizeof(*kcov), GFP_KERNEL);
513 	if (!kcov)
514 		return -ENOMEM;
515 	kcov->mode = KCOV_MODE_DISABLED;
516 	kcov->sequence = 1;
517 	refcount_set(&kcov->refcount, 1);
518 	spin_lock_init(&kcov->lock);
519 	filep->private_data = kcov;
520 	return nonseekable_open(inode, filep);
521 }
522 
523 static int kcov_close(struct inode *inode, struct file *filep)
524 {
525 	kcov_put(filep->private_data);
526 	return 0;
527 }
528 
529 static 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  */
548 static 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 
558 static 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 
575 static 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, kcov->size, kcov->area, kcov->mode,
604 				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(remote_arg->trace_mode);
628 		if (mode < 0)
629 			return mode;
630 		if ((unsigned long)remote_arg->area_size >
631 		    LONG_MAX / sizeof(unsigned long))
632 			return -EINVAL;
633 		kcov->mode = mode;
634 		t->kcov = kcov;
635 	        t->kcov_mode = KCOV_MODE_REMOTE;
636 		kcov->t = t;
637 		kcov->remote = true;
638 		kcov->remote_size = remote_arg->area_size;
639 		spin_lock_irqsave(&kcov_remote_lock, flags);
640 		for (i = 0; i < remote_arg->num_handles; i++) {
641 			if (!kcov_check_handle(remote_arg->handles[i],
642 						false, true, false)) {
643 				spin_unlock_irqrestore(&kcov_remote_lock,
644 							flags);
645 				kcov_disable(t, kcov);
646 				return -EINVAL;
647 			}
648 			remote = kcov_remote_add(kcov, remote_arg->handles[i]);
649 			if (IS_ERR(remote)) {
650 				spin_unlock_irqrestore(&kcov_remote_lock,
651 							flags);
652 				kcov_disable(t, kcov);
653 				return PTR_ERR(remote);
654 			}
655 		}
656 		if (remote_arg->common_handle) {
657 			if (!kcov_check_handle(remote_arg->common_handle,
658 						true, false, false)) {
659 				spin_unlock_irqrestore(&kcov_remote_lock,
660 							flags);
661 				kcov_disable(t, kcov);
662 				return -EINVAL;
663 			}
664 			remote = kcov_remote_add(kcov,
665 					remote_arg->common_handle);
666 			if (IS_ERR(remote)) {
667 				spin_unlock_irqrestore(&kcov_remote_lock,
668 							flags);
669 				kcov_disable(t, kcov);
670 				return PTR_ERR(remote);
671 			}
672 			t->kcov_handle = remote_arg->common_handle;
673 		}
674 		spin_unlock_irqrestore(&kcov_remote_lock, flags);
675 		/* Put either in kcov_task_exit() or in KCOV_DISABLE. */
676 		kcov_get(kcov);
677 		return 0;
678 	default:
679 		return -ENOTTY;
680 	}
681 }
682 
683 static long kcov_ioctl(struct file *filep, unsigned int cmd, unsigned long arg)
684 {
685 	struct kcov *kcov;
686 	int res;
687 	struct kcov_remote_arg *remote_arg = NULL;
688 	unsigned int remote_num_handles;
689 	unsigned long remote_arg_size;
690 	unsigned long size, flags;
691 	void *area;
692 
693 	kcov = filep->private_data;
694 	switch (cmd) {
695 	case KCOV_INIT_TRACE:
696 		/*
697 		 * Enable kcov in trace mode and setup buffer size.
698 		 * Must happen before anything else.
699 		 *
700 		 * First check the size argument - it must be at least 2
701 		 * to hold the current position and one PC.
702 		 */
703 		size = arg;
704 		if (size < 2 || size > INT_MAX / sizeof(unsigned long))
705 			return -EINVAL;
706 		area = vmalloc_user(size * sizeof(unsigned long));
707 		if (area == NULL)
708 			return -ENOMEM;
709 		spin_lock_irqsave(&kcov->lock, flags);
710 		if (kcov->mode != KCOV_MODE_DISABLED) {
711 			spin_unlock_irqrestore(&kcov->lock, flags);
712 			vfree(area);
713 			return -EBUSY;
714 		}
715 		kcov->area = area;
716 		kcov->size = size;
717 		kcov->mode = KCOV_MODE_INIT;
718 		spin_unlock_irqrestore(&kcov->lock, flags);
719 		return 0;
720 	case KCOV_REMOTE_ENABLE:
721 		if (get_user(remote_num_handles, (unsigned __user *)(arg +
722 				offsetof(struct kcov_remote_arg, num_handles))))
723 			return -EFAULT;
724 		if (remote_num_handles > KCOV_REMOTE_MAX_HANDLES)
725 			return -EINVAL;
726 		remote_arg_size = struct_size(remote_arg, handles,
727 					remote_num_handles);
728 		remote_arg = memdup_user((void __user *)arg, remote_arg_size);
729 		if (IS_ERR(remote_arg))
730 			return PTR_ERR(remote_arg);
731 		if (remote_arg->num_handles != remote_num_handles) {
732 			kfree(remote_arg);
733 			return -EINVAL;
734 		}
735 		arg = (unsigned long)remote_arg;
736 		fallthrough;
737 	default:
738 		/*
739 		 * All other commands can be normally executed under a spin lock, so we
740 		 * obtain and release it here in order to simplify kcov_ioctl_locked().
741 		 */
742 		spin_lock_irqsave(&kcov->lock, flags);
743 		res = kcov_ioctl_locked(kcov, cmd, arg);
744 		spin_unlock_irqrestore(&kcov->lock, flags);
745 		kfree(remote_arg);
746 		return res;
747 	}
748 }
749 
750 static const struct file_operations kcov_fops = {
751 	.open		= kcov_open,
752 	.unlocked_ioctl	= kcov_ioctl,
753 	.compat_ioctl	= kcov_ioctl,
754 	.mmap		= kcov_mmap,
755 	.release        = kcov_close,
756 };
757 
758 /*
759  * kcov_remote_start() and kcov_remote_stop() can be used to annotate a section
760  * of code in a kernel background thread or in a softirq to allow kcov to be
761  * used to collect coverage from that part of code.
762  *
763  * The handle argument of kcov_remote_start() identifies a code section that is
764  * used for coverage collection. A userspace process passes this handle to
765  * KCOV_REMOTE_ENABLE ioctl to make the used kcov device start collecting
766  * coverage for the code section identified by this handle.
767  *
768  * The usage of these annotations in the kernel code is different depending on
769  * the type of the kernel thread whose code is being annotated.
770  *
771  * For global kernel threads that are spawned in a limited number of instances
772  * (e.g. one USB hub_event() worker thread is spawned per USB HCD) and for
773  * softirqs, each instance must be assigned a unique 4-byte instance id. The
774  * instance id is then combined with a 1-byte subsystem id to get a handle via
775  * kcov_remote_handle(subsystem_id, instance_id).
776  *
777  * For local kernel threads that are spawned from system calls handler when a
778  * user interacts with some kernel interface (e.g. vhost workers), a handle is
779  * passed from a userspace process as the common_handle field of the
780  * kcov_remote_arg struct (note, that the user must generate a handle by using
781  * kcov_remote_handle() with KCOV_SUBSYSTEM_COMMON as the subsystem id and an
782  * arbitrary 4-byte non-zero number as the instance id). This common handle
783  * then gets saved into the task_struct of the process that issued the
784  * KCOV_REMOTE_ENABLE ioctl. When this process issues system calls that spawn
785  * kernel threads, the common handle must be retrieved via kcov_common_handle()
786  * and passed to the spawned threads via custom annotations. Those kernel
787  * threads must in turn be annotated with kcov_remote_start(common_handle) and
788  * kcov_remote_stop(). All of the threads that are spawned by the same process
789  * obtain the same handle, hence the name "common".
790  *
791  * See Documentation/dev-tools/kcov.rst for more details.
792  *
793  * Internally, kcov_remote_start() looks up the kcov device associated with the
794  * provided handle, allocates an area for coverage collection, and saves the
795  * pointers to kcov and area into the current task_struct to allow coverage to
796  * be collected via __sanitizer_cov_trace_pc().
797  * In turns kcov_remote_stop() clears those pointers from task_struct to stop
798  * collecting coverage and copies all collected coverage into the kcov area.
799  */
800 
801 static inline bool kcov_mode_enabled(unsigned int mode)
802 {
803 	return (mode & ~KCOV_IN_CTXSW) != KCOV_MODE_DISABLED;
804 }
805 
806 static void kcov_remote_softirq_start(struct task_struct *t)
807 {
808 	struct kcov_percpu_data *data = this_cpu_ptr(&kcov_percpu_data);
809 	unsigned int mode;
810 
811 	mode = READ_ONCE(t->kcov_mode);
812 	barrier();
813 	if (kcov_mode_enabled(mode)) {
814 		data->saved_mode = mode;
815 		data->saved_size = t->kcov_size;
816 		data->saved_area = t->kcov_area;
817 		data->saved_sequence = t->kcov_sequence;
818 		data->saved_kcov = t->kcov;
819 		kcov_stop(t);
820 	}
821 }
822 
823 static void kcov_remote_softirq_stop(struct task_struct *t)
824 {
825 	struct kcov_percpu_data *data = this_cpu_ptr(&kcov_percpu_data);
826 
827 	if (data->saved_kcov) {
828 		kcov_start(t, data->saved_kcov, data->saved_size,
829 				data->saved_area, data->saved_mode,
830 				data->saved_sequence);
831 		data->saved_mode = 0;
832 		data->saved_size = 0;
833 		data->saved_area = NULL;
834 		data->saved_sequence = 0;
835 		data->saved_kcov = NULL;
836 	}
837 }
838 
839 void kcov_remote_start(u64 handle)
840 {
841 	struct task_struct *t = current;
842 	struct kcov_remote *remote;
843 	struct kcov *kcov;
844 	unsigned int mode;
845 	void *area;
846 	unsigned int size;
847 	int sequence;
848 	unsigned long flags;
849 
850 	if (WARN_ON(!kcov_check_handle(handle, true, true, true)))
851 		return;
852 	if (!in_task() && !in_serving_softirq())
853 		return;
854 
855 	local_lock_irqsave(&kcov_percpu_data.lock, flags);
856 
857 	/*
858 	 * Check that kcov_remote_start() is not called twice in background
859 	 * threads nor called by user tasks (with enabled kcov).
860 	 */
861 	mode = READ_ONCE(t->kcov_mode);
862 	if (WARN_ON(in_task() && kcov_mode_enabled(mode))) {
863 		local_unlock_irqrestore(&kcov_percpu_data.lock, flags);
864 		return;
865 	}
866 	/*
867 	 * Check that kcov_remote_start() is not called twice in softirqs.
868 	 * Note, that kcov_remote_start() can be called from a softirq that
869 	 * happened while collecting coverage from a background thread.
870 	 */
871 	if (WARN_ON(in_serving_softirq() && t->kcov_softirq)) {
872 		local_unlock_irqrestore(&kcov_percpu_data.lock, flags);
873 		return;
874 	}
875 
876 	spin_lock(&kcov_remote_lock);
877 	remote = kcov_remote_find(handle);
878 	if (!remote) {
879 		spin_unlock(&kcov_remote_lock);
880 		local_unlock_irqrestore(&kcov_percpu_data.lock, flags);
881 		return;
882 	}
883 	kcov_debug("handle = %llx, context: %s\n", handle,
884 			in_task() ? "task" : "softirq");
885 	kcov = remote->kcov;
886 	/* Put in kcov_remote_stop(). */
887 	kcov_get(kcov);
888 	/*
889 	 * Read kcov fields before unlock to prevent races with
890 	 * KCOV_DISABLE / kcov_remote_reset().
891 	 */
892 	mode = kcov->mode;
893 	sequence = kcov->sequence;
894 	if (in_task()) {
895 		size = kcov->remote_size;
896 		area = kcov_remote_area_get(size);
897 	} else {
898 		size = CONFIG_KCOV_IRQ_AREA_SIZE;
899 		area = this_cpu_ptr(&kcov_percpu_data)->irq_area;
900 	}
901 	spin_unlock(&kcov_remote_lock);
902 
903 	/* Can only happen when in_task(). */
904 	if (!area) {
905 		local_unlock_irqrestore(&kcov_percpu_data.lock, flags);
906 		area = vmalloc(size * sizeof(unsigned long));
907 		if (!area) {
908 			kcov_put(kcov);
909 			return;
910 		}
911 		local_lock_irqsave(&kcov_percpu_data.lock, flags);
912 	}
913 
914 	/* Reset coverage size. */
915 	*(u64 *)area = 0;
916 
917 	if (in_serving_softirq()) {
918 		kcov_remote_softirq_start(t);
919 		t->kcov_softirq = 1;
920 	}
921 	kcov_start(t, kcov, size, area, mode, sequence);
922 
923 	local_unlock_irqrestore(&kcov_percpu_data.lock, flags);
924 
925 }
926 EXPORT_SYMBOL(kcov_remote_start);
927 
928 static void kcov_move_area(enum kcov_mode mode, void *dst_area,
929 				unsigned int dst_area_size, void *src_area)
930 {
931 	u64 word_size = sizeof(unsigned long);
932 	u64 count_size, entry_size_log;
933 	u64 dst_len, src_len;
934 	void *dst_entries, *src_entries;
935 	u64 dst_occupied, dst_free, bytes_to_move, entries_moved;
936 
937 	kcov_debug("%px %u <= %px %lu\n",
938 		dst_area, dst_area_size, src_area, *(unsigned long *)src_area);
939 
940 	switch (mode) {
941 	case KCOV_MODE_TRACE_PC:
942 		dst_len = READ_ONCE(*(unsigned long *)dst_area);
943 		src_len = *(unsigned long *)src_area;
944 		count_size = sizeof(unsigned long);
945 		entry_size_log = __ilog2_u64(sizeof(unsigned long));
946 		break;
947 	case KCOV_MODE_TRACE_CMP:
948 		dst_len = READ_ONCE(*(u64 *)dst_area);
949 		src_len = *(u64 *)src_area;
950 		count_size = sizeof(u64);
951 		BUILD_BUG_ON(!is_power_of_2(KCOV_WORDS_PER_CMP));
952 		entry_size_log = __ilog2_u64(sizeof(u64) * KCOV_WORDS_PER_CMP);
953 		break;
954 	default:
955 		WARN_ON(1);
956 		return;
957 	}
958 
959 	/* As arm can't divide u64 integers use log of entry size. */
960 	if (dst_len > ((dst_area_size * word_size - count_size) >>
961 				entry_size_log))
962 		return;
963 	dst_occupied = count_size + (dst_len << entry_size_log);
964 	dst_free = dst_area_size * word_size - dst_occupied;
965 	bytes_to_move = min(dst_free, src_len << entry_size_log);
966 	dst_entries = dst_area + dst_occupied;
967 	src_entries = src_area + count_size;
968 	memcpy(dst_entries, src_entries, bytes_to_move);
969 	entries_moved = bytes_to_move >> entry_size_log;
970 
971 	switch (mode) {
972 	case KCOV_MODE_TRACE_PC:
973 		WRITE_ONCE(*(unsigned long *)dst_area, dst_len + entries_moved);
974 		break;
975 	case KCOV_MODE_TRACE_CMP:
976 		WRITE_ONCE(*(u64 *)dst_area, dst_len + entries_moved);
977 		break;
978 	default:
979 		break;
980 	}
981 }
982 
983 /* See the comment before kcov_remote_start() for usage details. */
984 void kcov_remote_stop(void)
985 {
986 	struct task_struct *t = current;
987 	struct kcov *kcov;
988 	unsigned int mode;
989 	void *area;
990 	unsigned int size;
991 	int sequence;
992 	unsigned long flags;
993 
994 	if (!in_task() && !in_serving_softirq())
995 		return;
996 
997 	local_lock_irqsave(&kcov_percpu_data.lock, flags);
998 
999 	mode = READ_ONCE(t->kcov_mode);
1000 	barrier();
1001 	if (!kcov_mode_enabled(mode)) {
1002 		local_unlock_irqrestore(&kcov_percpu_data.lock, flags);
1003 		return;
1004 	}
1005 	/*
1006 	 * When in softirq, check if the corresponding kcov_remote_start()
1007 	 * actually found the remote handle and started collecting coverage.
1008 	 */
1009 	if (in_serving_softirq() && !t->kcov_softirq) {
1010 		local_unlock_irqrestore(&kcov_percpu_data.lock, flags);
1011 		return;
1012 	}
1013 	/* Make sure that kcov_softirq is only set when in softirq. */
1014 	if (WARN_ON(!in_serving_softirq() && t->kcov_softirq)) {
1015 		local_unlock_irqrestore(&kcov_percpu_data.lock, flags);
1016 		return;
1017 	}
1018 
1019 	kcov = t->kcov;
1020 	area = t->kcov_area;
1021 	size = t->kcov_size;
1022 	sequence = t->kcov_sequence;
1023 
1024 	kcov_stop(t);
1025 	if (in_serving_softirq()) {
1026 		t->kcov_softirq = 0;
1027 		kcov_remote_softirq_stop(t);
1028 	}
1029 
1030 	spin_lock(&kcov->lock);
1031 	/*
1032 	 * KCOV_DISABLE could have been called between kcov_remote_start()
1033 	 * and kcov_remote_stop(), hence the sequence check.
1034 	 */
1035 	if (sequence == kcov->sequence && kcov->remote)
1036 		kcov_move_area(kcov->mode, kcov->area, kcov->size, area);
1037 	spin_unlock(&kcov->lock);
1038 
1039 	if (in_task()) {
1040 		spin_lock(&kcov_remote_lock);
1041 		kcov_remote_area_put(area, size);
1042 		spin_unlock(&kcov_remote_lock);
1043 	}
1044 
1045 	local_unlock_irqrestore(&kcov_percpu_data.lock, flags);
1046 
1047 	/* Get in kcov_remote_start(). */
1048 	kcov_put(kcov);
1049 }
1050 EXPORT_SYMBOL(kcov_remote_stop);
1051 
1052 /* See the comment before kcov_remote_start() for usage details. */
1053 u64 kcov_common_handle(void)
1054 {
1055 	if (!in_task())
1056 		return 0;
1057 	return current->kcov_handle;
1058 }
1059 EXPORT_SYMBOL(kcov_common_handle);
1060 
1061 static int __init kcov_init(void)
1062 {
1063 	int cpu;
1064 
1065 	for_each_possible_cpu(cpu) {
1066 		void *area = vmalloc_node(CONFIG_KCOV_IRQ_AREA_SIZE *
1067 				sizeof(unsigned long), cpu_to_node(cpu));
1068 		if (!area)
1069 			return -ENOMEM;
1070 		per_cpu_ptr(&kcov_percpu_data, cpu)->irq_area = area;
1071 	}
1072 
1073 	/*
1074 	 * The kcov debugfs file won't ever get removed and thus,
1075 	 * there is no need to protect it against removal races. The
1076 	 * use of debugfs_create_file_unsafe() is actually safe here.
1077 	 */
1078 	debugfs_create_file_unsafe("kcov", 0600, NULL, NULL, &kcov_fops);
1079 
1080 	return 0;
1081 }
1082 
1083 device_initcall(kcov_init);
1084