xref: /openbmc/linux/kernel/kcov.c (revision 7ae5c03a)
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/mm.h>
15 #include <linux/preempt.h>
16 #include <linux/printk.h>
17 #include <linux/sched.h>
18 #include <linux/slab.h>
19 #include <linux/spinlock.h>
20 #include <linux/vmalloc.h>
21 #include <linux/debugfs.h>
22 #include <linux/uaccess.h>
23 #include <linux/kcov.h>
24 #include <linux/refcount.h>
25 #include <linux/log2.h>
26 #include <asm/setup.h>
27 
28 #define kcov_debug(fmt, ...) pr_debug("%s: " fmt, __func__, ##__VA_ARGS__)
29 
30 /* Number of 64-bit words written per one comparison: */
31 #define KCOV_WORDS_PER_CMP 4
32 
33 /*
34  * kcov descriptor (one per opened debugfs file).
35  * State transitions of the descriptor:
36  *  - initial state after open()
37  *  - then there must be a single ioctl(KCOV_INIT_TRACE) call
38  *  - then, mmap() call (several calls are allowed but not useful)
39  *  - then, ioctl(KCOV_ENABLE, arg), where arg is
40  *	KCOV_TRACE_PC - to trace only the PCs
41  *	or
42  *	KCOV_TRACE_CMP - to trace only the comparison operands
43  *  - then, ioctl(KCOV_DISABLE) to disable the task.
44  * Enabling/disabling ioctls can be repeated (only one task a time allowed).
45  */
46 struct kcov {
47 	/*
48 	 * Reference counter. We keep one for:
49 	 *  - opened file descriptor
50 	 *  - task with enabled coverage (we can't unwire it from another task)
51 	 *  - each code section for remote coverage collection
52 	 */
53 	refcount_t		refcount;
54 	/* The lock protects mode, size, area and t. */
55 	spinlock_t		lock;
56 	enum kcov_mode		mode;
57 	/* Size of arena (in long's). */
58 	unsigned int		size;
59 	/* Coverage buffer shared with user space. */
60 	void			*area;
61 	/* Task for which we collect coverage, or NULL. */
62 	struct task_struct	*t;
63 	/* Collecting coverage from remote (background) threads. */
64 	bool			remote;
65 	/* Size of remote area (in long's). */
66 	unsigned int		remote_size;
67 	/*
68 	 * Sequence is incremented each time kcov is reenabled, used by
69 	 * kcov_remote_stop(), see the comment there.
70 	 */
71 	int			sequence;
72 };
73 
74 struct kcov_remote_area {
75 	struct list_head	list;
76 	unsigned int		size;
77 };
78 
79 struct kcov_remote {
80 	u64			handle;
81 	struct kcov		*kcov;
82 	struct hlist_node	hnode;
83 };
84 
85 static DEFINE_SPINLOCK(kcov_remote_lock);
86 static DEFINE_HASHTABLE(kcov_remote_map, 4);
87 static struct list_head kcov_remote_areas = LIST_HEAD_INIT(kcov_remote_areas);
88 
89 struct kcov_percpu_data {
90 	void			*irq_area;
91 	local_lock_t		lock;
92 
93 	unsigned int		saved_mode;
94 	unsigned int		saved_size;
95 	void			*saved_area;
96 	struct kcov		*saved_kcov;
97 	int			saved_sequence;
98 };
99 
100 static DEFINE_PER_CPU(struct kcov_percpu_data, kcov_percpu_data) = {
101 	.lock = INIT_LOCAL_LOCK(lock),
102 };
103 
104 /* Must be called with kcov_remote_lock locked. */
105 static struct kcov_remote *kcov_remote_find(u64 handle)
106 {
107 	struct kcov_remote *remote;
108 
109 	hash_for_each_possible(kcov_remote_map, remote, hnode, handle) {
110 		if (remote->handle == handle)
111 			return remote;
112 	}
113 	return NULL;
114 }
115 
116 /* Must be called with kcov_remote_lock locked. */
117 static struct kcov_remote *kcov_remote_add(struct kcov *kcov, u64 handle)
118 {
119 	struct kcov_remote *remote;
120 
121 	if (kcov_remote_find(handle))
122 		return ERR_PTR(-EEXIST);
123 	remote = kmalloc(sizeof(*remote), GFP_ATOMIC);
124 	if (!remote)
125 		return ERR_PTR(-ENOMEM);
126 	remote->handle = handle;
127 	remote->kcov = kcov;
128 	hash_add(kcov_remote_map, &remote->hnode, handle);
129 	return remote;
130 }
131 
132 /* Must be called with kcov_remote_lock locked. */
133 static struct kcov_remote_area *kcov_remote_area_get(unsigned int size)
134 {
135 	struct kcov_remote_area *area;
136 	struct list_head *pos;
137 
138 	list_for_each(pos, &kcov_remote_areas) {
139 		area = list_entry(pos, struct kcov_remote_area, list);
140 		if (area->size == size) {
141 			list_del(&area->list);
142 			return area;
143 		}
144 	}
145 	return NULL;
146 }
147 
148 /* Must be called with kcov_remote_lock locked. */
149 static void kcov_remote_area_put(struct kcov_remote_area *area,
150 					unsigned int size)
151 {
152 	INIT_LIST_HEAD(&area->list);
153 	area->size = size;
154 	list_add(&area->list, &kcov_remote_areas);
155 }
156 
157 static notrace bool check_kcov_mode(enum kcov_mode needed_mode, struct task_struct *t)
158 {
159 	unsigned int mode;
160 
161 	/*
162 	 * We are interested in code coverage as a function of a syscall inputs,
163 	 * so we ignore code executed in interrupts, unless we are in a remote
164 	 * coverage collection section in a softirq.
165 	 */
166 	if (!in_task() && !(in_serving_softirq() && t->kcov_softirq))
167 		return false;
168 	mode = READ_ONCE(t->kcov_mode);
169 	/*
170 	 * There is some code that runs in interrupts but for which
171 	 * in_interrupt() returns false (e.g. preempt_schedule_irq()).
172 	 * READ_ONCE()/barrier() effectively provides load-acquire wrt
173 	 * interrupts, there are paired barrier()/WRITE_ONCE() in
174 	 * kcov_start().
175 	 */
176 	barrier();
177 	return mode == needed_mode;
178 }
179 
180 static notrace unsigned long canonicalize_ip(unsigned long ip)
181 {
182 #ifdef CONFIG_RANDOMIZE_BASE
183 	ip -= kaslr_offset();
184 #endif
185 	return ip;
186 }
187 
188 /*
189  * Entry point from instrumented code.
190  * This is called once per basic-block/edge.
191  */
192 void notrace __sanitizer_cov_trace_pc(void)
193 {
194 	struct task_struct *t;
195 	unsigned long *area;
196 	unsigned long ip = canonicalize_ip(_RET_IP_);
197 	unsigned long pos;
198 
199 	t = current;
200 	if (!check_kcov_mode(KCOV_MODE_TRACE_PC, t))
201 		return;
202 
203 	area = t->kcov_area;
204 	/* The first 64-bit word is the number of subsequent PCs. */
205 	pos = READ_ONCE(area[0]) + 1;
206 	if (likely(pos < t->kcov_size)) {
207 		/* Previously we write pc before updating pos. However, some
208 		 * early interrupt code could bypass check_kcov_mode() check
209 		 * and invoke __sanitizer_cov_trace_pc(). If such interrupt is
210 		 * raised between writing pc and updating pos, the pc could be
211 		 * overitten by the recursive __sanitizer_cov_trace_pc().
212 		 * Update pos before writing pc to avoid such interleaving.
213 		 */
214 		WRITE_ONCE(area[0], pos);
215 		barrier();
216 		area[pos] = ip;
217 	}
218 }
219 EXPORT_SYMBOL(__sanitizer_cov_trace_pc);
220 
221 #ifdef CONFIG_KCOV_ENABLE_COMPARISONS
222 static void notrace write_comp_data(u64 type, u64 arg1, u64 arg2, u64 ip)
223 {
224 	struct task_struct *t;
225 	u64 *area;
226 	u64 count, start_index, end_pos, max_pos;
227 
228 	t = current;
229 	if (!check_kcov_mode(KCOV_MODE_TRACE_CMP, t))
230 		return;
231 
232 	ip = canonicalize_ip(ip);
233 
234 	/*
235 	 * We write all comparison arguments and types as u64.
236 	 * The buffer was allocated for t->kcov_size unsigned longs.
237 	 */
238 	area = (u64 *)t->kcov_area;
239 	max_pos = t->kcov_size * sizeof(unsigned long);
240 
241 	count = READ_ONCE(area[0]);
242 
243 	/* Every record is KCOV_WORDS_PER_CMP 64-bit words. */
244 	start_index = 1 + count * KCOV_WORDS_PER_CMP;
245 	end_pos = (start_index + KCOV_WORDS_PER_CMP) * sizeof(u64);
246 	if (likely(end_pos <= max_pos)) {
247 		/* See comment in __sanitizer_cov_trace_pc(). */
248 		WRITE_ONCE(area[0], count + 1);
249 		barrier();
250 		area[start_index] = type;
251 		area[start_index + 1] = arg1;
252 		area[start_index + 2] = arg2;
253 		area[start_index + 3] = ip;
254 	}
255 }
256 
257 void notrace __sanitizer_cov_trace_cmp1(u8 arg1, u8 arg2)
258 {
259 	write_comp_data(KCOV_CMP_SIZE(0), arg1, arg2, _RET_IP_);
260 }
261 EXPORT_SYMBOL(__sanitizer_cov_trace_cmp1);
262 
263 void notrace __sanitizer_cov_trace_cmp2(u16 arg1, u16 arg2)
264 {
265 	write_comp_data(KCOV_CMP_SIZE(1), arg1, arg2, _RET_IP_);
266 }
267 EXPORT_SYMBOL(__sanitizer_cov_trace_cmp2);
268 
269 void notrace __sanitizer_cov_trace_cmp4(u32 arg1, u32 arg2)
270 {
271 	write_comp_data(KCOV_CMP_SIZE(2), arg1, arg2, _RET_IP_);
272 }
273 EXPORT_SYMBOL(__sanitizer_cov_trace_cmp4);
274 
275 void notrace __sanitizer_cov_trace_cmp8(u64 arg1, u64 arg2)
276 {
277 	write_comp_data(KCOV_CMP_SIZE(3), arg1, arg2, _RET_IP_);
278 }
279 EXPORT_SYMBOL(__sanitizer_cov_trace_cmp8);
280 
281 void notrace __sanitizer_cov_trace_const_cmp1(u8 arg1, u8 arg2)
282 {
283 	write_comp_data(KCOV_CMP_SIZE(0) | KCOV_CMP_CONST, arg1, arg2,
284 			_RET_IP_);
285 }
286 EXPORT_SYMBOL(__sanitizer_cov_trace_const_cmp1);
287 
288 void notrace __sanitizer_cov_trace_const_cmp2(u16 arg1, u16 arg2)
289 {
290 	write_comp_data(KCOV_CMP_SIZE(1) | KCOV_CMP_CONST, arg1, arg2,
291 			_RET_IP_);
292 }
293 EXPORT_SYMBOL(__sanitizer_cov_trace_const_cmp2);
294 
295 void notrace __sanitizer_cov_trace_const_cmp4(u32 arg1, u32 arg2)
296 {
297 	write_comp_data(KCOV_CMP_SIZE(2) | KCOV_CMP_CONST, arg1, arg2,
298 			_RET_IP_);
299 }
300 EXPORT_SYMBOL(__sanitizer_cov_trace_const_cmp4);
301 
302 void notrace __sanitizer_cov_trace_const_cmp8(u64 arg1, u64 arg2)
303 {
304 	write_comp_data(KCOV_CMP_SIZE(3) | KCOV_CMP_CONST, arg1, arg2,
305 			_RET_IP_);
306 }
307 EXPORT_SYMBOL(__sanitizer_cov_trace_const_cmp8);
308 
309 void notrace __sanitizer_cov_trace_switch(u64 val, u64 *cases)
310 {
311 	u64 i;
312 	u64 count = cases[0];
313 	u64 size = cases[1];
314 	u64 type = KCOV_CMP_CONST;
315 
316 	switch (size) {
317 	case 8:
318 		type |= KCOV_CMP_SIZE(0);
319 		break;
320 	case 16:
321 		type |= KCOV_CMP_SIZE(1);
322 		break;
323 	case 32:
324 		type |= KCOV_CMP_SIZE(2);
325 		break;
326 	case 64:
327 		type |= KCOV_CMP_SIZE(3);
328 		break;
329 	default:
330 		return;
331 	}
332 	for (i = 0; i < count; i++)
333 		write_comp_data(type, cases[i + 2], val, _RET_IP_);
334 }
335 EXPORT_SYMBOL(__sanitizer_cov_trace_switch);
336 #endif /* ifdef CONFIG_KCOV_ENABLE_COMPARISONS */
337 
338 static void kcov_start(struct task_struct *t, struct kcov *kcov,
339 			unsigned int size, void *area, enum kcov_mode mode,
340 			int sequence)
341 {
342 	kcov_debug("t = %px, size = %u, area = %px\n", t, size, area);
343 	t->kcov = kcov;
344 	/* Cache in task struct for performance. */
345 	t->kcov_size = size;
346 	t->kcov_area = area;
347 	t->kcov_sequence = sequence;
348 	/* See comment in check_kcov_mode(). */
349 	barrier();
350 	WRITE_ONCE(t->kcov_mode, mode);
351 }
352 
353 static void kcov_stop(struct task_struct *t)
354 {
355 	WRITE_ONCE(t->kcov_mode, KCOV_MODE_DISABLED);
356 	barrier();
357 	t->kcov = NULL;
358 	t->kcov_size = 0;
359 	t->kcov_area = NULL;
360 }
361 
362 static void kcov_task_reset(struct task_struct *t)
363 {
364 	kcov_stop(t);
365 	t->kcov_sequence = 0;
366 	t->kcov_handle = 0;
367 }
368 
369 void kcov_task_init(struct task_struct *t)
370 {
371 	kcov_task_reset(t);
372 	t->kcov_handle = current->kcov_handle;
373 }
374 
375 static void kcov_reset(struct kcov *kcov)
376 {
377 	kcov->t = NULL;
378 	kcov->mode = KCOV_MODE_INIT;
379 	kcov->remote = false;
380 	kcov->remote_size = 0;
381 	kcov->sequence++;
382 }
383 
384 static void kcov_remote_reset(struct kcov *kcov)
385 {
386 	int bkt;
387 	struct kcov_remote *remote;
388 	struct hlist_node *tmp;
389 	unsigned long flags;
390 
391 	spin_lock_irqsave(&kcov_remote_lock, flags);
392 	hash_for_each_safe(kcov_remote_map, bkt, tmp, remote, hnode) {
393 		if (remote->kcov != kcov)
394 			continue;
395 		hash_del(&remote->hnode);
396 		kfree(remote);
397 	}
398 	/* Do reset before unlock to prevent races with kcov_remote_start(). */
399 	kcov_reset(kcov);
400 	spin_unlock_irqrestore(&kcov_remote_lock, flags);
401 }
402 
403 static void kcov_disable(struct task_struct *t, struct kcov *kcov)
404 {
405 	kcov_task_reset(t);
406 	if (kcov->remote)
407 		kcov_remote_reset(kcov);
408 	else
409 		kcov_reset(kcov);
410 }
411 
412 static void kcov_get(struct kcov *kcov)
413 {
414 	refcount_inc(&kcov->refcount);
415 }
416 
417 static void kcov_put(struct kcov *kcov)
418 {
419 	if (refcount_dec_and_test(&kcov->refcount)) {
420 		kcov_remote_reset(kcov);
421 		vfree(kcov->area);
422 		kfree(kcov);
423 	}
424 }
425 
426 void kcov_task_exit(struct task_struct *t)
427 {
428 	struct kcov *kcov;
429 	unsigned long flags;
430 
431 	kcov = t->kcov;
432 	if (kcov == NULL)
433 		return;
434 
435 	spin_lock_irqsave(&kcov->lock, flags);
436 	kcov_debug("t = %px, kcov->t = %px\n", t, kcov->t);
437 	/*
438 	 * For KCOV_ENABLE devices we want to make sure that t->kcov->t == t,
439 	 * which comes down to:
440 	 *        WARN_ON(!kcov->remote && kcov->t != t);
441 	 *
442 	 * For KCOV_REMOTE_ENABLE devices, the exiting task is either:
443 	 *
444 	 * 1. A remote task between kcov_remote_start() and kcov_remote_stop().
445 	 *    In this case we should print a warning right away, since a task
446 	 *    shouldn't be exiting when it's in a kcov coverage collection
447 	 *    section. Here t points to the task that is collecting remote
448 	 *    coverage, and t->kcov->t points to the thread that created the
449 	 *    kcov device. Which means that to detect this case we need to
450 	 *    check that t != t->kcov->t, and this gives us the following:
451 	 *        WARN_ON(kcov->remote && kcov->t != t);
452 	 *
453 	 * 2. The task that created kcov exiting without calling KCOV_DISABLE,
454 	 *    and then again we make sure that t->kcov->t == t:
455 	 *        WARN_ON(kcov->remote && kcov->t != t);
456 	 *
457 	 * By combining all three checks into one we get:
458 	 */
459 	if (WARN_ON(kcov->t != t)) {
460 		spin_unlock_irqrestore(&kcov->lock, flags);
461 		return;
462 	}
463 	/* Just to not leave dangling references behind. */
464 	kcov_disable(t, kcov);
465 	spin_unlock_irqrestore(&kcov->lock, flags);
466 	kcov_put(kcov);
467 }
468 
469 static int kcov_mmap(struct file *filep, struct vm_area_struct *vma)
470 {
471 	int res = 0;
472 	struct kcov *kcov = vma->vm_file->private_data;
473 	unsigned long size, off;
474 	struct page *page;
475 	unsigned long flags;
476 
477 	spin_lock_irqsave(&kcov->lock, flags);
478 	size = kcov->size * sizeof(unsigned long);
479 	if (kcov->area == NULL || vma->vm_pgoff != 0 ||
480 	    vma->vm_end - vma->vm_start != size) {
481 		res = -EINVAL;
482 		goto exit;
483 	}
484 	spin_unlock_irqrestore(&kcov->lock, flags);
485 	vma->vm_flags |= VM_DONTEXPAND;
486 	for (off = 0; off < size; off += PAGE_SIZE) {
487 		page = vmalloc_to_page(kcov->area + off);
488 		res = vm_insert_page(vma, vma->vm_start + off, page);
489 		if (res) {
490 			pr_warn_once("kcov: vm_insert_page() failed\n");
491 			return res;
492 		}
493 	}
494 	return 0;
495 exit:
496 	spin_unlock_irqrestore(&kcov->lock, flags);
497 	return res;
498 }
499 
500 static int kcov_open(struct inode *inode, struct file *filep)
501 {
502 	struct kcov *kcov;
503 
504 	kcov = kzalloc(sizeof(*kcov), GFP_KERNEL);
505 	if (!kcov)
506 		return -ENOMEM;
507 	kcov->mode = KCOV_MODE_DISABLED;
508 	kcov->sequence = 1;
509 	refcount_set(&kcov->refcount, 1);
510 	spin_lock_init(&kcov->lock);
511 	filep->private_data = kcov;
512 	return nonseekable_open(inode, filep);
513 }
514 
515 static int kcov_close(struct inode *inode, struct file *filep)
516 {
517 	kcov_put(filep->private_data);
518 	return 0;
519 }
520 
521 static int kcov_get_mode(unsigned long arg)
522 {
523 	if (arg == KCOV_TRACE_PC)
524 		return KCOV_MODE_TRACE_PC;
525 	else if (arg == KCOV_TRACE_CMP)
526 #ifdef CONFIG_KCOV_ENABLE_COMPARISONS
527 		return KCOV_MODE_TRACE_CMP;
528 #else
529 		return -ENOTSUPP;
530 #endif
531 	else
532 		return -EINVAL;
533 }
534 
535 /*
536  * Fault in a lazily-faulted vmalloc area before it can be used by
537  * __santizer_cov_trace_pc(), to avoid recursion issues if any code on the
538  * vmalloc fault handling path is instrumented.
539  */
540 static void kcov_fault_in_area(struct kcov *kcov)
541 {
542 	unsigned long stride = PAGE_SIZE / sizeof(unsigned long);
543 	unsigned long *area = kcov->area;
544 	unsigned long offset;
545 
546 	for (offset = 0; offset < kcov->size; offset += stride)
547 		READ_ONCE(area[offset]);
548 }
549 
550 static inline bool kcov_check_handle(u64 handle, bool common_valid,
551 				bool uncommon_valid, bool zero_valid)
552 {
553 	if (handle & ~(KCOV_SUBSYSTEM_MASK | KCOV_INSTANCE_MASK))
554 		return false;
555 	switch (handle & KCOV_SUBSYSTEM_MASK) {
556 	case KCOV_SUBSYSTEM_COMMON:
557 		return (handle & KCOV_INSTANCE_MASK) ?
558 			common_valid : zero_valid;
559 	case KCOV_SUBSYSTEM_USB:
560 		return uncommon_valid;
561 	default:
562 		return false;
563 	}
564 	return false;
565 }
566 
567 static int kcov_ioctl_locked(struct kcov *kcov, unsigned int cmd,
568 			     unsigned long arg)
569 {
570 	struct task_struct *t;
571 	unsigned long flags, unused;
572 	int mode, i;
573 	struct kcov_remote_arg *remote_arg;
574 	struct kcov_remote *remote;
575 
576 	switch (cmd) {
577 	case KCOV_ENABLE:
578 		/*
579 		 * Enable coverage for the current task.
580 		 * At this point user must have been enabled trace mode,
581 		 * and mmapped the file. Coverage collection is disabled only
582 		 * at task exit or voluntary by KCOV_DISABLE. After that it can
583 		 * be enabled for another task.
584 		 */
585 		if (kcov->mode != KCOV_MODE_INIT || !kcov->area)
586 			return -EINVAL;
587 		t = current;
588 		if (kcov->t != NULL || t->kcov != NULL)
589 			return -EBUSY;
590 		mode = kcov_get_mode(arg);
591 		if (mode < 0)
592 			return mode;
593 		kcov_fault_in_area(kcov);
594 		kcov->mode = mode;
595 		kcov_start(t, kcov, kcov->size, kcov->area, kcov->mode,
596 				kcov->sequence);
597 		kcov->t = t;
598 		/* Put either in kcov_task_exit() or in KCOV_DISABLE. */
599 		kcov_get(kcov);
600 		return 0;
601 	case KCOV_DISABLE:
602 		/* Disable coverage for the current task. */
603 		unused = arg;
604 		if (unused != 0 || current->kcov != kcov)
605 			return -EINVAL;
606 		t = current;
607 		if (WARN_ON(kcov->t != t))
608 			return -EINVAL;
609 		kcov_disable(t, kcov);
610 		kcov_put(kcov);
611 		return 0;
612 	case KCOV_REMOTE_ENABLE:
613 		if (kcov->mode != KCOV_MODE_INIT || !kcov->area)
614 			return -EINVAL;
615 		t = current;
616 		if (kcov->t != NULL || t->kcov != NULL)
617 			return -EBUSY;
618 		remote_arg = (struct kcov_remote_arg *)arg;
619 		mode = kcov_get_mode(remote_arg->trace_mode);
620 		if (mode < 0)
621 			return mode;
622 		if (remote_arg->area_size > LONG_MAX / sizeof(unsigned long))
623 			return -EINVAL;
624 		kcov->mode = mode;
625 		t->kcov = kcov;
626 		kcov->t = t;
627 		kcov->remote = true;
628 		kcov->remote_size = remote_arg->area_size;
629 		spin_lock_irqsave(&kcov_remote_lock, flags);
630 		for (i = 0; i < remote_arg->num_handles; i++) {
631 			if (!kcov_check_handle(remote_arg->handles[i],
632 						false, true, false)) {
633 				spin_unlock_irqrestore(&kcov_remote_lock,
634 							flags);
635 				kcov_disable(t, kcov);
636 				return -EINVAL;
637 			}
638 			remote = kcov_remote_add(kcov, remote_arg->handles[i]);
639 			if (IS_ERR(remote)) {
640 				spin_unlock_irqrestore(&kcov_remote_lock,
641 							flags);
642 				kcov_disable(t, kcov);
643 				return PTR_ERR(remote);
644 			}
645 		}
646 		if (remote_arg->common_handle) {
647 			if (!kcov_check_handle(remote_arg->common_handle,
648 						true, false, false)) {
649 				spin_unlock_irqrestore(&kcov_remote_lock,
650 							flags);
651 				kcov_disable(t, kcov);
652 				return -EINVAL;
653 			}
654 			remote = kcov_remote_add(kcov,
655 					remote_arg->common_handle);
656 			if (IS_ERR(remote)) {
657 				spin_unlock_irqrestore(&kcov_remote_lock,
658 							flags);
659 				kcov_disable(t, kcov);
660 				return PTR_ERR(remote);
661 			}
662 			t->kcov_handle = remote_arg->common_handle;
663 		}
664 		spin_unlock_irqrestore(&kcov_remote_lock, flags);
665 		/* Put either in kcov_task_exit() or in KCOV_DISABLE. */
666 		kcov_get(kcov);
667 		return 0;
668 	default:
669 		return -ENOTTY;
670 	}
671 }
672 
673 static long kcov_ioctl(struct file *filep, unsigned int cmd, unsigned long arg)
674 {
675 	struct kcov *kcov;
676 	int res;
677 	struct kcov_remote_arg *remote_arg = NULL;
678 	unsigned int remote_num_handles;
679 	unsigned long remote_arg_size;
680 	unsigned long size, flags;
681 	void *area;
682 
683 	kcov = filep->private_data;
684 	switch (cmd) {
685 	case KCOV_INIT_TRACE:
686 		/*
687 		 * Enable kcov in trace mode and setup buffer size.
688 		 * Must happen before anything else.
689 		 *
690 		 * First check the size argument - it must be at least 2
691 		 * to hold the current position and one PC.
692 		 */
693 		size = arg;
694 		if (size < 2 || size > INT_MAX / sizeof(unsigned long))
695 			return -EINVAL;
696 		area = vmalloc_user(size * sizeof(unsigned long));
697 		if (area == NULL)
698 			return -ENOMEM;
699 		spin_lock_irqsave(&kcov->lock, flags);
700 		if (kcov->mode != KCOV_MODE_DISABLED) {
701 			spin_unlock_irqrestore(&kcov->lock, flags);
702 			vfree(area);
703 			return -EBUSY;
704 		}
705 		kcov->area = area;
706 		kcov->size = size;
707 		kcov->mode = KCOV_MODE_INIT;
708 		spin_unlock_irqrestore(&kcov->lock, flags);
709 		return 0;
710 	case KCOV_REMOTE_ENABLE:
711 		if (get_user(remote_num_handles, (unsigned __user *)(arg +
712 				offsetof(struct kcov_remote_arg, num_handles))))
713 			return -EFAULT;
714 		if (remote_num_handles > KCOV_REMOTE_MAX_HANDLES)
715 			return -EINVAL;
716 		remote_arg_size = struct_size(remote_arg, handles,
717 					remote_num_handles);
718 		remote_arg = memdup_user((void __user *)arg, remote_arg_size);
719 		if (IS_ERR(remote_arg))
720 			return PTR_ERR(remote_arg);
721 		if (remote_arg->num_handles != remote_num_handles) {
722 			kfree(remote_arg);
723 			return -EINVAL;
724 		}
725 		arg = (unsigned long)remote_arg;
726 		fallthrough;
727 	default:
728 		/*
729 		 * All other commands can be normally executed under a spin lock, so we
730 		 * obtain and release it here in order to simplify kcov_ioctl_locked().
731 		 */
732 		spin_lock_irqsave(&kcov->lock, flags);
733 		res = kcov_ioctl_locked(kcov, cmd, arg);
734 		spin_unlock_irqrestore(&kcov->lock, flags);
735 		kfree(remote_arg);
736 		return res;
737 	}
738 }
739 
740 static const struct file_operations kcov_fops = {
741 	.open		= kcov_open,
742 	.unlocked_ioctl	= kcov_ioctl,
743 	.compat_ioctl	= kcov_ioctl,
744 	.mmap		= kcov_mmap,
745 	.release        = kcov_close,
746 };
747 
748 /*
749  * kcov_remote_start() and kcov_remote_stop() can be used to annotate a section
750  * of code in a kernel background thread or in a softirq to allow kcov to be
751  * used to collect coverage from that part of code.
752  *
753  * The handle argument of kcov_remote_start() identifies a code section that is
754  * used for coverage collection. A userspace process passes this handle to
755  * KCOV_REMOTE_ENABLE ioctl to make the used kcov device start collecting
756  * coverage for the code section identified by this handle.
757  *
758  * The usage of these annotations in the kernel code is different depending on
759  * the type of the kernel thread whose code is being annotated.
760  *
761  * For global kernel threads that are spawned in a limited number of instances
762  * (e.g. one USB hub_event() worker thread is spawned per USB HCD) and for
763  * softirqs, each instance must be assigned a unique 4-byte instance id. The
764  * instance id is then combined with a 1-byte subsystem id to get a handle via
765  * kcov_remote_handle(subsystem_id, instance_id).
766  *
767  * For local kernel threads that are spawned from system calls handler when a
768  * user interacts with some kernel interface (e.g. vhost workers), a handle is
769  * passed from a userspace process as the common_handle field of the
770  * kcov_remote_arg struct (note, that the user must generate a handle by using
771  * kcov_remote_handle() with KCOV_SUBSYSTEM_COMMON as the subsystem id and an
772  * arbitrary 4-byte non-zero number as the instance id). This common handle
773  * then gets saved into the task_struct of the process that issued the
774  * KCOV_REMOTE_ENABLE ioctl. When this process issues system calls that spawn
775  * kernel threads, the common handle must be retrieved via kcov_common_handle()
776  * and passed to the spawned threads via custom annotations. Those kernel
777  * threads must in turn be annotated with kcov_remote_start(common_handle) and
778  * kcov_remote_stop(). All of the threads that are spawned by the same process
779  * obtain the same handle, hence the name "common".
780  *
781  * See Documentation/dev-tools/kcov.rst for more details.
782  *
783  * Internally, kcov_remote_start() looks up the kcov device associated with the
784  * provided handle, allocates an area for coverage collection, and saves the
785  * pointers to kcov and area into the current task_struct to allow coverage to
786  * be collected via __sanitizer_cov_trace_pc().
787  * In turns kcov_remote_stop() clears those pointers from task_struct to stop
788  * collecting coverage and copies all collected coverage into the kcov area.
789  */
790 
791 static inline bool kcov_mode_enabled(unsigned int mode)
792 {
793 	return (mode & ~KCOV_IN_CTXSW) != KCOV_MODE_DISABLED;
794 }
795 
796 static void kcov_remote_softirq_start(struct task_struct *t)
797 {
798 	struct kcov_percpu_data *data = this_cpu_ptr(&kcov_percpu_data);
799 	unsigned int mode;
800 
801 	mode = READ_ONCE(t->kcov_mode);
802 	barrier();
803 	if (kcov_mode_enabled(mode)) {
804 		data->saved_mode = mode;
805 		data->saved_size = t->kcov_size;
806 		data->saved_area = t->kcov_area;
807 		data->saved_sequence = t->kcov_sequence;
808 		data->saved_kcov = t->kcov;
809 		kcov_stop(t);
810 	}
811 }
812 
813 static void kcov_remote_softirq_stop(struct task_struct *t)
814 {
815 	struct kcov_percpu_data *data = this_cpu_ptr(&kcov_percpu_data);
816 
817 	if (data->saved_kcov) {
818 		kcov_start(t, data->saved_kcov, data->saved_size,
819 				data->saved_area, data->saved_mode,
820 				data->saved_sequence);
821 		data->saved_mode = 0;
822 		data->saved_size = 0;
823 		data->saved_area = NULL;
824 		data->saved_sequence = 0;
825 		data->saved_kcov = NULL;
826 	}
827 }
828 
829 void kcov_remote_start(u64 handle)
830 {
831 	struct task_struct *t = current;
832 	struct kcov_remote *remote;
833 	struct kcov *kcov;
834 	unsigned int mode;
835 	void *area;
836 	unsigned int size;
837 	int sequence;
838 	unsigned long flags;
839 
840 	if (WARN_ON(!kcov_check_handle(handle, true, true, true)))
841 		return;
842 	if (!in_task() && !in_serving_softirq())
843 		return;
844 
845 	local_lock_irqsave(&kcov_percpu_data.lock, flags);
846 
847 	/*
848 	 * Check that kcov_remote_start() is not called twice in background
849 	 * threads nor called by user tasks (with enabled kcov).
850 	 */
851 	mode = READ_ONCE(t->kcov_mode);
852 	if (WARN_ON(in_task() && kcov_mode_enabled(mode))) {
853 		local_unlock_irqrestore(&kcov_percpu_data.lock, flags);
854 		return;
855 	}
856 	/*
857 	 * Check that kcov_remote_start() is not called twice in softirqs.
858 	 * Note, that kcov_remote_start() can be called from a softirq that
859 	 * happened while collecting coverage from a background thread.
860 	 */
861 	if (WARN_ON(in_serving_softirq() && t->kcov_softirq)) {
862 		local_unlock_irqrestore(&kcov_percpu_data.lock, flags);
863 		return;
864 	}
865 
866 	spin_lock(&kcov_remote_lock);
867 	remote = kcov_remote_find(handle);
868 	if (!remote) {
869 		spin_unlock(&kcov_remote_lock);
870 		local_unlock_irqrestore(&kcov_percpu_data.lock, flags);
871 		return;
872 	}
873 	kcov_debug("handle = %llx, context: %s\n", handle,
874 			in_task() ? "task" : "softirq");
875 	kcov = remote->kcov;
876 	/* Put in kcov_remote_stop(). */
877 	kcov_get(kcov);
878 	/*
879 	 * Read kcov fields before unlock to prevent races with
880 	 * KCOV_DISABLE / kcov_remote_reset().
881 	 */
882 	mode = kcov->mode;
883 	sequence = kcov->sequence;
884 	if (in_task()) {
885 		size = kcov->remote_size;
886 		area = kcov_remote_area_get(size);
887 	} else {
888 		size = CONFIG_KCOV_IRQ_AREA_SIZE;
889 		area = this_cpu_ptr(&kcov_percpu_data)->irq_area;
890 	}
891 	spin_unlock(&kcov_remote_lock);
892 
893 	/* Can only happen when in_task(). */
894 	if (!area) {
895 		local_unlock_irqrestore(&kcov_percpu_data.lock, flags);
896 		area = vmalloc(size * sizeof(unsigned long));
897 		if (!area) {
898 			kcov_put(kcov);
899 			return;
900 		}
901 		local_lock_irqsave(&kcov_percpu_data.lock, flags);
902 	}
903 
904 	/* Reset coverage size. */
905 	*(u64 *)area = 0;
906 
907 	if (in_serving_softirq()) {
908 		kcov_remote_softirq_start(t);
909 		t->kcov_softirq = 1;
910 	}
911 	kcov_start(t, kcov, size, area, mode, sequence);
912 
913 	local_unlock_irqrestore(&kcov_percpu_data.lock, flags);
914 
915 }
916 EXPORT_SYMBOL(kcov_remote_start);
917 
918 static void kcov_move_area(enum kcov_mode mode, void *dst_area,
919 				unsigned int dst_area_size, void *src_area)
920 {
921 	u64 word_size = sizeof(unsigned long);
922 	u64 count_size, entry_size_log;
923 	u64 dst_len, src_len;
924 	void *dst_entries, *src_entries;
925 	u64 dst_occupied, dst_free, bytes_to_move, entries_moved;
926 
927 	kcov_debug("%px %u <= %px %lu\n",
928 		dst_area, dst_area_size, src_area, *(unsigned long *)src_area);
929 
930 	switch (mode) {
931 	case KCOV_MODE_TRACE_PC:
932 		dst_len = READ_ONCE(*(unsigned long *)dst_area);
933 		src_len = *(unsigned long *)src_area;
934 		count_size = sizeof(unsigned long);
935 		entry_size_log = __ilog2_u64(sizeof(unsigned long));
936 		break;
937 	case KCOV_MODE_TRACE_CMP:
938 		dst_len = READ_ONCE(*(u64 *)dst_area);
939 		src_len = *(u64 *)src_area;
940 		count_size = sizeof(u64);
941 		BUILD_BUG_ON(!is_power_of_2(KCOV_WORDS_PER_CMP));
942 		entry_size_log = __ilog2_u64(sizeof(u64) * KCOV_WORDS_PER_CMP);
943 		break;
944 	default:
945 		WARN_ON(1);
946 		return;
947 	}
948 
949 	/* As arm can't divide u64 integers use log of entry size. */
950 	if (dst_len > ((dst_area_size * word_size - count_size) >>
951 				entry_size_log))
952 		return;
953 	dst_occupied = count_size + (dst_len << entry_size_log);
954 	dst_free = dst_area_size * word_size - dst_occupied;
955 	bytes_to_move = min(dst_free, src_len << entry_size_log);
956 	dst_entries = dst_area + dst_occupied;
957 	src_entries = src_area + count_size;
958 	memcpy(dst_entries, src_entries, bytes_to_move);
959 	entries_moved = bytes_to_move >> entry_size_log;
960 
961 	switch (mode) {
962 	case KCOV_MODE_TRACE_PC:
963 		WRITE_ONCE(*(unsigned long *)dst_area, dst_len + entries_moved);
964 		break;
965 	case KCOV_MODE_TRACE_CMP:
966 		WRITE_ONCE(*(u64 *)dst_area, dst_len + entries_moved);
967 		break;
968 	default:
969 		break;
970 	}
971 }
972 
973 /* See the comment before kcov_remote_start() for usage details. */
974 void kcov_remote_stop(void)
975 {
976 	struct task_struct *t = current;
977 	struct kcov *kcov;
978 	unsigned int mode;
979 	void *area;
980 	unsigned int size;
981 	int sequence;
982 	unsigned long flags;
983 
984 	if (!in_task() && !in_serving_softirq())
985 		return;
986 
987 	local_lock_irqsave(&kcov_percpu_data.lock, flags);
988 
989 	mode = READ_ONCE(t->kcov_mode);
990 	barrier();
991 	if (!kcov_mode_enabled(mode)) {
992 		local_unlock_irqrestore(&kcov_percpu_data.lock, flags);
993 		return;
994 	}
995 	/*
996 	 * When in softirq, check if the corresponding kcov_remote_start()
997 	 * actually found the remote handle and started collecting coverage.
998 	 */
999 	if (in_serving_softirq() && !t->kcov_softirq) {
1000 		local_unlock_irqrestore(&kcov_percpu_data.lock, flags);
1001 		return;
1002 	}
1003 	/* Make sure that kcov_softirq is only set when in softirq. */
1004 	if (WARN_ON(!in_serving_softirq() && t->kcov_softirq)) {
1005 		local_unlock_irqrestore(&kcov_percpu_data.lock, flags);
1006 		return;
1007 	}
1008 
1009 	kcov = t->kcov;
1010 	area = t->kcov_area;
1011 	size = t->kcov_size;
1012 	sequence = t->kcov_sequence;
1013 
1014 	kcov_stop(t);
1015 	if (in_serving_softirq()) {
1016 		t->kcov_softirq = 0;
1017 		kcov_remote_softirq_stop(t);
1018 	}
1019 
1020 	spin_lock(&kcov->lock);
1021 	/*
1022 	 * KCOV_DISABLE could have been called between kcov_remote_start()
1023 	 * and kcov_remote_stop(), hence the sequence check.
1024 	 */
1025 	if (sequence == kcov->sequence && kcov->remote)
1026 		kcov_move_area(kcov->mode, kcov->area, kcov->size, area);
1027 	spin_unlock(&kcov->lock);
1028 
1029 	if (in_task()) {
1030 		spin_lock(&kcov_remote_lock);
1031 		kcov_remote_area_put(area, size);
1032 		spin_unlock(&kcov_remote_lock);
1033 	}
1034 
1035 	local_unlock_irqrestore(&kcov_percpu_data.lock, flags);
1036 
1037 	/* Get in kcov_remote_start(). */
1038 	kcov_put(kcov);
1039 }
1040 EXPORT_SYMBOL(kcov_remote_stop);
1041 
1042 /* See the comment before kcov_remote_start() for usage details. */
1043 u64 kcov_common_handle(void)
1044 {
1045 	if (!in_task())
1046 		return 0;
1047 	return current->kcov_handle;
1048 }
1049 EXPORT_SYMBOL(kcov_common_handle);
1050 
1051 static int __init kcov_init(void)
1052 {
1053 	int cpu;
1054 
1055 	for_each_possible_cpu(cpu) {
1056 		void *area = vmalloc_node(CONFIG_KCOV_IRQ_AREA_SIZE *
1057 				sizeof(unsigned long), cpu_to_node(cpu));
1058 		if (!area)
1059 			return -ENOMEM;
1060 		per_cpu_ptr(&kcov_percpu_data, cpu)->irq_area = area;
1061 	}
1062 
1063 	/*
1064 	 * The kcov debugfs file won't ever get removed and thus,
1065 	 * there is no need to protect it against removal races. The
1066 	 * use of debugfs_create_file_unsafe() is actually safe here.
1067 	 */
1068 	debugfs_create_file_unsafe("kcov", 0600, NULL, NULL, &kcov_fops);
1069 
1070 	return 0;
1071 }
1072 
1073 device_initcall(kcov_init);
1074