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 /* 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, type, ip, 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(&kcsan_counters[KCSAN_COUNTER_REPORT_RACES]); 516 } 517 518 if (is_assert) 519 atomic_long_inc(&kcsan_counters[KCSAN_COUNTER_ASSERT_FAILURES]); 520 else 521 atomic_long_inc(&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((unsigned long)ptr, size)) { 558 atomic_long_inc(&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((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(&kcsan_counters[KCSAN_COUNTER_NO_CAPACITY]); 599 goto out_unlock; 600 } 601 602 atomic_long_inc(&kcsan_counters[KCSAN_COUNTER_SETUP_WATCHPOINTS]); 603 atomic_long_inc(&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(&kcsan_counters[KCSAN_COUNTER_ASSERT_FAILURES]); 677 678 kcsan_report_known_origin(ptr, size, type, ip, 679 value_change, watchpoint - watchpoints, 680 old, new, 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(&kcsan_counters[KCSAN_COUNTER_RACES_UNKNOWN_ORIGIN]); 685 if (is_assert) 686 atomic_long_inc(&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, type, ip, 690 old, new, 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(&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((unsigned long)ptr, size, 738 !(type & KCSAN_ACCESS_WRITE), 739 &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(&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(&ctx->scoped_accesses); 924 list_add(&sa->list, &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(&sa->list); 941 if (list_empty(&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(sa->ptr, sa->size, sa->type, 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, 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(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(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(reorder_access->ptr, reorder_access->size, 1131 reorder_access->type, reorder_access->ip); 1132 reorder_access->size = 0; 1133 reorder_access->stack_depth = INT_MIN; 1134 } 1135 out: 1136 add_kcsan_stack_depth(-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 DEFINE_TSAN_ATOMIC_OPS(64); 1274 1275 void __tsan_atomic_thread_fence(int memorder); 1276 void __tsan_atomic_thread_fence(int memorder) 1277 { 1278 kcsan_atomic_builtin_memorder(memorder); 1279 __atomic_thread_fence(memorder); 1280 } 1281 EXPORT_SYMBOL(__tsan_atomic_thread_fence); 1282 1283 /* 1284 * In instrumented files, we emit instrumentation for barriers by mapping the 1285 * kernel barriers to an __atomic_signal_fence(), which is interpreted specially 1286 * and otherwise has no relation to a real __atomic_signal_fence(). No known 1287 * kernel code uses __atomic_signal_fence(). 1288 * 1289 * Since fsanitize=thread instrumentation handles __atomic_signal_fence(), which 1290 * are turned into calls to __tsan_atomic_signal_fence(), such instrumentation 1291 * can be disabled via the __no_kcsan function attribute (vs. an explicit call 1292 * which could not). When __no_kcsan is requested, __atomic_signal_fence() 1293 * generates no code. 1294 * 1295 * Note: The result of using __atomic_signal_fence() with KCSAN enabled is 1296 * potentially limiting the compiler's ability to reorder operations; however, 1297 * if barriers were instrumented with explicit calls (without LTO), the compiler 1298 * couldn't optimize much anyway. The result of a hypothetical architecture 1299 * using __atomic_signal_fence() in normal code would be KCSAN false negatives. 1300 */ 1301 void __tsan_atomic_signal_fence(int memorder); 1302 noinline void __tsan_atomic_signal_fence(int memorder) 1303 { 1304 switch (memorder) { 1305 case __KCSAN_BARRIER_TO_SIGNAL_FENCE_mb: 1306 __kcsan_mb(); 1307 break; 1308 case __KCSAN_BARRIER_TO_SIGNAL_FENCE_wmb: 1309 __kcsan_wmb(); 1310 break; 1311 case __KCSAN_BARRIER_TO_SIGNAL_FENCE_rmb: 1312 __kcsan_rmb(); 1313 break; 1314 case __KCSAN_BARRIER_TO_SIGNAL_FENCE_release: 1315 __kcsan_release(); 1316 break; 1317 default: 1318 break; 1319 } 1320 } 1321 EXPORT_SYMBOL(__tsan_atomic_signal_fence); 1322 1323 #ifdef __HAVE_ARCH_MEMSET 1324 void *__tsan_memset(void *s, int c, size_t count); 1325 noinline void *__tsan_memset(void *s, int c, size_t count) 1326 { 1327 /* 1328 * Instead of not setting up watchpoints where accessed size is greater 1329 * than MAX_ENCODABLE_SIZE, truncate checked size to MAX_ENCODABLE_SIZE. 1330 */ 1331 size_t check_len = min_t(size_t, count, MAX_ENCODABLE_SIZE); 1332 1333 check_access(s, check_len, KCSAN_ACCESS_WRITE, _RET_IP_); 1334 return memset(s, c, count); 1335 } 1336 #else 1337 void *__tsan_memset(void *s, int c, size_t count) __alias(memset); 1338 #endif 1339 EXPORT_SYMBOL(__tsan_memset); 1340 1341 #ifdef __HAVE_ARCH_MEMMOVE 1342 void *__tsan_memmove(void *dst, const void *src, size_t len); 1343 noinline void *__tsan_memmove(void *dst, const void *src, size_t len) 1344 { 1345 size_t check_len = min_t(size_t, len, MAX_ENCODABLE_SIZE); 1346 1347 check_access(dst, check_len, KCSAN_ACCESS_WRITE, _RET_IP_); 1348 check_access(src, check_len, 0, _RET_IP_); 1349 return memmove(dst, src, len); 1350 } 1351 #else 1352 void *__tsan_memmove(void *dst, const void *src, size_t len) __alias(memmove); 1353 #endif 1354 EXPORT_SYMBOL(__tsan_memmove); 1355 1356 #ifdef __HAVE_ARCH_MEMCPY 1357 void *__tsan_memcpy(void *dst, const void *src, size_t len); 1358 noinline void *__tsan_memcpy(void *dst, const void *src, size_t len) 1359 { 1360 size_t check_len = min_t(size_t, len, MAX_ENCODABLE_SIZE); 1361 1362 check_access(dst, check_len, KCSAN_ACCESS_WRITE, _RET_IP_); 1363 check_access(src, check_len, 0, _RET_IP_); 1364 return memcpy(dst, src, len); 1365 } 1366 #else 1367 void *__tsan_memcpy(void *dst, const void *src, size_t len) __alias(memcpy); 1368 #endif 1369 EXPORT_SYMBOL(__tsan_memcpy); 1370