summaryrefslogtreecommitdiff
path: root/kernel/kcsan/core.c
blob: 9147ff6a12e56c437d2d663ce341ab397c2417d0 (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
// SPDX-License-Identifier: GPL-2.0

#include <linux/atomic.h>
#include <linux/bug.h>
#include <linux/delay.h>
#include <linux/export.h>
#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/list.h>
#include <linux/moduleparam.h>
#include <linux/percpu.h>
#include <linux/preempt.h>
#include <linux/random.h>
#include <linux/sched.h>
#include <linux/uaccess.h>

#include "atomic.h"
#include "encoding.h"
#include "kcsan.h"

static bool kcsan_early_enable = IS_ENABLED(CONFIG_KCSAN_EARLY_ENABLE);
unsigned int kcsan_udelay_task = CONFIG_KCSAN_UDELAY_TASK;
unsigned int kcsan_udelay_interrupt = CONFIG_KCSAN_UDELAY_INTERRUPT;
static long kcsan_skip_watch = CONFIG_KCSAN_SKIP_WATCH;
static bool kcsan_interrupt_watcher = IS_ENABLED(CONFIG_KCSAN_INTERRUPT_WATCHER);

#ifdef MODULE_PARAM_PREFIX
#undef MODULE_PARAM_PREFIX
#endif
#define MODULE_PARAM_PREFIX "kcsan."
module_param_named(early_enable, kcsan_early_enable, bool, 0);
module_param_named(udelay_task, kcsan_udelay_task, uint, 0644);
module_param_named(udelay_interrupt, kcsan_udelay_interrupt, uint, 0644);
module_param_named(skip_watch, kcsan_skip_watch, long, 0644);
module_param_named(interrupt_watcher, kcsan_interrupt_watcher, bool, 0444);

bool kcsan_enabled;

/* Per-CPU kcsan_ctx for interrupts */
static DEFINE_PER_CPU(struct kcsan_ctx, kcsan_cpu_ctx) = {
	.disable_count		= 0,
	.atomic_next		= 0,
	.atomic_nest_count	= 0,
	.in_flat_atomic		= false,
	.access_mask		= 0,
	.scoped_accesses	= {LIST_POISON1, NULL},
};

/*
 * Helper macros to index into adjacent slots, starting from address slot
 * itself, followed by the right and left slots.
 *
 * The purpose is 2-fold:
 *
 *	1. if during insertion the address slot is already occupied, check if
 *	   any adjacent slots are free;
 *	2. accesses that straddle a slot boundary due to size that exceeds a
 *	   slot's range may check adjacent slots if any watchpoint matches.
 *
 * Note that accesses with very large size may still miss a watchpoint; however,
 * given this should be rare, this is a reasonable trade-off to make, since this
 * will avoid:
 *
 *	1. excessive contention between watchpoint checks and setup;
 *	2. larger number of simultaneous watchpoints without sacrificing
 *	   performance.
 *
 * Example: SLOT_IDX values for KCSAN_CHECK_ADJACENT=1, where i is [0, 1, 2]:
 *
 *   slot=0:  [ 1,  2,  0]
 *   slot=9:  [10, 11,  9]
 *   slot=63: [64, 65, 63]
 */
#define SLOT_IDX(slot, i) (slot + ((i + KCSAN_CHECK_ADJACENT) % NUM_SLOTS))

/*
 * SLOT_IDX_FAST is used in the fast-path. Not first checking the address's primary
 * slot (middle) is fine if we assume that races occur rarely. The set of
 * indices {SLOT_IDX(slot, i) | i in [0, NUM_SLOTS)} is equivalent to
 * {SLOT_IDX_FAST(slot, i) | i in [0, NUM_SLOTS)}.
 */
#define SLOT_IDX_FAST(slot, i) (slot + i)

/*
 * Watchpoints, with each entry encoded as defined in encoding.h: in order to be
 * able to safely update and access a watchpoint without introducing locking
 * overhead, we encode each watchpoint as a single atomic long. The initial
 * zero-initialized state matches INVALID_WATCHPOINT.
 *
 * Add NUM_SLOTS-1 entries to account for overflow; this helps avoid having to
 * use more complicated SLOT_IDX_FAST calculation with modulo in the fast-path.
 */
static atomic_long_t watchpoints[CONFIG_KCSAN_NUM_WATCHPOINTS + NUM_SLOTS-1];

/*
 * Instructions to skip watching counter, used in should_watch(). We use a
 * per-CPU counter to avoid excessive contention.
 */
static DEFINE_PER_CPU(long, kcsan_skip);

static __always_inline atomic_long_t *find_watchpoint(unsigned long addr,
						      size_t size,
						      bool expect_write,
						      long *encoded_watchpoint)
{
	const int slot = watchpoint_slot(addr);
	const unsigned long addr_masked = addr & WATCHPOINT_ADDR_MASK;
	atomic_long_t *watchpoint;
	unsigned long wp_addr_masked;
	size_t wp_size;
	bool is_write;
	int i;

	BUILD_BUG_ON(CONFIG_KCSAN_NUM_WATCHPOINTS < NUM_SLOTS);

	for (i = 0; i < NUM_SLOTS; ++i) {
		watchpoint = &watchpoints[SLOT_IDX_FAST(slot, i)];
		*encoded_watchpoint = atomic_long_read(watchpoint);
		if (!decode_watchpoint(*encoded_watchpoint, &wp_addr_masked,
				       &wp_size, &is_write))
			continue;

		if (expect_write && !is_write)
			continue;

		/* Check if the watchpoint matches the access. */
		if (matching_access(wp_addr_masked, wp_size, addr_masked, size))
			return watchpoint;
	}

	return NULL;
}

static inline atomic_long_t *
insert_watchpoint(unsigned long addr, size_t size, bool is_write)
{
	const int slot = watchpoint_slot(addr);
	const long encoded_watchpoint = encode_watchpoint(addr, size, is_write);
	atomic_long_t *watchpoint;
	int i;

	/* Check slot index logic, ensuring we stay within array bounds. */
	BUILD_BUG_ON(SLOT_IDX(0, 0) != KCSAN_CHECK_ADJACENT);
	BUILD_BUG_ON(SLOT_IDX(0, KCSAN_CHECK_ADJACENT+1) != 0);
	BUILD_BUG_ON(SLOT_IDX(CONFIG_KCSAN_NUM_WATCHPOINTS-1, KCSAN_CHECK_ADJACENT) != ARRAY_SIZE(watchpoints)-1);
	BUILD_BUG_ON(SLOT_IDX(CONFIG_KCSAN_NUM_WATCHPOINTS-1, KCSAN_CHECK_ADJACENT+1) != ARRAY_SIZE(watchpoints) - NUM_SLOTS);

	for (i = 0; i < NUM_SLOTS; ++i) {
		long expect_val = INVALID_WATCHPOINT;

		/* Try to acquire this slot. */
		watchpoint = &watchpoints[SLOT_IDX(slot, i)];
		if (atomic_long_try_cmpxchg_relaxed(watchpoint, &expect_val, encoded_watchpoint))
			return watchpoint;
	}

	return NULL;
}

/*
 * Return true if watchpoint was successfully consumed, false otherwise.
 *
 * This may return false if:
 *
 *	1. another thread already consumed the watchpoint;
 *	2. the thread that set up the watchpoint already removed it;
 *	3. the watchpoint was removed and then re-used.
 */
static __always_inline bool
try_consume_watchpoint(atomic_long_t *watchpoint, long encoded_watchpoint)
{
	return atomic_long_try_cmpxchg_relaxed(watchpoint, &encoded_watchpoint, CONSUMED_WATCHPOINT);
}

/* Return true if watchpoint was not touched, false if already consumed. */
static inline bool consume_watchpoint(atomic_long_t *watchpoint)
{
	return atomic_long_xchg_relaxed(watchpoint, CONSUMED_WATCHPOINT) != CONSUMED_WATCHPOINT;
}

/* Remove the watchpoint -- its slot may be reused after. */
static inline void remove_watchpoint(atomic_long_t *watchpoint)
{
	atomic_long_set(watchpoint, INVALID_WATCHPOINT);
}

static __always_inline struct kcsan_ctx *get_ctx(void)
{
	/*
	 * In interrupts, use raw_cpu_ptr to avoid unnecessary checks, that would
	 * also result in calls that generate warnings in uaccess regions.
	 */
	return in_task() ? &current->kcsan_ctx : raw_cpu_ptr(&kcsan_cpu_ctx);
}

/* Check scoped accesses; never inline because this is a slow-path! */
static noinline void kcsan_check_scoped_accesses(void)
{
	struct kcsan_ctx *ctx = get_ctx();
	struct list_head *prev_save = ctx->scoped_accesses.prev;
	struct kcsan_scoped_access *scoped_access;

	ctx->scoped_accesses.prev = NULL;  /* Avoid recursion. */
	list_for_each_entry(scoped_access, &ctx->scoped_accesses, list)
		__kcsan_check_access(scoped_access->ptr, scoped_access->size, scoped_access->type);
	ctx->scoped_accesses.prev = prev_save;
}

/* Rules for generic atomic accesses. Called from fast-path. */
static __always_inline bool
is_atomic(const volatile void *ptr, size_t size, int type, struct kcsan_ctx *ctx)
{
	if (type & KCSAN_ACCESS_ATOMIC)
		return true;

	/*
	 * Unless explicitly declared atomic, never consider an assertion access
	 * as atomic. This allows using them also in atomic regions, such as
	 * seqlocks, without implicitly changing their semantics.
	 */
	if (type & KCSAN_ACCESS_ASSERT)
		return false;

	if (IS_ENABLED(CONFIG_KCSAN_ASSUME_PLAIN_WRITES_ATOMIC) &&
	    (type & KCSAN_ACCESS_WRITE) && size <= sizeof(long) &&
	    IS_ALIGNED((unsigned long)ptr, size))
		return true; /* Assume aligned writes up to word size are atomic. */

	if (ctx->atomic_next > 0) {
		/*
		 * Because we do not have separate contexts for nested
		 * interrupts, in case atomic_next is set, we simply assume that
		 * the outer interrupt set atomic_next. In the worst case, we
		 * will conservatively consider operations as atomic. This is a
		 * reasonable trade-off to make, since this case should be
		 * extremely rare; however, even if extremely rare, it could
		 * lead to false positives otherwise.
		 */
		if ((hardirq_count() >> HARDIRQ_SHIFT) < 2)
			--ctx->atomic_next; /* in task, or outer interrupt */
		return true;
	}

	return ctx->atomic_nest_count > 0 || ctx->in_flat_atomic;
}

static __always_inline bool
should_watch(const volatile void *ptr, size_t size, int type, struct kcsan_ctx *ctx)
{
	/*
	 * Never set up watchpoints when memory operations are atomic.
	 *
	 * Need to check this first, before kcsan_skip check below: (1) atomics
	 * should not count towards skipped instructions, and (2) to actually
	 * decrement kcsan_atomic_next for consecutive instruction stream.
	 */
	if (is_atomic(ptr, size, type, ctx))
		return false;

	if (this_cpu_dec_return(kcsan_skip) >= 0)
		return false;

	/*
	 * NOTE: If we get here, kcsan_skip must always be reset in slow path
	 * via reset_kcsan_skip() to avoid underflow.
	 */

	/* this operation should be watched */
	return true;
}

static inline void reset_kcsan_skip(void)
{
	long skip_count = kcsan_skip_watch -
			  (IS_ENABLED(CONFIG_KCSAN_SKIP_WATCH_RANDOMIZE) ?
				   prandom_u32_max(kcsan_skip_watch) :
				   0);
	this_cpu_write(kcsan_skip, skip_count);
}

static __always_inline bool kcsan_is_enabled(void)
{
	return READ_ONCE(kcsan_enabled) && get_ctx()->disable_count == 0;
}

static inline unsigned int get_delay(void)
{
	unsigned int delay = in_task() ? kcsan_udelay_task : kcsan_udelay_interrupt;
	return delay - (IS_ENABLED(CONFIG_KCSAN_DELAY_RANDOMIZE) ?
				prandom_u32_max(delay) :
				0);
}

void kcsan_save_irqtrace(struct task_struct *task)
{
#ifdef CONFIG_TRACE_IRQFLAGS
	task->kcsan_save_irqtrace = task->irqtrace;
#endif
}

void kcsan_restore_irqtrace(struct task_struct *task)
{
#ifdef CONFIG_TRACE_IRQFLAGS
	task->irqtrace = task->kcsan_save_irqtrace;
#endif
}

/*
 * Pull everything together: check_access() below contains the performance
 * critical operations; the fast-path (including check_access) functions should
 * all be inlinable by the instrumentation functions.
 *
 * The slow-path (kcsan_found_watchpoint, kcsan_setup_watchpoint) are
 * non-inlinable -- note that, we prefix these with "kcsan_" to ensure they can
 * be filtered from the stacktrace, as well as give them unique names for the
 * UACCESS whitelist of objtool. Each function uses user_access_save/restore(),
 * since they do not access any user memory, but instrumentation is still
 * emitted in UACCESS regions.
 */

static noinline void kcsan_found_watchpoint(const volatile void *ptr,
					    size_t size,
					    int type,
					    atomic_long_t *watchpoint,
					    long encoded_watchpoint)
{
	unsigned long flags;
	bool consumed;

	if (!kcsan_is_enabled())
		return;

	/*
	 * The access_mask check relies on value-change comparison. To avoid
	 * reporting a race where e.g. the writer set up the watchpoint, but the
	 * reader has access_mask!=0, we have to ignore the found watchpoint.
	 */
	if (get_ctx()->access_mask != 0)
		return;

	/*
	 * Consume the watchpoint as soon as possible, to minimize the chances
	 * of !consumed. Consuming the watchpoint must always be guarded by
	 * kcsan_is_enabled() check, as otherwise we might erroneously
	 * triggering reports when disabled.
	 */
	consumed = try_consume_watchpoint(watchpoint, encoded_watchpoint);

	/* keep this after try_consume_watchpoint */
	flags = user_access_save();

	if (consumed) {
		kcsan_save_irqtrace(current);
		kcsan_report(ptr, size, type, KCSAN_VALUE_CHANGE_MAYBE,
			     KCSAN_REPORT_CONSUMED_WATCHPOINT,
			     watchpoint - watchpoints);
		kcsan_restore_irqtrace(current);
	} else {
		/*
		 * The other thread may not print any diagnostics, as it has
		 * already removed the watchpoint, or another thread consumed
		 * the watchpoint before this thread.
		 */
		kcsan_counter_inc(KCSAN_COUNTER_REPORT_RACES);
	}

	if ((type & KCSAN_ACCESS_ASSERT) != 0)
		kcsan_counter_inc(KCSAN_COUNTER_ASSERT_FAILURES);
	else
		kcsan_counter_inc(KCSAN_COUNTER_DATA_RACES);

	user_access_restore(flags);
}

static noinline void
kcsan_setup_watchpoint(const volatile void *ptr, size_t size, int type)
{
	const bool is_write = (type & KCSAN_ACCESS_WRITE) != 0;
	const bool is_assert = (type & KCSAN_ACCESS_ASSERT) != 0;
	atomic_long_t *watchpoint;
	union {
		u8 _1;
		u16 _2;
		u32 _4;
		u64 _8;
	} expect_value;
	unsigned long access_mask;
	enum kcsan_value_change value_change = KCSAN_VALUE_CHANGE_MAYBE;
	unsigned long ua_flags = user_access_save();
	unsigned long irq_flags = 0;

	/*
	 * Always reset kcsan_skip counter in slow-path to avoid underflow; see
	 * should_watch().
	 */
	reset_kcsan_skip();

	if (!kcsan_is_enabled())
		goto out;

	/*
	 * Special atomic rules: unlikely to be true, so we check them here in
	 * the slow-path, and not in the fast-path in is_atomic(). Call after
	 * kcsan_is_enabled(), as we may access memory that is not yet
	 * initialized during early boot.
	 */
	if (!is_assert && kcsan_is_atomic_special(ptr))
		goto out;

	if (!check_encodable((unsigned long)ptr, size)) {
		kcsan_counter_inc(KCSAN_COUNTER_UNENCODABLE_ACCESSES);
		goto out;
	}

	/*
	 * Save and restore the IRQ state trace touched by KCSAN, since KCSAN's
	 * runtime is entered for every memory access, and potentially useful
	 * information is lost if dirtied by KCSAN.
	 */
	kcsan_save_irqtrace(current);
	if (!kcsan_interrupt_watcher)
		local_irq_save(irq_flags);

	watchpoint = insert_watchpoint((unsigned long)ptr, size, is_write);
	if (watchpoint == NULL) {
		/*
		 * Out of capacity: the size of 'watchpoints', and the frequency
		 * with which should_watch() returns true should be tweaked so
		 * that this case happens very rarely.
		 */
		kcsan_counter_inc(KCSAN_COUNTER_NO_CAPACITY);
		goto out_unlock;
	}

	kcsan_counter_inc(KCSAN_COUNTER_SETUP_WATCHPOINTS);
	kcsan_counter_inc(KCSAN_COUNTER_USED_WATCHPOINTS);

	/*
	 * Read the current value, to later check and infer a race if the data
	 * was modified via a non-instrumented access, e.g. from a device.
	 */
	expect_value._8 = 0;
	switch (size) {
	case 1:
		expect_value._1 = READ_ONCE(*(const u8 *)ptr);
		break;
	case 2:
		expect_value._2 = READ_ONCE(*(const u16 *)ptr);
		break;
	case 4:
		expect_value._4 = READ_ONCE(*(const u32 *)ptr);
		break;
	case 8:
		expect_value._8 = READ_ONCE(*(const u64 *)ptr);
		break;
	default:
		break; /* ignore; we do not diff the values */
	}

	if (IS_ENABLED(CONFIG_KCSAN_DEBUG)) {
		kcsan_disable_current();
		pr_err("KCSAN: watching %s, size: %zu, addr: %px [slot: %d, encoded: %lx]\n",
		       is_write ? "write" : "read", size, ptr,
		       watchpoint_slot((unsigned long)ptr),
		       encode_watchpoint((unsigned long)ptr, size, is_write));
		kcsan_enable_current();
	}

	/*
	 * Delay this thread, to increase probability of observing a racy
	 * conflicting access.
	 */
	udelay(get_delay());

	/*
	 * Re-read value, and check if it is as expected; if not, we infer a
	 * racy access.
	 */
	access_mask = get_ctx()->access_mask;
	switch (size) {
	case 1:
		expect_value._1 ^= READ_ONCE(*(const u8 *)ptr);
		if (access_mask)
			expect_value._1 &= (u8)access_mask;
		break;
	case 2:
		expect_value._2 ^= READ_ONCE(*(const u16 *)ptr);
		if (access_mask)
			expect_value._2 &= (u16)access_mask;
		break;
	case 4:
		expect_value._4 ^= READ_ONCE(*(const u32 *)ptr);
		if (access_mask)
			expect_value._4 &= (u32)access_mask;
		break;
	case 8:
		expect_value._8 ^= READ_ONCE(*(const u64 *)ptr);
		if (access_mask)
			expect_value._8 &= (u64)access_mask;
		break;
	default:
		break; /* ignore; we do not diff the values */
	}

	/* Were we able to observe a value-change? */
	if (expect_value._8 != 0)
		value_change = KCSAN_VALUE_CHANGE_TRUE;

	/* Check if this access raced with another. */
	if (!consume_watchpoint(watchpoint)) {
		/*
		 * Depending on the access type, map a value_change of MAYBE to
		 * TRUE (always report) or FALSE (never report).
		 */
		if (value_change == KCSAN_VALUE_CHANGE_MAYBE) {
			if (access_mask != 0) {
				/*
				 * For access with access_mask, we require a
				 * value-change, as it is likely that races on
				 * ~access_mask bits are expected.
				 */
				value_change = KCSAN_VALUE_CHANGE_FALSE;
			} else if (size > 8 || is_assert) {
				/* Always assume a value-change. */
				value_change = KCSAN_VALUE_CHANGE_TRUE;
			}
		}

		/*
		 * No need to increment 'data_races' counter, as the racing
		 * thread already did.
		 *
		 * Count 'assert_failures' for each failed ASSERT access,
		 * therefore both this thread and the racing thread may
		 * increment this counter.
		 */
		if (is_assert && value_change == KCSAN_VALUE_CHANGE_TRUE)
			kcsan_counter_inc(KCSAN_COUNTER_ASSERT_FAILURES);

		kcsan_report(ptr, size, type, value_change, KCSAN_REPORT_RACE_SIGNAL,
			     watchpoint - watchpoints);
	} else if (value_change == KCSAN_VALUE_CHANGE_TRUE) {
		/* Inferring a race, since the value should not have changed. */

		kcsan_counter_inc(KCSAN_COUNTER_RACES_UNKNOWN_ORIGIN);
		if (is_assert)
			kcsan_counter_inc(KCSAN_COUNTER_ASSERT_FAILURES);

		if (IS_ENABLED(CONFIG_KCSAN_REPORT_RACE_UNKNOWN_ORIGIN) || is_assert)
			kcsan_report(ptr, size, type, KCSAN_VALUE_CHANGE_TRUE,
				     KCSAN_REPORT_RACE_UNKNOWN_ORIGIN,
				     watchpoint - watchpoints);
	}

	/*
	 * Remove watchpoint; must be after reporting, since the slot may be
	 * reused after this point.
	 */
	remove_watchpoint(watchpoint);
	kcsan_counter_dec(KCSAN_COUNTER_USED_WATCHPOINTS);
out_unlock:
	if (!kcsan_interrupt_watcher)
		local_irq_restore(irq_flags);
	kcsan_restore_irqtrace(current);
out:
	user_access_restore(ua_flags);
}

static __always_inline void check_access(const volatile void *ptr, size_t size,
					 int type)
{
	const bool is_write = (type & KCSAN_ACCESS_WRITE) != 0;
	atomic_long_t *watchpoint;
	long encoded_watchpoint;

	/*
	 * Do nothing for 0 sized check; this comparison will be optimized out
	 * for constant sized instrumentation (__tsan_{read,write}N).
	 */
	if (unlikely(size == 0))
		return;

	/*
	 * Avoid user_access_save in fast-path: find_watchpoint is safe without
	 * user_access_save, as the address that ptr points to is only used to
	 * check if a watchpoint exists; ptr is never dereferenced.
	 */
	watchpoint = find_watchpoint((unsigned long)ptr, size, !is_write,
				     &encoded_watchpoint);
	/*
	 * It is safe to check kcsan_is_enabled() after find_watchpoint in the
	 * slow-path, as long as no state changes that cause a race to be
	 * detected and reported have occurred until kcsan_is_enabled() is
	 * checked.
	 */

	if (unlikely(watchpoint != NULL))
		kcsan_found_watchpoint(ptr, size, type, watchpoint,
				       encoded_watchpoint);
	else {
		struct kcsan_ctx *ctx = get_ctx(); /* Call only once in fast-path. */

		if (unlikely(should_watch(ptr, size, type, ctx)))
			kcsan_setup_watchpoint(ptr, size, type);
		else if (unlikely(ctx->scoped_accesses.prev))
			kcsan_check_scoped_accesses();
	}
}

/* === Public interface ===================================================== */

void __init kcsan_init(void)
{
	BUG_ON(!in_task());

	kcsan_debugfs_init();

	/*
	 * We are in the init task, and no other tasks should be running;
	 * WRITE_ONCE without memory barrier is sufficient.
	 */
	if (kcsan_early_enable)
		WRITE_ONCE(kcsan_enabled, true);
}

/* === Exported interface =================================================== */

void kcsan_disable_current(void)
{
	++get_ctx()->disable_count;
}
EXPORT_SYMBOL(kcsan_disable_current);

void kcsan_enable_current(void)
{
	if (get_ctx()->disable_count-- == 0) {
		/*
		 * Warn if kcsan_enable_current() calls are unbalanced with
		 * kcsan_disable_current() calls, which causes disable_count to
		 * become negative and should not happen.
		 */
		kcsan_disable_current(); /* restore to 0, KCSAN still enabled */
		kcsan_disable_current(); /* disable to generate warning */
		WARN(1, "Unbalanced %s()", __func__);
		kcsan_enable_current();
	}
}
EXPORT_SYMBOL(kcsan_enable_current);

void kcsan_enable_current_nowarn(void)
{
	if (get_ctx()->disable_count-- == 0)
		kcsan_disable_current();
}
EXPORT_SYMBOL(kcsan_enable_current_nowarn);

void kcsan_nestable_atomic_begin(void)
{
	/*
	 * Do *not* check and warn if we are in a flat atomic region: nestable
	 * and flat atomic regions are independent from each other.
	 * See include/linux/kcsan.h: struct kcsan_ctx comments for more
	 * comments.
	 */

	++get_ctx()->atomic_nest_count;
}
EXPORT_SYMBOL(kcsan_nestable_atomic_begin);

void kcsan_nestable_atomic_end(void)
{
	if (get_ctx()->atomic_nest_count-- == 0) {
		/*
		 * Warn if kcsan_nestable_atomic_end() calls are unbalanced with
		 * kcsan_nestable_atomic_begin() calls, which causes
		 * atomic_nest_count to become negative and should not happen.
		 */
		kcsan_nestable_atomic_begin(); /* restore to 0 */
		kcsan_disable_current(); /* disable to generate warning */
		WARN(1, "Unbalanced %s()", __func__);
		kcsan_enable_current();
	}
}
EXPORT_SYMBOL(kcsan_nestable_atomic_end);

void kcsan_flat_atomic_begin(void)
{
	get_ctx()->in_flat_atomic = true;
}
EXPORT_SYMBOL(kcsan_flat_atomic_begin);

void kcsan_flat_atomic_end(void)
{
	get_ctx()->in_flat_atomic = false;
}
EXPORT_SYMBOL(kcsan_flat_atomic_end);

void kcsan_atomic_next(int n)
{
	get_ctx()->atomic_next = n;
}
EXPORT_SYMBOL(kcsan_atomic_next);

void kcsan_set_access_mask(unsigned long mask)
{
	get_ctx()->access_mask = mask;
}
EXPORT_SYMBOL(kcsan_set_access_mask);

struct kcsan_scoped_access *
kcsan_begin_scoped_access(const volatile void *ptr, size_t size, int type,
			  struct kcsan_scoped_access *sa)
{
	struct kcsan_ctx *ctx = get_ctx();

	__kcsan_check_access(ptr, size, type);

	ctx->disable_count++; /* Disable KCSAN, in case list debugging is on. */

	INIT_LIST_HEAD(&sa->list);
	sa->ptr = ptr;
	sa->size = size;
	sa->type = type;

	if (!ctx->scoped_accesses.prev) /* Lazy initialize list head. */
		INIT_LIST_HEAD(&ctx->scoped_accesses);
	list_add(&sa->list, &ctx->scoped_accesses);

	ctx->disable_count--;
	return sa;
}
EXPORT_SYMBOL(kcsan_begin_scoped_access);

void kcsan_end_scoped_access(struct kcsan_scoped_access *sa)
{
	struct kcsan_ctx *ctx = get_ctx();

	if (WARN(!ctx->scoped_accesses.prev, "Unbalanced %s()?", __func__))
		return;

	ctx->disable_count++; /* Disable KCSAN, in case list debugging is on. */

	list_del(&sa->list);
	if (list_empty(&ctx->scoped_accesses))
		/*
		 * Ensure we do not enter kcsan_check_scoped_accesses()
		 * slow-path if unnecessary, and avoids requiring list_empty()
		 * in the fast-path (to avoid a READ_ONCE() and potential
		 * uaccess warning).
		 */
		ctx->scoped_accesses.prev = NULL;

	ctx->disable_count--;

	__kcsan_check_access(sa->ptr, sa->size, sa->type);
}
EXPORT_SYMBOL(kcsan_end_scoped_access);

void __kcsan_check_access(const volatile void *ptr, size_t size, int type)
{
	check_access(ptr, size, type);
}
EXPORT_SYMBOL(__kcsan_check_access);

/*
 * KCSAN uses the same instrumentation that is emitted by supported compilers
 * for ThreadSanitizer (TSAN).
 *
 * When enabled, the compiler emits instrumentation calls (the functions
 * prefixed with "__tsan" below) for all loads and stores that it generated;
 * inline asm is not instrumented.
 *
 * Note that, not all supported compiler versions distinguish aligned/unaligned
 * accesses, but e.g. recent versions of Clang do. We simply alias the unaligned
 * version to the generic version, which can handle both.
 */

#define DEFINE_TSAN_READ_WRITE(size)                                           \
	void __tsan_read##size(void *ptr);                                     \
	void __tsan_read##size(void *ptr)                                      \
	{                                                                      \
		check_access(ptr, size, 0);                                    \
	}                                                                      \
	EXPORT_SYMBOL(__tsan_read##size);                                      \
	void __tsan_unaligned_read##size(void *ptr)                            \
		__alias(__tsan_read##size);                                    \
	EXPORT_SYMBOL(__tsan_unaligned_read##size);                            \
	void __tsan_write##size(void *ptr);                                    \
	void __tsan_write##size(void *ptr)                                     \
	{                                                                      \
		check_access(ptr, size, KCSAN_ACCESS_WRITE);                   \
	}                                                                      \
	EXPORT_SYMBOL(__tsan_write##size);                                     \
	void __tsan_unaligned_write##size(void *ptr)                           \
		__alias(__tsan_write##size);                                   \
	EXPORT_SYMBOL(__tsan_unaligned_write##size)

DEFINE_TSAN_READ_WRITE(1);
DEFINE_TSAN_READ_WRITE(2);
DEFINE_TSAN_READ_WRITE(4);
DEFINE_TSAN_READ_WRITE(8);
DEFINE_TSAN_READ_WRITE(16);

void __tsan_read_range(void *ptr, size_t size);
void __tsan_read_range(void *ptr, size_t size)
{
	check_access(ptr, size, 0);
}
EXPORT_SYMBOL(__tsan_read_range);

void __tsan_write_range(void *ptr, size_t size);
void __tsan_write_range(void *ptr, size_t size)
{
	check_access(ptr, size, KCSAN_ACCESS_WRITE);
}
EXPORT_SYMBOL(__tsan_write_range);

/*
 * Use of explicit volatile is generally disallowed [1], however, volatile is
 * still used in various concurrent context, whether in low-level
 * synchronization primitives or for legacy reasons.
 * [1] https://lwn.net/Articles/233479/
 *
 * We only consider volatile accesses atomic if they are aligned and would pass
 * the size-check of compiletime_assert_rwonce_type().
 */
#define DEFINE_TSAN_VOLATILE_READ_WRITE(size)                                  \
	void __tsan_volatile_read##size(void *ptr);                            \
	void __tsan_volatile_read##size(void *ptr)                             \
	{                                                                      \
		const bool is_atomic = size <= sizeof(long long) &&            \
				       IS_ALIGNED((unsigned long)ptr, size);   \
		if (IS_ENABLED(CONFIG_KCSAN_IGNORE_ATOMICS) && is_atomic)      \
			return;                                                \
		check_access(ptr, size, is_atomic ? KCSAN_ACCESS_ATOMIC : 0);  \
	}                                                                      \
	EXPORT_SYMBOL(__tsan_volatile_read##size);                             \
	void __tsan_unaligned_volatile_read##size(void *ptr)                   \
		__alias(__tsan_volatile_read##size);                           \
	EXPORT_SYMBOL(__tsan_unaligned_volatile_read##size);                   \
	void __tsan_volatile_write##size(void *ptr);                           \
	void __tsan_volatile_write##size(void *ptr)                            \
	{                                                                      \
		const bool is_atomic = size <= sizeof(long long) &&            \
				       IS_ALIGNED((unsigned long)ptr, size);   \
		if (IS_ENABLED(CONFIG_KCSAN_IGNORE_ATOMICS) && is_atomic)      \
			return;                                                \
		check_access(ptr, size,                                        \
			     KCSAN_ACCESS_WRITE |                              \
				     (is_atomic ? KCSAN_ACCESS_ATOMIC : 0));   \
	}                                                                      \
	EXPORT_SYMBOL(__tsan_volatile_write##size);                            \
	void __tsan_unaligned_volatile_write##size(void *ptr)                  \
		__alias(__tsan_volatile_write##size);                          \
	EXPORT_SYMBOL(__tsan_unaligned_volatile_write##size)

DEFINE_TSAN_VOLATILE_READ_WRITE(1);
DEFINE_TSAN_VOLATILE_READ_WRITE(2);
DEFINE_TSAN_VOLATILE_READ_WRITE(4);
DEFINE_TSAN_VOLATILE_READ_WRITE(8);
DEFINE_TSAN_VOLATILE_READ_WRITE(16);

/*
 * The below are not required by KCSAN, but can still be emitted by the
 * compiler.
 */
void __tsan_func_entry(void *call_pc);
void __tsan_func_entry(void *call_pc)
{
}
EXPORT_SYMBOL(__tsan_func_entry);
void __tsan_func_exit(void);
void __tsan_func_exit(void)
{
}
EXPORT_SYMBOL(__tsan_func_exit);
void __tsan_init(void);
void __tsan_init(void)
{
}
EXPORT_SYMBOL(__tsan_init);