aboutsummaryrefslogtreecommitdiff
path: root/kernel/kcov.c
blob: e19c84b02452eb2d0c0fa46ac3248535c6a81736 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
// SPDX-License-Identifier: GPL-2.0
#define pr_fmt(fmt) "kcov: " fmt

#define DISABLE_BRANCH_PROFILING
#include <linux/atomic.h>
#include <linux/compiler.h>
#include <linux/errno.h>
#include <linux/export.h>
#include <linux/types.h>
#include <linux/file.h>
#include <linux/fs.h>
#include <linux/hashtable.h>
#include <linux/init.h>
#include <linux/mm.h>
#include <linux/preempt.h>
#include <linux/printk.h>
#include <linux/sched.h>
#include <linux/slab.h>
#include <linux/spinlock.h>
#include <linux/vmalloc.h>
#include <linux/debugfs.h>
#include <linux/uaccess.h>
#include <linux/kcov.h>
#include <linux/refcount.h>
#include <linux/log2.h>
#include <asm/setup.h>

#define kcov_debug(fmt, ...) pr_debug("%s: " fmt, __func__, ##__VA_ARGS__)

/* Number of 64-bit words written per one comparison: */
#define KCOV_WORDS_PER_CMP 4

/*
 * kcov descriptor (one per opened debugfs file).
 * State transitions of the descriptor:
 *  - initial state after open()
 *  - then there must be a single ioctl(KCOV_INIT_TRACE) call
 *  - then, mmap() call (several calls are allowed but not useful)
 *  - then, ioctl(KCOV_ENABLE, arg), where arg is
 *	KCOV_TRACE_PC - to trace only the PCs
 *	or
 *	KCOV_TRACE_CMP - to trace only the comparison operands
 *  - then, ioctl(KCOV_DISABLE) to disable the task.
 * Enabling/disabling ioctls can be repeated (only one task a time allowed).
 */
struct kcov {
	/*
	 * Reference counter. We keep one for:
	 *  - opened file descriptor
	 *  - task with enabled coverage (we can't unwire it from another task)
	 *  - each code section for remote coverage collection
	 */
	refcount_t		refcount;
	/* The lock protects mode, size, area and t. */
	spinlock_t		lock;
	enum kcov_mode		mode;
	/* Size of arena (in long's). */
	unsigned int		size;
	/* Coverage buffer shared with user space. */
	void			*area;
	/* Task for which we collect coverage, or NULL. */
	struct task_struct	*t;
	/* Collecting coverage from remote (background) threads. */
	bool			remote;
	/* Size of remote area (in long's). */
	unsigned int		remote_size;
	/*
	 * Sequence is incremented each time kcov is reenabled, used by
	 * kcov_remote_stop(), see the comment there.
	 */
	int			sequence;
};

struct kcov_remote_area {
	struct list_head	list;
	unsigned int		size;
};

struct kcov_remote {
	u64			handle;
	struct kcov		*kcov;
	struct hlist_node	hnode;
};

static DEFINE_SPINLOCK(kcov_remote_lock);
static DEFINE_HASHTABLE(kcov_remote_map, 4);
static struct list_head kcov_remote_areas = LIST_HEAD_INIT(kcov_remote_areas);

struct kcov_percpu_data {
	void			*irq_area;
	local_lock_t		lock;

	unsigned int		saved_mode;
	unsigned int		saved_size;
	void			*saved_area;
	struct kcov		*saved_kcov;
	int			saved_sequence;
};

static DEFINE_PER_CPU(struct kcov_percpu_data, kcov_percpu_data) = {
	.lock = INIT_LOCAL_LOCK(lock),
};

/* Must be called with kcov_remote_lock locked. */
static struct kcov_remote *kcov_remote_find(u64 handle)
{
	struct kcov_remote *remote;

	hash_for_each_possible(kcov_remote_map, remote, hnode, handle) {
		if (remote->handle == handle)
			return remote;
	}
	return NULL;
}

/* Must be called with kcov_remote_lock locked. */
static struct kcov_remote *kcov_remote_add(struct kcov *kcov, u64 handle)
{
	struct kcov_remote *remote;

	if (kcov_remote_find(handle))
		return ERR_PTR(-EEXIST);
	remote = kmalloc(sizeof(*remote), GFP_ATOMIC);
	if (!remote)
		return ERR_PTR(-ENOMEM);
	remote->handle = handle;
	remote->kcov = kcov;
	hash_add(kcov_remote_map, &remote->hnode, handle);
	return remote;
}

/* Must be called with kcov_remote_lock locked. */
static struct kcov_remote_area *kcov_remote_area_get(unsigned int size)
{
	struct kcov_remote_area *area;
	struct list_head *pos;

	list_for_each(pos, &kcov_remote_areas) {
		area = list_entry(pos, struct kcov_remote_area, list);
		if (area->size == size) {
			list_del(&area->list);
			return area;
		}
	}
	return NULL;
}

/* Must be called with kcov_remote_lock locked. */
static void kcov_remote_area_put(struct kcov_remote_area *area,
					unsigned int size)
{
	INIT_LIST_HEAD(&area->list);
	area->size = size;
	list_add(&area->list, &kcov_remote_areas);
}

static notrace bool check_kcov_mode(enum kcov_mode needed_mode, struct task_struct *t)
{
	unsigned int mode;

	/*
	 * We are interested in code coverage as a function of a syscall inputs,
	 * so we ignore code executed in interrupts, unless we are in a remote
	 * coverage collection section in a softirq.
	 */
	if (!in_task() && !(in_serving_softirq() && t->kcov_softirq))
		return false;
	mode = READ_ONCE(t->kcov_mode);
	/*
	 * There is some code that runs in interrupts but for which
	 * in_interrupt() returns false (e.g. preempt_schedule_irq()).
	 * READ_ONCE()/barrier() effectively provides load-acquire wrt
	 * interrupts, there are paired barrier()/WRITE_ONCE() in
	 * kcov_start().
	 */
	barrier();
	return mode == needed_mode;
}

static notrace unsigned long canonicalize_ip(unsigned long ip)
{
#ifdef CONFIG_RANDOMIZE_BASE
	ip -= kaslr_offset();
#endif
	return ip;
}

/*
 * Entry point from instrumented code.
 * This is called once per basic-block/edge.
 */
void notrace __sanitizer_cov_trace_pc(void)
{
	struct task_struct *t;
	unsigned long *area;
	unsigned long ip = canonicalize_ip(_RET_IP_);
	unsigned long pos;

	t = current;
	if (!check_kcov_mode(KCOV_MODE_TRACE_PC, t))
		return;

	area = t->kcov_area;
	/* The first 64-bit word is the number of subsequent PCs. */
	pos = READ_ONCE(area[0]) + 1;
	if (likely(pos < t->kcov_size)) {
		/* Previously we write pc before updating pos. However, some
		 * early interrupt code could bypass check_kcov_mode() check
		 * and invoke __sanitizer_cov_trace_pc(). If such interrupt is
		 * raised between writing pc and updating pos, the pc could be
		 * overitten by the recursive __sanitizer_cov_trace_pc().
		 * Update pos before writing pc to avoid such interleaving.
		 */
		WRITE_ONCE(area[0], pos);
		barrier();
		area[pos] = ip;
	}
}
EXPORT_SYMBOL(__sanitizer_cov_trace_pc);

#ifdef CONFIG_KCOV_ENABLE_COMPARISONS
static void notrace write_comp_data(u64 type, u64 arg1, u64 arg2, u64 ip)
{
	struct task_struct *t;
	u64 *area;
	u64 count, start_index, end_pos, max_pos;

	t = current;
	if (!check_kcov_mode(KCOV_MODE_TRACE_CMP, t))
		return;

	ip = canonicalize_ip(ip);

	/*
	 * We write all comparison arguments and types as u64.
	 * The buffer was allocated for t->kcov_size unsigned longs.
	 */
	area = (u64 *)t->kcov_area;
	max_pos = t->kcov_size * sizeof(unsigned long);

	count = READ_ONCE(area[0]);

	/* Every record is KCOV_WORDS_PER_CMP 64-bit words. */
	start_index = 1 + count * KCOV_WORDS_PER_CMP;
	end_pos = (start_index + KCOV_WORDS_PER_CMP) * sizeof(u64);
	if (likely(end_pos <= max_pos)) {
		/* See comment in __sanitizer_cov_trace_pc(). */
		WRITE_ONCE(area[0], count + 1);
		barrier();
		area[start_index] = type;
		area[start_index + 1] = arg1;
		area[start_index + 2] = arg2;
		area[start_index + 3] = ip;
	}
}

void notrace __sanitizer_cov_trace_cmp1(u8 arg1, u8 arg2)
{
	write_comp_data(KCOV_CMP_SIZE(0), arg1, arg2, _RET_IP_);
}
EXPORT_SYMBOL(__sanitizer_cov_trace_cmp1);

void notrace __sanitizer_cov_trace_cmp2(u16 arg1, u16 arg2)
{
	write_comp_data(KCOV_CMP_SIZE(1), arg1, arg2, _RET_IP_);
}
EXPORT_SYMBOL(__sanitizer_cov_trace_cmp2);

void notrace __sanitizer_cov_trace_cmp4(u32 arg1, u32 arg2)
{
	write_comp_data(KCOV_CMP_SIZE(2), arg1, arg2, _RET_IP_);
}
EXPORT_SYMBOL(__sanitizer_cov_trace_cmp4);

void notrace __sanitizer_cov_trace_cmp8(u64 arg1, u64 arg2)
{
	write_comp_data(KCOV_CMP_SIZE(3), arg1, arg2, _RET_IP_);
}
EXPORT_SYMBOL(__sanitizer_cov_trace_cmp8);

void notrace __sanitizer_cov_trace_const_cmp1(u8 arg1, u8 arg2)
{
	write_comp_data(KCOV_CMP_SIZE(0) | KCOV_CMP_CONST, arg1, arg2,
			_RET_IP_);
}
EXPORT_SYMBOL(__sanitizer_cov_trace_const_cmp1);

void notrace __sanitizer_cov_trace_const_cmp2(u16 arg1, u16 arg2)
{
	write_comp_data(KCOV_CMP_SIZE(1) | KCOV_CMP_CONST, arg1, arg2,
			_RET_IP_);
}
EXPORT_SYMBOL(__sanitizer_cov_trace_const_cmp2);

void notrace __sanitizer_cov_trace_const_cmp4(u32 arg1, u32 arg2)
{
	write_comp_data(KCOV_CMP_SIZE(2) | KCOV_CMP_CONST, arg1, arg2,
			_RET_IP_);
}
EXPORT_SYMBOL(__sanitizer_cov_trace_const_cmp4);

void notrace __sanitizer_cov_trace_const_cmp8(u64 arg1, u64 arg2)
{
	write_comp_data(KCOV_CMP_SIZE(3) | KCOV_CMP_CONST, arg1, arg2,
			_RET_IP_);
}
EXPORT_SYMBOL(__sanitizer_cov_trace_const_cmp8);

void notrace __sanitizer_cov_trace_switch(u64 val, u64 *cases)
{
	u64 i;
	u64 count = cases[0];
	u64 size = cases[1];
	u64 type = KCOV_CMP_CONST;

	switch (size) {
	case 8:
		type |= KCOV_CMP_SIZE(0);
		break;
	case 16:
		type |= KCOV_CMP_SIZE(1);
		break;
	case 32:
		type |= KCOV_CMP_SIZE(2);
		break;
	case 64:
		type |= KCOV_CMP_SIZE(3);
		break;
	default:
		return;
	}
	for (i = 0; i < count; i++)
		write_comp_data(type, cases[i + 2], val, _RET_IP_);
}
EXPORT_SYMBOL(__sanitizer_cov_trace_switch);
#endif /* ifdef CONFIG_KCOV_ENABLE_COMPARISONS */

static void kcov_start(struct task_struct *t, struct kcov *kcov,
			unsigned int size, void *area, enum kcov_mode mode,
			int sequence)
{
	kcov_debug("t = %px, size = %u, area = %px\n", t, size, area);
	t->kcov = kcov;
	/* Cache in task struct for performance. */
	t->kcov_size = size;
	t->kcov_area = area;
	t->kcov_sequence = sequence;
	/* See comment in check_kcov_mode(). */
	barrier();
	WRITE_ONCE(t->kcov_mode, mode);
}

static void kcov_stop(struct task_struct *t)
{
	WRITE_ONCE(t->kcov_mode, KCOV_MODE_DISABLED);
	barrier();
	t->kcov = NULL;
	t->kcov_size = 0;
	t->kcov_area = NULL;
}

static void kcov_task_reset(struct task_struct *t)
{
	kcov_stop(t);
	t->kcov_sequence = 0;
	t->kcov_handle = 0;
}

void kcov_task_init(struct task_struct *t)
{
	kcov_task_reset(t);
	t->kcov_handle = current->kcov_handle;
}

static void kcov_reset(struct kcov *kcov)
{
	kcov->t = NULL;
	kcov->mode = KCOV_MODE_INIT;
	kcov->remote = false;
	kcov->remote_size = 0;
	kcov->sequence++;
}

static void kcov_remote_reset(struct kcov *kcov)
{
	int bkt;
	struct kcov_remote *remote;
	struct hlist_node *tmp;
	unsigned long flags;

	spin_lock_irqsave(&kcov_remote_lock, flags);
	hash_for_each_safe(kcov_remote_map, bkt, tmp, remote, hnode) {
		if (remote->kcov != kcov)
			continue;
		hash_del(&remote->hnode);
		kfree(remote);
	}
	/* Do reset before unlock to prevent races with kcov_remote_start(). */
	kcov_reset(kcov);
	spin_unlock_irqrestore(&kcov_remote_lock, flags);
}

static void kcov_disable(struct task_struct *t, struct kcov *kcov)
{
	kcov_task_reset(t);
	if (kcov->remote)
		kcov_remote_reset(kcov);
	else
		kcov_reset(kcov);
}

static void kcov_get(struct kcov *kcov)
{
	refcount_inc(&kcov->refcount);
}

static void kcov_put(struct kcov *kcov)
{
	if (refcount_dec_and_test(&kcov->refcount)) {
		kcov_remote_reset(kcov);
		vfree(kcov->area);
		kfree(kcov);
	}
}

void kcov_task_exit(struct task_struct *t)
{
	struct kcov *kcov;
	unsigned long flags;

	kcov = t->kcov;
	if (kcov == NULL)
		return;

	spin_lock_irqsave(&kcov->lock, flags);
	kcov_debug("t = %px, kcov->t = %px\n", t, kcov->t);
	/*
	 * For KCOV_ENABLE devices we want to make sure that t->kcov->t == t,
	 * which comes down to:
	 *        WARN_ON(!kcov->remote && kcov->t != t);
	 *
	 * For KCOV_REMOTE_ENABLE devices, the exiting task is either:
	 *
	 * 1. A remote task between kcov_remote_start() and kcov_remote_stop().
	 *    In this case we should print a warning right away, since a task
	 *    shouldn't be exiting when it's in a kcov coverage collection
	 *    section. Here t points to the task that is collecting remote
	 *    coverage, and t->kcov->t points to the thread that created the
	 *    kcov device. Which means that to detect this case we need to
	 *    check that t != t->kcov->t, and this gives us the following:
	 *        WARN_ON(kcov->remote && kcov->t != t);
	 *
	 * 2. The task that created kcov exiting without calling KCOV_DISABLE,
	 *    and then again we make sure that t->kcov->t == t:
	 *        WARN_ON(kcov->remote && kcov->t != t);
	 *
	 * By combining all three checks into one we get:
	 */
	if (WARN_ON(kcov->t != t)) {
		spin_unlock_irqrestore(&kcov->lock, flags);
		return;
	}
	/* Just to not leave dangling references behind. */
	kcov_disable(t, kcov);
	spin_unlock_irqrestore(&kcov->lock, flags);
	kcov_put(kcov);
}

static int kcov_mmap(struct file *filep, struct vm_area_struct *vma)
{
	int res = 0;
	struct kcov *kcov = vma->vm_file->private_data;
	unsigned long size, off;
	struct page *page;
	unsigned long flags;

	spin_lock_irqsave(&kcov->lock, flags);
	size = kcov->size * sizeof(unsigned long);
	if (kcov->area == NULL || vma->vm_pgoff != 0 ||
	    vma->vm_end - vma->vm_start != size) {
		res = -EINVAL;
		goto exit;
	}
	spin_unlock_irqrestore(&kcov->lock, flags);
	vma->vm_flags |= VM_DONTEXPAND;
	for (off = 0; off < size; off += PAGE_SIZE) {
		page = vmalloc_to_page(kcov->area + off);
		res = vm_insert_page(vma, vma->vm_start + off, page);
		if (res) {
			pr_warn_once("kcov: vm_insert_page() failed\n");
			return res;
		}
	}
	return 0;
exit:
	spin_unlock_irqrestore(&kcov->lock, flags);
	return res;
}

static int kcov_open(struct inode *inode, struct file *filep)
{
	struct kcov *kcov;

	kcov = kzalloc(sizeof(*kcov), GFP_KERNEL);
	if (!kcov)
		return -ENOMEM;
	kcov->mode = KCOV_MODE_DISABLED;
	kcov->sequence = 1;
	refcount_set(&kcov->refcount, 1);
	spin_lock_init(&kcov->lock);
	filep->private_data = kcov;
	return nonseekable_open(inode, filep);
}

static int kcov_close(struct inode *inode, struct file *filep)
{
	kcov_put(filep->private_data);
	return 0;
}

static int kcov_get_mode(unsigned long arg)
{
	if (arg == KCOV_TRACE_PC)
		return KCOV_MODE_TRACE_PC;
	else if (arg == KCOV_TRACE_CMP)
#ifdef CONFIG_KCOV_ENABLE_COMPARISONS
		return KCOV_MODE_TRACE_CMP;
#else
		return -ENOTSUPP;
#endif
	else
		return -EINVAL;
}

/*
 * Fault in a lazily-faulted vmalloc area before it can be used by
 * __santizer_cov_trace_pc(), to avoid recursion issues if any code on the
 * vmalloc fault handling path is instrumented.
 */
static void kcov_fault_in_area(struct kcov *kcov)
{
	unsigned long stride = PAGE_SIZE / sizeof(unsigned long);
	unsigned long *area = kcov->area;
	unsigned long offset;

	for (offset = 0; offset < kcov->size; offset += stride)
		READ_ONCE(area[offset]);
}

static inline bool kcov_check_handle(u64 handle, bool common_valid,
				bool uncommon_valid, bool zero_valid)
{
	if (handle & ~(KCOV_SUBSYSTEM_MASK | KCOV_INSTANCE_MASK))
		return false;
	switch (handle & KCOV_SUBSYSTEM_MASK) {
	case KCOV_SUBSYSTEM_COMMON:
		return (handle & KCOV_INSTANCE_MASK) ?
			common_valid : zero_valid;
	case KCOV_SUBSYSTEM_USB:
		return uncommon_valid;
	default:
		return false;
	}
	return false;
}

static int kcov_ioctl_locked(struct kcov *kcov, unsigned int cmd,
			     unsigned long arg)
{
	struct task_struct *t;
	unsigned long flags, unused;
	int mode, i;
	struct kcov_remote_arg *remote_arg;
	struct kcov_remote *remote;

	switch (cmd) {
	case KCOV_ENABLE:
		/*
		 * Enable coverage for the current task.
		 * At this point user must have been enabled trace mode,
		 * and mmapped the file. Coverage collection is disabled only
		 * at task exit or voluntary by KCOV_DISABLE. After that it can
		 * be enabled for another task.
		 */
		if (kcov->mode != KCOV_MODE_INIT || !kcov->area)
			return -EINVAL;
		t = current;
		if (kcov->t != NULL || t->kcov != NULL)
			return -EBUSY;
		mode = kcov_get_mode(arg);
		if (mode < 0)
			return mode;
		kcov_fault_in_area(kcov);
		kcov->mode = mode;
		kcov_start(t, kcov, kcov->size, kcov->area, kcov->mode,
				kcov->sequence);
		kcov->t = t;
		/* Put either in kcov_task_exit() or in KCOV_DISABLE. */
		kcov_get(kcov);
		return 0;
	case KCOV_DISABLE:
		/* Disable coverage for the current task. */
		unused = arg;
		if (unused != 0 || current->kcov != kcov)
			return -EINVAL;
		t = current;
		if (WARN_ON(kcov->t != t))
			return -EINVAL;
		kcov_disable(t, kcov);
		kcov_put(kcov);
		return 0;
	case KCOV_REMOTE_ENABLE:
		if (kcov->mode != KCOV_MODE_INIT || !kcov->area)
			return -EINVAL;
		t = current;
		if (kcov->t != NULL || t->kcov != NULL)
			return -EBUSY;
		remote_arg = (struct kcov_remote_arg *)arg;
		mode = kcov_get_mode(remote_arg->trace_mode);
		if (mode < 0)
			return mode;
		if (remote_arg->area_size > LONG_MAX / sizeof(unsigned long))
			return -EINVAL;
		kcov->mode = mode;
		t->kcov = kcov;
		kcov->t = t;
		kcov->remote = true;
		kcov->remote_size = remote_arg->area_size;
		spin_lock_irqsave(&kcov_remote_lock, flags);
		for (i = 0; i < remote_arg->num_handles; i++) {
			if (!kcov_check_handle(remote_arg->handles[i],
						false, true, false)) {
				spin_unlock_irqrestore(&kcov_remote_lock,
							flags);
				kcov_disable(t, kcov);
				return -EINVAL;
			}
			remote = kcov_remote_add(kcov, remote_arg->handles[i]);
			if (IS_ERR(remote)) {
				spin_unlock_irqrestore(&kcov_remote_lock,
							flags);
				kcov_disable(t, kcov);
				return PTR_ERR(remote);
			}
		}
		if (remote_arg->common_handle) {
			if (!kcov_check_handle(remote_arg->common_handle,
						true, false, false)) {
				spin_unlock_irqrestore(&kcov_remote_lock,
							flags);
				kcov_disable(t, kcov);
				return -EINVAL;
			}
			remote = kcov_remote_add(kcov,
					remote_arg->common_handle);
			if (IS_ERR(remote)) {
				spin_unlock_irqrestore(&kcov_remote_lock,
							flags);
				kcov_disable(t, kcov);
				return PTR_ERR(remote);
			}
			t->kcov_handle = remote_arg->common_handle;
		}
		spin_unlock_irqrestore(&kcov_remote_lock, flags);
		/* Put either in kcov_task_exit() or in KCOV_DISABLE. */
		kcov_get(kcov);
		return 0;
	default:
		return -ENOTTY;
	}
}

static long kcov_ioctl(struct file *filep, unsigned int cmd, unsigned long arg)
{
	struct kcov *kcov;
	int res;
	struct kcov_remote_arg *remote_arg = NULL;
	unsigned int remote_num_handles;
	unsigned long remote_arg_size;
	unsigned long size, flags;
	void *area;

	kcov = filep->private_data;
	switch (cmd) {
	case KCOV_INIT_TRACE:
		/*
		 * Enable kcov in trace mode and setup buffer size.
		 * Must happen before anything else.
		 *
		 * First check the size argument - it must be at least 2
		 * to hold the current position and one PC.
		 */
		size = arg;
		if (size < 2 || size > INT_MAX / sizeof(unsigned long))
			return -EINVAL;
		area = vmalloc_user(size * sizeof(unsigned long));
		if (area == NULL)
			return -ENOMEM;
		spin_lock_irqsave(&kcov->lock, flags);
		if (kcov->mode != KCOV_MODE_DISABLED) {
			spin_unlock_irqrestore(&kcov->lock, flags);
			vfree(area);
			return -EBUSY;
		}
		kcov->area = area;
		kcov->size = size;
		kcov->mode = KCOV_MODE_INIT;
		spin_unlock_irqrestore(&kcov->lock, flags);
		return 0;
	case KCOV_REMOTE_ENABLE:
		if (get_user(remote_num_handles, (unsigned __user *)(arg +
				offsetof(struct kcov_remote_arg, num_handles))))
			return -EFAULT;
		if (remote_num_handles > KCOV_REMOTE_MAX_HANDLES)
			return -EINVAL;
		remote_arg_size = struct_size(remote_arg, handles,
					remote_num_handles);
		remote_arg = memdup_user((void __user *)arg, remote_arg_size);
		if (IS_ERR(remote_arg))
			return PTR_ERR(remote_arg);
		if (remote_arg->num_handles != remote_num_handles) {
			kfree(remote_arg);
			return -EINVAL;
		}
		arg = (unsigned long)remote_arg;
		fallthrough;
	default:
		/*
		 * All other commands can be normally executed under a spin lock, so we
		 * obtain and release it here in order to simplify kcov_ioctl_locked().
		 */
		spin_lock_irqsave(&kcov->lock, flags);
		res = kcov_ioctl_locked(kcov, cmd, arg);
		spin_unlock_irqrestore(&kcov->lock, flags);
		kfree(remote_arg);
		return res;
	}
}

static const struct file_operations kcov_fops = {
	.open		= kcov_open,
	.unlocked_ioctl	= kcov_ioctl,
	.compat_ioctl	= kcov_ioctl,
	.mmap		= kcov_mmap,
	.release        = kcov_close,
};

/*
 * kcov_remote_start() and kcov_remote_stop() can be used to annotate a section
 * of code in a kernel background thread or in a softirq to allow kcov to be
 * used to collect coverage from that part of code.
 *
 * The handle argument of kcov_remote_start() identifies a code section that is
 * used for coverage collection. A userspace process passes this handle to
 * KCOV_REMOTE_ENABLE ioctl to make the used kcov device start collecting
 * coverage for the code section identified by this handle.
 *
 * The usage of these annotations in the kernel code is different depending on
 * the type of the kernel thread whose code is being annotated.
 *
 * For global kernel threads that are spawned in a limited number of instances
 * (e.g. one USB hub_event() worker thread is spawned per USB HCD) and for
 * softirqs, each instance must be assigned a unique 4-byte instance id. The
 * instance id is then combined with a 1-byte subsystem id to get a handle via
 * kcov_remote_handle(subsystem_id, instance_id).
 *
 * For local kernel threads that are spawned from system calls handler when a
 * user interacts with some kernel interface (e.g. vhost workers), a handle is
 * passed from a userspace process as the common_handle field of the
 * kcov_remote_arg struct (note, that the user must generate a handle by using
 * kcov_remote_handle() with KCOV_SUBSYSTEM_COMMON as the subsystem id and an
 * arbitrary 4-byte non-zero number as the instance id). This common handle
 * then gets saved into the task_struct of the process that issued the
 * KCOV_REMOTE_ENABLE ioctl. When this process issues system calls that spawn
 * kernel threads, the common handle must be retrieved via kcov_common_handle()
 * and passed to the spawned threads via custom annotations. Those kernel
 * threads must in turn be annotated with kcov_remote_start(common_handle) and
 * kcov_remote_stop(). All of the threads that are spawned by the same process
 * obtain the same handle, hence the name "common".
 *
 * See Documentation/dev-tools/kcov.rst for more details.
 *
 * Internally, kcov_remote_start() looks up the kcov device associated with the
 * provided handle, allocates an area for coverage collection, and saves the
 * pointers to kcov and area into the current task_struct to allow coverage to
 * be collected via __sanitizer_cov_trace_pc().
 * In turns kcov_remote_stop() clears those pointers from task_struct to stop
 * collecting coverage and copies all collected coverage into the kcov area.
 */

static inline bool kcov_mode_enabled(unsigned int mode)
{
	return (mode & ~KCOV_IN_CTXSW) != KCOV_MODE_DISABLED;
}

static void kcov_remote_softirq_start(struct task_struct *t)
{
	struct kcov_percpu_data *data = this_cpu_ptr(&kcov_percpu_data);
	unsigned int mode;

	mode = READ_ONCE(t->kcov_mode);
	barrier();
	if (kcov_mode_enabled(mode)) {
		data->saved_mode = mode;
		data->saved_size = t->kcov_size;
		data->saved_area = t->kcov_area;
		data->saved_sequence = t->kcov_sequence;
		data->saved_kcov = t->kcov;
		kcov_stop(t);
	}
}

static void kcov_remote_softirq_stop(struct task_struct *t)
{
	struct kcov_percpu_data *data = this_cpu_ptr(&kcov_percpu_data);

	if (data->saved_kcov) {
		kcov_start(t, data->saved_kcov, data->saved_size,
				data->saved_area, data->saved_mode,
				data->saved_sequence);
		data->saved_mode = 0;
		data->saved_size = 0;
		data->saved_area = NULL;
		data->saved_sequence = 0;
		data->saved_kcov = NULL;
	}
}

void kcov_remote_start(u64 handle)
{
	struct task_struct *t = current;
	struct kcov_remote *remote;
	struct kcov *kcov;
	unsigned int mode;
	void *area;
	unsigned int size;
	int sequence;
	unsigned long flags;

	if (WARN_ON(!kcov_check_handle(handle, true, true, true)))
		return;
	if (!in_task() && !in_serving_softirq())
		return;

	local_lock_irqsave(&kcov_percpu_data.lock, flags);

	/*
	 * Check that kcov_remote_start() is not called twice in background
	 * threads nor called by user tasks (with enabled kcov).
	 */
	mode = READ_ONCE(t->kcov_mode);
	if (WARN_ON(in_task() && kcov_mode_enabled(mode))) {
		local_unlock_irqrestore(&kcov_percpu_data.lock, flags);
		return;
	}
	/*
	 * Check that kcov_remote_start() is not called twice in softirqs.
	 * Note, that kcov_remote_start() can be called from a softirq that
	 * happened while collecting coverage from a background thread.
	 */
	if (WARN_ON(in_serving_softirq() && t->kcov_softirq)) {
		local_unlock_irqrestore(&kcov_percpu_data.lock, flags);
		return;
	}

	spin_lock(&kcov_remote_lock);
	remote = kcov_remote_find(handle);
	if (!remote) {
		spin_unlock(&kcov_remote_lock);
		local_unlock_irqrestore(&kcov_percpu_data.lock, flags);
		return;
	}
	kcov_debug("handle = %llx, context: %s\n", handle,
			in_task() ? "task" : "softirq");
	kcov = remote->kcov;
	/* Put in kcov_remote_stop(). */
	kcov_get(kcov);
	/*
	 * Read kcov fields before unlock to prevent races with
	 * KCOV_DISABLE / kcov_remote_reset().
	 */
	mode = kcov->mode;
	sequence = kcov->sequence;
	if (in_task()) {
		size = kcov->remote_size;
		area = kcov_remote_area_get(size);
	} else {
		size = CONFIG_KCOV_IRQ_AREA_SIZE;
		area = this_cpu_ptr(&kcov_percpu_data)->irq_area;
	}
	spin_unlock(&kcov_remote_lock);

	/* Can only happen when in_task(). */
	if (!area) {
		local_unlock_irqrestore(&kcov_percpu_data.lock, flags);
		area = vmalloc(size * sizeof(unsigned long));
		if (!area) {
			kcov_put(kcov);
			return;
		}
		local_lock_irqsave(&kcov_percpu_data.lock, flags);
	}

	/* Reset coverage size. */
	*(u64 *)area = 0;

	if (in_serving_softirq()) {
		kcov_remote_softirq_start(t);
		t->kcov_softirq = 1;
	}
	kcov_start(t, kcov, size, area, mode, sequence);

	local_unlock_irqrestore(&kcov_percpu_data.lock, flags);

}
EXPORT_SYMBOL(kcov_remote_start);

static void kcov_move_area(enum kcov_mode mode, void *dst_area,
				unsigned int dst_area_size, void *src_area)
{
	u64 word_size = sizeof(unsigned long);
	u64 count_size, entry_size_log;
	u64 dst_len, src_len;
	void *dst_entries, *src_entries;
	u64 dst_occupied, dst_free, bytes_to_move, entries_moved;

	kcov_debug("%px %u <= %px %lu\n",
		dst_area, dst_area_size, src_area, *(unsigned long *)src_area);

	switch (mode) {
	case KCOV_MODE_TRACE_PC:
		dst_len = READ_ONCE(*(unsigned long *)dst_area);
		src_len = *(unsigned long *)src_area;
		count_size = sizeof(unsigned long);
		entry_size_log = __ilog2_u64(sizeof(unsigned long));
		break;
	case KCOV_MODE_TRACE_CMP:
		dst_len = READ_ONCE(*(u64 *)dst_area);
		src_len = *(u64 *)src_area;
		count_size = sizeof(u64);
		BUILD_BUG_ON(!is_power_of_2(KCOV_WORDS_PER_CMP));
		entry_size_log = __ilog2_u64(sizeof(u64) * KCOV_WORDS_PER_CMP);
		break;
	default:
		WARN_ON(1);
		return;
	}

	/* As arm can't divide u64 integers use log of entry size. */
	if (dst_len > ((dst_area_size * word_size - count_size) >>
				entry_size_log))
		return;
	dst_occupied = count_size + (dst_len << entry_size_log);
	dst_free = dst_area_size * word_size - dst_occupied;
	bytes_to_move = min(dst_free, src_len << entry_size_log);
	dst_entries = dst_area + dst_occupied;
	src_entries = src_area + count_size;
	memcpy(dst_entries, src_entries, bytes_to_move);
	entries_moved = bytes_to_move >> entry_size_log;

	switch (mode) {
	case KCOV_MODE_TRACE_PC:
		WRITE_ONCE(*(unsigned long *)dst_area, dst_len + entries_moved);
		break;
	case KCOV_MODE_TRACE_CMP:
		WRITE_ONCE(*(u64 *)dst_area, dst_len + entries_moved);
		break;
	default:
		break;
	}
}

/* See the comment before kcov_remote_start() for usage details. */
void kcov_remote_stop(void)
{
	struct task_struct *t = current;
	struct kcov *kcov;
	unsigned int mode;
	void *area;
	unsigned int size;
	int sequence;
	unsigned long flags;

	if (!in_task() && !in_serving_softirq())
		return;

	local_lock_irqsave(&kcov_percpu_data.lock, flags);

	mode = READ_ONCE(t->kcov_mode);
	barrier();
	if (!kcov_mode_enabled(mode)) {
		local_unlock_irqrestore(&kcov_percpu_data.lock, flags);
		return;
	}
	/*
	 * When in softirq, check if the corresponding kcov_remote_start()
	 * actually found the remote handle and started collecting coverage.
	 */
	if (in_serving_softirq() && !t->kcov_softirq) {
		local_unlock_irqrestore(&kcov_percpu_data.lock, flags);
		return;
	}
	/* Make sure that kcov_softirq is only set when in softirq. */
	if (WARN_ON(!in_serving_softirq() && t->kcov_softirq)) {
		local_unlock_irqrestore(&kcov_percpu_data.lock, flags);
		return;
	}

	kcov = t->kcov;
	area = t->kcov_area;
	size = t->kcov_size;
	sequence = t->kcov_sequence;

	kcov_stop(t);
	if (in_serving_softirq()) {
		t->kcov_softirq = 0;
		kcov_remote_softirq_stop(t);
	}

	spin_lock(&kcov->lock);
	/*
	 * KCOV_DISABLE could have been called between kcov_remote_start()
	 * and kcov_remote_stop(), hence the sequence check.
	 */
	if (sequence == kcov->sequence && kcov->remote)
		kcov_move_area(kcov->mode, kcov->area, kcov->size, area);
	spin_unlock(&kcov->lock);

	if (in_task()) {
		spin_lock(&kcov_remote_lock);
		kcov_remote_area_put(area, size);
		spin_unlock(&kcov_remote_lock);
	}

	local_unlock_irqrestore(&kcov_percpu_data.lock, flags);

	/* Get in kcov_remote_start(). */
	kcov_put(kcov);
}
EXPORT_SYMBOL(kcov_remote_stop);

/* See the comment before kcov_remote_start() for usage details. */
u64 kcov_common_handle(void)
{
	if (!in_task())
		return 0;
	return current->kcov_handle;
}
EXPORT_SYMBOL(kcov_common_handle);

static int __init kcov_init(void)
{
	int cpu;

	for_each_possible_cpu(cpu) {
		void *area = vmalloc_node(CONFIG_KCOV_IRQ_AREA_SIZE *
				sizeof(unsigned long), cpu_to_node(cpu));
		if (!area)
			return -ENOMEM;
		per_cpu_ptr(&kcov_percpu_data, cpu)->irq_area = area;
	}

	/*
	 * The kcov debugfs file won't ever get removed and thus,
	 * there is no need to protect it against removal races. The
	 * use of debugfs_create_file_unsafe() is actually safe here.
	 */
	debugfs_create_file_unsafe("kcov", 0600, NULL, NULL, &kcov_fops);

	return 0;
}

device_initcall(kcov_init);