1 | // SPDX-License-Identifier: GPL-2.0 |
2 | /* |
3 | * KCSAN core runtime. |
4 | * |
5 | * Copyright (C) 2019, Google LLC. |
6 | */ |
7 | |
8 | #define pr_fmt(fmt) "kcsan: " fmt |
9 | |
10 | #include <linux/atomic.h> |
11 | #include <linux/bug.h> |
12 | #include <linux/delay.h> |
13 | #include <linux/export.h> |
14 | #include <linux/init.h> |
15 | #include <linux/kernel.h> |
16 | #include <linux/list.h> |
17 | #include <linux/minmax.h> |
18 | #include <linux/moduleparam.h> |
19 | #include <linux/percpu.h> |
20 | #include <linux/preempt.h> |
21 | #include <linux/sched.h> |
22 | #include <linux/string.h> |
23 | #include <linux/uaccess.h> |
24 | |
25 | #include "encoding.h" |
26 | #include "kcsan.h" |
27 | #include "permissive.h" |
28 | |
29 | static bool kcsan_early_enable = IS_ENABLED(CONFIG_KCSAN_EARLY_ENABLE); |
30 | unsigned int kcsan_udelay_task = CONFIG_KCSAN_UDELAY_TASK; |
31 | unsigned int kcsan_udelay_interrupt = CONFIG_KCSAN_UDELAY_INTERRUPT; |
32 | static long kcsan_skip_watch = CONFIG_KCSAN_SKIP_WATCH; |
33 | static bool kcsan_interrupt_watcher = IS_ENABLED(CONFIG_KCSAN_INTERRUPT_WATCHER); |
34 | |
35 | #ifdef MODULE_PARAM_PREFIX |
36 | #undef MODULE_PARAM_PREFIX |
37 | #endif |
38 | #define MODULE_PARAM_PREFIX "kcsan." |
39 | module_param_named(early_enable, kcsan_early_enable, bool, 0); |
40 | module_param_named(udelay_task, kcsan_udelay_task, uint, 0644); |
41 | module_param_named(udelay_interrupt, kcsan_udelay_interrupt, uint, 0644); |
42 | module_param_named(skip_watch, kcsan_skip_watch, long, 0644); |
43 | module_param_named(interrupt_watcher, kcsan_interrupt_watcher, bool, 0444); |
44 | |
45 | #ifdef CONFIG_KCSAN_WEAK_MEMORY |
46 | static bool kcsan_weak_memory = true; |
47 | module_param_named(weak_memory, kcsan_weak_memory, bool, 0644); |
48 | #else |
49 | #define kcsan_weak_memory false |
50 | #endif |
51 | |
52 | bool kcsan_enabled; |
53 | |
54 | /* Per-CPU kcsan_ctx for interrupts */ |
55 | static DEFINE_PER_CPU(struct kcsan_ctx, kcsan_cpu_ctx) = { |
56 | .scoped_accesses = {LIST_POISON1, NULL}, |
57 | }; |
58 | |
59 | /* |
60 | * Helper macros to index into adjacent slots, starting from address slot |
61 | * itself, followed by the right and left slots. |
62 | * |
63 | * The purpose is 2-fold: |
64 | * |
65 | * 1. if during insertion the address slot is already occupied, check if |
66 | * any adjacent slots are free; |
67 | * 2. accesses that straddle a slot boundary due to size that exceeds a |
68 | * slot's range may check adjacent slots if any watchpoint matches. |
69 | * |
70 | * Note that accesses with very large size may still miss a watchpoint; however, |
71 | * given this should be rare, this is a reasonable trade-off to make, since this |
72 | * will avoid: |
73 | * |
74 | * 1. excessive contention between watchpoint checks and setup; |
75 | * 2. larger number of simultaneous watchpoints without sacrificing |
76 | * performance. |
77 | * |
78 | * Example: SLOT_IDX values for KCSAN_CHECK_ADJACENT=1, where i is [0, 1, 2]: |
79 | * |
80 | * slot=0: [ 1, 2, 0] |
81 | * slot=9: [10, 11, 9] |
82 | * slot=63: [64, 65, 63] |
83 | */ |
84 | #define SLOT_IDX(slot, i) (slot + ((i + KCSAN_CHECK_ADJACENT) % NUM_SLOTS)) |
85 | |
86 | /* |
87 | * SLOT_IDX_FAST is used in the fast-path. Not first checking the address's primary |
88 | * slot (middle) is fine if we assume that races occur rarely. The set of |
89 | * indices {SLOT_IDX(slot, i) | i in [0, NUM_SLOTS)} is equivalent to |
90 | * {SLOT_IDX_FAST(slot, i) | i in [0, NUM_SLOTS)}. |
91 | */ |
92 | #define SLOT_IDX_FAST(slot, i) (slot + i) |
93 | |
94 | /* |
95 | * Watchpoints, with each entry encoded as defined in encoding.h: in order to be |
96 | * able to safely update and access a watchpoint without introducing locking |
97 | * overhead, we encode each watchpoint as a single atomic long. The initial |
98 | * zero-initialized state matches INVALID_WATCHPOINT. |
99 | * |
100 | * Add NUM_SLOTS-1 entries to account for overflow; this helps avoid having to |
101 | * use more complicated SLOT_IDX_FAST calculation with modulo in the fast-path. |
102 | */ |
103 | static atomic_long_t watchpoints[CONFIG_KCSAN_NUM_WATCHPOINTS + NUM_SLOTS-1]; |
104 | |
105 | /* |
106 | * Instructions to skip watching counter, used in should_watch(). We use a |
107 | * per-CPU counter to avoid excessive contention. |
108 | */ |
109 | static DEFINE_PER_CPU(long, kcsan_skip); |
110 | |
111 | /* For kcsan_prandom_u32_max(). */ |
112 | static DEFINE_PER_CPU(u32, kcsan_rand_state); |
113 | |
114 | static __always_inline atomic_long_t *find_watchpoint(unsigned long addr, |
115 | size_t size, |
116 | bool expect_write, |
117 | long *encoded_watchpoint) |
118 | { |
119 | const int slot = watchpoint_slot(addr); |
120 | const unsigned long addr_masked = addr & WATCHPOINT_ADDR_MASK; |
121 | atomic_long_t *watchpoint; |
122 | unsigned long wp_addr_masked; |
123 | size_t wp_size; |
124 | bool is_write; |
125 | int i; |
126 | |
127 | BUILD_BUG_ON(CONFIG_KCSAN_NUM_WATCHPOINTS < NUM_SLOTS); |
128 | |
129 | for (i = 0; i < NUM_SLOTS; ++i) { |
130 | watchpoint = &watchpoints[SLOT_IDX_FAST(slot, i)]; |
131 | *encoded_watchpoint = atomic_long_read(v: watchpoint); |
132 | if (!decode_watchpoint(watchpoint: *encoded_watchpoint, addr_masked: &wp_addr_masked, |
133 | size: &wp_size, is_write: &is_write)) |
134 | continue; |
135 | |
136 | if (expect_write && !is_write) |
137 | continue; |
138 | |
139 | /* Check if the watchpoint matches the access. */ |
140 | if (matching_access(addr1: wp_addr_masked, size1: wp_size, addr2: addr_masked, size2: size)) |
141 | return watchpoint; |
142 | } |
143 | |
144 | return NULL; |
145 | } |
146 | |
147 | static inline atomic_long_t * |
148 | insert_watchpoint(unsigned long addr, size_t size, bool is_write) |
149 | { |
150 | const int slot = watchpoint_slot(addr); |
151 | const long encoded_watchpoint = encode_watchpoint(addr, size, is_write); |
152 | atomic_long_t *watchpoint; |
153 | int i; |
154 | |
155 | /* Check slot index logic, ensuring we stay within array bounds. */ |
156 | BUILD_BUG_ON(SLOT_IDX(0, 0) != KCSAN_CHECK_ADJACENT); |
157 | BUILD_BUG_ON(SLOT_IDX(0, KCSAN_CHECK_ADJACENT+1) != 0); |
158 | BUILD_BUG_ON(SLOT_IDX(CONFIG_KCSAN_NUM_WATCHPOINTS-1, KCSAN_CHECK_ADJACENT) != ARRAY_SIZE(watchpoints)-1); |
159 | BUILD_BUG_ON(SLOT_IDX(CONFIG_KCSAN_NUM_WATCHPOINTS-1, KCSAN_CHECK_ADJACENT+1) != ARRAY_SIZE(watchpoints) - NUM_SLOTS); |
160 | |
161 | for (i = 0; i < NUM_SLOTS; ++i) { |
162 | long expect_val = INVALID_WATCHPOINT; |
163 | |
164 | /* Try to acquire this slot. */ |
165 | watchpoint = &watchpoints[SLOT_IDX(slot, i)]; |
166 | if (atomic_long_try_cmpxchg_relaxed(v: watchpoint, old: &expect_val, new: encoded_watchpoint)) |
167 | return watchpoint; |
168 | } |
169 | |
170 | return NULL; |
171 | } |
172 | |
173 | /* |
174 | * Return true if watchpoint was successfully consumed, false otherwise. |
175 | * |
176 | * This may return false if: |
177 | * |
178 | * 1. another thread already consumed the watchpoint; |
179 | * 2. the thread that set up the watchpoint already removed it; |
180 | * 3. the watchpoint was removed and then re-used. |
181 | */ |
182 | static __always_inline bool |
183 | try_consume_watchpoint(atomic_long_t *watchpoint, long encoded_watchpoint) |
184 | { |
185 | return atomic_long_try_cmpxchg_relaxed(v: watchpoint, old: &encoded_watchpoint, CONSUMED_WATCHPOINT); |
186 | } |
187 | |
188 | /* Return true if watchpoint was not touched, false if already consumed. */ |
189 | static inline bool consume_watchpoint(atomic_long_t *watchpoint) |
190 | { |
191 | return atomic_long_xchg_relaxed(v: watchpoint, CONSUMED_WATCHPOINT) != CONSUMED_WATCHPOINT; |
192 | } |
193 | |
194 | /* Remove the watchpoint -- its slot may be reused after. */ |
195 | static inline void remove_watchpoint(atomic_long_t *watchpoint) |
196 | { |
197 | atomic_long_set(v: watchpoint, INVALID_WATCHPOINT); |
198 | } |
199 | |
200 | static __always_inline struct kcsan_ctx *get_ctx(void) |
201 | { |
202 | /* |
203 | * In interrupts, use raw_cpu_ptr to avoid unnecessary checks, that would |
204 | * also result in calls that generate warnings in uaccess regions. |
205 | */ |
206 | return in_task() ? ¤t->kcsan_ctx : raw_cpu_ptr(&kcsan_cpu_ctx); |
207 | } |
208 | |
209 | static __always_inline void |
210 | check_access(const volatile void *ptr, size_t size, int type, unsigned long ip); |
211 | |
212 | /* Check scoped accesses; never inline because this is a slow-path! */ |
213 | static noinline void kcsan_check_scoped_accesses(void) |
214 | { |
215 | struct kcsan_ctx *ctx = get_ctx(); |
216 | struct kcsan_scoped_access *scoped_access; |
217 | |
218 | if (ctx->disable_scoped) |
219 | return; |
220 | |
221 | ctx->disable_scoped++; |
222 | list_for_each_entry(scoped_access, &ctx->scoped_accesses, list) { |
223 | check_access(ptr: scoped_access->ptr, size: scoped_access->size, |
224 | type: scoped_access->type, ip: scoped_access->ip); |
225 | } |
226 | ctx->disable_scoped--; |
227 | } |
228 | |
229 | /* Rules for generic atomic accesses. Called from fast-path. */ |
230 | static __always_inline bool |
231 | is_atomic(struct kcsan_ctx *ctx, const volatile void *ptr, size_t size, int type) |
232 | { |
233 | if (type & KCSAN_ACCESS_ATOMIC) |
234 | return true; |
235 | |
236 | /* |
237 | * Unless explicitly declared atomic, never consider an assertion access |
238 | * as atomic. This allows using them also in atomic regions, such as |
239 | * seqlocks, without implicitly changing their semantics. |
240 | */ |
241 | if (type & KCSAN_ACCESS_ASSERT) |
242 | return false; |
243 | |
244 | if (IS_ENABLED(CONFIG_KCSAN_ASSUME_PLAIN_WRITES_ATOMIC) && |
245 | (type & KCSAN_ACCESS_WRITE) && size <= sizeof(long) && |
246 | !(type & KCSAN_ACCESS_COMPOUND) && IS_ALIGNED((unsigned long)ptr, size)) |
247 | return true; /* Assume aligned writes up to word size are atomic. */ |
248 | |
249 | if (ctx->atomic_next > 0) { |
250 | /* |
251 | * Because we do not have separate contexts for nested |
252 | * interrupts, in case atomic_next is set, we simply assume that |
253 | * the outer interrupt set atomic_next. In the worst case, we |
254 | * will conservatively consider operations as atomic. This is a |
255 | * reasonable trade-off to make, since this case should be |
256 | * extremely rare; however, even if extremely rare, it could |
257 | * lead to false positives otherwise. |
258 | */ |
259 | if ((hardirq_count() >> HARDIRQ_SHIFT) < 2) |
260 | --ctx->atomic_next; /* in task, or outer interrupt */ |
261 | return true; |
262 | } |
263 | |
264 | return ctx->atomic_nest_count > 0 || ctx->in_flat_atomic; |
265 | } |
266 | |
267 | static __always_inline bool |
268 | should_watch(struct kcsan_ctx *ctx, const volatile void *ptr, size_t size, int type) |
269 | { |
270 | /* |
271 | * Never set up watchpoints when memory operations are atomic. |
272 | * |
273 | * Need to check this first, before kcsan_skip check below: (1) atomics |
274 | * should not count towards skipped instructions, and (2) to actually |
275 | * decrement kcsan_atomic_next for consecutive instruction stream. |
276 | */ |
277 | if (is_atomic(ctx, ptr, size, type)) |
278 | return false; |
279 | |
280 | if (this_cpu_dec_return(kcsan_skip) >= 0) |
281 | return false; |
282 | |
283 | /* |
284 | * NOTE: If we get here, kcsan_skip must always be reset in slow path |
285 | * via reset_kcsan_skip() to avoid underflow. |
286 | */ |
287 | |
288 | /* this operation should be watched */ |
289 | return true; |
290 | } |
291 | |
292 | /* |
293 | * Returns a pseudo-random number in interval [0, ep_ro). Simple linear |
294 | * congruential generator, using constants from "Numerical Recipes". |
295 | */ |
296 | static u32 kcsan_prandom_u32_max(u32 ep_ro) |
297 | { |
298 | u32 state = this_cpu_read(kcsan_rand_state); |
299 | |
300 | state = 1664525 * state + 1013904223; |
301 | this_cpu_write(kcsan_rand_state, state); |
302 | |
303 | return state % ep_ro; |
304 | } |
305 | |
306 | static inline void reset_kcsan_skip(void) |
307 | { |
308 | long skip_count = kcsan_skip_watch - |
309 | (IS_ENABLED(CONFIG_KCSAN_SKIP_WATCH_RANDOMIZE) ? |
310 | kcsan_prandom_u32_max(ep_ro: kcsan_skip_watch) : |
311 | 0); |
312 | this_cpu_write(kcsan_skip, skip_count); |
313 | } |
314 | |
315 | static __always_inline bool kcsan_is_enabled(struct kcsan_ctx *ctx) |
316 | { |
317 | return READ_ONCE(kcsan_enabled) && !ctx->disable_count; |
318 | } |
319 | |
320 | /* Introduce delay depending on context and configuration. */ |
321 | static void delay_access(int type) |
322 | { |
323 | unsigned int delay = in_task() ? kcsan_udelay_task : kcsan_udelay_interrupt; |
324 | /* For certain access types, skew the random delay to be longer. */ |
325 | unsigned int skew_delay_order = |
326 | (type & (KCSAN_ACCESS_COMPOUND | KCSAN_ACCESS_ASSERT)) ? 1 : 0; |
327 | |
328 | delay -= IS_ENABLED(CONFIG_KCSAN_DELAY_RANDOMIZE) ? |
329 | kcsan_prandom_u32_max(ep_ro: delay >> skew_delay_order) : |
330 | 0; |
331 | udelay(delay); |
332 | } |
333 | |
334 | /* |
335 | * Reads the instrumented memory for value change detection; value change |
336 | * detection is currently done for accesses up to a size of 8 bytes. |
337 | */ |
338 | static __always_inline u64 read_instrumented_memory(const volatile void *ptr, size_t size) |
339 | { |
340 | /* |
341 | * In the below we don't necessarily need the read of the location to |
342 | * be atomic, and we don't use READ_ONCE(), since all we need for race |
343 | * detection is to observe 2 different values. |
344 | * |
345 | * Furthermore, on certain architectures (such as arm64), READ_ONCE() |
346 | * may turn into more complex instructions than a plain load that cannot |
347 | * do unaligned accesses. |
348 | */ |
349 | switch (size) { |
350 | case 1: return *(const volatile u8 *)ptr; |
351 | case 2: return *(const volatile u16 *)ptr; |
352 | case 4: return *(const volatile u32 *)ptr; |
353 | case 8: return *(const volatile u64 *)ptr; |
354 | default: return 0; /* Ignore; we do not diff the values. */ |
355 | } |
356 | } |
357 | |
358 | void kcsan_save_irqtrace(struct task_struct *task) |
359 | { |
360 | #ifdef CONFIG_TRACE_IRQFLAGS |
361 | task->kcsan_save_irqtrace = task->irqtrace; |
362 | #endif |
363 | } |
364 | |
365 | void kcsan_restore_irqtrace(struct task_struct *task) |
366 | { |
367 | #ifdef CONFIG_TRACE_IRQFLAGS |
368 | task->irqtrace = task->kcsan_save_irqtrace; |
369 | #endif |
370 | } |
371 | |
372 | static __always_inline int get_kcsan_stack_depth(void) |
373 | { |
374 | #ifdef CONFIG_KCSAN_WEAK_MEMORY |
375 | return current->kcsan_stack_depth; |
376 | #else |
377 | BUILD_BUG(); |
378 | return 0; |
379 | #endif |
380 | } |
381 | |
382 | static __always_inline void add_kcsan_stack_depth(int val) |
383 | { |
384 | #ifdef CONFIG_KCSAN_WEAK_MEMORY |
385 | current->kcsan_stack_depth += val; |
386 | #else |
387 | BUILD_BUG(); |
388 | #endif |
389 | } |
390 | |
391 | static __always_inline struct kcsan_scoped_access *get_reorder_access(struct kcsan_ctx *ctx) |
392 | { |
393 | #ifdef CONFIG_KCSAN_WEAK_MEMORY |
394 | return ctx->disable_scoped ? NULL : &ctx->reorder_access; |
395 | #else |
396 | return NULL; |
397 | #endif |
398 | } |
399 | |
400 | static __always_inline bool |
401 | find_reorder_access(struct kcsan_ctx *ctx, const volatile void *ptr, size_t size, |
402 | int type, unsigned long ip) |
403 | { |
404 | struct kcsan_scoped_access *reorder_access = get_reorder_access(ctx); |
405 | |
406 | if (!reorder_access) |
407 | return false; |
408 | |
409 | /* |
410 | * Note: If accesses are repeated while reorder_access is identical, |
411 | * never matches the new access, because !(type & KCSAN_ACCESS_SCOPED). |
412 | */ |
413 | return reorder_access->ptr == ptr && reorder_access->size == size && |
414 | reorder_access->type == type && reorder_access->ip == ip; |
415 | } |
416 | |
417 | static inline void |
418 | set_reorder_access(struct kcsan_ctx *ctx, const volatile void *ptr, size_t size, |
419 | int type, unsigned long ip) |
420 | { |
421 | struct kcsan_scoped_access *reorder_access = get_reorder_access(ctx); |
422 | |
423 | if (!reorder_access || !kcsan_weak_memory) |
424 | return; |
425 | |
426 | /* |
427 | * To avoid nested interrupts or scheduler (which share kcsan_ctx) |
428 | * reading an inconsistent reorder_access, ensure that the below has |
429 | * exclusive access to reorder_access by disallowing concurrent use. |
430 | */ |
431 | ctx->disable_scoped++; |
432 | barrier(); |
433 | reorder_access->ptr = ptr; |
434 | reorder_access->size = size; |
435 | reorder_access->type = type | KCSAN_ACCESS_SCOPED; |
436 | reorder_access->ip = ip; |
437 | reorder_access->stack_depth = get_kcsan_stack_depth(); |
438 | barrier(); |
439 | ctx->disable_scoped--; |
440 | } |
441 | |
442 | /* |
443 | * Pull everything together: check_access() below contains the performance |
444 | * critical operations; the fast-path (including check_access) functions should |
445 | * all be inlinable by the instrumentation functions. |
446 | * |
447 | * The slow-path (kcsan_found_watchpoint, kcsan_setup_watchpoint) are |
448 | * non-inlinable -- note that, we prefix these with "kcsan_" to ensure they can |
449 | * be filtered from the stacktrace, as well as give them unique names for the |
450 | * UACCESS whitelist of objtool. Each function uses user_access_save/restore(), |
451 | * since they do not access any user memory, but instrumentation is still |
452 | * emitted in UACCESS regions. |
453 | */ |
454 | |
455 | static noinline void kcsan_found_watchpoint(const volatile void *ptr, |
456 | size_t size, |
457 | int type, |
458 | unsigned long ip, |
459 | atomic_long_t *watchpoint, |
460 | long encoded_watchpoint) |
461 | { |
462 | const bool is_assert = (type & KCSAN_ACCESS_ASSERT) != 0; |
463 | struct kcsan_ctx *ctx = get_ctx(); |
464 | unsigned long flags; |
465 | bool consumed; |
466 | |
467 | /* |
468 | * We know a watchpoint exists. Let's try to keep the race-window |
469 | * between here and finally consuming the watchpoint below as small as |
470 | * possible -- avoid unneccessarily complex code until consumed. |
471 | */ |
472 | |
473 | if (!kcsan_is_enabled(ctx)) |
474 | return; |
475 | |
476 | /* |
477 | * The access_mask check relies on value-change comparison. To avoid |
478 | * reporting a race where e.g. the writer set up the watchpoint, but the |
479 | * reader has access_mask!=0, we have to ignore the found watchpoint. |
480 | * |
481 | * reorder_access is never created from an access with access_mask set. |
482 | */ |
483 | if (ctx->access_mask && !find_reorder_access(ctx, ptr, size, type, ip)) |
484 | return; |
485 | |
486 | /* |
487 | * If the other thread does not want to ignore the access, and there was |
488 | * a value change as a result of this thread's operation, we will still |
489 | * generate a report of unknown origin. |
490 | * |
491 | * Use CONFIG_KCSAN_REPORT_RACE_UNKNOWN_ORIGIN=n to filter. |
492 | */ |
493 | if (!is_assert && kcsan_ignore_address(ptr)) |
494 | return; |
495 | |
496 | /* |
497 | * Consuming the watchpoint must be guarded by kcsan_is_enabled() to |
498 | * avoid erroneously triggering reports if the context is disabled. |
499 | */ |
500 | consumed = try_consume_watchpoint(watchpoint, encoded_watchpoint); |
501 | |
502 | /* keep this after try_consume_watchpoint */ |
503 | flags = user_access_save(); |
504 | |
505 | if (consumed) { |
506 | kcsan_save_irqtrace(current); |
507 | kcsan_report_set_info(ptr, size, access_type: type, ip, watchpoint_idx: watchpoint - watchpoints); |
508 | kcsan_restore_irqtrace(current); |
509 | } else { |
510 | /* |
511 | * The other thread may not print any diagnostics, as it has |
512 | * already removed the watchpoint, or another thread consumed |
513 | * the watchpoint before this thread. |
514 | */ |
515 | atomic_long_inc(v: &kcsan_counters[KCSAN_COUNTER_REPORT_RACES]); |
516 | } |
517 | |
518 | if (is_assert) |
519 | atomic_long_inc(v: &kcsan_counters[KCSAN_COUNTER_ASSERT_FAILURES]); |
520 | else |
521 | atomic_long_inc(v: &kcsan_counters[KCSAN_COUNTER_DATA_RACES]); |
522 | |
523 | user_access_restore(flags); |
524 | } |
525 | |
526 | static noinline void |
527 | kcsan_setup_watchpoint(const volatile void *ptr, size_t size, int type, unsigned long ip) |
528 | { |
529 | const bool is_write = (type & KCSAN_ACCESS_WRITE) != 0; |
530 | const bool is_assert = (type & KCSAN_ACCESS_ASSERT) != 0; |
531 | atomic_long_t *watchpoint; |
532 | u64 old, new, diff; |
533 | enum kcsan_value_change value_change = KCSAN_VALUE_CHANGE_MAYBE; |
534 | bool interrupt_watcher = kcsan_interrupt_watcher; |
535 | unsigned long ua_flags = user_access_save(); |
536 | struct kcsan_ctx *ctx = get_ctx(); |
537 | unsigned long access_mask = ctx->access_mask; |
538 | unsigned long irq_flags = 0; |
539 | bool is_reorder_access; |
540 | |
541 | /* |
542 | * Always reset kcsan_skip counter in slow-path to avoid underflow; see |
543 | * should_watch(). |
544 | */ |
545 | reset_kcsan_skip(); |
546 | |
547 | if (!kcsan_is_enabled(ctx)) |
548 | goto out; |
549 | |
550 | /* |
551 | * Check to-ignore addresses after kcsan_is_enabled(), as we may access |
552 | * memory that is not yet initialized during early boot. |
553 | */ |
554 | if (!is_assert && kcsan_ignore_address(ptr)) |
555 | goto out; |
556 | |
557 | if (!check_encodable(addr: (unsigned long)ptr, size)) { |
558 | atomic_long_inc(v: &kcsan_counters[KCSAN_COUNTER_UNENCODABLE_ACCESSES]); |
559 | goto out; |
560 | } |
561 | |
562 | /* |
563 | * The local CPU cannot observe reordering of its own accesses, and |
564 | * therefore we need to take care of 2 cases to avoid false positives: |
565 | * |
566 | * 1. Races of the reordered access with interrupts. To avoid, if |
567 | * the current access is reorder_access, disable interrupts. |
568 | * 2. Avoid races of scoped accesses from nested interrupts (below). |
569 | */ |
570 | is_reorder_access = find_reorder_access(ctx, ptr, size, type, ip); |
571 | if (is_reorder_access) |
572 | interrupt_watcher = false; |
573 | /* |
574 | * Avoid races of scoped accesses from nested interrupts (or scheduler). |
575 | * Assume setting up a watchpoint for a non-scoped (normal) access that |
576 | * also conflicts with a current scoped access. In a nested interrupt, |
577 | * which shares the context, it would check a conflicting scoped access. |
578 | * To avoid, disable scoped access checking. |
579 | */ |
580 | ctx->disable_scoped++; |
581 | |
582 | /* |
583 | * Save and restore the IRQ state trace touched by KCSAN, since KCSAN's |
584 | * runtime is entered for every memory access, and potentially useful |
585 | * information is lost if dirtied by KCSAN. |
586 | */ |
587 | kcsan_save_irqtrace(current); |
588 | if (!interrupt_watcher) |
589 | local_irq_save(irq_flags); |
590 | |
591 | watchpoint = insert_watchpoint(addr: (unsigned long)ptr, size, is_write); |
592 | if (watchpoint == NULL) { |
593 | /* |
594 | * Out of capacity: the size of 'watchpoints', and the frequency |
595 | * with which should_watch() returns true should be tweaked so |
596 | * that this case happens very rarely. |
597 | */ |
598 | atomic_long_inc(v: &kcsan_counters[KCSAN_COUNTER_NO_CAPACITY]); |
599 | goto out_unlock; |
600 | } |
601 | |
602 | atomic_long_inc(v: &kcsan_counters[KCSAN_COUNTER_SETUP_WATCHPOINTS]); |
603 | atomic_long_inc(v: &kcsan_counters[KCSAN_COUNTER_USED_WATCHPOINTS]); |
604 | |
605 | /* |
606 | * Read the current value, to later check and infer a race if the data |
607 | * was modified via a non-instrumented access, e.g. from a device. |
608 | */ |
609 | old = is_reorder_access ? 0 : read_instrumented_memory(ptr, size); |
610 | |
611 | /* |
612 | * Delay this thread, to increase probability of observing a racy |
613 | * conflicting access. |
614 | */ |
615 | delay_access(type); |
616 | |
617 | /* |
618 | * Re-read value, and check if it is as expected; if not, we infer a |
619 | * racy access. |
620 | */ |
621 | if (!is_reorder_access) { |
622 | new = read_instrumented_memory(ptr, size); |
623 | } else { |
624 | /* |
625 | * Reordered accesses cannot be used for value change detection, |
626 | * because the memory location may no longer be accessible and |
627 | * could result in a fault. |
628 | */ |
629 | new = 0; |
630 | access_mask = 0; |
631 | } |
632 | |
633 | diff = old ^ new; |
634 | if (access_mask) |
635 | diff &= access_mask; |
636 | |
637 | /* |
638 | * Check if we observed a value change. |
639 | * |
640 | * Also check if the data race should be ignored (the rules depend on |
641 | * non-zero diff); if it is to be ignored, the below rules for |
642 | * KCSAN_VALUE_CHANGE_MAYBE apply. |
643 | */ |
644 | if (diff && !kcsan_ignore_data_race(size, type, old, new, diff)) |
645 | value_change = KCSAN_VALUE_CHANGE_TRUE; |
646 | |
647 | /* Check if this access raced with another. */ |
648 | if (!consume_watchpoint(watchpoint)) { |
649 | /* |
650 | * Depending on the access type, map a value_change of MAYBE to |
651 | * TRUE (always report) or FALSE (never report). |
652 | */ |
653 | if (value_change == KCSAN_VALUE_CHANGE_MAYBE) { |
654 | if (access_mask != 0) { |
655 | /* |
656 | * For access with access_mask, we require a |
657 | * value-change, as it is likely that races on |
658 | * ~access_mask bits are expected. |
659 | */ |
660 | value_change = KCSAN_VALUE_CHANGE_FALSE; |
661 | } else if (size > 8 || is_assert) { |
662 | /* Always assume a value-change. */ |
663 | value_change = KCSAN_VALUE_CHANGE_TRUE; |
664 | } |
665 | } |
666 | |
667 | /* |
668 | * No need to increment 'data_races' counter, as the racing |
669 | * thread already did. |
670 | * |
671 | * Count 'assert_failures' for each failed ASSERT access, |
672 | * therefore both this thread and the racing thread may |
673 | * increment this counter. |
674 | */ |
675 | if (is_assert && value_change == KCSAN_VALUE_CHANGE_TRUE) |
676 | atomic_long_inc(v: &kcsan_counters[KCSAN_COUNTER_ASSERT_FAILURES]); |
677 | |
678 | kcsan_report_known_origin(ptr, size, access_type: type, ip, |
679 | value_change, watchpoint_idx: watchpoint - watchpoints, |
680 | old, new, mask: access_mask); |
681 | } else if (value_change == KCSAN_VALUE_CHANGE_TRUE) { |
682 | /* Inferring a race, since the value should not have changed. */ |
683 | |
684 | atomic_long_inc(v: &kcsan_counters[KCSAN_COUNTER_RACES_UNKNOWN_ORIGIN]); |
685 | if (is_assert) |
686 | atomic_long_inc(v: &kcsan_counters[KCSAN_COUNTER_ASSERT_FAILURES]); |
687 | |
688 | if (IS_ENABLED(CONFIG_KCSAN_REPORT_RACE_UNKNOWN_ORIGIN) || is_assert) { |
689 | kcsan_report_unknown_origin(ptr, size, access_type: type, ip, |
690 | old, new, mask: access_mask); |
691 | } |
692 | } |
693 | |
694 | /* |
695 | * Remove watchpoint; must be after reporting, since the slot may be |
696 | * reused after this point. |
697 | */ |
698 | remove_watchpoint(watchpoint); |
699 | atomic_long_dec(v: &kcsan_counters[KCSAN_COUNTER_USED_WATCHPOINTS]); |
700 | |
701 | out_unlock: |
702 | if (!interrupt_watcher) |
703 | local_irq_restore(irq_flags); |
704 | kcsan_restore_irqtrace(current); |
705 | ctx->disable_scoped--; |
706 | |
707 | /* |
708 | * Reordered accesses cannot be used for value change detection, |
709 | * therefore never consider for reordering if access_mask is set. |
710 | * ASSERT_EXCLUSIVE are not real accesses, ignore them as well. |
711 | */ |
712 | if (!access_mask && !is_assert) |
713 | set_reorder_access(ctx, ptr, size, type, ip); |
714 | out: |
715 | user_access_restore(ua_flags); |
716 | } |
717 | |
718 | static __always_inline void |
719 | check_access(const volatile void *ptr, size_t size, int type, unsigned long ip) |
720 | { |
721 | atomic_long_t *watchpoint; |
722 | long encoded_watchpoint; |
723 | |
724 | /* |
725 | * Do nothing for 0 sized check; this comparison will be optimized out |
726 | * for constant sized instrumentation (__tsan_{read,write}N). |
727 | */ |
728 | if (unlikely(size == 0)) |
729 | return; |
730 | |
731 | again: |
732 | /* |
733 | * Avoid user_access_save in fast-path: find_watchpoint is safe without |
734 | * user_access_save, as the address that ptr points to is only used to |
735 | * check if a watchpoint exists; ptr is never dereferenced. |
736 | */ |
737 | watchpoint = find_watchpoint(addr: (unsigned long)ptr, size, |
738 | expect_write: !(type & KCSAN_ACCESS_WRITE), |
739 | encoded_watchpoint: &encoded_watchpoint); |
740 | /* |
741 | * It is safe to check kcsan_is_enabled() after find_watchpoint in the |
742 | * slow-path, as long as no state changes that cause a race to be |
743 | * detected and reported have occurred until kcsan_is_enabled() is |
744 | * checked. |
745 | */ |
746 | |
747 | if (unlikely(watchpoint != NULL)) |
748 | kcsan_found_watchpoint(ptr, size, type, ip, watchpoint, encoded_watchpoint); |
749 | else { |
750 | struct kcsan_ctx *ctx = get_ctx(); /* Call only once in fast-path. */ |
751 | |
752 | if (unlikely(should_watch(ctx, ptr, size, type))) { |
753 | kcsan_setup_watchpoint(ptr, size, type, ip); |
754 | return; |
755 | } |
756 | |
757 | if (!(type & KCSAN_ACCESS_SCOPED)) { |
758 | struct kcsan_scoped_access *reorder_access = get_reorder_access(ctx); |
759 | |
760 | if (reorder_access) { |
761 | /* |
762 | * reorder_access check: simulates reordering of |
763 | * the access after subsequent operations. |
764 | */ |
765 | ptr = reorder_access->ptr; |
766 | type = reorder_access->type; |
767 | ip = reorder_access->ip; |
768 | /* |
769 | * Upon a nested interrupt, this context's |
770 | * reorder_access can be modified (shared ctx). |
771 | * We know that upon return, reorder_access is |
772 | * always invalidated by setting size to 0 via |
773 | * __tsan_func_exit(). Therefore we must read |
774 | * and check size after the other fields. |
775 | */ |
776 | barrier(); |
777 | size = READ_ONCE(reorder_access->size); |
778 | if (size) |
779 | goto again; |
780 | } |
781 | } |
782 | |
783 | /* |
784 | * Always checked last, right before returning from runtime; |
785 | * if reorder_access is valid, checked after it was checked. |
786 | */ |
787 | if (unlikely(ctx->scoped_accesses.prev)) |
788 | kcsan_check_scoped_accesses(); |
789 | } |
790 | } |
791 | |
792 | /* === Public interface ===================================================== */ |
793 | |
794 | void __init kcsan_init(void) |
795 | { |
796 | int cpu; |
797 | |
798 | BUG_ON(!in_task()); |
799 | |
800 | for_each_possible_cpu(cpu) |
801 | per_cpu(kcsan_rand_state, cpu) = (u32)get_cycles(); |
802 | |
803 | /* |
804 | * We are in the init task, and no other tasks should be running; |
805 | * WRITE_ONCE without memory barrier is sufficient. |
806 | */ |
807 | if (kcsan_early_enable) { |
808 | pr_info("enabled early\n" ); |
809 | WRITE_ONCE(kcsan_enabled, true); |
810 | } |
811 | |
812 | if (IS_ENABLED(CONFIG_KCSAN_REPORT_VALUE_CHANGE_ONLY) || |
813 | IS_ENABLED(CONFIG_KCSAN_ASSUME_PLAIN_WRITES_ATOMIC) || |
814 | IS_ENABLED(CONFIG_KCSAN_PERMISSIVE) || |
815 | IS_ENABLED(CONFIG_KCSAN_IGNORE_ATOMICS)) { |
816 | pr_warn("non-strict mode configured - use CONFIG_KCSAN_STRICT=y to see all data races\n" ); |
817 | } else { |
818 | pr_info("strict mode configured\n" ); |
819 | } |
820 | } |
821 | |
822 | /* === Exported interface =================================================== */ |
823 | |
824 | void kcsan_disable_current(void) |
825 | { |
826 | ++get_ctx()->disable_count; |
827 | } |
828 | EXPORT_SYMBOL(kcsan_disable_current); |
829 | |
830 | void kcsan_enable_current(void) |
831 | { |
832 | if (get_ctx()->disable_count-- == 0) { |
833 | /* |
834 | * Warn if kcsan_enable_current() calls are unbalanced with |
835 | * kcsan_disable_current() calls, which causes disable_count to |
836 | * become negative and should not happen. |
837 | */ |
838 | kcsan_disable_current(); /* restore to 0, KCSAN still enabled */ |
839 | kcsan_disable_current(); /* disable to generate warning */ |
840 | WARN(1, "Unbalanced %s()" , __func__); |
841 | kcsan_enable_current(); |
842 | } |
843 | } |
844 | EXPORT_SYMBOL(kcsan_enable_current); |
845 | |
846 | void kcsan_enable_current_nowarn(void) |
847 | { |
848 | if (get_ctx()->disable_count-- == 0) |
849 | kcsan_disable_current(); |
850 | } |
851 | EXPORT_SYMBOL(kcsan_enable_current_nowarn); |
852 | |
853 | void kcsan_nestable_atomic_begin(void) |
854 | { |
855 | /* |
856 | * Do *not* check and warn if we are in a flat atomic region: nestable |
857 | * and flat atomic regions are independent from each other. |
858 | * See include/linux/kcsan.h: struct kcsan_ctx comments for more |
859 | * comments. |
860 | */ |
861 | |
862 | ++get_ctx()->atomic_nest_count; |
863 | } |
864 | EXPORT_SYMBOL(kcsan_nestable_atomic_begin); |
865 | |
866 | void kcsan_nestable_atomic_end(void) |
867 | { |
868 | if (get_ctx()->atomic_nest_count-- == 0) { |
869 | /* |
870 | * Warn if kcsan_nestable_atomic_end() calls are unbalanced with |
871 | * kcsan_nestable_atomic_begin() calls, which causes |
872 | * atomic_nest_count to become negative and should not happen. |
873 | */ |
874 | kcsan_nestable_atomic_begin(); /* restore to 0 */ |
875 | kcsan_disable_current(); /* disable to generate warning */ |
876 | WARN(1, "Unbalanced %s()" , __func__); |
877 | kcsan_enable_current(); |
878 | } |
879 | } |
880 | EXPORT_SYMBOL(kcsan_nestable_atomic_end); |
881 | |
882 | void kcsan_flat_atomic_begin(void) |
883 | { |
884 | get_ctx()->in_flat_atomic = true; |
885 | } |
886 | EXPORT_SYMBOL(kcsan_flat_atomic_begin); |
887 | |
888 | void kcsan_flat_atomic_end(void) |
889 | { |
890 | get_ctx()->in_flat_atomic = false; |
891 | } |
892 | EXPORT_SYMBOL(kcsan_flat_atomic_end); |
893 | |
894 | void kcsan_atomic_next(int n) |
895 | { |
896 | get_ctx()->atomic_next = n; |
897 | } |
898 | EXPORT_SYMBOL(kcsan_atomic_next); |
899 | |
900 | void kcsan_set_access_mask(unsigned long mask) |
901 | { |
902 | get_ctx()->access_mask = mask; |
903 | } |
904 | EXPORT_SYMBOL(kcsan_set_access_mask); |
905 | |
906 | struct kcsan_scoped_access * |
907 | kcsan_begin_scoped_access(const volatile void *ptr, size_t size, int type, |
908 | struct kcsan_scoped_access *sa) |
909 | { |
910 | struct kcsan_ctx *ctx = get_ctx(); |
911 | |
912 | check_access(ptr, size, type, _RET_IP_); |
913 | |
914 | ctx->disable_count++; /* Disable KCSAN, in case list debugging is on. */ |
915 | |
916 | INIT_LIST_HEAD(list: &sa->list); |
917 | sa->ptr = ptr; |
918 | sa->size = size; |
919 | sa->type = type; |
920 | sa->ip = _RET_IP_; |
921 | |
922 | if (!ctx->scoped_accesses.prev) /* Lazy initialize list head. */ |
923 | INIT_LIST_HEAD(list: &ctx->scoped_accesses); |
924 | list_add(new: &sa->list, head: &ctx->scoped_accesses); |
925 | |
926 | ctx->disable_count--; |
927 | return sa; |
928 | } |
929 | EXPORT_SYMBOL(kcsan_begin_scoped_access); |
930 | |
931 | void kcsan_end_scoped_access(struct kcsan_scoped_access *sa) |
932 | { |
933 | struct kcsan_ctx *ctx = get_ctx(); |
934 | |
935 | if (WARN(!ctx->scoped_accesses.prev, "Unbalanced %s()?" , __func__)) |
936 | return; |
937 | |
938 | ctx->disable_count++; /* Disable KCSAN, in case list debugging is on. */ |
939 | |
940 | list_del(entry: &sa->list); |
941 | if (list_empty(head: &ctx->scoped_accesses)) |
942 | /* |
943 | * Ensure we do not enter kcsan_check_scoped_accesses() |
944 | * slow-path if unnecessary, and avoids requiring list_empty() |
945 | * in the fast-path (to avoid a READ_ONCE() and potential |
946 | * uaccess warning). |
947 | */ |
948 | ctx->scoped_accesses.prev = NULL; |
949 | |
950 | ctx->disable_count--; |
951 | |
952 | check_access(ptr: sa->ptr, size: sa->size, type: sa->type, ip: sa->ip); |
953 | } |
954 | EXPORT_SYMBOL(kcsan_end_scoped_access); |
955 | |
956 | void __kcsan_check_access(const volatile void *ptr, size_t size, int type) |
957 | { |
958 | check_access(ptr, size, type, _RET_IP_); |
959 | } |
960 | EXPORT_SYMBOL(__kcsan_check_access); |
961 | |
962 | #define DEFINE_MEMORY_BARRIER(name, order_before_cond) \ |
963 | void __kcsan_##name(void) \ |
964 | { \ |
965 | struct kcsan_scoped_access *sa = get_reorder_access(get_ctx()); \ |
966 | if (!sa) \ |
967 | return; \ |
968 | if (order_before_cond) \ |
969 | sa->size = 0; \ |
970 | } \ |
971 | EXPORT_SYMBOL(__kcsan_##name) |
972 | |
973 | DEFINE_MEMORY_BARRIER(mb, true); |
974 | DEFINE_MEMORY_BARRIER(wmb, sa->type & (KCSAN_ACCESS_WRITE | KCSAN_ACCESS_COMPOUND)); |
975 | DEFINE_MEMORY_BARRIER(rmb, !(sa->type & KCSAN_ACCESS_WRITE) || (sa->type & KCSAN_ACCESS_COMPOUND)); |
976 | DEFINE_MEMORY_BARRIER(release, true); |
977 | |
978 | /* |
979 | * KCSAN uses the same instrumentation that is emitted by supported compilers |
980 | * for ThreadSanitizer (TSAN). |
981 | * |
982 | * When enabled, the compiler emits instrumentation calls (the functions |
983 | * prefixed with "__tsan" below) for all loads and stores that it generated; |
984 | * inline asm is not instrumented. |
985 | * |
986 | * Note that, not all supported compiler versions distinguish aligned/unaligned |
987 | * accesses, but e.g. recent versions of Clang do. We simply alias the unaligned |
988 | * version to the generic version, which can handle both. |
989 | */ |
990 | |
991 | #define DEFINE_TSAN_READ_WRITE(size) \ |
992 | void __tsan_read##size(void *ptr); \ |
993 | void __tsan_read##size(void *ptr) \ |
994 | { \ |
995 | check_access(ptr, size, 0, _RET_IP_); \ |
996 | } \ |
997 | EXPORT_SYMBOL(__tsan_read##size); \ |
998 | void __tsan_unaligned_read##size(void *ptr) \ |
999 | __alias(__tsan_read##size); \ |
1000 | EXPORT_SYMBOL(__tsan_unaligned_read##size); \ |
1001 | void __tsan_write##size(void *ptr); \ |
1002 | void __tsan_write##size(void *ptr) \ |
1003 | { \ |
1004 | check_access(ptr, size, KCSAN_ACCESS_WRITE, _RET_IP_); \ |
1005 | } \ |
1006 | EXPORT_SYMBOL(__tsan_write##size); \ |
1007 | void __tsan_unaligned_write##size(void *ptr) \ |
1008 | __alias(__tsan_write##size); \ |
1009 | EXPORT_SYMBOL(__tsan_unaligned_write##size); \ |
1010 | void __tsan_read_write##size(void *ptr); \ |
1011 | void __tsan_read_write##size(void *ptr) \ |
1012 | { \ |
1013 | check_access(ptr, size, \ |
1014 | KCSAN_ACCESS_COMPOUND | KCSAN_ACCESS_WRITE, \ |
1015 | _RET_IP_); \ |
1016 | } \ |
1017 | EXPORT_SYMBOL(__tsan_read_write##size); \ |
1018 | void __tsan_unaligned_read_write##size(void *ptr) \ |
1019 | __alias(__tsan_read_write##size); \ |
1020 | EXPORT_SYMBOL(__tsan_unaligned_read_write##size) |
1021 | |
1022 | DEFINE_TSAN_READ_WRITE(1); |
1023 | DEFINE_TSAN_READ_WRITE(2); |
1024 | DEFINE_TSAN_READ_WRITE(4); |
1025 | DEFINE_TSAN_READ_WRITE(8); |
1026 | DEFINE_TSAN_READ_WRITE(16); |
1027 | |
1028 | void __tsan_read_range(void *ptr, size_t size); |
1029 | void __tsan_read_range(void *ptr, size_t size) |
1030 | { |
1031 | check_access(ptr, size, type: 0, _RET_IP_); |
1032 | } |
1033 | EXPORT_SYMBOL(__tsan_read_range); |
1034 | |
1035 | void __tsan_write_range(void *ptr, size_t size); |
1036 | void __tsan_write_range(void *ptr, size_t size) |
1037 | { |
1038 | check_access(ptr, size, KCSAN_ACCESS_WRITE, _RET_IP_); |
1039 | } |
1040 | EXPORT_SYMBOL(__tsan_write_range); |
1041 | |
1042 | /* |
1043 | * Use of explicit volatile is generally disallowed [1], however, volatile is |
1044 | * still used in various concurrent context, whether in low-level |
1045 | * synchronization primitives or for legacy reasons. |
1046 | * [1] https://lwn.net/Articles/233479/ |
1047 | * |
1048 | * We only consider volatile accesses atomic if they are aligned and would pass |
1049 | * the size-check of compiletime_assert_rwonce_type(). |
1050 | */ |
1051 | #define DEFINE_TSAN_VOLATILE_READ_WRITE(size) \ |
1052 | void __tsan_volatile_read##size(void *ptr); \ |
1053 | void __tsan_volatile_read##size(void *ptr) \ |
1054 | { \ |
1055 | const bool is_atomic = size <= sizeof(long long) && \ |
1056 | IS_ALIGNED((unsigned long)ptr, size); \ |
1057 | if (IS_ENABLED(CONFIG_KCSAN_IGNORE_ATOMICS) && is_atomic) \ |
1058 | return; \ |
1059 | check_access(ptr, size, is_atomic ? KCSAN_ACCESS_ATOMIC : 0, \ |
1060 | _RET_IP_); \ |
1061 | } \ |
1062 | EXPORT_SYMBOL(__tsan_volatile_read##size); \ |
1063 | void __tsan_unaligned_volatile_read##size(void *ptr) \ |
1064 | __alias(__tsan_volatile_read##size); \ |
1065 | EXPORT_SYMBOL(__tsan_unaligned_volatile_read##size); \ |
1066 | void __tsan_volatile_write##size(void *ptr); \ |
1067 | void __tsan_volatile_write##size(void *ptr) \ |
1068 | { \ |
1069 | const bool is_atomic = size <= sizeof(long long) && \ |
1070 | IS_ALIGNED((unsigned long)ptr, size); \ |
1071 | if (IS_ENABLED(CONFIG_KCSAN_IGNORE_ATOMICS) && is_atomic) \ |
1072 | return; \ |
1073 | check_access(ptr, size, \ |
1074 | KCSAN_ACCESS_WRITE | \ |
1075 | (is_atomic ? KCSAN_ACCESS_ATOMIC : 0), \ |
1076 | _RET_IP_); \ |
1077 | } \ |
1078 | EXPORT_SYMBOL(__tsan_volatile_write##size); \ |
1079 | void __tsan_unaligned_volatile_write##size(void *ptr) \ |
1080 | __alias(__tsan_volatile_write##size); \ |
1081 | EXPORT_SYMBOL(__tsan_unaligned_volatile_write##size) |
1082 | |
1083 | DEFINE_TSAN_VOLATILE_READ_WRITE(1); |
1084 | DEFINE_TSAN_VOLATILE_READ_WRITE(2); |
1085 | DEFINE_TSAN_VOLATILE_READ_WRITE(4); |
1086 | DEFINE_TSAN_VOLATILE_READ_WRITE(8); |
1087 | DEFINE_TSAN_VOLATILE_READ_WRITE(16); |
1088 | |
1089 | /* |
1090 | * Function entry and exit are used to determine the validty of reorder_access. |
1091 | * Reordering of the access ends at the end of the function scope where the |
1092 | * access happened. This is done for two reasons: |
1093 | * |
1094 | * 1. Artificially limits the scope where missing barriers are detected. |
1095 | * This minimizes false positives due to uninstrumented functions that |
1096 | * contain the required barriers but were missed. |
1097 | * |
1098 | * 2. Simplifies generating the stack trace of the access. |
1099 | */ |
1100 | void __tsan_func_entry(void *call_pc); |
1101 | noinline void __tsan_func_entry(void *call_pc) |
1102 | { |
1103 | if (!IS_ENABLED(CONFIG_KCSAN_WEAK_MEMORY)) |
1104 | return; |
1105 | |
1106 | add_kcsan_stack_depth(val: 1); |
1107 | } |
1108 | EXPORT_SYMBOL(__tsan_func_entry); |
1109 | |
1110 | void __tsan_func_exit(void); |
1111 | noinline void __tsan_func_exit(void) |
1112 | { |
1113 | struct kcsan_scoped_access *reorder_access; |
1114 | |
1115 | if (!IS_ENABLED(CONFIG_KCSAN_WEAK_MEMORY)) |
1116 | return; |
1117 | |
1118 | reorder_access = get_reorder_access(ctx: get_ctx()); |
1119 | if (!reorder_access) |
1120 | goto out; |
1121 | |
1122 | if (get_kcsan_stack_depth() <= reorder_access->stack_depth) { |
1123 | /* |
1124 | * Access check to catch cases where write without a barrier |
1125 | * (supposed release) was last access in function: because |
1126 | * instrumentation is inserted before the real access, a data |
1127 | * race due to the write giving up a c-s would only be caught if |
1128 | * we do the conflicting access after. |
1129 | */ |
1130 | check_access(ptr: reorder_access->ptr, size: reorder_access->size, |
1131 | type: reorder_access->type, ip: reorder_access->ip); |
1132 | reorder_access->size = 0; |
1133 | reorder_access->stack_depth = INT_MIN; |
1134 | } |
1135 | out: |
1136 | add_kcsan_stack_depth(val: -1); |
1137 | } |
1138 | EXPORT_SYMBOL(__tsan_func_exit); |
1139 | |
1140 | void __tsan_init(void); |
1141 | void __tsan_init(void) |
1142 | { |
1143 | } |
1144 | EXPORT_SYMBOL(__tsan_init); |
1145 | |
1146 | /* |
1147 | * Instrumentation for atomic builtins (__atomic_*, __sync_*). |
1148 | * |
1149 | * Normal kernel code _should not_ be using them directly, but some |
1150 | * architectures may implement some or all atomics using the compilers' |
1151 | * builtins. |
1152 | * |
1153 | * Note: If an architecture decides to fully implement atomics using the |
1154 | * builtins, because they are implicitly instrumented by KCSAN (and KASAN, |
1155 | * etc.), implementing the ARCH_ATOMIC interface (to get instrumentation via |
1156 | * atomic-instrumented) is no longer necessary. |
1157 | * |
1158 | * TSAN instrumentation replaces atomic accesses with calls to any of the below |
1159 | * functions, whose job is to also execute the operation itself. |
1160 | */ |
1161 | |
1162 | static __always_inline void kcsan_atomic_builtin_memorder(int memorder) |
1163 | { |
1164 | if (memorder == __ATOMIC_RELEASE || |
1165 | memorder == __ATOMIC_SEQ_CST || |
1166 | memorder == __ATOMIC_ACQ_REL) |
1167 | __kcsan_release(); |
1168 | } |
1169 | |
1170 | #define DEFINE_TSAN_ATOMIC_LOAD_STORE(bits) \ |
1171 | u##bits __tsan_atomic##bits##_load(const u##bits *ptr, int memorder); \ |
1172 | u##bits __tsan_atomic##bits##_load(const u##bits *ptr, int memorder) \ |
1173 | { \ |
1174 | kcsan_atomic_builtin_memorder(memorder); \ |
1175 | if (!IS_ENABLED(CONFIG_KCSAN_IGNORE_ATOMICS)) { \ |
1176 | check_access(ptr, bits / BITS_PER_BYTE, KCSAN_ACCESS_ATOMIC, _RET_IP_); \ |
1177 | } \ |
1178 | return __atomic_load_n(ptr, memorder); \ |
1179 | } \ |
1180 | EXPORT_SYMBOL(__tsan_atomic##bits##_load); \ |
1181 | void __tsan_atomic##bits##_store(u##bits *ptr, u##bits v, int memorder); \ |
1182 | void __tsan_atomic##bits##_store(u##bits *ptr, u##bits v, int memorder) \ |
1183 | { \ |
1184 | kcsan_atomic_builtin_memorder(memorder); \ |
1185 | if (!IS_ENABLED(CONFIG_KCSAN_IGNORE_ATOMICS)) { \ |
1186 | check_access(ptr, bits / BITS_PER_BYTE, \ |
1187 | KCSAN_ACCESS_WRITE | KCSAN_ACCESS_ATOMIC, _RET_IP_); \ |
1188 | } \ |
1189 | __atomic_store_n(ptr, v, memorder); \ |
1190 | } \ |
1191 | EXPORT_SYMBOL(__tsan_atomic##bits##_store) |
1192 | |
1193 | #define DEFINE_TSAN_ATOMIC_RMW(op, bits, suffix) \ |
1194 | u##bits __tsan_atomic##bits##_##op(u##bits *ptr, u##bits v, int memorder); \ |
1195 | u##bits __tsan_atomic##bits##_##op(u##bits *ptr, u##bits v, int memorder) \ |
1196 | { \ |
1197 | kcsan_atomic_builtin_memorder(memorder); \ |
1198 | if (!IS_ENABLED(CONFIG_KCSAN_IGNORE_ATOMICS)) { \ |
1199 | check_access(ptr, bits / BITS_PER_BYTE, \ |
1200 | KCSAN_ACCESS_COMPOUND | KCSAN_ACCESS_WRITE | \ |
1201 | KCSAN_ACCESS_ATOMIC, _RET_IP_); \ |
1202 | } \ |
1203 | return __atomic_##op##suffix(ptr, v, memorder); \ |
1204 | } \ |
1205 | EXPORT_SYMBOL(__tsan_atomic##bits##_##op) |
1206 | |
1207 | /* |
1208 | * Note: CAS operations are always classified as write, even in case they |
1209 | * fail. We cannot perform check_access() after a write, as it might lead to |
1210 | * false positives, in cases such as: |
1211 | * |
1212 | * T0: __atomic_compare_exchange_n(&p->flag, &old, 1, ...) |
1213 | * |
1214 | * T1: if (__atomic_load_n(&p->flag, ...)) { |
1215 | * modify *p; |
1216 | * p->flag = 0; |
1217 | * } |
1218 | * |
1219 | * The only downside is that, if there are 3 threads, with one CAS that |
1220 | * succeeds, another CAS that fails, and an unmarked racing operation, we may |
1221 | * point at the wrong CAS as the source of the race. However, if we assume that |
1222 | * all CAS can succeed in some other execution, the data race is still valid. |
1223 | */ |
1224 | #define DEFINE_TSAN_ATOMIC_CMPXCHG(bits, strength, weak) \ |
1225 | int __tsan_atomic##bits##_compare_exchange_##strength(u##bits *ptr, u##bits *exp, \ |
1226 | u##bits val, int mo, int fail_mo); \ |
1227 | int __tsan_atomic##bits##_compare_exchange_##strength(u##bits *ptr, u##bits *exp, \ |
1228 | u##bits val, int mo, int fail_mo) \ |
1229 | { \ |
1230 | kcsan_atomic_builtin_memorder(mo); \ |
1231 | if (!IS_ENABLED(CONFIG_KCSAN_IGNORE_ATOMICS)) { \ |
1232 | check_access(ptr, bits / BITS_PER_BYTE, \ |
1233 | KCSAN_ACCESS_COMPOUND | KCSAN_ACCESS_WRITE | \ |
1234 | KCSAN_ACCESS_ATOMIC, _RET_IP_); \ |
1235 | } \ |
1236 | return __atomic_compare_exchange_n(ptr, exp, val, weak, mo, fail_mo); \ |
1237 | } \ |
1238 | EXPORT_SYMBOL(__tsan_atomic##bits##_compare_exchange_##strength) |
1239 | |
1240 | #define DEFINE_TSAN_ATOMIC_CMPXCHG_VAL(bits) \ |
1241 | u##bits __tsan_atomic##bits##_compare_exchange_val(u##bits *ptr, u##bits exp, u##bits val, \ |
1242 | int mo, int fail_mo); \ |
1243 | u##bits __tsan_atomic##bits##_compare_exchange_val(u##bits *ptr, u##bits exp, u##bits val, \ |
1244 | int mo, int fail_mo) \ |
1245 | { \ |
1246 | kcsan_atomic_builtin_memorder(mo); \ |
1247 | if (!IS_ENABLED(CONFIG_KCSAN_IGNORE_ATOMICS)) { \ |
1248 | check_access(ptr, bits / BITS_PER_BYTE, \ |
1249 | KCSAN_ACCESS_COMPOUND | KCSAN_ACCESS_WRITE | \ |
1250 | KCSAN_ACCESS_ATOMIC, _RET_IP_); \ |
1251 | } \ |
1252 | __atomic_compare_exchange_n(ptr, &exp, val, 0, mo, fail_mo); \ |
1253 | return exp; \ |
1254 | } \ |
1255 | EXPORT_SYMBOL(__tsan_atomic##bits##_compare_exchange_val) |
1256 | |
1257 | #define DEFINE_TSAN_ATOMIC_OPS(bits) \ |
1258 | DEFINE_TSAN_ATOMIC_LOAD_STORE(bits); \ |
1259 | DEFINE_TSAN_ATOMIC_RMW(exchange, bits, _n); \ |
1260 | DEFINE_TSAN_ATOMIC_RMW(fetch_add, bits, ); \ |
1261 | DEFINE_TSAN_ATOMIC_RMW(fetch_sub, bits, ); \ |
1262 | DEFINE_TSAN_ATOMIC_RMW(fetch_and, bits, ); \ |
1263 | DEFINE_TSAN_ATOMIC_RMW(fetch_or, bits, ); \ |
1264 | DEFINE_TSAN_ATOMIC_RMW(fetch_xor, bits, ); \ |
1265 | DEFINE_TSAN_ATOMIC_RMW(fetch_nand, bits, ); \ |
1266 | DEFINE_TSAN_ATOMIC_CMPXCHG(bits, strong, 0); \ |
1267 | DEFINE_TSAN_ATOMIC_CMPXCHG(bits, weak, 1); \ |
1268 | DEFINE_TSAN_ATOMIC_CMPXCHG_VAL(bits) |
1269 | |
1270 | DEFINE_TSAN_ATOMIC_OPS(8); |
1271 | DEFINE_TSAN_ATOMIC_OPS(16); |
1272 | DEFINE_TSAN_ATOMIC_OPS(32); |
1273 | #ifdef CONFIG_64BIT |
1274 | DEFINE_TSAN_ATOMIC_OPS(64); |
1275 | #endif |
1276 | |
1277 | void __tsan_atomic_thread_fence(int memorder); |
1278 | void __tsan_atomic_thread_fence(int memorder) |
1279 | { |
1280 | kcsan_atomic_builtin_memorder(memorder); |
1281 | __atomic_thread_fence(memorder); |
1282 | } |
1283 | EXPORT_SYMBOL(__tsan_atomic_thread_fence); |
1284 | |
1285 | /* |
1286 | * In instrumented files, we emit instrumentation for barriers by mapping the |
1287 | * kernel barriers to an __atomic_signal_fence(), which is interpreted specially |
1288 | * and otherwise has no relation to a real __atomic_signal_fence(). No known |
1289 | * kernel code uses __atomic_signal_fence(). |
1290 | * |
1291 | * Since fsanitize=thread instrumentation handles __atomic_signal_fence(), which |
1292 | * are turned into calls to __tsan_atomic_signal_fence(), such instrumentation |
1293 | * can be disabled via the __no_kcsan function attribute (vs. an explicit call |
1294 | * which could not). When __no_kcsan is requested, __atomic_signal_fence() |
1295 | * generates no code. |
1296 | * |
1297 | * Note: The result of using __atomic_signal_fence() with KCSAN enabled is |
1298 | * potentially limiting the compiler's ability to reorder operations; however, |
1299 | * if barriers were instrumented with explicit calls (without LTO), the compiler |
1300 | * couldn't optimize much anyway. The result of a hypothetical architecture |
1301 | * using __atomic_signal_fence() in normal code would be KCSAN false negatives. |
1302 | */ |
1303 | void __tsan_atomic_signal_fence(int memorder); |
1304 | noinline void __tsan_atomic_signal_fence(int memorder) |
1305 | { |
1306 | switch (memorder) { |
1307 | case __KCSAN_BARRIER_TO_SIGNAL_FENCE_mb: |
1308 | __kcsan_mb(); |
1309 | break; |
1310 | case __KCSAN_BARRIER_TO_SIGNAL_FENCE_wmb: |
1311 | __kcsan_wmb(); |
1312 | break; |
1313 | case __KCSAN_BARRIER_TO_SIGNAL_FENCE_rmb: |
1314 | __kcsan_rmb(); |
1315 | break; |
1316 | case __KCSAN_BARRIER_TO_SIGNAL_FENCE_release: |
1317 | __kcsan_release(); |
1318 | break; |
1319 | default: |
1320 | break; |
1321 | } |
1322 | } |
1323 | EXPORT_SYMBOL(__tsan_atomic_signal_fence); |
1324 | |
1325 | #ifdef __HAVE_ARCH_MEMSET |
1326 | void *__tsan_memset(void *s, int c, size_t count); |
1327 | noinline void *__tsan_memset(void *s, int c, size_t count) |
1328 | { |
1329 | /* |
1330 | * Instead of not setting up watchpoints where accessed size is greater |
1331 | * than MAX_ENCODABLE_SIZE, truncate checked size to MAX_ENCODABLE_SIZE. |
1332 | */ |
1333 | size_t check_len = min_t(size_t, count, MAX_ENCODABLE_SIZE); |
1334 | |
1335 | check_access(ptr: s, size: check_len, KCSAN_ACCESS_WRITE, _RET_IP_); |
1336 | return memset(s, c, count); |
1337 | } |
1338 | #else |
1339 | void *__tsan_memset(void *s, int c, size_t count) __alias(memset); |
1340 | #endif |
1341 | EXPORT_SYMBOL(__tsan_memset); |
1342 | |
1343 | #ifdef __HAVE_ARCH_MEMMOVE |
1344 | void *__tsan_memmove(void *dst, const void *src, size_t len); |
1345 | noinline void *__tsan_memmove(void *dst, const void *src, size_t len) |
1346 | { |
1347 | size_t check_len = min_t(size_t, len, MAX_ENCODABLE_SIZE); |
1348 | |
1349 | check_access(ptr: dst, size: check_len, KCSAN_ACCESS_WRITE, _RET_IP_); |
1350 | check_access(ptr: src, size: check_len, type: 0, _RET_IP_); |
1351 | return memmove(dst, src, len); |
1352 | } |
1353 | #else |
1354 | void *__tsan_memmove(void *dst, const void *src, size_t len) __alias(memmove); |
1355 | #endif |
1356 | EXPORT_SYMBOL(__tsan_memmove); |
1357 | |
1358 | #ifdef __HAVE_ARCH_MEMCPY |
1359 | void *__tsan_memcpy(void *dst, const void *src, size_t len); |
1360 | noinline void *__tsan_memcpy(void *dst, const void *src, size_t len) |
1361 | { |
1362 | size_t check_len = min_t(size_t, len, MAX_ENCODABLE_SIZE); |
1363 | |
1364 | check_access(ptr: dst, size: check_len, KCSAN_ACCESS_WRITE, _RET_IP_); |
1365 | check_access(ptr: src, size: check_len, type: 0, _RET_IP_); |
1366 | return memcpy(dst, src, len); |
1367 | } |
1368 | #else |
1369 | void *__tsan_memcpy(void *dst, const void *src, size_t len) __alias(memcpy); |
1370 | #endif |
1371 | EXPORT_SYMBOL(__tsan_memcpy); |
1372 | |