1 // SPDX-License-Identifier: GPL-2.0
3 #include <linux/atomic.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>
21 static bool kcsan_early_enable
= IS_ENABLED(CONFIG_KCSAN_EARLY_ENABLE
);
22 unsigned int kcsan_udelay_task
= CONFIG_KCSAN_UDELAY_TASK
;
23 unsigned int kcsan_udelay_interrupt
= CONFIG_KCSAN_UDELAY_INTERRUPT
;
24 static long kcsan_skip_watch
= CONFIG_KCSAN_SKIP_WATCH
;
25 static bool kcsan_interrupt_watcher
= IS_ENABLED(CONFIG_KCSAN_INTERRUPT_WATCHER
);
27 #ifdef MODULE_PARAM_PREFIX
28 #undef MODULE_PARAM_PREFIX
30 #define MODULE_PARAM_PREFIX "kcsan."
31 module_param_named(early_enable
, kcsan_early_enable
, bool, 0);
32 module_param_named(udelay_task
, kcsan_udelay_task
, uint
, 0644);
33 module_param_named(udelay_interrupt
, kcsan_udelay_interrupt
, uint
, 0644);
34 module_param_named(skip_watch
, kcsan_skip_watch
, long, 0644);
35 module_param_named(interrupt_watcher
, kcsan_interrupt_watcher
, bool, 0444);
39 /* Per-CPU kcsan_ctx for interrupts */
40 static DEFINE_PER_CPU(struct kcsan_ctx
, kcsan_cpu_ctx
) = {
43 .atomic_nest_count
= 0,
44 .in_flat_atomic
= false,
46 .scoped_accesses
= {LIST_POISON1
, NULL
},
50 * Helper macros to index into adjacent slots, starting from address slot
51 * itself, followed by the right and left slots.
53 * The purpose is 2-fold:
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.
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
64 * 1. excessive contention between watchpoint checks and setup;
65 * 2. larger number of simultaneous watchpoints without sacrificing
68 * Example: SLOT_IDX values for KCSAN_CHECK_ADJACENT=1, where i is [0, 1, 2]:
72 * slot=63: [64, 65, 63]
74 #define SLOT_IDX(slot, i) (slot + ((i + KCSAN_CHECK_ADJACENT) % NUM_SLOTS))
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)}.
82 #define SLOT_IDX_FAST(slot, i) (slot + i)
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.
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.
93 static atomic_long_t watchpoints
[CONFIG_KCSAN_NUM_WATCHPOINTS
+ NUM_SLOTS
-1];
96 * Instructions to skip watching counter, used in should_watch(). We use a
97 * per-CPU counter to avoid excessive contention.
99 static DEFINE_PER_CPU(long, kcsan_skip
);
101 static __always_inline atomic_long_t
*find_watchpoint(unsigned long addr
,
104 long *encoded_watchpoint
)
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
;
114 BUILD_BUG_ON(CONFIG_KCSAN_NUM_WATCHPOINTS
< NUM_SLOTS
);
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
))
123 if (expect_write
&& !is_write
)
126 /* Check if the watchpoint matches the access. */
127 if (matching_access(wp_addr_masked
, wp_size
, addr_masked
, size
))
134 static inline atomic_long_t
*
135 insert_watchpoint(unsigned long addr
, size_t size
, bool is_write
)
137 const int slot
= watchpoint_slot(addr
);
138 const long encoded_watchpoint
= encode_watchpoint(addr
, size
, is_write
);
139 atomic_long_t
*watchpoint
;
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
);
148 for (i
= 0; i
< NUM_SLOTS
; ++i
) {
149 long expect_val
= INVALID_WATCHPOINT
;
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
))
161 * Return true if watchpoint was successfully consumed, false otherwise.
163 * This may return false if:
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.
169 static __always_inline
bool
170 try_consume_watchpoint(atomic_long_t
*watchpoint
, long encoded_watchpoint
)
172 return atomic_long_try_cmpxchg_relaxed(watchpoint
, &encoded_watchpoint
, CONSUMED_WATCHPOINT
);
175 /* Return true if watchpoint was not touched, false if already consumed. */
176 static inline bool consume_watchpoint(atomic_long_t
*watchpoint
)
178 return atomic_long_xchg_relaxed(watchpoint
, CONSUMED_WATCHPOINT
) != CONSUMED_WATCHPOINT
;
181 /* Remove the watchpoint -- its slot may be reused after. */
182 static inline void remove_watchpoint(atomic_long_t
*watchpoint
)
184 atomic_long_set(watchpoint
, INVALID_WATCHPOINT
);
187 static __always_inline
struct kcsan_ctx
*get_ctx(void)
190 * In interrupts, use raw_cpu_ptr to avoid unnecessary checks, that would
191 * also result in calls that generate warnings in uaccess regions.
193 return in_task() ? ¤t
->kcsan_ctx
: raw_cpu_ptr(&kcsan_cpu_ctx
);
196 /* Check scoped accesses; never inline because this is a slow-path! */
197 static noinline
void kcsan_check_scoped_accesses(void)
199 struct kcsan_ctx
*ctx
= get_ctx();
200 struct list_head
*prev_save
= ctx
->scoped_accesses
.prev
;
201 struct kcsan_scoped_access
*scoped_access
;
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
;
209 /* Rules for generic atomic accesses. Called from fast-path. */
210 static __always_inline
bool
211 is_atomic(const volatile void *ptr
, size_t size
, int type
, struct kcsan_ctx
*ctx
)
213 if (type
& KCSAN_ACCESS_ATOMIC
)
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.
221 if (type
& KCSAN_ACCESS_ASSERT
)
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. */
229 if (ctx
->atomic_next
> 0) {
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.
239 if ((hardirq_count() >> HARDIRQ_SHIFT
) < 2)
240 --ctx
->atomic_next
; /* in task, or outer interrupt */
244 return ctx
->atomic_nest_count
> 0 || ctx
->in_flat_atomic
;
247 static __always_inline
bool
248 should_watch(const volatile void *ptr
, size_t size
, int type
, struct kcsan_ctx
*ctx
)
251 * Never set up watchpoints when memory operations are atomic.
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.
257 if (is_atomic(ptr
, size
, type
, ctx
))
260 if (this_cpu_dec_return(kcsan_skip
) >= 0)
264 * NOTE: If we get here, kcsan_skip must always be reset in slow path
265 * via reset_kcsan_skip() to avoid underflow.
268 /* this operation should be watched */
272 static inline void reset_kcsan_skip(void)
274 long skip_count
= kcsan_skip_watch
-
275 (IS_ENABLED(CONFIG_KCSAN_SKIP_WATCH_RANDOMIZE
) ?
276 prandom_u32_max(kcsan_skip_watch
) :
278 this_cpu_write(kcsan_skip
, skip_count
);
281 static __always_inline
bool kcsan_is_enabled(void)
283 return READ_ONCE(kcsan_enabled
) && get_ctx()->disable_count
== 0;
286 static inline unsigned int get_delay(void)
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
) :
295 * Pull everything together: check_access() below contains the performance
296 * critical operations; the fast-path (including check_access) functions should
297 * all be inlinable by the instrumentation functions.
299 * The slow-path (kcsan_found_watchpoint, kcsan_setup_watchpoint) are
300 * non-inlinable -- note that, we prefix these with "kcsan_" to ensure they can
301 * be filtered from the stacktrace, as well as give them unique names for the
302 * UACCESS whitelist of objtool. Each function uses user_access_save/restore(),
303 * since they do not access any user memory, but instrumentation is still
304 * emitted in UACCESS regions.
307 static noinline
void kcsan_found_watchpoint(const volatile void *ptr
,
310 atomic_long_t
*watchpoint
,
311 long encoded_watchpoint
)
316 if (!kcsan_is_enabled())
320 * The access_mask check relies on value-change comparison. To avoid
321 * reporting a race where e.g. the writer set up the watchpoint, but the
322 * reader has access_mask!=0, we have to ignore the found watchpoint.
324 if (get_ctx()->access_mask
!= 0)
328 * Consume the watchpoint as soon as possible, to minimize the chances
329 * of !consumed. Consuming the watchpoint must always be guarded by
330 * kcsan_is_enabled() check, as otherwise we might erroneously
331 * triggering reports when disabled.
333 consumed
= try_consume_watchpoint(watchpoint
, encoded_watchpoint
);
335 /* keep this after try_consume_watchpoint */
336 flags
= user_access_save();
339 kcsan_report(ptr
, size
, type
, KCSAN_VALUE_CHANGE_MAYBE
,
340 KCSAN_REPORT_CONSUMED_WATCHPOINT
,
341 watchpoint
- watchpoints
);
344 * The other thread may not print any diagnostics, as it has
345 * already removed the watchpoint, or another thread consumed
346 * the watchpoint before this thread.
348 kcsan_counter_inc(KCSAN_COUNTER_REPORT_RACES
);
351 if ((type
& KCSAN_ACCESS_ASSERT
) != 0)
352 kcsan_counter_inc(KCSAN_COUNTER_ASSERT_FAILURES
);
354 kcsan_counter_inc(KCSAN_COUNTER_DATA_RACES
);
356 user_access_restore(flags
);
360 kcsan_setup_watchpoint(const volatile void *ptr
, size_t size
, int type
)
362 const bool is_write
= (type
& KCSAN_ACCESS_WRITE
) != 0;
363 const bool is_assert
= (type
& KCSAN_ACCESS_ASSERT
) != 0;
364 atomic_long_t
*watchpoint
;
371 unsigned long access_mask
;
372 enum kcsan_value_change value_change
= KCSAN_VALUE_CHANGE_MAYBE
;
373 unsigned long ua_flags
= user_access_save();
374 unsigned long irq_flags
= 0;
377 * Always reset kcsan_skip counter in slow-path to avoid underflow; see
382 if (!kcsan_is_enabled())
386 * Special atomic rules: unlikely to be true, so we check them here in
387 * the slow-path, and not in the fast-path in is_atomic(). Call after
388 * kcsan_is_enabled(), as we may access memory that is not yet
389 * initialized during early boot.
391 if (!is_assert
&& kcsan_is_atomic_special(ptr
))
394 if (!check_encodable((unsigned long)ptr
, size
)) {
395 kcsan_counter_inc(KCSAN_COUNTER_UNENCODABLE_ACCESSES
);
399 if (!kcsan_interrupt_watcher
)
400 /* Use raw to avoid lockdep recursion via IRQ flags tracing. */
401 raw_local_irq_save(irq_flags
);
403 watchpoint
= insert_watchpoint((unsigned long)ptr
, size
, is_write
);
404 if (watchpoint
== NULL
) {
406 * Out of capacity: the size of 'watchpoints', and the frequency
407 * with which should_watch() returns true should be tweaked so
408 * that this case happens very rarely.
410 kcsan_counter_inc(KCSAN_COUNTER_NO_CAPACITY
);
414 kcsan_counter_inc(KCSAN_COUNTER_SETUP_WATCHPOINTS
);
415 kcsan_counter_inc(KCSAN_COUNTER_USED_WATCHPOINTS
);
418 * Read the current value, to later check and infer a race if the data
419 * was modified via a non-instrumented access, e.g. from a device.
424 expect_value
._1
= READ_ONCE(*(const u8
*)ptr
);
427 expect_value
._2
= READ_ONCE(*(const u16
*)ptr
);
430 expect_value
._4
= READ_ONCE(*(const u32
*)ptr
);
433 expect_value
._8
= READ_ONCE(*(const u64
*)ptr
);
436 break; /* ignore; we do not diff the values */
439 if (IS_ENABLED(CONFIG_KCSAN_DEBUG
)) {
440 kcsan_disable_current();
441 pr_err("KCSAN: watching %s, size: %zu, addr: %px [slot: %d, encoded: %lx]\n",
442 is_write
? "write" : "read", size
, ptr
,
443 watchpoint_slot((unsigned long)ptr
),
444 encode_watchpoint((unsigned long)ptr
, size
, is_write
));
445 kcsan_enable_current();
449 * Delay this thread, to increase probability of observing a racy
450 * conflicting access.
455 * Re-read value, and check if it is as expected; if not, we infer a
458 access_mask
= get_ctx()->access_mask
;
461 expect_value
._1
^= READ_ONCE(*(const u8
*)ptr
);
463 expect_value
._1
&= (u8
)access_mask
;
466 expect_value
._2
^= READ_ONCE(*(const u16
*)ptr
);
468 expect_value
._2
&= (u16
)access_mask
;
471 expect_value
._4
^= READ_ONCE(*(const u32
*)ptr
);
473 expect_value
._4
&= (u32
)access_mask
;
476 expect_value
._8
^= READ_ONCE(*(const u64
*)ptr
);
478 expect_value
._8
&= (u64
)access_mask
;
481 break; /* ignore; we do not diff the values */
484 /* Were we able to observe a value-change? */
485 if (expect_value
._8
!= 0)
486 value_change
= KCSAN_VALUE_CHANGE_TRUE
;
488 /* Check if this access raced with another. */
489 if (!consume_watchpoint(watchpoint
)) {
491 * Depending on the access type, map a value_change of MAYBE to
492 * TRUE (always report) or FALSE (never report).
494 if (value_change
== KCSAN_VALUE_CHANGE_MAYBE
) {
495 if (access_mask
!= 0) {
497 * For access with access_mask, we require a
498 * value-change, as it is likely that races on
499 * ~access_mask bits are expected.
501 value_change
= KCSAN_VALUE_CHANGE_FALSE
;
502 } else if (size
> 8 || is_assert
) {
503 /* Always assume a value-change. */
504 value_change
= KCSAN_VALUE_CHANGE_TRUE
;
509 * No need to increment 'data_races' counter, as the racing
510 * thread already did.
512 * Count 'assert_failures' for each failed ASSERT access,
513 * therefore both this thread and the racing thread may
514 * increment this counter.
516 if (is_assert
&& value_change
== KCSAN_VALUE_CHANGE_TRUE
)
517 kcsan_counter_inc(KCSAN_COUNTER_ASSERT_FAILURES
);
519 kcsan_report(ptr
, size
, type
, value_change
, KCSAN_REPORT_RACE_SIGNAL
,
520 watchpoint
- watchpoints
);
521 } else if (value_change
== KCSAN_VALUE_CHANGE_TRUE
) {
522 /* Inferring a race, since the value should not have changed. */
524 kcsan_counter_inc(KCSAN_COUNTER_RACES_UNKNOWN_ORIGIN
);
526 kcsan_counter_inc(KCSAN_COUNTER_ASSERT_FAILURES
);
528 if (IS_ENABLED(CONFIG_KCSAN_REPORT_RACE_UNKNOWN_ORIGIN
) || is_assert
)
529 kcsan_report(ptr
, size
, type
, KCSAN_VALUE_CHANGE_TRUE
,
530 KCSAN_REPORT_RACE_UNKNOWN_ORIGIN
,
531 watchpoint
- watchpoints
);
535 * Remove watchpoint; must be after reporting, since the slot may be
536 * reused after this point.
538 remove_watchpoint(watchpoint
);
539 kcsan_counter_dec(KCSAN_COUNTER_USED_WATCHPOINTS
);
541 if (!kcsan_interrupt_watcher
)
542 raw_local_irq_restore(irq_flags
);
544 user_access_restore(ua_flags
);
547 static __always_inline
void check_access(const volatile void *ptr
, size_t size
,
550 const bool is_write
= (type
& KCSAN_ACCESS_WRITE
) != 0;
551 atomic_long_t
*watchpoint
;
552 long encoded_watchpoint
;
555 * Do nothing for 0 sized check; this comparison will be optimized out
556 * for constant sized instrumentation (__tsan_{read,write}N).
558 if (unlikely(size
== 0))
562 * Avoid user_access_save in fast-path: find_watchpoint is safe without
563 * user_access_save, as the address that ptr points to is only used to
564 * check if a watchpoint exists; ptr is never dereferenced.
566 watchpoint
= find_watchpoint((unsigned long)ptr
, size
, !is_write
,
567 &encoded_watchpoint
);
569 * It is safe to check kcsan_is_enabled() after find_watchpoint in the
570 * slow-path, as long as no state changes that cause a race to be
571 * detected and reported have occurred until kcsan_is_enabled() is
575 if (unlikely(watchpoint
!= NULL
))
576 kcsan_found_watchpoint(ptr
, size
, type
, watchpoint
,
579 struct kcsan_ctx
*ctx
= get_ctx(); /* Call only once in fast-path. */
581 if (unlikely(should_watch(ptr
, size
, type
, ctx
)))
582 kcsan_setup_watchpoint(ptr
, size
, type
);
583 else if (unlikely(ctx
->scoped_accesses
.prev
))
584 kcsan_check_scoped_accesses();
588 /* === Public interface ===================================================== */
590 void __init
kcsan_init(void)
594 kcsan_debugfs_init();
597 * We are in the init task, and no other tasks should be running;
598 * WRITE_ONCE without memory barrier is sufficient.
600 if (kcsan_early_enable
)
601 WRITE_ONCE(kcsan_enabled
, true);
604 /* === Exported interface =================================================== */
606 void kcsan_disable_current(void)
608 ++get_ctx()->disable_count
;
610 EXPORT_SYMBOL(kcsan_disable_current
);
612 void kcsan_enable_current(void)
614 if (get_ctx()->disable_count
-- == 0) {
616 * Warn if kcsan_enable_current() calls are unbalanced with
617 * kcsan_disable_current() calls, which causes disable_count to
618 * become negative and should not happen.
620 kcsan_disable_current(); /* restore to 0, KCSAN still enabled */
621 kcsan_disable_current(); /* disable to generate warning */
622 WARN(1, "Unbalanced %s()", __func__
);
623 kcsan_enable_current();
626 EXPORT_SYMBOL(kcsan_enable_current
);
628 void kcsan_enable_current_nowarn(void)
630 if (get_ctx()->disable_count
-- == 0)
631 kcsan_disable_current();
633 EXPORT_SYMBOL(kcsan_enable_current_nowarn
);
635 void kcsan_nestable_atomic_begin(void)
638 * Do *not* check and warn if we are in a flat atomic region: nestable
639 * and flat atomic regions are independent from each other.
640 * See include/linux/kcsan.h: struct kcsan_ctx comments for more
644 ++get_ctx()->atomic_nest_count
;
646 EXPORT_SYMBOL(kcsan_nestable_atomic_begin
);
648 void kcsan_nestable_atomic_end(void)
650 if (get_ctx()->atomic_nest_count
-- == 0) {
652 * Warn if kcsan_nestable_atomic_end() calls are unbalanced with
653 * kcsan_nestable_atomic_begin() calls, which causes
654 * atomic_nest_count to become negative and should not happen.
656 kcsan_nestable_atomic_begin(); /* restore to 0 */
657 kcsan_disable_current(); /* disable to generate warning */
658 WARN(1, "Unbalanced %s()", __func__
);
659 kcsan_enable_current();
662 EXPORT_SYMBOL(kcsan_nestable_atomic_end
);
664 void kcsan_flat_atomic_begin(void)
666 get_ctx()->in_flat_atomic
= true;
668 EXPORT_SYMBOL(kcsan_flat_atomic_begin
);
670 void kcsan_flat_atomic_end(void)
672 get_ctx()->in_flat_atomic
= false;
674 EXPORT_SYMBOL(kcsan_flat_atomic_end
);
676 void kcsan_atomic_next(int n
)
678 get_ctx()->atomic_next
= n
;
680 EXPORT_SYMBOL(kcsan_atomic_next
);
682 void kcsan_set_access_mask(unsigned long mask
)
684 get_ctx()->access_mask
= mask
;
686 EXPORT_SYMBOL(kcsan_set_access_mask
);
688 struct kcsan_scoped_access
*
689 kcsan_begin_scoped_access(const volatile void *ptr
, size_t size
, int type
,
690 struct kcsan_scoped_access
*sa
)
692 struct kcsan_ctx
*ctx
= get_ctx();
694 __kcsan_check_access(ptr
, size
, type
);
696 ctx
->disable_count
++; /* Disable KCSAN, in case list debugging is on. */
698 INIT_LIST_HEAD(&sa
->list
);
703 if (!ctx
->scoped_accesses
.prev
) /* Lazy initialize list head. */
704 INIT_LIST_HEAD(&ctx
->scoped_accesses
);
705 list_add(&sa
->list
, &ctx
->scoped_accesses
);
707 ctx
->disable_count
--;
710 EXPORT_SYMBOL(kcsan_begin_scoped_access
);
712 void kcsan_end_scoped_access(struct kcsan_scoped_access
*sa
)
714 struct kcsan_ctx
*ctx
= get_ctx();
716 if (WARN(!ctx
->scoped_accesses
.prev
, "Unbalanced %s()?", __func__
))
719 ctx
->disable_count
++; /* Disable KCSAN, in case list debugging is on. */
722 if (list_empty(&ctx
->scoped_accesses
))
724 * Ensure we do not enter kcsan_check_scoped_accesses()
725 * slow-path if unnecessary, and avoids requiring list_empty()
726 * in the fast-path (to avoid a READ_ONCE() and potential
729 ctx
->scoped_accesses
.prev
= NULL
;
731 ctx
->disable_count
--;
733 __kcsan_check_access(sa
->ptr
, sa
->size
, sa
->type
);
735 EXPORT_SYMBOL(kcsan_end_scoped_access
);
737 void __kcsan_check_access(const volatile void *ptr
, size_t size
, int type
)
739 check_access(ptr
, size
, type
);
741 EXPORT_SYMBOL(__kcsan_check_access
);
744 * KCSAN uses the same instrumentation that is emitted by supported compilers
745 * for ThreadSanitizer (TSAN).
747 * When enabled, the compiler emits instrumentation calls (the functions
748 * prefixed with "__tsan" below) for all loads and stores that it generated;
749 * inline asm is not instrumented.
751 * Note that, not all supported compiler versions distinguish aligned/unaligned
752 * accesses, but e.g. recent versions of Clang do. We simply alias the unaligned
753 * version to the generic version, which can handle both.
756 #define DEFINE_TSAN_READ_WRITE(size) \
757 void __tsan_read##size(void *ptr) \
759 check_access(ptr, size, 0); \
761 EXPORT_SYMBOL(__tsan_read##size); \
762 void __tsan_unaligned_read##size(void *ptr) \
763 __alias(__tsan_read##size); \
764 EXPORT_SYMBOL(__tsan_unaligned_read##size); \
765 void __tsan_write##size(void *ptr) \
767 check_access(ptr, size, KCSAN_ACCESS_WRITE); \
769 EXPORT_SYMBOL(__tsan_write##size); \
770 void __tsan_unaligned_write##size(void *ptr) \
771 __alias(__tsan_write##size); \
772 EXPORT_SYMBOL(__tsan_unaligned_write##size)
774 DEFINE_TSAN_READ_WRITE(1);
775 DEFINE_TSAN_READ_WRITE(2);
776 DEFINE_TSAN_READ_WRITE(4);
777 DEFINE_TSAN_READ_WRITE(8);
778 DEFINE_TSAN_READ_WRITE(16);
780 void __tsan_read_range(void *ptr
, size_t size
)
782 check_access(ptr
, size
, 0);
784 EXPORT_SYMBOL(__tsan_read_range
);
786 void __tsan_write_range(void *ptr
, size_t size
)
788 check_access(ptr
, size
, KCSAN_ACCESS_WRITE
);
790 EXPORT_SYMBOL(__tsan_write_range
);
793 * Use of explicit volatile is generally disallowed [1], however, volatile is
794 * still used in various concurrent context, whether in low-level
795 * synchronization primitives or for legacy reasons.
796 * [1] https://lwn.net/Articles/233479/
798 * We only consider volatile accesses atomic if they are aligned and would pass
799 * the size-check of compiletime_assert_rwonce_type().
801 #define DEFINE_TSAN_VOLATILE_READ_WRITE(size) \
802 void __tsan_volatile_read##size(void *ptr) \
804 const bool is_atomic = size <= sizeof(long long) && \
805 IS_ALIGNED((unsigned long)ptr, size); \
806 if (IS_ENABLED(CONFIG_KCSAN_IGNORE_ATOMICS) && is_atomic) \
808 check_access(ptr, size, is_atomic ? KCSAN_ACCESS_ATOMIC : 0); \
810 EXPORT_SYMBOL(__tsan_volatile_read##size); \
811 void __tsan_unaligned_volatile_read##size(void *ptr) \
812 __alias(__tsan_volatile_read##size); \
813 EXPORT_SYMBOL(__tsan_unaligned_volatile_read##size); \
814 void __tsan_volatile_write##size(void *ptr) \
816 const bool is_atomic = size <= sizeof(long long) && \
817 IS_ALIGNED((unsigned long)ptr, size); \
818 if (IS_ENABLED(CONFIG_KCSAN_IGNORE_ATOMICS) && is_atomic) \
820 check_access(ptr, size, \
821 KCSAN_ACCESS_WRITE | \
822 (is_atomic ? KCSAN_ACCESS_ATOMIC : 0)); \
824 EXPORT_SYMBOL(__tsan_volatile_write##size); \
825 void __tsan_unaligned_volatile_write##size(void *ptr) \
826 __alias(__tsan_volatile_write##size); \
827 EXPORT_SYMBOL(__tsan_unaligned_volatile_write##size)
829 DEFINE_TSAN_VOLATILE_READ_WRITE(1);
830 DEFINE_TSAN_VOLATILE_READ_WRITE(2);
831 DEFINE_TSAN_VOLATILE_READ_WRITE(4);
832 DEFINE_TSAN_VOLATILE_READ_WRITE(8);
833 DEFINE_TSAN_VOLATILE_READ_WRITE(16);
836 * The below are not required by KCSAN, but can still be emitted by the
839 void __tsan_func_entry(void *call_pc
)
842 EXPORT_SYMBOL(__tsan_func_entry
);
843 void __tsan_func_exit(void)
846 EXPORT_SYMBOL(__tsan_func_exit
);
847 void __tsan_init(void)
850 EXPORT_SYMBOL(__tsan_init
);