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(watchpoint); 132 if (!decode_watchpoint(*encoded_watchpoint, &wp_addr_masked, 133 &wp_size, &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(wp_addr_masked, wp_size, addr_masked, 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(watchpoint, &expect_val, 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(watchpoint, &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(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(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(scoped_access->ptr, scoped_access->size, 224 scoped_access->type, 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(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(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 switch (size) { 341 case 1: return READ_ONCE(*(const u8 *)ptr); 342 case 2: return READ_ONCE(*(const u16 *)ptr); 343 case 4: return READ_ONCE(*(const u32 *)ptr); 344 case 8: return READ_ONCE(*(const u64 *)ptr); 345 default: return 0; /* Ignore; we do not diff the values. */ 346 } 347 } 348 349 void kcsan_save_irqtrace(struct task_struct *task) 350 { 351 #ifdef CONFIG_TRACE_IRQFLAGS 352 task->kcsan_save_irqtrace = task->irqtrace; 353 #endif 354 } 355 356 void kcsan_restore_irqtrace(struct task_struct *task) 357 { 358 #ifdef CONFIG_TRACE_IRQFLAGS 359 task->irqtrace = task->kcsan_save_irqtrace; 360 #endif 361 } 362 363 static __always_inline int get_kcsan_stack_depth(void) 364 { 365 #ifdef CONFIG_KCSAN_WEAK_MEMORY 366 return current->kcsan_stack_depth; 367 #else 368 BUILD_BUG(); 369 return 0; 370 #endif 371 } 372 373 static __always_inline void add_kcsan_stack_depth(int val) 374 { 375 #ifdef CONFIG_KCSAN_WEAK_MEMORY 376 current->kcsan_stack_depth += val; 377 #else 378 BUILD_BUG(); 379 #endif 380 } 381 382 static __always_inline struct kcsan_scoped_access *get_reorder_access(struct kcsan_ctx *ctx) 383 { 384 #ifdef CONFIG_KCSAN_WEAK_MEMORY 385 return ctx->disable_scoped ? NULL : &ctx->reorder_access; 386 #else 387 return NULL; 388 #endif 389 } 390 391 static __always_inline bool 392 find_reorder_access(struct kcsan_ctx *ctx, const volatile void *ptr, size_t size, 393 int type, unsigned long ip) 394 { 395 struct kcsan_scoped_access *reorder_access = get_reorder_access(ctx); 396 397 if (!reorder_access) 398 return false; 399 400 /* 401 * Note: If accesses are repeated while reorder_access is identical, 402 * never matches the new access, because !(type & KCSAN_ACCESS_SCOPED). 403 */ 404 return reorder_access->ptr == ptr && reorder_access->size == size && 405 reorder_access->type == type && reorder_access->ip == ip; 406 } 407 408 static inline void 409 set_reorder_access(struct kcsan_ctx *ctx, const volatile void *ptr, size_t size, 410 int type, unsigned long ip) 411 { 412 struct kcsan_scoped_access *reorder_access = get_reorder_access(ctx); 413 414 if (!reorder_access || !kcsan_weak_memory) 415 return; 416 417 /* 418 * To avoid nested interrupts or scheduler (which share kcsan_ctx) 419 * reading an inconsistent reorder_access, ensure that the below has 420 * exclusive access to reorder_access by disallowing concurrent use. 421 */ 422 ctx->disable_scoped++; 423 barrier(); 424 reorder_access->ptr = ptr; 425 reorder_access->size = size; 426 reorder_access->type = type | KCSAN_ACCESS_SCOPED; 427 reorder_access->ip = ip; 428 reorder_access->stack_depth = get_kcsan_stack_depth(); 429 barrier(); 430 ctx->disable_scoped--; 431 } 432 433 /* 434 * Pull everything together: check_access() below contains the performance 435 * critical operations; the fast-path (including check_access) functions should 436 * all be inlinable by the instrumentation functions. 437 * 438 * The slow-path (kcsan_found_watchpoint, kcsan_setup_watchpoint) are 439 * non-inlinable -- note that, we prefix these with "kcsan_" to ensure they can 440 * be filtered from the stacktrace, as well as give them unique names for the 441 * UACCESS whitelist of objtool. Each function uses user_access_save/restore(), 442 * since they do not access any user memory, but instrumentation is still 443 * emitted in UACCESS regions. 444 */ 445 446 static noinline void kcsan_found_watchpoint(const volatile void *ptr, 447 size_t size, 448 int type, 449 unsigned long ip, 450 atomic_long_t *watchpoint, 451 long encoded_watchpoint) 452 { 453 const bool is_assert = (type & KCSAN_ACCESS_ASSERT) != 0; 454 struct kcsan_ctx *ctx = get_ctx(); 455 unsigned long flags; 456 bool consumed; 457 458 /* 459 * We know a watchpoint exists. Let's try to keep the race-window 460 * between here and finally consuming the watchpoint below as small as 461 * possible -- avoid unneccessarily complex code until consumed. 462 */ 463 464 if (!kcsan_is_enabled(ctx)) 465 return; 466 467 /* 468 * The access_mask check relies on value-change comparison. To avoid 469 * reporting a race where e.g. the writer set up the watchpoint, but the 470 * reader has access_mask!=0, we have to ignore the found watchpoint. 471 * 472 * reorder_access is never created from an access with access_mask set. 473 */ 474 if (ctx->access_mask && !find_reorder_access(ctx, ptr, size, type, ip)) 475 return; 476 477 /* 478 * If the other thread does not want to ignore the access, and there was 479 * a value change as a result of this thread's operation, we will still 480 * generate a report of unknown origin. 481 * 482 * Use CONFIG_KCSAN_REPORT_RACE_UNKNOWN_ORIGIN=n to filter. 483 */ 484 if (!is_assert && kcsan_ignore_address(ptr)) 485 return; 486 487 /* 488 * Consuming the watchpoint must be guarded by kcsan_is_enabled() to 489 * avoid erroneously triggering reports if the context is disabled. 490 */ 491 consumed = try_consume_watchpoint(watchpoint, encoded_watchpoint); 492 493 /* keep this after try_consume_watchpoint */ 494 flags = user_access_save(); 495 496 if (consumed) { 497 kcsan_save_irqtrace(current); 498 kcsan_report_set_info(ptr, size, type, ip, watchpoint - watchpoints); 499 kcsan_restore_irqtrace(current); 500 } else { 501 /* 502 * The other thread may not print any diagnostics, as it has 503 * already removed the watchpoint, or another thread consumed 504 * the watchpoint before this thread. 505 */ 506 atomic_long_inc(&kcsan_counters[KCSAN_COUNTER_REPORT_RACES]); 507 } 508 509 if (is_assert) 510 atomic_long_inc(&kcsan_counters[KCSAN_COUNTER_ASSERT_FAILURES]); 511 else 512 atomic_long_inc(&kcsan_counters[KCSAN_COUNTER_DATA_RACES]); 513 514 user_access_restore(flags); 515 } 516 517 static noinline void 518 kcsan_setup_watchpoint(const volatile void *ptr, size_t size, int type, unsigned long ip) 519 { 520 const bool is_write = (type & KCSAN_ACCESS_WRITE) != 0; 521 const bool is_assert = (type & KCSAN_ACCESS_ASSERT) != 0; 522 atomic_long_t *watchpoint; 523 u64 old, new, diff; 524 enum kcsan_value_change value_change = KCSAN_VALUE_CHANGE_MAYBE; 525 bool interrupt_watcher = kcsan_interrupt_watcher; 526 unsigned long ua_flags = user_access_save(); 527 struct kcsan_ctx *ctx = get_ctx(); 528 unsigned long access_mask = ctx->access_mask; 529 unsigned long irq_flags = 0; 530 bool is_reorder_access; 531 532 /* 533 * Always reset kcsan_skip counter in slow-path to avoid underflow; see 534 * should_watch(). 535 */ 536 reset_kcsan_skip(); 537 538 if (!kcsan_is_enabled(ctx)) 539 goto out; 540 541 /* 542 * Check to-ignore addresses after kcsan_is_enabled(), as we may access 543 * memory that is not yet initialized during early boot. 544 */ 545 if (!is_assert && kcsan_ignore_address(ptr)) 546 goto out; 547 548 if (!check_encodable((unsigned long)ptr, size)) { 549 atomic_long_inc(&kcsan_counters[KCSAN_COUNTER_UNENCODABLE_ACCESSES]); 550 goto out; 551 } 552 553 /* 554 * The local CPU cannot observe reordering of its own accesses, and 555 * therefore we need to take care of 2 cases to avoid false positives: 556 * 557 * 1. Races of the reordered access with interrupts. To avoid, if 558 * the current access is reorder_access, disable interrupts. 559 * 2. Avoid races of scoped accesses from nested interrupts (below). 560 */ 561 is_reorder_access = find_reorder_access(ctx, ptr, size, type, ip); 562 if (is_reorder_access) 563 interrupt_watcher = false; 564 /* 565 * Avoid races of scoped accesses from nested interrupts (or scheduler). 566 * Assume setting up a watchpoint for a non-scoped (normal) access that 567 * also conflicts with a current scoped access. In a nested interrupt, 568 * which shares the context, it would check a conflicting scoped access. 569 * To avoid, disable scoped access checking. 570 */ 571 ctx->disable_scoped++; 572 573 /* 574 * Save and restore the IRQ state trace touched by KCSAN, since KCSAN's 575 * runtime is entered for every memory access, and potentially useful 576 * information is lost if dirtied by KCSAN. 577 */ 578 kcsan_save_irqtrace(current); 579 if (!interrupt_watcher) 580 local_irq_save(irq_flags); 581 582 watchpoint = insert_watchpoint((unsigned long)ptr, size, is_write); 583 if (watchpoint == NULL) { 584 /* 585 * Out of capacity: the size of 'watchpoints', and the frequency 586 * with which should_watch() returns true should be tweaked so 587 * that this case happens very rarely. 588 */ 589 atomic_long_inc(&kcsan_counters[KCSAN_COUNTER_NO_CAPACITY]); 590 goto out_unlock; 591 } 592 593 atomic_long_inc(&kcsan_counters[KCSAN_COUNTER_SETUP_WATCHPOINTS]); 594 atomic_long_inc(&kcsan_counters[KCSAN_COUNTER_USED_WATCHPOINTS]); 595 596 /* 597 * Read the current value, to later check and infer a race if the data 598 * was modified via a non-instrumented access, e.g. from a device. 599 */ 600 old = is_reorder_access ? 0 : read_instrumented_memory(ptr, size); 601 602 /* 603 * Delay this thread, to increase probability of observing a racy 604 * conflicting access. 605 */ 606 delay_access(type); 607 608 /* 609 * Re-read value, and check if it is as expected; if not, we infer a 610 * racy access. 611 */ 612 if (!is_reorder_access) { 613 new = read_instrumented_memory(ptr, size); 614 } else { 615 /* 616 * Reordered accesses cannot be used for value change detection, 617 * because the memory location may no longer be accessible and 618 * could result in a fault. 619 */ 620 new = 0; 621 access_mask = 0; 622 } 623 624 diff = old ^ new; 625 if (access_mask) 626 diff &= access_mask; 627 628 /* 629 * Check if we observed a value change. 630 * 631 * Also check if the data race should be ignored (the rules depend on 632 * non-zero diff); if it is to be ignored, the below rules for 633 * KCSAN_VALUE_CHANGE_MAYBE apply. 634 */ 635 if (diff && !kcsan_ignore_data_race(size, type, old, new, diff)) 636 value_change = KCSAN_VALUE_CHANGE_TRUE; 637 638 /* Check if this access raced with another. */ 639 if (!consume_watchpoint(watchpoint)) { 640 /* 641 * Depending on the access type, map a value_change of MAYBE to 642 * TRUE (always report) or FALSE (never report). 643 */ 644 if (value_change == KCSAN_VALUE_CHANGE_MAYBE) { 645 if (access_mask != 0) { 646 /* 647 * For access with access_mask, we require a 648 * value-change, as it is likely that races on 649 * ~access_mask bits are expected. 650 */ 651 value_change = KCSAN_VALUE_CHANGE_FALSE; 652 } else if (size > 8 || is_assert) { 653 /* Always assume a value-change. */ 654 value_change = KCSAN_VALUE_CHANGE_TRUE; 655 } 656 } 657 658 /* 659 * No need to increment 'data_races' counter, as the racing 660 * thread already did. 661 * 662 * Count 'assert_failures' for each failed ASSERT access, 663 * therefore both this thread and the racing thread may 664 * increment this counter. 665 */ 666 if (is_assert && value_change == KCSAN_VALUE_CHANGE_TRUE) 667 atomic_long_inc(&kcsan_counters[KCSAN_COUNTER_ASSERT_FAILURES]); 668 669 kcsan_report_known_origin(ptr, size, type, ip, 670 value_change, watchpoint - watchpoints, 671 old, new, access_mask); 672 } else if (value_change == KCSAN_VALUE_CHANGE_TRUE) { 673 /* Inferring a race, since the value should not have changed. */ 674 675 atomic_long_inc(&kcsan_counters[KCSAN_COUNTER_RACES_UNKNOWN_ORIGIN]); 676 if (is_assert) 677 atomic_long_inc(&kcsan_counters[KCSAN_COUNTER_ASSERT_FAILURES]); 678 679 if (IS_ENABLED(CONFIG_KCSAN_REPORT_RACE_UNKNOWN_ORIGIN) || is_assert) { 680 kcsan_report_unknown_origin(ptr, size, type, ip, 681 old, new, access_mask); 682 } 683 } 684 685 /* 686 * Remove watchpoint; must be after reporting, since the slot may be 687 * reused after this point. 688 */ 689 remove_watchpoint(watchpoint); 690 atomic_long_dec(&kcsan_counters[KCSAN_COUNTER_USED_WATCHPOINTS]); 691 692 out_unlock: 693 if (!interrupt_watcher) 694 local_irq_restore(irq_flags); 695 kcsan_restore_irqtrace(current); 696 ctx->disable_scoped--; 697 698 /* 699 * Reordered accesses cannot be used for value change detection, 700 * therefore never consider for reordering if access_mask is set. 701 * ASSERT_EXCLUSIVE are not real accesses, ignore them as well. 702 */ 703 if (!access_mask && !is_assert) 704 set_reorder_access(ctx, ptr, size, type, ip); 705 out: 706 user_access_restore(ua_flags); 707 } 708 709 static __always_inline void 710 check_access(const volatile void *ptr, size_t size, int type, unsigned long ip) 711 { 712 atomic_long_t *watchpoint; 713 long encoded_watchpoint; 714 715 /* 716 * Do nothing for 0 sized check; this comparison will be optimized out 717 * for constant sized instrumentation (__tsan_{read,write}N). 718 */ 719 if (unlikely(size == 0)) 720 return; 721 722 again: 723 /* 724 * Avoid user_access_save in fast-path: find_watchpoint is safe without 725 * user_access_save, as the address that ptr points to is only used to 726 * check if a watchpoint exists; ptr is never dereferenced. 727 */ 728 watchpoint = find_watchpoint((unsigned long)ptr, size, 729 !(type & KCSAN_ACCESS_WRITE), 730 &encoded_watchpoint); 731 /* 732 * It is safe to check kcsan_is_enabled() after find_watchpoint in the 733 * slow-path, as long as no state changes that cause a race to be 734 * detected and reported have occurred until kcsan_is_enabled() is 735 * checked. 736 */ 737 738 if (unlikely(watchpoint != NULL)) 739 kcsan_found_watchpoint(ptr, size, type, ip, watchpoint, encoded_watchpoint); 740 else { 741 struct kcsan_ctx *ctx = get_ctx(); /* Call only once in fast-path. */ 742 743 if (unlikely(should_watch(ctx, ptr, size, type))) { 744 kcsan_setup_watchpoint(ptr, size, type, ip); 745 return; 746 } 747 748 if (!(type & KCSAN_ACCESS_SCOPED)) { 749 struct kcsan_scoped_access *reorder_access = get_reorder_access(ctx); 750 751 if (reorder_access) { 752 /* 753 * reorder_access check: simulates reordering of 754 * the access after subsequent operations. 755 */ 756 ptr = reorder_access->ptr; 757 type = reorder_access->type; 758 ip = reorder_access->ip; 759 /* 760 * Upon a nested interrupt, this context's 761 * reorder_access can be modified (shared ctx). 762 * We know that upon return, reorder_access is 763 * always invalidated by setting size to 0 via 764 * __tsan_func_exit(). Therefore we must read 765 * and check size after the other fields. 766 */ 767 barrier(); 768 size = READ_ONCE(reorder_access->size); 769 if (size) 770 goto again; 771 } 772 } 773 774 /* 775 * Always checked last, right before returning from runtime; 776 * if reorder_access is valid, checked after it was checked. 777 */ 778 if (unlikely(ctx->scoped_accesses.prev)) 779 kcsan_check_scoped_accesses(); 780 } 781 } 782 783 /* === Public interface ===================================================== */ 784 785 void __init kcsan_init(void) 786 { 787 int cpu; 788 789 BUG_ON(!in_task()); 790 791 for_each_possible_cpu(cpu) 792 per_cpu(kcsan_rand_state, cpu) = (u32)get_cycles(); 793 794 /* 795 * We are in the init task, and no other tasks should be running; 796 * WRITE_ONCE without memory barrier is sufficient. 797 */ 798 if (kcsan_early_enable) { 799 pr_info("enabled early\n"); 800 WRITE_ONCE(kcsan_enabled, true); 801 } 802 803 if (IS_ENABLED(CONFIG_KCSAN_REPORT_VALUE_CHANGE_ONLY) || 804 IS_ENABLED(CONFIG_KCSAN_ASSUME_PLAIN_WRITES_ATOMIC) || 805 IS_ENABLED(CONFIG_KCSAN_PERMISSIVE) || 806 IS_ENABLED(CONFIG_KCSAN_IGNORE_ATOMICS)) { 807 pr_warn("non-strict mode configured - use CONFIG_KCSAN_STRICT=y to see all data races\n"); 808 } else { 809 pr_info("strict mode configured\n"); 810 } 811 } 812 813 /* === Exported interface =================================================== */ 814 815 void kcsan_disable_current(void) 816 { 817 ++get_ctx()->disable_count; 818 } 819 EXPORT_SYMBOL(kcsan_disable_current); 820 821 void kcsan_enable_current(void) 822 { 823 if (get_ctx()->disable_count-- == 0) { 824 /* 825 * Warn if kcsan_enable_current() calls are unbalanced with 826 * kcsan_disable_current() calls, which causes disable_count to 827 * become negative and should not happen. 828 */ 829 kcsan_disable_current(); /* restore to 0, KCSAN still enabled */ 830 kcsan_disable_current(); /* disable to generate warning */ 831 WARN(1, "Unbalanced %s()", __func__); 832 kcsan_enable_current(); 833 } 834 } 835 EXPORT_SYMBOL(kcsan_enable_current); 836 837 void kcsan_enable_current_nowarn(void) 838 { 839 if (get_ctx()->disable_count-- == 0) 840 kcsan_disable_current(); 841 } 842 EXPORT_SYMBOL(kcsan_enable_current_nowarn); 843 844 void kcsan_nestable_atomic_begin(void) 845 { 846 /* 847 * Do *not* check and warn if we are in a flat atomic region: nestable 848 * and flat atomic regions are independent from each other. 849 * See include/linux/kcsan.h: struct kcsan_ctx comments for more 850 * comments. 851 */ 852 853 ++get_ctx()->atomic_nest_count; 854 } 855 EXPORT_SYMBOL(kcsan_nestable_atomic_begin); 856 857 void kcsan_nestable_atomic_end(void) 858 { 859 if (get_ctx()->atomic_nest_count-- == 0) { 860 /* 861 * Warn if kcsan_nestable_atomic_end() calls are unbalanced with 862 * kcsan_nestable_atomic_begin() calls, which causes 863 * atomic_nest_count to become negative and should not happen. 864 */ 865 kcsan_nestable_atomic_begin(); /* restore to 0 */ 866 kcsan_disable_current(); /* disable to generate warning */ 867 WARN(1, "Unbalanced %s()", __func__); 868 kcsan_enable_current(); 869 } 870 } 871 EXPORT_SYMBOL(kcsan_nestable_atomic_end); 872 873 void kcsan_flat_atomic_begin(void) 874 { 875 get_ctx()->in_flat_atomic = true; 876 } 877 EXPORT_SYMBOL(kcsan_flat_atomic_begin); 878 879 void kcsan_flat_atomic_end(void) 880 { 881 get_ctx()->in_flat_atomic = false; 882 } 883 EXPORT_SYMBOL(kcsan_flat_atomic_end); 884 885 void kcsan_atomic_next(int n) 886 { 887 get_ctx()->atomic_next = n; 888 } 889 EXPORT_SYMBOL(kcsan_atomic_next); 890 891 void kcsan_set_access_mask(unsigned long mask) 892 { 893 get_ctx()->access_mask = mask; 894 } 895 EXPORT_SYMBOL(kcsan_set_access_mask); 896 897 struct kcsan_scoped_access * 898 kcsan_begin_scoped_access(const volatile void *ptr, size_t size, int type, 899 struct kcsan_scoped_access *sa) 900 { 901 struct kcsan_ctx *ctx = get_ctx(); 902 903 check_access(ptr, size, type, _RET_IP_); 904 905 ctx->disable_count++; /* Disable KCSAN, in case list debugging is on. */ 906 907 INIT_LIST_HEAD(&sa->list); 908 sa->ptr = ptr; 909 sa->size = size; 910 sa->type = type; 911 sa->ip = _RET_IP_; 912 913 if (!ctx->scoped_accesses.prev) /* Lazy initialize list head. */ 914 INIT_LIST_HEAD(&ctx->scoped_accesses); 915 list_add(&sa->list, &ctx->scoped_accesses); 916 917 ctx->disable_count--; 918 return sa; 919 } 920 EXPORT_SYMBOL(kcsan_begin_scoped_access); 921 922 void kcsan_end_scoped_access(struct kcsan_scoped_access *sa) 923 { 924 struct kcsan_ctx *ctx = get_ctx(); 925 926 if (WARN(!ctx->scoped_accesses.prev, "Unbalanced %s()?", __func__)) 927 return; 928 929 ctx->disable_count++; /* Disable KCSAN, in case list debugging is on. */ 930 931 list_del(&sa->list); 932 if (list_empty(&ctx->scoped_accesses)) 933 /* 934 * Ensure we do not enter kcsan_check_scoped_accesses() 935 * slow-path if unnecessary, and avoids requiring list_empty() 936 * in the fast-path (to avoid a READ_ONCE() and potential 937 * uaccess warning). 938 */ 939 ctx->scoped_accesses.prev = NULL; 940 941 ctx->disable_count--; 942 943 check_access(sa->ptr, sa->size, sa->type, sa->ip); 944 } 945 EXPORT_SYMBOL(kcsan_end_scoped_access); 946 947 void __kcsan_check_access(const volatile void *ptr, size_t size, int type) 948 { 949 check_access(ptr, size, type, _RET_IP_); 950 } 951 EXPORT_SYMBOL(__kcsan_check_access); 952 953 #define DEFINE_MEMORY_BARRIER(name, order_before_cond) \ 954 void __kcsan_##name(void) \ 955 { \ 956 struct kcsan_scoped_access *sa = get_reorder_access(get_ctx()); \ 957 if (!sa) \ 958 return; \ 959 if (order_before_cond) \ 960 sa->size = 0; \ 961 } \ 962 EXPORT_SYMBOL(__kcsan_##name) 963 964 DEFINE_MEMORY_BARRIER(mb, true); 965 DEFINE_MEMORY_BARRIER(wmb, sa->type & (KCSAN_ACCESS_WRITE | KCSAN_ACCESS_COMPOUND)); 966 DEFINE_MEMORY_BARRIER(rmb, !(sa->type & KCSAN_ACCESS_WRITE) || (sa->type & KCSAN_ACCESS_COMPOUND)); 967 DEFINE_MEMORY_BARRIER(release, true); 968 969 /* 970 * KCSAN uses the same instrumentation that is emitted by supported compilers 971 * for ThreadSanitizer (TSAN). 972 * 973 * When enabled, the compiler emits instrumentation calls (the functions 974 * prefixed with "__tsan" below) for all loads and stores that it generated; 975 * inline asm is not instrumented. 976 * 977 * Note that, not all supported compiler versions distinguish aligned/unaligned 978 * accesses, but e.g. recent versions of Clang do. We simply alias the unaligned 979 * version to the generic version, which can handle both. 980 */ 981 982 #define DEFINE_TSAN_READ_WRITE(size) \ 983 void __tsan_read##size(void *ptr); \ 984 void __tsan_read##size(void *ptr) \ 985 { \ 986 check_access(ptr, size, 0, _RET_IP_); \ 987 } \ 988 EXPORT_SYMBOL(__tsan_read##size); \ 989 void __tsan_unaligned_read##size(void *ptr) \ 990 __alias(__tsan_read##size); \ 991 EXPORT_SYMBOL(__tsan_unaligned_read##size); \ 992 void __tsan_write##size(void *ptr); \ 993 void __tsan_write##size(void *ptr) \ 994 { \ 995 check_access(ptr, size, KCSAN_ACCESS_WRITE, _RET_IP_); \ 996 } \ 997 EXPORT_SYMBOL(__tsan_write##size); \ 998 void __tsan_unaligned_write##size(void *ptr) \ 999 __alias(__tsan_write##size); \ 1000 EXPORT_SYMBOL(__tsan_unaligned_write##size); \ 1001 void __tsan_read_write##size(void *ptr); \ 1002 void __tsan_read_write##size(void *ptr) \ 1003 { \ 1004 check_access(ptr, size, \ 1005 KCSAN_ACCESS_COMPOUND | KCSAN_ACCESS_WRITE, \ 1006 _RET_IP_); \ 1007 } \ 1008 EXPORT_SYMBOL(__tsan_read_write##size); \ 1009 void __tsan_unaligned_read_write##size(void *ptr) \ 1010 __alias(__tsan_read_write##size); \ 1011 EXPORT_SYMBOL(__tsan_unaligned_read_write##size) 1012 1013 DEFINE_TSAN_READ_WRITE(1); 1014 DEFINE_TSAN_READ_WRITE(2); 1015 DEFINE_TSAN_READ_WRITE(4); 1016 DEFINE_TSAN_READ_WRITE(8); 1017 DEFINE_TSAN_READ_WRITE(16); 1018 1019 void __tsan_read_range(void *ptr, size_t size); 1020 void __tsan_read_range(void *ptr, size_t size) 1021 { 1022 check_access(ptr, size, 0, _RET_IP_); 1023 } 1024 EXPORT_SYMBOL(__tsan_read_range); 1025 1026 void __tsan_write_range(void *ptr, size_t size); 1027 void __tsan_write_range(void *ptr, size_t size) 1028 { 1029 check_access(ptr, size, KCSAN_ACCESS_WRITE, _RET_IP_); 1030 } 1031 EXPORT_SYMBOL(__tsan_write_range); 1032 1033 /* 1034 * Use of explicit volatile is generally disallowed [1], however, volatile is 1035 * still used in various concurrent context, whether in low-level 1036 * synchronization primitives or for legacy reasons. 1037 * [1] https://lwn.net/Articles/233479/ 1038 * 1039 * We only consider volatile accesses atomic if they are aligned and would pass 1040 * the size-check of compiletime_assert_rwonce_type(). 1041 */ 1042 #define DEFINE_TSAN_VOLATILE_READ_WRITE(size) \ 1043 void __tsan_volatile_read##size(void *ptr); \ 1044 void __tsan_volatile_read##size(void *ptr) \ 1045 { \ 1046 const bool is_atomic = size <= sizeof(long long) && \ 1047 IS_ALIGNED((unsigned long)ptr, size); \ 1048 if (IS_ENABLED(CONFIG_KCSAN_IGNORE_ATOMICS) && is_atomic) \ 1049 return; \ 1050 check_access(ptr, size, is_atomic ? KCSAN_ACCESS_ATOMIC : 0, \ 1051 _RET_IP_); \ 1052 } \ 1053 EXPORT_SYMBOL(__tsan_volatile_read##size); \ 1054 void __tsan_unaligned_volatile_read##size(void *ptr) \ 1055 __alias(__tsan_volatile_read##size); \ 1056 EXPORT_SYMBOL(__tsan_unaligned_volatile_read##size); \ 1057 void __tsan_volatile_write##size(void *ptr); \ 1058 void __tsan_volatile_write##size(void *ptr) \ 1059 { \ 1060 const bool is_atomic = size <= sizeof(long long) && \ 1061 IS_ALIGNED((unsigned long)ptr, size); \ 1062 if (IS_ENABLED(CONFIG_KCSAN_IGNORE_ATOMICS) && is_atomic) \ 1063 return; \ 1064 check_access(ptr, size, \ 1065 KCSAN_ACCESS_WRITE | \ 1066 (is_atomic ? KCSAN_ACCESS_ATOMIC : 0), \ 1067 _RET_IP_); \ 1068 } \ 1069 EXPORT_SYMBOL(__tsan_volatile_write##size); \ 1070 void __tsan_unaligned_volatile_write##size(void *ptr) \ 1071 __alias(__tsan_volatile_write##size); \ 1072 EXPORT_SYMBOL(__tsan_unaligned_volatile_write##size) 1073 1074 DEFINE_TSAN_VOLATILE_READ_WRITE(1); 1075 DEFINE_TSAN_VOLATILE_READ_WRITE(2); 1076 DEFINE_TSAN_VOLATILE_READ_WRITE(4); 1077 DEFINE_TSAN_VOLATILE_READ_WRITE(8); 1078 DEFINE_TSAN_VOLATILE_READ_WRITE(16); 1079 1080 /* 1081 * Function entry and exit are used to determine the validty of reorder_access. 1082 * Reordering of the access ends at the end of the function scope where the 1083 * access happened. This is done for two reasons: 1084 * 1085 * 1. Artificially limits the scope where missing barriers are detected. 1086 * This minimizes false positives due to uninstrumented functions that 1087 * contain the required barriers but were missed. 1088 * 1089 * 2. Simplifies generating the stack trace of the access. 1090 */ 1091 void __tsan_func_entry(void *call_pc); 1092 noinline void __tsan_func_entry(void *call_pc) 1093 { 1094 if (!IS_ENABLED(CONFIG_KCSAN_WEAK_MEMORY)) 1095 return; 1096 1097 add_kcsan_stack_depth(1); 1098 } 1099 EXPORT_SYMBOL(__tsan_func_entry); 1100 1101 void __tsan_func_exit(void); 1102 noinline void __tsan_func_exit(void) 1103 { 1104 struct kcsan_scoped_access *reorder_access; 1105 1106 if (!IS_ENABLED(CONFIG_KCSAN_WEAK_MEMORY)) 1107 return; 1108 1109 reorder_access = get_reorder_access(get_ctx()); 1110 if (!reorder_access) 1111 goto out; 1112 1113 if (get_kcsan_stack_depth() <= reorder_access->stack_depth) { 1114 /* 1115 * Access check to catch cases where write without a barrier 1116 * (supposed release) was last access in function: because 1117 * instrumentation is inserted before the real access, a data 1118 * race due to the write giving up a c-s would only be caught if 1119 * we do the conflicting access after. 1120 */ 1121 check_access(reorder_access->ptr, reorder_access->size, 1122 reorder_access->type, reorder_access->ip); 1123 reorder_access->size = 0; 1124 reorder_access->stack_depth = INT_MIN; 1125 } 1126 out: 1127 add_kcsan_stack_depth(-1); 1128 } 1129 EXPORT_SYMBOL(__tsan_func_exit); 1130 1131 void __tsan_init(void); 1132 void __tsan_init(void) 1133 { 1134 } 1135 EXPORT_SYMBOL(__tsan_init); 1136 1137 /* 1138 * Instrumentation for atomic builtins (__atomic_*, __sync_*). 1139 * 1140 * Normal kernel code _should not_ be using them directly, but some 1141 * architectures may implement some or all atomics using the compilers' 1142 * builtins. 1143 * 1144 * Note: If an architecture decides to fully implement atomics using the 1145 * builtins, because they are implicitly instrumented by KCSAN (and KASAN, 1146 * etc.), implementing the ARCH_ATOMIC interface (to get instrumentation via 1147 * atomic-instrumented) is no longer necessary. 1148 * 1149 * TSAN instrumentation replaces atomic accesses with calls to any of the below 1150 * functions, whose job is to also execute the operation itself. 1151 */ 1152 1153 static __always_inline void kcsan_atomic_builtin_memorder(int memorder) 1154 { 1155 if (memorder == __ATOMIC_RELEASE || 1156 memorder == __ATOMIC_SEQ_CST || 1157 memorder == __ATOMIC_ACQ_REL) 1158 __kcsan_release(); 1159 } 1160 1161 #define DEFINE_TSAN_ATOMIC_LOAD_STORE(bits) \ 1162 u##bits __tsan_atomic##bits##_load(const u##bits *ptr, int memorder); \ 1163 u##bits __tsan_atomic##bits##_load(const u##bits *ptr, int memorder) \ 1164 { \ 1165 kcsan_atomic_builtin_memorder(memorder); \ 1166 if (!IS_ENABLED(CONFIG_KCSAN_IGNORE_ATOMICS)) { \ 1167 check_access(ptr, bits / BITS_PER_BYTE, KCSAN_ACCESS_ATOMIC, _RET_IP_); \ 1168 } \ 1169 return __atomic_load_n(ptr, memorder); \ 1170 } \ 1171 EXPORT_SYMBOL(__tsan_atomic##bits##_load); \ 1172 void __tsan_atomic##bits##_store(u##bits *ptr, u##bits v, int memorder); \ 1173 void __tsan_atomic##bits##_store(u##bits *ptr, u##bits v, int memorder) \ 1174 { \ 1175 kcsan_atomic_builtin_memorder(memorder); \ 1176 if (!IS_ENABLED(CONFIG_KCSAN_IGNORE_ATOMICS)) { \ 1177 check_access(ptr, bits / BITS_PER_BYTE, \ 1178 KCSAN_ACCESS_WRITE | KCSAN_ACCESS_ATOMIC, _RET_IP_); \ 1179 } \ 1180 __atomic_store_n(ptr, v, memorder); \ 1181 } \ 1182 EXPORT_SYMBOL(__tsan_atomic##bits##_store) 1183 1184 #define DEFINE_TSAN_ATOMIC_RMW(op, bits, suffix) \ 1185 u##bits __tsan_atomic##bits##_##op(u##bits *ptr, u##bits v, int memorder); \ 1186 u##bits __tsan_atomic##bits##_##op(u##bits *ptr, u##bits v, int memorder) \ 1187 { \ 1188 kcsan_atomic_builtin_memorder(memorder); \ 1189 if (!IS_ENABLED(CONFIG_KCSAN_IGNORE_ATOMICS)) { \ 1190 check_access(ptr, bits / BITS_PER_BYTE, \ 1191 KCSAN_ACCESS_COMPOUND | KCSAN_ACCESS_WRITE | \ 1192 KCSAN_ACCESS_ATOMIC, _RET_IP_); \ 1193 } \ 1194 return __atomic_##op##suffix(ptr, v, memorder); \ 1195 } \ 1196 EXPORT_SYMBOL(__tsan_atomic##bits##_##op) 1197 1198 /* 1199 * Note: CAS operations are always classified as write, even in case they 1200 * fail. We cannot perform check_access() after a write, as it might lead to 1201 * false positives, in cases such as: 1202 * 1203 * T0: __atomic_compare_exchange_n(&p->flag, &old, 1, ...) 1204 * 1205 * T1: if (__atomic_load_n(&p->flag, ...)) { 1206 * modify *p; 1207 * p->flag = 0; 1208 * } 1209 * 1210 * The only downside is that, if there are 3 threads, with one CAS that 1211 * succeeds, another CAS that fails, and an unmarked racing operation, we may 1212 * point at the wrong CAS as the source of the race. However, if we assume that 1213 * all CAS can succeed in some other execution, the data race is still valid. 1214 */ 1215 #define DEFINE_TSAN_ATOMIC_CMPXCHG(bits, strength, weak) \ 1216 int __tsan_atomic##bits##_compare_exchange_##strength(u##bits *ptr, u##bits *exp, \ 1217 u##bits val, int mo, int fail_mo); \ 1218 int __tsan_atomic##bits##_compare_exchange_##strength(u##bits *ptr, u##bits *exp, \ 1219 u##bits val, int mo, int fail_mo) \ 1220 { \ 1221 kcsan_atomic_builtin_memorder(mo); \ 1222 if (!IS_ENABLED(CONFIG_KCSAN_IGNORE_ATOMICS)) { \ 1223 check_access(ptr, bits / BITS_PER_BYTE, \ 1224 KCSAN_ACCESS_COMPOUND | KCSAN_ACCESS_WRITE | \ 1225 KCSAN_ACCESS_ATOMIC, _RET_IP_); \ 1226 } \ 1227 return __atomic_compare_exchange_n(ptr, exp, val, weak, mo, fail_mo); \ 1228 } \ 1229 EXPORT_SYMBOL(__tsan_atomic##bits##_compare_exchange_##strength) 1230 1231 #define DEFINE_TSAN_ATOMIC_CMPXCHG_VAL(bits) \ 1232 u##bits __tsan_atomic##bits##_compare_exchange_val(u##bits *ptr, u##bits exp, u##bits val, \ 1233 int mo, int fail_mo); \ 1234 u##bits __tsan_atomic##bits##_compare_exchange_val(u##bits *ptr, u##bits exp, u##bits val, \ 1235 int mo, int fail_mo) \ 1236 { \ 1237 kcsan_atomic_builtin_memorder(mo); \ 1238 if (!IS_ENABLED(CONFIG_KCSAN_IGNORE_ATOMICS)) { \ 1239 check_access(ptr, bits / BITS_PER_BYTE, \ 1240 KCSAN_ACCESS_COMPOUND | KCSAN_ACCESS_WRITE | \ 1241 KCSAN_ACCESS_ATOMIC, _RET_IP_); \ 1242 } \ 1243 __atomic_compare_exchange_n(ptr, &exp, val, 0, mo, fail_mo); \ 1244 return exp; \ 1245 } \ 1246 EXPORT_SYMBOL(__tsan_atomic##bits##_compare_exchange_val) 1247 1248 #define DEFINE_TSAN_ATOMIC_OPS(bits) \ 1249 DEFINE_TSAN_ATOMIC_LOAD_STORE(bits); \ 1250 DEFINE_TSAN_ATOMIC_RMW(exchange, bits, _n); \ 1251 DEFINE_TSAN_ATOMIC_RMW(fetch_add, bits, ); \ 1252 DEFINE_TSAN_ATOMIC_RMW(fetch_sub, bits, ); \ 1253 DEFINE_TSAN_ATOMIC_RMW(fetch_and, bits, ); \ 1254 DEFINE_TSAN_ATOMIC_RMW(fetch_or, bits, ); \ 1255 DEFINE_TSAN_ATOMIC_RMW(fetch_xor, bits, ); \ 1256 DEFINE_TSAN_ATOMIC_RMW(fetch_nand, bits, ); \ 1257 DEFINE_TSAN_ATOMIC_CMPXCHG(bits, strong, 0); \ 1258 DEFINE_TSAN_ATOMIC_CMPXCHG(bits, weak, 1); \ 1259 DEFINE_TSAN_ATOMIC_CMPXCHG_VAL(bits) 1260 1261 DEFINE_TSAN_ATOMIC_OPS(8); 1262 DEFINE_TSAN_ATOMIC_OPS(16); 1263 DEFINE_TSAN_ATOMIC_OPS(32); 1264 DEFINE_TSAN_ATOMIC_OPS(64); 1265 1266 void __tsan_atomic_thread_fence(int memorder); 1267 void __tsan_atomic_thread_fence(int memorder) 1268 { 1269 kcsan_atomic_builtin_memorder(memorder); 1270 __atomic_thread_fence(memorder); 1271 } 1272 EXPORT_SYMBOL(__tsan_atomic_thread_fence); 1273 1274 /* 1275 * In instrumented files, we emit instrumentation for barriers by mapping the 1276 * kernel barriers to an __atomic_signal_fence(), which is interpreted specially 1277 * and otherwise has no relation to a real __atomic_signal_fence(). No known 1278 * kernel code uses __atomic_signal_fence(). 1279 * 1280 * Since fsanitize=thread instrumentation handles __atomic_signal_fence(), which 1281 * are turned into calls to __tsan_atomic_signal_fence(), such instrumentation 1282 * can be disabled via the __no_kcsan function attribute (vs. an explicit call 1283 * which could not). When __no_kcsan is requested, __atomic_signal_fence() 1284 * generates no code. 1285 * 1286 * Note: The result of using __atomic_signal_fence() with KCSAN enabled is 1287 * potentially limiting the compiler's ability to reorder operations; however, 1288 * if barriers were instrumented with explicit calls (without LTO), the compiler 1289 * couldn't optimize much anyway. The result of a hypothetical architecture 1290 * using __atomic_signal_fence() in normal code would be KCSAN false negatives. 1291 */ 1292 void __tsan_atomic_signal_fence(int memorder); 1293 noinline void __tsan_atomic_signal_fence(int memorder) 1294 { 1295 switch (memorder) { 1296 case __KCSAN_BARRIER_TO_SIGNAL_FENCE_mb: 1297 __kcsan_mb(); 1298 break; 1299 case __KCSAN_BARRIER_TO_SIGNAL_FENCE_wmb: 1300 __kcsan_wmb(); 1301 break; 1302 case __KCSAN_BARRIER_TO_SIGNAL_FENCE_rmb: 1303 __kcsan_rmb(); 1304 break; 1305 case __KCSAN_BARRIER_TO_SIGNAL_FENCE_release: 1306 __kcsan_release(); 1307 break; 1308 default: 1309 break; 1310 } 1311 } 1312 EXPORT_SYMBOL(__tsan_atomic_signal_fence); 1313 1314 #ifdef __HAVE_ARCH_MEMSET 1315 void *__tsan_memset(void *s, int c, size_t count); 1316 noinline void *__tsan_memset(void *s, int c, size_t count) 1317 { 1318 /* 1319 * Instead of not setting up watchpoints where accessed size is greater 1320 * than MAX_ENCODABLE_SIZE, truncate checked size to MAX_ENCODABLE_SIZE. 1321 */ 1322 size_t check_len = min_t(size_t, count, MAX_ENCODABLE_SIZE); 1323 1324 check_access(s, check_len, KCSAN_ACCESS_WRITE, _RET_IP_); 1325 return memset(s, c, count); 1326 } 1327 #else 1328 void *__tsan_memset(void *s, int c, size_t count) __alias(memset); 1329 #endif 1330 EXPORT_SYMBOL(__tsan_memset); 1331 1332 #ifdef __HAVE_ARCH_MEMMOVE 1333 void *__tsan_memmove(void *dst, const void *src, size_t len); 1334 noinline void *__tsan_memmove(void *dst, const void *src, size_t len) 1335 { 1336 size_t check_len = min_t(size_t, len, MAX_ENCODABLE_SIZE); 1337 1338 check_access(dst, check_len, KCSAN_ACCESS_WRITE, _RET_IP_); 1339 check_access(src, check_len, 0, _RET_IP_); 1340 return memmove(dst, src, len); 1341 } 1342 #else 1343 void *__tsan_memmove(void *dst, const void *src, size_t len) __alias(memmove); 1344 #endif 1345 EXPORT_SYMBOL(__tsan_memmove); 1346 1347 #ifdef __HAVE_ARCH_MEMCPY 1348 void *__tsan_memcpy(void *dst, const void *src, size_t len); 1349 noinline void *__tsan_memcpy(void *dst, const void *src, size_t len) 1350 { 1351 size_t check_len = min_t(size_t, len, MAX_ENCODABLE_SIZE); 1352 1353 check_access(dst, check_len, KCSAN_ACCESS_WRITE, _RET_IP_); 1354 check_access(src, check_len, 0, _RET_IP_); 1355 return memcpy(dst, src, len); 1356 } 1357 #else 1358 void *__tsan_memcpy(void *dst, const void *src, size_t len) __alias(memcpy); 1359 #endif 1360 EXPORT_SYMBOL(__tsan_memcpy); 1361