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