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1// SPDX-License-Identifier: GPL-2.0
2
3#include <linux/atomic.h>
4#include <linux/bug.h>
5#include <linux/delay.h>
6#include <linux/export.h>
7#include <linux/init.h>
8#include <linux/kernel.h>
9#include <linux/list.h>
10#include <linux/moduleparam.h>
11#include <linux/percpu.h>
12#include <linux/preempt.h>
13#include <linux/random.h>
14#include <linux/sched.h>
15#include <linux/uaccess.h>
16
17#include "atomic.h"
18#include "encoding.h"
19#include "kcsan.h"
20
21static bool kcsan_early_enable = IS_ENABLED(CONFIG_KCSAN_EARLY_ENABLE);
22unsigned int kcsan_udelay_task = CONFIG_KCSAN_UDELAY_TASK;
23unsigned int kcsan_udelay_interrupt = CONFIG_KCSAN_UDELAY_INTERRUPT;
24static long kcsan_skip_watch = CONFIG_KCSAN_SKIP_WATCH;
25static bool kcsan_interrupt_watcher = IS_ENABLED(CONFIG_KCSAN_INTERRUPT_WATCHER);
26
27#ifdef MODULE_PARAM_PREFIX
28#undef MODULE_PARAM_PREFIX
29#endif
30#define MODULE_PARAM_PREFIX "kcsan."
31module_param_named(early_enable, kcsan_early_enable, bool, 0);
32module_param_named(udelay_task, kcsan_udelay_task, uint, 0644);
33module_param_named(udelay_interrupt, kcsan_udelay_interrupt, uint, 0644);
34module_param_named(skip_watch, kcsan_skip_watch, long, 0644);
35module_param_named(interrupt_watcher, kcsan_interrupt_watcher, bool, 0444);
36
37bool kcsan_enabled;
38
39/* Per-CPU kcsan_ctx for interrupts */
40static DEFINE_PER_CPU(struct kcsan_ctx, kcsan_cpu_ctx) = {
41 .disable_count = 0,
42 .atomic_next = 0,
43 .atomic_nest_count = 0,
44 .in_flat_atomic = false,
45 .access_mask = 0,
46 .scoped_accesses = {LIST_POISON1, NULL},
47};
48
49/*
50 * Helper macros to index into adjacent slots, starting from address slot
51 * itself, followed by the right and left slots.
52 *
53 * The purpose is 2-fold:
54 *
55 * 1. if during insertion the address slot is already occupied, check if
56 * any adjacent slots are free;
57 * 2. accesses that straddle a slot boundary due to size that exceeds a
58 * slot's range may check adjacent slots if any watchpoint matches.
59 *
60 * Note that accesses with very large size may still miss a watchpoint; however,
61 * given this should be rare, this is a reasonable trade-off to make, since this
62 * will avoid:
63 *
64 * 1. excessive contention between watchpoint checks and setup;
65 * 2. larger number of simultaneous watchpoints without sacrificing
66 * performance.
67 *
68 * Example: SLOT_IDX values for KCSAN_CHECK_ADJACENT=1, where i is [0, 1, 2]:
69 *
70 * slot=0: [ 1, 2, 0]
71 * slot=9: [10, 11, 9]
72 * slot=63: [64, 65, 63]
73 */
74#define SLOT_IDX(slot, i) (slot + ((i + KCSAN_CHECK_ADJACENT) % NUM_SLOTS))
75
76/*
77 * SLOT_IDX_FAST is used in the fast-path. Not first checking the address's primary
78 * slot (middle) is fine if we assume that races occur rarely. The set of
79 * indices {SLOT_IDX(slot, i) | i in [0, NUM_SLOTS)} is equivalent to
80 * {SLOT_IDX_FAST(slot, i) | i in [0, NUM_SLOTS)}.
81 */
82#define SLOT_IDX_FAST(slot, i) (slot + i)
83
84/*
85 * Watchpoints, with each entry encoded as defined in encoding.h: in order to be
86 * able to safely update and access a watchpoint without introducing locking
87 * overhead, we encode each watchpoint as a single atomic long. The initial
88 * zero-initialized state matches INVALID_WATCHPOINT.
89 *
90 * Add NUM_SLOTS-1 entries to account for overflow; this helps avoid having to
91 * use more complicated SLOT_IDX_FAST calculation with modulo in the fast-path.
92 */
93static atomic_long_t watchpoints[CONFIG_KCSAN_NUM_WATCHPOINTS + NUM_SLOTS-1];
94
95/*
96 * Instructions to skip watching counter, used in should_watch(). We use a
97 * per-CPU counter to avoid excessive contention.
98 */
99static DEFINE_PER_CPU(long, kcsan_skip);
100
101static __always_inline atomic_long_t *find_watchpoint(unsigned long addr,
102 size_t size,
103 bool expect_write,
104 long *encoded_watchpoint)
105{
106 const int slot = watchpoint_slot(addr);
107 const unsigned long addr_masked = addr & WATCHPOINT_ADDR_MASK;
108 atomic_long_t *watchpoint;
109 unsigned long wp_addr_masked;
110 size_t wp_size;
111 bool is_write;
112 int i;
113
114 BUILD_BUG_ON(CONFIG_KCSAN_NUM_WATCHPOINTS < NUM_SLOTS);
115
116 for (i = 0; i < NUM_SLOTS; ++i) {
117 watchpoint = &watchpoints[SLOT_IDX_FAST(slot, i)];
118 *encoded_watchpoint = atomic_long_read(watchpoint);
119 if (!decode_watchpoint(*encoded_watchpoint, &wp_addr_masked,
120 &wp_size, &is_write))
121 continue;
122
123 if (expect_write && !is_write)
124 continue;
125
126 /* Check if the watchpoint matches the access. */
127 if (matching_access(wp_addr_masked, wp_size, addr_masked, size))
128 return watchpoint;
129 }
130
131 return NULL;
132}
133
134static inline atomic_long_t *
135insert_watchpoint(unsigned long addr, size_t size, bool is_write)
136{
137 const int slot = watchpoint_slot(addr);
138 const long encoded_watchpoint = encode_watchpoint(addr, size, is_write);
139 atomic_long_t *watchpoint;
140 int i;
141
142 /* Check slot index logic, ensuring we stay within array bounds. */
143 BUILD_BUG_ON(SLOT_IDX(0, 0) != KCSAN_CHECK_ADJACENT);
144 BUILD_BUG_ON(SLOT_IDX(0, KCSAN_CHECK_ADJACENT+1) != 0);
145 BUILD_BUG_ON(SLOT_IDX(CONFIG_KCSAN_NUM_WATCHPOINTS-1, KCSAN_CHECK_ADJACENT) != ARRAY_SIZE(watchpoints)-1);
146 BUILD_BUG_ON(SLOT_IDX(CONFIG_KCSAN_NUM_WATCHPOINTS-1, KCSAN_CHECK_ADJACENT+1) != ARRAY_SIZE(watchpoints) - NUM_SLOTS);
147
148 for (i = 0; i < NUM_SLOTS; ++i) {
149 long expect_val = INVALID_WATCHPOINT;
150
151 /* Try to acquire this slot. */
152 watchpoint = &watchpoints[SLOT_IDX(slot, i)];
153 if (atomic_long_try_cmpxchg_relaxed(watchpoint, &expect_val, encoded_watchpoint))
154 return watchpoint;
155 }
156
157 return NULL;
158}
159
160/*
161 * Return true if watchpoint was successfully consumed, false otherwise.
162 *
163 * This may return false if:
164 *
165 * 1. another thread already consumed the watchpoint;
166 * 2. the thread that set up the watchpoint already removed it;
167 * 3. the watchpoint was removed and then re-used.
168 */
169static __always_inline bool
170try_consume_watchpoint(atomic_long_t *watchpoint, long encoded_watchpoint)
171{
172 return atomic_long_try_cmpxchg_relaxed(watchpoint, &encoded_watchpoint, CONSUMED_WATCHPOINT);
173}
174
175/* Return true if watchpoint was not touched, false if already consumed. */
176static inline bool consume_watchpoint(atomic_long_t *watchpoint)
177{
178 return atomic_long_xchg_relaxed(watchpoint, CONSUMED_WATCHPOINT) != CONSUMED_WATCHPOINT;
179}
180
181/* Remove the watchpoint -- its slot may be reused after. */
182static inline void remove_watchpoint(atomic_long_t *watchpoint)
183{
184 atomic_long_set(watchpoint, INVALID_WATCHPOINT);
185}
186
187static __always_inline struct kcsan_ctx *get_ctx(void)
188{
189 /*
190 * In interrupts, use raw_cpu_ptr to avoid unnecessary checks, that would
191 * also result in calls that generate warnings in uaccess regions.
192 */
193 return in_task() ? ¤t->kcsan_ctx : raw_cpu_ptr(&kcsan_cpu_ctx);
194}
195
196/* Check scoped accesses; never inline because this is a slow-path! */
197static noinline void kcsan_check_scoped_accesses(void)
198{
199 struct kcsan_ctx *ctx = get_ctx();
200 struct list_head *prev_save = ctx->scoped_accesses.prev;
201 struct kcsan_scoped_access *scoped_access;
202
203 ctx->scoped_accesses.prev = NULL; /* Avoid recursion. */
204 list_for_each_entry(scoped_access, &ctx->scoped_accesses, list)
205 __kcsan_check_access(scoped_access->ptr, scoped_access->size, scoped_access->type);
206 ctx->scoped_accesses.prev = prev_save;
207}
208
209/* Rules for generic atomic accesses. Called from fast-path. */
210static __always_inline bool
211is_atomic(const volatile void *ptr, size_t size, int type, struct kcsan_ctx *ctx)
212{
213 if (type & KCSAN_ACCESS_ATOMIC)
214 return true;
215
216 /*
217 * Unless explicitly declared atomic, never consider an assertion access
218 * as atomic. This allows using them also in atomic regions, such as
219 * seqlocks, without implicitly changing their semantics.
220 */
221 if (type & KCSAN_ACCESS_ASSERT)
222 return false;
223
224 if (IS_ENABLED(CONFIG_KCSAN_ASSUME_PLAIN_WRITES_ATOMIC) &&
225 (type & KCSAN_ACCESS_WRITE) && size <= sizeof(long) &&
226 IS_ALIGNED((unsigned long)ptr, size))
227 return true; /* Assume aligned writes up to word size are atomic. */
228
229 if (ctx->atomic_next > 0) {
230 /*
231 * Because we do not have separate contexts for nested
232 * interrupts, in case atomic_next is set, we simply assume that
233 * the outer interrupt set atomic_next. In the worst case, we
234 * will conservatively consider operations as atomic. This is a
235 * reasonable trade-off to make, since this case should be
236 * extremely rare; however, even if extremely rare, it could
237 * lead to false positives otherwise.
238 */
239 if ((hardirq_count() >> HARDIRQ_SHIFT) < 2)
240 --ctx->atomic_next; /* in task, or outer interrupt */
241 return true;
242 }
243
244 return ctx->atomic_nest_count > 0 || ctx->in_flat_atomic;
245}
246
247static __always_inline bool
248should_watch(const volatile void *ptr, size_t size, int type, struct kcsan_ctx *ctx)
249{
250 /*
251 * Never set up watchpoints when memory operations are atomic.
252 *
253 * Need to check this first, before kcsan_skip check below: (1) atomics
254 * should not count towards skipped instructions, and (2) to actually
255 * decrement kcsan_atomic_next for consecutive instruction stream.
256 */
257 if (is_atomic(ptr, size, type, ctx))
258 return false;
259
260 if (this_cpu_dec_return(kcsan_skip) >= 0)
261 return false;
262
263 /*
264 * NOTE: If we get here, kcsan_skip must always be reset in slow path
265 * via reset_kcsan_skip() to avoid underflow.
266 */
267
268 /* this operation should be watched */
269 return true;
270}
271
272static inline void reset_kcsan_skip(void)
273{
274 long skip_count = kcsan_skip_watch -
275 (IS_ENABLED(CONFIG_KCSAN_SKIP_WATCH_RANDOMIZE) ?
276 prandom_u32_max(kcsan_skip_watch) :
277 0);
278 this_cpu_write(kcsan_skip, skip_count);
279}
280
281static __always_inline bool kcsan_is_enabled(void)
282{
283 return READ_ONCE(kcsan_enabled) && get_ctx()->disable_count == 0;
284}
285
286static inline unsigned int get_delay(void)
287{
288 unsigned int delay = in_task() ? kcsan_udelay_task : kcsan_udelay_interrupt;
289 return delay - (IS_ENABLED(CONFIG_KCSAN_DELAY_RANDOMIZE) ?
290 prandom_u32_max(delay) :
291 0);
292}
293
294void kcsan_save_irqtrace(struct task_struct *task)
295{
296#ifdef CONFIG_TRACE_IRQFLAGS
297 task->kcsan_save_irqtrace = task->irqtrace;
298#endif
299}
300
301void kcsan_restore_irqtrace(struct task_struct *task)
302{
303#ifdef CONFIG_TRACE_IRQFLAGS
304 task->irqtrace = task->kcsan_save_irqtrace;
305#endif
306}
307
308/*
309 * Pull everything together: check_access() below contains the performance
310 * critical operations; the fast-path (including check_access) functions should
311 * all be inlinable by the instrumentation functions.
312 *
313 * The slow-path (kcsan_found_watchpoint, kcsan_setup_watchpoint) are
314 * non-inlinable -- note that, we prefix these with "kcsan_" to ensure they can
315 * be filtered from the stacktrace, as well as give them unique names for the
316 * UACCESS whitelist of objtool. Each function uses user_access_save/restore(),
317 * since they do not access any user memory, but instrumentation is still
318 * emitted in UACCESS regions.
319 */
320
321static noinline void kcsan_found_watchpoint(const volatile void *ptr,
322 size_t size,
323 int type,
324 atomic_long_t *watchpoint,
325 long encoded_watchpoint)
326{
327 unsigned long flags;
328 bool consumed;
329
330 if (!kcsan_is_enabled())
331 return;
332
333 /*
334 * The access_mask check relies on value-change comparison. To avoid
335 * reporting a race where e.g. the writer set up the watchpoint, but the
336 * reader has access_mask!=0, we have to ignore the found watchpoint.
337 */
338 if (get_ctx()->access_mask != 0)
339 return;
340
341 /*
342 * Consume the watchpoint as soon as possible, to minimize the chances
343 * of !consumed. Consuming the watchpoint must always be guarded by
344 * kcsan_is_enabled() check, as otherwise we might erroneously
345 * triggering reports when disabled.
346 */
347 consumed = try_consume_watchpoint(watchpoint, encoded_watchpoint);
348
349 /* keep this after try_consume_watchpoint */
350 flags = user_access_save();
351
352 if (consumed) {
353 kcsan_save_irqtrace(current);
354 kcsan_report(ptr, size, type, KCSAN_VALUE_CHANGE_MAYBE,
355 KCSAN_REPORT_CONSUMED_WATCHPOINT,
356 watchpoint - watchpoints);
357 kcsan_restore_irqtrace(current);
358 } else {
359 /*
360 * The other thread may not print any diagnostics, as it has
361 * already removed the watchpoint, or another thread consumed
362 * the watchpoint before this thread.
363 */
364 kcsan_counter_inc(KCSAN_COUNTER_REPORT_RACES);
365 }
366
367 if ((type & KCSAN_ACCESS_ASSERT) != 0)
368 kcsan_counter_inc(KCSAN_COUNTER_ASSERT_FAILURES);
369 else
370 kcsan_counter_inc(KCSAN_COUNTER_DATA_RACES);
371
372 user_access_restore(flags);
373}
374
375static noinline void
376kcsan_setup_watchpoint(const volatile void *ptr, size_t size, int type)
377{
378 const bool is_write = (type & KCSAN_ACCESS_WRITE) != 0;
379 const bool is_assert = (type & KCSAN_ACCESS_ASSERT) != 0;
380 atomic_long_t *watchpoint;
381 union {
382 u8 _1;
383 u16 _2;
384 u32 _4;
385 u64 _8;
386 } expect_value;
387 unsigned long access_mask;
388 enum kcsan_value_change value_change = KCSAN_VALUE_CHANGE_MAYBE;
389 unsigned long ua_flags = user_access_save();
390 unsigned long irq_flags = 0;
391
392 /*
393 * Always reset kcsan_skip counter in slow-path to avoid underflow; see
394 * should_watch().
395 */
396 reset_kcsan_skip();
397
398 if (!kcsan_is_enabled())
399 goto out;
400
401 /*
402 * Special atomic rules: unlikely to be true, so we check them here in
403 * the slow-path, and not in the fast-path in is_atomic(). Call after
404 * kcsan_is_enabled(), as we may access memory that is not yet
405 * initialized during early boot.
406 */
407 if (!is_assert && kcsan_is_atomic_special(ptr))
408 goto out;
409
410 if (!check_encodable((unsigned long)ptr, size)) {
411 kcsan_counter_inc(KCSAN_COUNTER_UNENCODABLE_ACCESSES);
412 goto out;
413 }
414
415 /*
416 * Save and restore the IRQ state trace touched by KCSAN, since KCSAN's
417 * runtime is entered for every memory access, and potentially useful
418 * information is lost if dirtied by KCSAN.
419 */
420 kcsan_save_irqtrace(current);
421 if (!kcsan_interrupt_watcher)
422 local_irq_save(irq_flags);
423
424 watchpoint = insert_watchpoint((unsigned long)ptr, size, is_write);
425 if (watchpoint == NULL) {
426 /*
427 * Out of capacity: the size of 'watchpoints', and the frequency
428 * with which should_watch() returns true should be tweaked so
429 * that this case happens very rarely.
430 */
431 kcsan_counter_inc(KCSAN_COUNTER_NO_CAPACITY);
432 goto out_unlock;
433 }
434
435 kcsan_counter_inc(KCSAN_COUNTER_SETUP_WATCHPOINTS);
436 kcsan_counter_inc(KCSAN_COUNTER_USED_WATCHPOINTS);
437
438 /*
439 * Read the current value, to later check and infer a race if the data
440 * was modified via a non-instrumented access, e.g. from a device.
441 */
442 expect_value._8 = 0;
443 switch (size) {
444 case 1:
445 expect_value._1 = READ_ONCE(*(const u8 *)ptr);
446 break;
447 case 2:
448 expect_value._2 = READ_ONCE(*(const u16 *)ptr);
449 break;
450 case 4:
451 expect_value._4 = READ_ONCE(*(const u32 *)ptr);
452 break;
453 case 8:
454 expect_value._8 = READ_ONCE(*(const u64 *)ptr);
455 break;
456 default:
457 break; /* ignore; we do not diff the values */
458 }
459
460 if (IS_ENABLED(CONFIG_KCSAN_DEBUG)) {
461 kcsan_disable_current();
462 pr_err("KCSAN: watching %s, size: %zu, addr: %px [slot: %d, encoded: %lx]\n",
463 is_write ? "write" : "read", size, ptr,
464 watchpoint_slot((unsigned long)ptr),
465 encode_watchpoint((unsigned long)ptr, size, is_write));
466 kcsan_enable_current();
467 }
468
469 /*
470 * Delay this thread, to increase probability of observing a racy
471 * conflicting access.
472 */
473 udelay(get_delay());
474
475 /*
476 * Re-read value, and check if it is as expected; if not, we infer a
477 * racy access.
478 */
479 access_mask = get_ctx()->access_mask;
480 switch (size) {
481 case 1:
482 expect_value._1 ^= READ_ONCE(*(const u8 *)ptr);
483 if (access_mask)
484 expect_value._1 &= (u8)access_mask;
485 break;
486 case 2:
487 expect_value._2 ^= READ_ONCE(*(const u16 *)ptr);
488 if (access_mask)
489 expect_value._2 &= (u16)access_mask;
490 break;
491 case 4:
492 expect_value._4 ^= READ_ONCE(*(const u32 *)ptr);
493 if (access_mask)
494 expect_value._4 &= (u32)access_mask;
495 break;
496 case 8:
497 expect_value._8 ^= READ_ONCE(*(const u64 *)ptr);
498 if (access_mask)
499 expect_value._8 &= (u64)access_mask;
500 break;
501 default:
502 break; /* ignore; we do not diff the values */
503 }
504
505 /* Were we able to observe a value-change? */
506 if (expect_value._8 != 0)
507 value_change = KCSAN_VALUE_CHANGE_TRUE;
508
509 /* Check if this access raced with another. */
510 if (!consume_watchpoint(watchpoint)) {
511 /*
512 * Depending on the access type, map a value_change of MAYBE to
513 * TRUE (always report) or FALSE (never report).
514 */
515 if (value_change == KCSAN_VALUE_CHANGE_MAYBE) {
516 if (access_mask != 0) {
517 /*
518 * For access with access_mask, we require a
519 * value-change, as it is likely that races on
520 * ~access_mask bits are expected.
521 */
522 value_change = KCSAN_VALUE_CHANGE_FALSE;
523 } else if (size > 8 || is_assert) {
524 /* Always assume a value-change. */
525 value_change = KCSAN_VALUE_CHANGE_TRUE;
526 }
527 }
528
529 /*
530 * No need to increment 'data_races' counter, as the racing
531 * thread already did.
532 *
533 * Count 'assert_failures' for each failed ASSERT access,
534 * therefore both this thread and the racing thread may
535 * increment this counter.
536 */
537 if (is_assert && value_change == KCSAN_VALUE_CHANGE_TRUE)
538 kcsan_counter_inc(KCSAN_COUNTER_ASSERT_FAILURES);
539
540 kcsan_report(ptr, size, type, value_change, KCSAN_REPORT_RACE_SIGNAL,
541 watchpoint - watchpoints);
542 } else if (value_change == KCSAN_VALUE_CHANGE_TRUE) {
543 /* Inferring a race, since the value should not have changed. */
544
545 kcsan_counter_inc(KCSAN_COUNTER_RACES_UNKNOWN_ORIGIN);
546 if (is_assert)
547 kcsan_counter_inc(KCSAN_COUNTER_ASSERT_FAILURES);
548
549 if (IS_ENABLED(CONFIG_KCSAN_REPORT_RACE_UNKNOWN_ORIGIN) || is_assert)
550 kcsan_report(ptr, size, type, KCSAN_VALUE_CHANGE_TRUE,
551 KCSAN_REPORT_RACE_UNKNOWN_ORIGIN,
552 watchpoint - watchpoints);
553 }
554
555 /*
556 * Remove watchpoint; must be after reporting, since the slot may be
557 * reused after this point.
558 */
559 remove_watchpoint(watchpoint);
560 kcsan_counter_dec(KCSAN_COUNTER_USED_WATCHPOINTS);
561out_unlock:
562 if (!kcsan_interrupt_watcher)
563 local_irq_restore(irq_flags);
564 kcsan_restore_irqtrace(current);
565out:
566 user_access_restore(ua_flags);
567}
568
569static __always_inline void check_access(const volatile void *ptr, size_t size,
570 int type)
571{
572 const bool is_write = (type & KCSAN_ACCESS_WRITE) != 0;
573 atomic_long_t *watchpoint;
574 long encoded_watchpoint;
575
576 /*
577 * Do nothing for 0 sized check; this comparison will be optimized out
578 * for constant sized instrumentation (__tsan_{read,write}N).
579 */
580 if (unlikely(size == 0))
581 return;
582
583 /*
584 * Avoid user_access_save in fast-path: find_watchpoint is safe without
585 * user_access_save, as the address that ptr points to is only used to
586 * check if a watchpoint exists; ptr is never dereferenced.
587 */
588 watchpoint = find_watchpoint((unsigned long)ptr, size, !is_write,
589 &encoded_watchpoint);
590 /*
591 * It is safe to check kcsan_is_enabled() after find_watchpoint in the
592 * slow-path, as long as no state changes that cause a race to be
593 * detected and reported have occurred until kcsan_is_enabled() is
594 * checked.
595 */
596
597 if (unlikely(watchpoint != NULL))
598 kcsan_found_watchpoint(ptr, size, type, watchpoint,
599 encoded_watchpoint);
600 else {
601 struct kcsan_ctx *ctx = get_ctx(); /* Call only once in fast-path. */
602
603 if (unlikely(should_watch(ptr, size, type, ctx)))
604 kcsan_setup_watchpoint(ptr, size, type);
605 else if (unlikely(ctx->scoped_accesses.prev))
606 kcsan_check_scoped_accesses();
607 }
608}
609
610/* === Public interface ===================================================== */
611
612void __init kcsan_init(void)
613{
614 BUG_ON(!in_task());
615
616 kcsan_debugfs_init();
617
618 /*
619 * We are in the init task, and no other tasks should be running;
620 * WRITE_ONCE without memory barrier is sufficient.
621 */
622 if (kcsan_early_enable)
623 WRITE_ONCE(kcsan_enabled, true);
624}
625
626/* === Exported interface =================================================== */
627
628void kcsan_disable_current(void)
629{
630 ++get_ctx()->disable_count;
631}
632EXPORT_SYMBOL(kcsan_disable_current);
633
634void kcsan_enable_current(void)
635{
636 if (get_ctx()->disable_count-- == 0) {
637 /*
638 * Warn if kcsan_enable_current() calls are unbalanced with
639 * kcsan_disable_current() calls, which causes disable_count to
640 * become negative and should not happen.
641 */
642 kcsan_disable_current(); /* restore to 0, KCSAN still enabled */
643 kcsan_disable_current(); /* disable to generate warning */
644 WARN(1, "Unbalanced %s()", __func__);
645 kcsan_enable_current();
646 }
647}
648EXPORT_SYMBOL(kcsan_enable_current);
649
650void kcsan_enable_current_nowarn(void)
651{
652 if (get_ctx()->disable_count-- == 0)
653 kcsan_disable_current();
654}
655EXPORT_SYMBOL(kcsan_enable_current_nowarn);
656
657void kcsan_nestable_atomic_begin(void)
658{
659 /*
660 * Do *not* check and warn if we are in a flat atomic region: nestable
661 * and flat atomic regions are independent from each other.
662 * See include/linux/kcsan.h: struct kcsan_ctx comments for more
663 * comments.
664 */
665
666 ++get_ctx()->atomic_nest_count;
667}
668EXPORT_SYMBOL(kcsan_nestable_atomic_begin);
669
670void kcsan_nestable_atomic_end(void)
671{
672 if (get_ctx()->atomic_nest_count-- == 0) {
673 /*
674 * Warn if kcsan_nestable_atomic_end() calls are unbalanced with
675 * kcsan_nestable_atomic_begin() calls, which causes
676 * atomic_nest_count to become negative and should not happen.
677 */
678 kcsan_nestable_atomic_begin(); /* restore to 0 */
679 kcsan_disable_current(); /* disable to generate warning */
680 WARN(1, "Unbalanced %s()", __func__);
681 kcsan_enable_current();
682 }
683}
684EXPORT_SYMBOL(kcsan_nestable_atomic_end);
685
686void kcsan_flat_atomic_begin(void)
687{
688 get_ctx()->in_flat_atomic = true;
689}
690EXPORT_SYMBOL(kcsan_flat_atomic_begin);
691
692void kcsan_flat_atomic_end(void)
693{
694 get_ctx()->in_flat_atomic = false;
695}
696EXPORT_SYMBOL(kcsan_flat_atomic_end);
697
698void kcsan_atomic_next(int n)
699{
700 get_ctx()->atomic_next = n;
701}
702EXPORT_SYMBOL(kcsan_atomic_next);
703
704void kcsan_set_access_mask(unsigned long mask)
705{
706 get_ctx()->access_mask = mask;
707}
708EXPORT_SYMBOL(kcsan_set_access_mask);
709
710struct kcsan_scoped_access *
711kcsan_begin_scoped_access(const volatile void *ptr, size_t size, int type,
712 struct kcsan_scoped_access *sa)
713{
714 struct kcsan_ctx *ctx = get_ctx();
715
716 __kcsan_check_access(ptr, size, type);
717
718 ctx->disable_count++; /* Disable KCSAN, in case list debugging is on. */
719
720 INIT_LIST_HEAD(&sa->list);
721 sa->ptr = ptr;
722 sa->size = size;
723 sa->type = type;
724
725 if (!ctx->scoped_accesses.prev) /* Lazy initialize list head. */
726 INIT_LIST_HEAD(&ctx->scoped_accesses);
727 list_add(&sa->list, &ctx->scoped_accesses);
728
729 ctx->disable_count--;
730 return sa;
731}
732EXPORT_SYMBOL(kcsan_begin_scoped_access);
733
734void kcsan_end_scoped_access(struct kcsan_scoped_access *sa)
735{
736 struct kcsan_ctx *ctx = get_ctx();
737
738 if (WARN(!ctx->scoped_accesses.prev, "Unbalanced %s()?", __func__))
739 return;
740
741 ctx->disable_count++; /* Disable KCSAN, in case list debugging is on. */
742
743 list_del(&sa->list);
744 if (list_empty(&ctx->scoped_accesses))
745 /*
746 * Ensure we do not enter kcsan_check_scoped_accesses()
747 * slow-path if unnecessary, and avoids requiring list_empty()
748 * in the fast-path (to avoid a READ_ONCE() and potential
749 * uaccess warning).
750 */
751 ctx->scoped_accesses.prev = NULL;
752
753 ctx->disable_count--;
754
755 __kcsan_check_access(sa->ptr, sa->size, sa->type);
756}
757EXPORT_SYMBOL(kcsan_end_scoped_access);
758
759void __kcsan_check_access(const volatile void *ptr, size_t size, int type)
760{
761 check_access(ptr, size, type);
762}
763EXPORT_SYMBOL(__kcsan_check_access);
764
765/*
766 * KCSAN uses the same instrumentation that is emitted by supported compilers
767 * for ThreadSanitizer (TSAN).
768 *
769 * When enabled, the compiler emits instrumentation calls (the functions
770 * prefixed with "__tsan" below) for all loads and stores that it generated;
771 * inline asm is not instrumented.
772 *
773 * Note that, not all supported compiler versions distinguish aligned/unaligned
774 * accesses, but e.g. recent versions of Clang do. We simply alias the unaligned
775 * version to the generic version, which can handle both.
776 */
777
778#define DEFINE_TSAN_READ_WRITE(size) \
779 void __tsan_read##size(void *ptr); \
780 void __tsan_read##size(void *ptr) \
781 { \
782 check_access(ptr, size, 0); \
783 } \
784 EXPORT_SYMBOL(__tsan_read##size); \
785 void __tsan_unaligned_read##size(void *ptr) \
786 __alias(__tsan_read##size); \
787 EXPORT_SYMBOL(__tsan_unaligned_read##size); \
788 void __tsan_write##size(void *ptr); \
789 void __tsan_write##size(void *ptr) \
790 { \
791 check_access(ptr, size, KCSAN_ACCESS_WRITE); \
792 } \
793 EXPORT_SYMBOL(__tsan_write##size); \
794 void __tsan_unaligned_write##size(void *ptr) \
795 __alias(__tsan_write##size); \
796 EXPORT_SYMBOL(__tsan_unaligned_write##size)
797
798DEFINE_TSAN_READ_WRITE(1);
799DEFINE_TSAN_READ_WRITE(2);
800DEFINE_TSAN_READ_WRITE(4);
801DEFINE_TSAN_READ_WRITE(8);
802DEFINE_TSAN_READ_WRITE(16);
803
804void __tsan_read_range(void *ptr, size_t size);
805void __tsan_read_range(void *ptr, size_t size)
806{
807 check_access(ptr, size, 0);
808}
809EXPORT_SYMBOL(__tsan_read_range);
810
811void __tsan_write_range(void *ptr, size_t size);
812void __tsan_write_range(void *ptr, size_t size)
813{
814 check_access(ptr, size, KCSAN_ACCESS_WRITE);
815}
816EXPORT_SYMBOL(__tsan_write_range);
817
818/*
819 * Use of explicit volatile is generally disallowed [1], however, volatile is
820 * still used in various concurrent context, whether in low-level
821 * synchronization primitives or for legacy reasons.
822 * [1] https://lwn.net/Articles/233479/
823 *
824 * We only consider volatile accesses atomic if they are aligned and would pass
825 * the size-check of compiletime_assert_rwonce_type().
826 */
827#define DEFINE_TSAN_VOLATILE_READ_WRITE(size) \
828 void __tsan_volatile_read##size(void *ptr); \
829 void __tsan_volatile_read##size(void *ptr) \
830 { \
831 const bool is_atomic = size <= sizeof(long long) && \
832 IS_ALIGNED((unsigned long)ptr, size); \
833 if (IS_ENABLED(CONFIG_KCSAN_IGNORE_ATOMICS) && is_atomic) \
834 return; \
835 check_access(ptr, size, is_atomic ? KCSAN_ACCESS_ATOMIC : 0); \
836 } \
837 EXPORT_SYMBOL(__tsan_volatile_read##size); \
838 void __tsan_unaligned_volatile_read##size(void *ptr) \
839 __alias(__tsan_volatile_read##size); \
840 EXPORT_SYMBOL(__tsan_unaligned_volatile_read##size); \
841 void __tsan_volatile_write##size(void *ptr); \
842 void __tsan_volatile_write##size(void *ptr) \
843 { \
844 const bool is_atomic = size <= sizeof(long long) && \
845 IS_ALIGNED((unsigned long)ptr, size); \
846 if (IS_ENABLED(CONFIG_KCSAN_IGNORE_ATOMICS) && is_atomic) \
847 return; \
848 check_access(ptr, size, \
849 KCSAN_ACCESS_WRITE | \
850 (is_atomic ? KCSAN_ACCESS_ATOMIC : 0)); \
851 } \
852 EXPORT_SYMBOL(__tsan_volatile_write##size); \
853 void __tsan_unaligned_volatile_write##size(void *ptr) \
854 __alias(__tsan_volatile_write##size); \
855 EXPORT_SYMBOL(__tsan_unaligned_volatile_write##size)
856
857DEFINE_TSAN_VOLATILE_READ_WRITE(1);
858DEFINE_TSAN_VOLATILE_READ_WRITE(2);
859DEFINE_TSAN_VOLATILE_READ_WRITE(4);
860DEFINE_TSAN_VOLATILE_READ_WRITE(8);
861DEFINE_TSAN_VOLATILE_READ_WRITE(16);
862
863/*
864 * The below are not required by KCSAN, but can still be emitted by the
865 * compiler.
866 */
867void __tsan_func_entry(void *call_pc);
868void __tsan_func_entry(void *call_pc)
869{
870}
871EXPORT_SYMBOL(__tsan_func_entry);
872void __tsan_func_exit(void);
873void __tsan_func_exit(void)
874{
875}
876EXPORT_SYMBOL(__tsan_func_exit);
877void __tsan_init(void);
878void __tsan_init(void)
879{
880}
881EXPORT_SYMBOL(__tsan_init);