]> git.proxmox.com Git - mirror_ubuntu-jammy-kernel.git/blob - kernel/kcsan/core.c
net: macb: fix macb_get/set_wol() when moving to phylink
[mirror_ubuntu-jammy-kernel.git] / kernel / kcsan / core.c
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
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);
26
27 #ifdef MODULE_PARAM_PREFIX
28 #undef MODULE_PARAM_PREFIX
29 #endif
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);
36
37 bool kcsan_enabled;
38
39 /* Per-CPU kcsan_ctx for interrupts */
40 static 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 */
93 static 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 */
99 static DEFINE_PER_CPU(long, kcsan_skip);
100
101 static __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
134 static inline atomic_long_t *
135 insert_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 */
169 static __always_inline bool
170 try_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. */
176 static 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. */
182 static inline void remove_watchpoint(atomic_long_t *watchpoint)
183 {
184 atomic_long_set(watchpoint, INVALID_WATCHPOINT);
185 }
186
187 static __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() ? &current->kcsan_ctx : raw_cpu_ptr(&kcsan_cpu_ctx);
194 }
195
196 /* Check scoped accesses; never inline because this is a slow-path! */
197 static 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. */
210 static __always_inline bool
211 is_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
247 static __always_inline bool
248 should_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
272 static 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
281 static __always_inline bool kcsan_is_enabled(void)
282 {
283 return READ_ONCE(kcsan_enabled) && get_ctx()->disable_count == 0;
284 }
285
286 static 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
294 /*
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.
298 *
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.
305 */
306
307 static noinline void kcsan_found_watchpoint(const volatile void *ptr,
308 size_t size,
309 int type,
310 atomic_long_t *watchpoint,
311 long encoded_watchpoint)
312 {
313 unsigned long flags;
314 bool consumed;
315
316 if (!kcsan_is_enabled())
317 return;
318
319 /*
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.
323 */
324 if (get_ctx()->access_mask != 0)
325 return;
326
327 /*
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.
332 */
333 consumed = try_consume_watchpoint(watchpoint, encoded_watchpoint);
334
335 /* keep this after try_consume_watchpoint */
336 flags = user_access_save();
337
338 if (consumed) {
339 kcsan_report(ptr, size, type, KCSAN_VALUE_CHANGE_MAYBE,
340 KCSAN_REPORT_CONSUMED_WATCHPOINT,
341 watchpoint - watchpoints);
342 } else {
343 /*
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.
347 */
348 kcsan_counter_inc(KCSAN_COUNTER_REPORT_RACES);
349 }
350
351 if ((type & KCSAN_ACCESS_ASSERT) != 0)
352 kcsan_counter_inc(KCSAN_COUNTER_ASSERT_FAILURES);
353 else
354 kcsan_counter_inc(KCSAN_COUNTER_DATA_RACES);
355
356 user_access_restore(flags);
357 }
358
359 static noinline void
360 kcsan_setup_watchpoint(const volatile void *ptr, size_t size, int type)
361 {
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;
365 union {
366 u8 _1;
367 u16 _2;
368 u32 _4;
369 u64 _8;
370 } expect_value;
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;
375
376 /*
377 * Always reset kcsan_skip counter in slow-path to avoid underflow; see
378 * should_watch().
379 */
380 reset_kcsan_skip();
381
382 if (!kcsan_is_enabled())
383 goto out;
384
385 /*
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.
390 */
391 if (!is_assert && kcsan_is_atomic_special(ptr))
392 goto out;
393
394 if (!check_encodable((unsigned long)ptr, size)) {
395 kcsan_counter_inc(KCSAN_COUNTER_UNENCODABLE_ACCESSES);
396 goto out;
397 }
398
399 if (!kcsan_interrupt_watcher)
400 /* Use raw to avoid lockdep recursion via IRQ flags tracing. */
401 raw_local_irq_save(irq_flags);
402
403 watchpoint = insert_watchpoint((unsigned long)ptr, size, is_write);
404 if (watchpoint == NULL) {
405 /*
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.
409 */
410 kcsan_counter_inc(KCSAN_COUNTER_NO_CAPACITY);
411 goto out_unlock;
412 }
413
414 kcsan_counter_inc(KCSAN_COUNTER_SETUP_WATCHPOINTS);
415 kcsan_counter_inc(KCSAN_COUNTER_USED_WATCHPOINTS);
416
417 /*
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.
420 */
421 expect_value._8 = 0;
422 switch (size) {
423 case 1:
424 expect_value._1 = READ_ONCE(*(const u8 *)ptr);
425 break;
426 case 2:
427 expect_value._2 = READ_ONCE(*(const u16 *)ptr);
428 break;
429 case 4:
430 expect_value._4 = READ_ONCE(*(const u32 *)ptr);
431 break;
432 case 8:
433 expect_value._8 = READ_ONCE(*(const u64 *)ptr);
434 break;
435 default:
436 break; /* ignore; we do not diff the values */
437 }
438
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();
446 }
447
448 /*
449 * Delay this thread, to increase probability of observing a racy
450 * conflicting access.
451 */
452 udelay(get_delay());
453
454 /*
455 * Re-read value, and check if it is as expected; if not, we infer a
456 * racy access.
457 */
458 access_mask = get_ctx()->access_mask;
459 switch (size) {
460 case 1:
461 expect_value._1 ^= READ_ONCE(*(const u8 *)ptr);
462 if (access_mask)
463 expect_value._1 &= (u8)access_mask;
464 break;
465 case 2:
466 expect_value._2 ^= READ_ONCE(*(const u16 *)ptr);
467 if (access_mask)
468 expect_value._2 &= (u16)access_mask;
469 break;
470 case 4:
471 expect_value._4 ^= READ_ONCE(*(const u32 *)ptr);
472 if (access_mask)
473 expect_value._4 &= (u32)access_mask;
474 break;
475 case 8:
476 expect_value._8 ^= READ_ONCE(*(const u64 *)ptr);
477 if (access_mask)
478 expect_value._8 &= (u64)access_mask;
479 break;
480 default:
481 break; /* ignore; we do not diff the values */
482 }
483
484 /* Were we able to observe a value-change? */
485 if (expect_value._8 != 0)
486 value_change = KCSAN_VALUE_CHANGE_TRUE;
487
488 /* Check if this access raced with another. */
489 if (!consume_watchpoint(watchpoint)) {
490 /*
491 * Depending on the access type, map a value_change of MAYBE to
492 * TRUE (always report) or FALSE (never report).
493 */
494 if (value_change == KCSAN_VALUE_CHANGE_MAYBE) {
495 if (access_mask != 0) {
496 /*
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.
500 */
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;
505 }
506 }
507
508 /*
509 * No need to increment 'data_races' counter, as the racing
510 * thread already did.
511 *
512 * Count 'assert_failures' for each failed ASSERT access,
513 * therefore both this thread and the racing thread may
514 * increment this counter.
515 */
516 if (is_assert && value_change == KCSAN_VALUE_CHANGE_TRUE)
517 kcsan_counter_inc(KCSAN_COUNTER_ASSERT_FAILURES);
518
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. */
523
524 kcsan_counter_inc(KCSAN_COUNTER_RACES_UNKNOWN_ORIGIN);
525 if (is_assert)
526 kcsan_counter_inc(KCSAN_COUNTER_ASSERT_FAILURES);
527
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);
532 }
533
534 /*
535 * Remove watchpoint; must be after reporting, since the slot may be
536 * reused after this point.
537 */
538 remove_watchpoint(watchpoint);
539 kcsan_counter_dec(KCSAN_COUNTER_USED_WATCHPOINTS);
540 out_unlock:
541 if (!kcsan_interrupt_watcher)
542 raw_local_irq_restore(irq_flags);
543 out:
544 user_access_restore(ua_flags);
545 }
546
547 static __always_inline void check_access(const volatile void *ptr, size_t size,
548 int type)
549 {
550 const bool is_write = (type & KCSAN_ACCESS_WRITE) != 0;
551 atomic_long_t *watchpoint;
552 long encoded_watchpoint;
553
554 /*
555 * Do nothing for 0 sized check; this comparison will be optimized out
556 * for constant sized instrumentation (__tsan_{read,write}N).
557 */
558 if (unlikely(size == 0))
559 return;
560
561 /*
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.
565 */
566 watchpoint = find_watchpoint((unsigned long)ptr, size, !is_write,
567 &encoded_watchpoint);
568 /*
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
572 * checked.
573 */
574
575 if (unlikely(watchpoint != NULL))
576 kcsan_found_watchpoint(ptr, size, type, watchpoint,
577 encoded_watchpoint);
578 else {
579 struct kcsan_ctx *ctx = get_ctx(); /* Call only once in fast-path. */
580
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();
585 }
586 }
587
588 /* === Public interface ===================================================== */
589
590 void __init kcsan_init(void)
591 {
592 BUG_ON(!in_task());
593
594 kcsan_debugfs_init();
595
596 /*
597 * We are in the init task, and no other tasks should be running;
598 * WRITE_ONCE without memory barrier is sufficient.
599 */
600 if (kcsan_early_enable)
601 WRITE_ONCE(kcsan_enabled, true);
602 }
603
604 /* === Exported interface =================================================== */
605
606 void kcsan_disable_current(void)
607 {
608 ++get_ctx()->disable_count;
609 }
610 EXPORT_SYMBOL(kcsan_disable_current);
611
612 void kcsan_enable_current(void)
613 {
614 if (get_ctx()->disable_count-- == 0) {
615 /*
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.
619 */
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();
624 }
625 }
626 EXPORT_SYMBOL(kcsan_enable_current);
627
628 void kcsan_enable_current_nowarn(void)
629 {
630 if (get_ctx()->disable_count-- == 0)
631 kcsan_disable_current();
632 }
633 EXPORT_SYMBOL(kcsan_enable_current_nowarn);
634
635 void kcsan_nestable_atomic_begin(void)
636 {
637 /*
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
641 * comments.
642 */
643
644 ++get_ctx()->atomic_nest_count;
645 }
646 EXPORT_SYMBOL(kcsan_nestable_atomic_begin);
647
648 void kcsan_nestable_atomic_end(void)
649 {
650 if (get_ctx()->atomic_nest_count-- == 0) {
651 /*
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.
655 */
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();
660 }
661 }
662 EXPORT_SYMBOL(kcsan_nestable_atomic_end);
663
664 void kcsan_flat_atomic_begin(void)
665 {
666 get_ctx()->in_flat_atomic = true;
667 }
668 EXPORT_SYMBOL(kcsan_flat_atomic_begin);
669
670 void kcsan_flat_atomic_end(void)
671 {
672 get_ctx()->in_flat_atomic = false;
673 }
674 EXPORT_SYMBOL(kcsan_flat_atomic_end);
675
676 void kcsan_atomic_next(int n)
677 {
678 get_ctx()->atomic_next = n;
679 }
680 EXPORT_SYMBOL(kcsan_atomic_next);
681
682 void kcsan_set_access_mask(unsigned long mask)
683 {
684 get_ctx()->access_mask = mask;
685 }
686 EXPORT_SYMBOL(kcsan_set_access_mask);
687
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)
691 {
692 struct kcsan_ctx *ctx = get_ctx();
693
694 __kcsan_check_access(ptr, size, type);
695
696 ctx->disable_count++; /* Disable KCSAN, in case list debugging is on. */
697
698 INIT_LIST_HEAD(&sa->list);
699 sa->ptr = ptr;
700 sa->size = size;
701 sa->type = type;
702
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);
706
707 ctx->disable_count--;
708 return sa;
709 }
710 EXPORT_SYMBOL(kcsan_begin_scoped_access);
711
712 void kcsan_end_scoped_access(struct kcsan_scoped_access *sa)
713 {
714 struct kcsan_ctx *ctx = get_ctx();
715
716 if (WARN(!ctx->scoped_accesses.prev, "Unbalanced %s()?", __func__))
717 return;
718
719 ctx->disable_count++; /* Disable KCSAN, in case list debugging is on. */
720
721 list_del(&sa->list);
722 if (list_empty(&ctx->scoped_accesses))
723 /*
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
727 * uaccess warning).
728 */
729 ctx->scoped_accesses.prev = NULL;
730
731 ctx->disable_count--;
732
733 __kcsan_check_access(sa->ptr, sa->size, sa->type);
734 }
735 EXPORT_SYMBOL(kcsan_end_scoped_access);
736
737 void __kcsan_check_access(const volatile void *ptr, size_t size, int type)
738 {
739 check_access(ptr, size, type);
740 }
741 EXPORT_SYMBOL(__kcsan_check_access);
742
743 /*
744 * KCSAN uses the same instrumentation that is emitted by supported compilers
745 * for ThreadSanitizer (TSAN).
746 *
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.
750 *
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.
754 */
755
756 #define DEFINE_TSAN_READ_WRITE(size) \
757 void __tsan_read##size(void *ptr) \
758 { \
759 check_access(ptr, size, 0); \
760 } \
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) \
766 { \
767 check_access(ptr, size, KCSAN_ACCESS_WRITE); \
768 } \
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)
773
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);
779
780 void __tsan_read_range(void *ptr, size_t size)
781 {
782 check_access(ptr, size, 0);
783 }
784 EXPORT_SYMBOL(__tsan_read_range);
785
786 void __tsan_write_range(void *ptr, size_t size)
787 {
788 check_access(ptr, size, KCSAN_ACCESS_WRITE);
789 }
790 EXPORT_SYMBOL(__tsan_write_range);
791
792 /*
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/
797 *
798 * We only consider volatile accesses atomic if they are aligned and would pass
799 * the size-check of compiletime_assert_rwonce_type().
800 */
801 #define DEFINE_TSAN_VOLATILE_READ_WRITE(size) \
802 void __tsan_volatile_read##size(void *ptr) \
803 { \
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) \
807 return; \
808 check_access(ptr, size, is_atomic ? KCSAN_ACCESS_ATOMIC : 0); \
809 } \
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) \
815 { \
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) \
819 return; \
820 check_access(ptr, size, \
821 KCSAN_ACCESS_WRITE | \
822 (is_atomic ? KCSAN_ACCESS_ATOMIC : 0)); \
823 } \
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)
828
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);
834
835 /*
836 * The below are not required by KCSAN, but can still be emitted by the
837 * compiler.
838 */
839 void __tsan_func_entry(void *call_pc)
840 {
841 }
842 EXPORT_SYMBOL(__tsan_func_entry);
843 void __tsan_func_exit(void)
844 {
845 }
846 EXPORT_SYMBOL(__tsan_func_exit);
847 void __tsan_init(void)
848 {
849 }
850 EXPORT_SYMBOL(__tsan_init);