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 "atomic.h" 24 #include "encoding.h" 25 #include "kcsan.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 bool kcsan_enabled; 44 45 /* Per-CPU kcsan_ctx for interrupts */ 46 static DEFINE_PER_CPU(struct kcsan_ctx, kcsan_cpu_ctx) = { 47 .disable_count = 0, 48 .atomic_next = 0, 49 .atomic_nest_count = 0, 50 .in_flat_atomic = false, 51 .access_mask = 0, 52 .scoped_accesses = {LIST_POISON1, NULL}, 53 }; 54 55 /* 56 * Helper macros to index into adjacent slots, starting from address slot 57 * itself, followed by the right and left slots. 58 * 59 * The purpose is 2-fold: 60 * 61 * 1. if during insertion the address slot is already occupied, check if 62 * any adjacent slots are free; 63 * 2. accesses that straddle a slot boundary due to size that exceeds a 64 * slot's range may check adjacent slots if any watchpoint matches. 65 * 66 * Note that accesses with very large size may still miss a watchpoint; however, 67 * given this should be rare, this is a reasonable trade-off to make, since this 68 * will avoid: 69 * 70 * 1. excessive contention between watchpoint checks and setup; 71 * 2. larger number of simultaneous watchpoints without sacrificing 72 * performance. 73 * 74 * Example: SLOT_IDX values for KCSAN_CHECK_ADJACENT=1, where i is [0, 1, 2]: 75 * 76 * slot=0: [ 1, 2, 0] 77 * slot=9: [10, 11, 9] 78 * slot=63: [64, 65, 63] 79 */ 80 #define SLOT_IDX(slot, i) (slot + ((i + KCSAN_CHECK_ADJACENT) % NUM_SLOTS)) 81 82 /* 83 * SLOT_IDX_FAST is used in the fast-path. Not first checking the address's primary 84 * slot (middle) is fine if we assume that races occur rarely. The set of 85 * indices {SLOT_IDX(slot, i) | i in [0, NUM_SLOTS)} is equivalent to 86 * {SLOT_IDX_FAST(slot, i) | i in [0, NUM_SLOTS)}. 87 */ 88 #define SLOT_IDX_FAST(slot, i) (slot + i) 89 90 /* 91 * Watchpoints, with each entry encoded as defined in encoding.h: in order to be 92 * able to safely update and access a watchpoint without introducing locking 93 * overhead, we encode each watchpoint as a single atomic long. The initial 94 * zero-initialized state matches INVALID_WATCHPOINT. 95 * 96 * Add NUM_SLOTS-1 entries to account for overflow; this helps avoid having to 97 * use more complicated SLOT_IDX_FAST calculation with modulo in the fast-path. 98 */ 99 static atomic_long_t watchpoints[CONFIG_KCSAN_NUM_WATCHPOINTS + NUM_SLOTS-1]; 100 101 /* 102 * Instructions to skip watching counter, used in should_watch(). We use a 103 * per-CPU counter to avoid excessive contention. 104 */ 105 static DEFINE_PER_CPU(long, kcsan_skip); 106 107 /* For kcsan_prandom_u32_max(). */ 108 static DEFINE_PER_CPU(u32, kcsan_rand_state); 109 110 static __always_inline atomic_long_t *find_watchpoint(unsigned long addr, 111 size_t size, 112 bool expect_write, 113 long *encoded_watchpoint) 114 { 115 const int slot = watchpoint_slot(addr); 116 const unsigned long addr_masked = addr & WATCHPOINT_ADDR_MASK; 117 atomic_long_t *watchpoint; 118 unsigned long wp_addr_masked; 119 size_t wp_size; 120 bool is_write; 121 int i; 122 123 BUILD_BUG_ON(CONFIG_KCSAN_NUM_WATCHPOINTS < NUM_SLOTS); 124 125 for (i = 0; i < NUM_SLOTS; ++i) { 126 watchpoint = &watchpoints[SLOT_IDX_FAST(slot, i)]; 127 *encoded_watchpoint = atomic_long_read(watchpoint); 128 if (!decode_watchpoint(*encoded_watchpoint, &wp_addr_masked, 129 &wp_size, &is_write)) 130 continue; 131 132 if (expect_write && !is_write) 133 continue; 134 135 /* Check if the watchpoint matches the access. */ 136 if (matching_access(wp_addr_masked, wp_size, addr_masked, size)) 137 return watchpoint; 138 } 139 140 return NULL; 141 } 142 143 static inline atomic_long_t * 144 insert_watchpoint(unsigned long addr, size_t size, bool is_write) 145 { 146 const int slot = watchpoint_slot(addr); 147 const long encoded_watchpoint = encode_watchpoint(addr, size, is_write); 148 atomic_long_t *watchpoint; 149 int i; 150 151 /* Check slot index logic, ensuring we stay within array bounds. */ 152 BUILD_BUG_ON(SLOT_IDX(0, 0) != KCSAN_CHECK_ADJACENT); 153 BUILD_BUG_ON(SLOT_IDX(0, KCSAN_CHECK_ADJACENT+1) != 0); 154 BUILD_BUG_ON(SLOT_IDX(CONFIG_KCSAN_NUM_WATCHPOINTS-1, KCSAN_CHECK_ADJACENT) != ARRAY_SIZE(watchpoints)-1); 155 BUILD_BUG_ON(SLOT_IDX(CONFIG_KCSAN_NUM_WATCHPOINTS-1, KCSAN_CHECK_ADJACENT+1) != ARRAY_SIZE(watchpoints) - NUM_SLOTS); 156 157 for (i = 0; i < NUM_SLOTS; ++i) { 158 long expect_val = INVALID_WATCHPOINT; 159 160 /* Try to acquire this slot. */ 161 watchpoint = &watchpoints[SLOT_IDX(slot, i)]; 162 if (atomic_long_try_cmpxchg_relaxed(watchpoint, &expect_val, encoded_watchpoint)) 163 return watchpoint; 164 } 165 166 return NULL; 167 } 168 169 /* 170 * Return true if watchpoint was successfully consumed, false otherwise. 171 * 172 * This may return false if: 173 * 174 * 1. another thread already consumed the watchpoint; 175 * 2. the thread that set up the watchpoint already removed it; 176 * 3. the watchpoint was removed and then re-used. 177 */ 178 static __always_inline bool 179 try_consume_watchpoint(atomic_long_t *watchpoint, long encoded_watchpoint) 180 { 181 return atomic_long_try_cmpxchg_relaxed(watchpoint, &encoded_watchpoint, CONSUMED_WATCHPOINT); 182 } 183 184 /* Return true if watchpoint was not touched, false if already consumed. */ 185 static inline bool consume_watchpoint(atomic_long_t *watchpoint) 186 { 187 return atomic_long_xchg_relaxed(watchpoint, CONSUMED_WATCHPOINT) != CONSUMED_WATCHPOINT; 188 } 189 190 /* Remove the watchpoint -- its slot may be reused after. */ 191 static inline void remove_watchpoint(atomic_long_t *watchpoint) 192 { 193 atomic_long_set(watchpoint, INVALID_WATCHPOINT); 194 } 195 196 static __always_inline struct kcsan_ctx *get_ctx(void) 197 { 198 /* 199 * In interrupts, use raw_cpu_ptr to avoid unnecessary checks, that would 200 * also result in calls that generate warnings in uaccess regions. 201 */ 202 return in_task() ? ¤t->kcsan_ctx : raw_cpu_ptr(&kcsan_cpu_ctx); 203 } 204 205 /* Check scoped accesses; never inline because this is a slow-path! */ 206 static noinline void kcsan_check_scoped_accesses(void) 207 { 208 struct kcsan_ctx *ctx = get_ctx(); 209 struct list_head *prev_save = ctx->scoped_accesses.prev; 210 struct kcsan_scoped_access *scoped_access; 211 212 ctx->scoped_accesses.prev = NULL; /* Avoid recursion. */ 213 list_for_each_entry(scoped_access, &ctx->scoped_accesses, list) 214 __kcsan_check_access(scoped_access->ptr, scoped_access->size, scoped_access->type); 215 ctx->scoped_accesses.prev = prev_save; 216 } 217 218 /* Rules for generic atomic accesses. Called from fast-path. */ 219 static __always_inline bool 220 is_atomic(const volatile void *ptr, size_t size, int type, struct kcsan_ctx *ctx) 221 { 222 if (type & KCSAN_ACCESS_ATOMIC) 223 return true; 224 225 /* 226 * Unless explicitly declared atomic, never consider an assertion access 227 * as atomic. This allows using them also in atomic regions, such as 228 * seqlocks, without implicitly changing their semantics. 229 */ 230 if (type & KCSAN_ACCESS_ASSERT) 231 return false; 232 233 if (IS_ENABLED(CONFIG_KCSAN_ASSUME_PLAIN_WRITES_ATOMIC) && 234 (type & KCSAN_ACCESS_WRITE) && size <= sizeof(long) && 235 !(type & KCSAN_ACCESS_COMPOUND) && IS_ALIGNED((unsigned long)ptr, size)) 236 return true; /* Assume aligned writes up to word size are atomic. */ 237 238 if (ctx->atomic_next > 0) { 239 /* 240 * Because we do not have separate contexts for nested 241 * interrupts, in case atomic_next is set, we simply assume that 242 * the outer interrupt set atomic_next. In the worst case, we 243 * will conservatively consider operations as atomic. This is a 244 * reasonable trade-off to make, since this case should be 245 * extremely rare; however, even if extremely rare, it could 246 * lead to false positives otherwise. 247 */ 248 if ((hardirq_count() >> HARDIRQ_SHIFT) < 2) 249 --ctx->atomic_next; /* in task, or outer interrupt */ 250 return true; 251 } 252 253 return ctx->atomic_nest_count > 0 || ctx->in_flat_atomic; 254 } 255 256 static __always_inline bool 257 should_watch(const volatile void *ptr, size_t size, int type, struct kcsan_ctx *ctx) 258 { 259 /* 260 * Never set up watchpoints when memory operations are atomic. 261 * 262 * Need to check this first, before kcsan_skip check below: (1) atomics 263 * should not count towards skipped instructions, and (2) to actually 264 * decrement kcsan_atomic_next for consecutive instruction stream. 265 */ 266 if (is_atomic(ptr, size, type, ctx)) 267 return false; 268 269 if (this_cpu_dec_return(kcsan_skip) >= 0) 270 return false; 271 272 /* 273 * NOTE: If we get here, kcsan_skip must always be reset in slow path 274 * via reset_kcsan_skip() to avoid underflow. 275 */ 276 277 /* this operation should be watched */ 278 return true; 279 } 280 281 /* 282 * Returns a pseudo-random number in interval [0, ep_ro). Simple linear 283 * congruential generator, using constants from "Numerical Recipes". 284 */ 285 static u32 kcsan_prandom_u32_max(u32 ep_ro) 286 { 287 u32 state = this_cpu_read(kcsan_rand_state); 288 289 state = 1664525 * state + 1013904223; 290 this_cpu_write(kcsan_rand_state, state); 291 292 return state % ep_ro; 293 } 294 295 static inline void reset_kcsan_skip(void) 296 { 297 long skip_count = kcsan_skip_watch - 298 (IS_ENABLED(CONFIG_KCSAN_SKIP_WATCH_RANDOMIZE) ? 299 kcsan_prandom_u32_max(kcsan_skip_watch) : 300 0); 301 this_cpu_write(kcsan_skip, skip_count); 302 } 303 304 static __always_inline bool kcsan_is_enabled(void) 305 { 306 return READ_ONCE(kcsan_enabled) && get_ctx()->disable_count == 0; 307 } 308 309 /* Introduce delay depending on context and configuration. */ 310 static void delay_access(int type) 311 { 312 unsigned int delay = in_task() ? kcsan_udelay_task : kcsan_udelay_interrupt; 313 /* For certain access types, skew the random delay to be longer. */ 314 unsigned int skew_delay_order = 315 (type & (KCSAN_ACCESS_COMPOUND | KCSAN_ACCESS_ASSERT)) ? 1 : 0; 316 317 delay -= IS_ENABLED(CONFIG_KCSAN_DELAY_RANDOMIZE) ? 318 kcsan_prandom_u32_max(delay >> skew_delay_order) : 319 0; 320 udelay(delay); 321 } 322 323 void kcsan_save_irqtrace(struct task_struct *task) 324 { 325 #ifdef CONFIG_TRACE_IRQFLAGS 326 task->kcsan_save_irqtrace = task->irqtrace; 327 #endif 328 } 329 330 void kcsan_restore_irqtrace(struct task_struct *task) 331 { 332 #ifdef CONFIG_TRACE_IRQFLAGS 333 task->irqtrace = task->kcsan_save_irqtrace; 334 #endif 335 } 336 337 /* 338 * Pull everything together: check_access() below contains the performance 339 * critical operations; the fast-path (including check_access) functions should 340 * all be inlinable by the instrumentation functions. 341 * 342 * The slow-path (kcsan_found_watchpoint, kcsan_setup_watchpoint) are 343 * non-inlinable -- note that, we prefix these with "kcsan_" to ensure they can 344 * be filtered from the stacktrace, as well as give them unique names for the 345 * UACCESS whitelist of objtool. Each function uses user_access_save/restore(), 346 * since they do not access any user memory, but instrumentation is still 347 * emitted in UACCESS regions. 348 */ 349 350 static noinline void kcsan_found_watchpoint(const volatile void *ptr, 351 size_t size, 352 int type, 353 atomic_long_t *watchpoint, 354 long encoded_watchpoint) 355 { 356 unsigned long flags; 357 bool consumed; 358 359 if (!kcsan_is_enabled()) 360 return; 361 362 /* 363 * The access_mask check relies on value-change comparison. To avoid 364 * reporting a race where e.g. the writer set up the watchpoint, but the 365 * reader has access_mask!=0, we have to ignore the found watchpoint. 366 */ 367 if (get_ctx()->access_mask != 0) 368 return; 369 370 /* 371 * Consume the watchpoint as soon as possible, to minimize the chances 372 * of !consumed. Consuming the watchpoint must always be guarded by 373 * kcsan_is_enabled() check, as otherwise we might erroneously 374 * triggering reports when disabled. 375 */ 376 consumed = try_consume_watchpoint(watchpoint, encoded_watchpoint); 377 378 /* keep this after try_consume_watchpoint */ 379 flags = user_access_save(); 380 381 if (consumed) { 382 kcsan_save_irqtrace(current); 383 kcsan_report_set_info(ptr, size, type, watchpoint - watchpoints); 384 kcsan_restore_irqtrace(current); 385 } else { 386 /* 387 * The other thread may not print any diagnostics, as it has 388 * already removed the watchpoint, or another thread consumed 389 * the watchpoint before this thread. 390 */ 391 atomic_long_inc(&kcsan_counters[KCSAN_COUNTER_REPORT_RACES]); 392 } 393 394 if ((type & KCSAN_ACCESS_ASSERT) != 0) 395 atomic_long_inc(&kcsan_counters[KCSAN_COUNTER_ASSERT_FAILURES]); 396 else 397 atomic_long_inc(&kcsan_counters[KCSAN_COUNTER_DATA_RACES]); 398 399 user_access_restore(flags); 400 } 401 402 static noinline void 403 kcsan_setup_watchpoint(const volatile void *ptr, size_t size, int type) 404 { 405 const bool is_write = (type & KCSAN_ACCESS_WRITE) != 0; 406 const bool is_assert = (type & KCSAN_ACCESS_ASSERT) != 0; 407 atomic_long_t *watchpoint; 408 u64 old, new, diff; 409 unsigned long access_mask; 410 enum kcsan_value_change value_change = KCSAN_VALUE_CHANGE_MAYBE; 411 unsigned long ua_flags = user_access_save(); 412 unsigned long irq_flags = 0; 413 414 /* 415 * Always reset kcsan_skip counter in slow-path to avoid underflow; see 416 * should_watch(). 417 */ 418 reset_kcsan_skip(); 419 420 if (!kcsan_is_enabled()) 421 goto out; 422 423 /* 424 * Special atomic rules: unlikely to be true, so we check them here in 425 * the slow-path, and not in the fast-path in is_atomic(). Call after 426 * kcsan_is_enabled(), as we may access memory that is not yet 427 * initialized during early boot. 428 */ 429 if (!is_assert && kcsan_is_atomic_special(ptr)) 430 goto out; 431 432 if (!check_encodable((unsigned long)ptr, size)) { 433 atomic_long_inc(&kcsan_counters[KCSAN_COUNTER_UNENCODABLE_ACCESSES]); 434 goto out; 435 } 436 437 /* 438 * Save and restore the IRQ state trace touched by KCSAN, since KCSAN's 439 * runtime is entered for every memory access, and potentially useful 440 * information is lost if dirtied by KCSAN. 441 */ 442 kcsan_save_irqtrace(current); 443 if (!kcsan_interrupt_watcher) 444 local_irq_save(irq_flags); 445 446 watchpoint = insert_watchpoint((unsigned long)ptr, size, is_write); 447 if (watchpoint == NULL) { 448 /* 449 * Out of capacity: the size of 'watchpoints', and the frequency 450 * with which should_watch() returns true should be tweaked so 451 * that this case happens very rarely. 452 */ 453 atomic_long_inc(&kcsan_counters[KCSAN_COUNTER_NO_CAPACITY]); 454 goto out_unlock; 455 } 456 457 atomic_long_inc(&kcsan_counters[KCSAN_COUNTER_SETUP_WATCHPOINTS]); 458 atomic_long_inc(&kcsan_counters[KCSAN_COUNTER_USED_WATCHPOINTS]); 459 460 /* 461 * Read the current value, to later check and infer a race if the data 462 * was modified via a non-instrumented access, e.g. from a device. 463 */ 464 old = 0; 465 switch (size) { 466 case 1: 467 old = READ_ONCE(*(const u8 *)ptr); 468 break; 469 case 2: 470 old = READ_ONCE(*(const u16 *)ptr); 471 break; 472 case 4: 473 old = READ_ONCE(*(const u32 *)ptr); 474 break; 475 case 8: 476 old = READ_ONCE(*(const u64 *)ptr); 477 break; 478 default: 479 break; /* ignore; we do not diff the values */ 480 } 481 482 if (IS_ENABLED(CONFIG_KCSAN_DEBUG)) { 483 kcsan_disable_current(); 484 pr_err("watching %s, size: %zu, addr: %px [slot: %d, encoded: %lx]\n", 485 is_write ? "write" : "read", size, ptr, 486 watchpoint_slot((unsigned long)ptr), 487 encode_watchpoint((unsigned long)ptr, size, is_write)); 488 kcsan_enable_current(); 489 } 490 491 /* 492 * Delay this thread, to increase probability of observing a racy 493 * conflicting access. 494 */ 495 delay_access(type); 496 497 /* 498 * Re-read value, and check if it is as expected; if not, we infer a 499 * racy access. 500 */ 501 access_mask = get_ctx()->access_mask; 502 new = 0; 503 switch (size) { 504 case 1: 505 new = READ_ONCE(*(const u8 *)ptr); 506 break; 507 case 2: 508 new = READ_ONCE(*(const u16 *)ptr); 509 break; 510 case 4: 511 new = READ_ONCE(*(const u32 *)ptr); 512 break; 513 case 8: 514 new = READ_ONCE(*(const u64 *)ptr); 515 break; 516 default: 517 break; /* ignore; we do not diff the values */ 518 } 519 520 diff = old ^ new; 521 if (access_mask) 522 diff &= access_mask; 523 524 /* Were we able to observe a value-change? */ 525 if (diff != 0) 526 value_change = KCSAN_VALUE_CHANGE_TRUE; 527 528 /* Check if this access raced with another. */ 529 if (!consume_watchpoint(watchpoint)) { 530 /* 531 * Depending on the access type, map a value_change of MAYBE to 532 * TRUE (always report) or FALSE (never report). 533 */ 534 if (value_change == KCSAN_VALUE_CHANGE_MAYBE) { 535 if (access_mask != 0) { 536 /* 537 * For access with access_mask, we require a 538 * value-change, as it is likely that races on 539 * ~access_mask bits are expected. 540 */ 541 value_change = KCSAN_VALUE_CHANGE_FALSE; 542 } else if (size > 8 || is_assert) { 543 /* Always assume a value-change. */ 544 value_change = KCSAN_VALUE_CHANGE_TRUE; 545 } 546 } 547 548 /* 549 * No need to increment 'data_races' counter, as the racing 550 * thread already did. 551 * 552 * Count 'assert_failures' for each failed ASSERT access, 553 * therefore both this thread and the racing thread may 554 * increment this counter. 555 */ 556 if (is_assert && value_change == KCSAN_VALUE_CHANGE_TRUE) 557 atomic_long_inc(&kcsan_counters[KCSAN_COUNTER_ASSERT_FAILURES]); 558 559 kcsan_report_known_origin(ptr, size, type, value_change, 560 watchpoint - watchpoints, 561 old, new, access_mask); 562 } else if (value_change == KCSAN_VALUE_CHANGE_TRUE) { 563 /* Inferring a race, since the value should not have changed. */ 564 565 atomic_long_inc(&kcsan_counters[KCSAN_COUNTER_RACES_UNKNOWN_ORIGIN]); 566 if (is_assert) 567 atomic_long_inc(&kcsan_counters[KCSAN_COUNTER_ASSERT_FAILURES]); 568 569 if (IS_ENABLED(CONFIG_KCSAN_REPORT_RACE_UNKNOWN_ORIGIN) || is_assert) 570 kcsan_report_unknown_origin(ptr, size, type, old, new, access_mask); 571 } 572 573 /* 574 * Remove watchpoint; must be after reporting, since the slot may be 575 * reused after this point. 576 */ 577 remove_watchpoint(watchpoint); 578 atomic_long_dec(&kcsan_counters[KCSAN_COUNTER_USED_WATCHPOINTS]); 579 out_unlock: 580 if (!kcsan_interrupt_watcher) 581 local_irq_restore(irq_flags); 582 kcsan_restore_irqtrace(current); 583 out: 584 user_access_restore(ua_flags); 585 } 586 587 static __always_inline void check_access(const volatile void *ptr, size_t size, 588 int type) 589 { 590 const bool is_write = (type & KCSAN_ACCESS_WRITE) != 0; 591 atomic_long_t *watchpoint; 592 long encoded_watchpoint; 593 594 /* 595 * Do nothing for 0 sized check; this comparison will be optimized out 596 * for constant sized instrumentation (__tsan_{read,write}N). 597 */ 598 if (unlikely(size == 0)) 599 return; 600 601 /* 602 * Avoid user_access_save in fast-path: find_watchpoint is safe without 603 * user_access_save, as the address that ptr points to is only used to 604 * check if a watchpoint exists; ptr is never dereferenced. 605 */ 606 watchpoint = find_watchpoint((unsigned long)ptr, size, !is_write, 607 &encoded_watchpoint); 608 /* 609 * It is safe to check kcsan_is_enabled() after find_watchpoint in the 610 * slow-path, as long as no state changes that cause a race to be 611 * detected and reported have occurred until kcsan_is_enabled() is 612 * checked. 613 */ 614 615 if (unlikely(watchpoint != NULL)) 616 kcsan_found_watchpoint(ptr, size, type, watchpoint, 617 encoded_watchpoint); 618 else { 619 struct kcsan_ctx *ctx = get_ctx(); /* Call only once in fast-path. */ 620 621 if (unlikely(should_watch(ptr, size, type, ctx))) 622 kcsan_setup_watchpoint(ptr, size, type); 623 else if (unlikely(ctx->scoped_accesses.prev)) 624 kcsan_check_scoped_accesses(); 625 } 626 } 627 628 /* === Public interface ===================================================== */ 629 630 void __init kcsan_init(void) 631 { 632 int cpu; 633 634 BUG_ON(!in_task()); 635 636 for_each_possible_cpu(cpu) 637 per_cpu(kcsan_rand_state, cpu) = (u32)get_cycles(); 638 639 /* 640 * We are in the init task, and no other tasks should be running; 641 * WRITE_ONCE without memory barrier is sufficient. 642 */ 643 if (kcsan_early_enable) { 644 pr_info("enabled early\n"); 645 WRITE_ONCE(kcsan_enabled, true); 646 } 647 } 648 649 /* === Exported interface =================================================== */ 650 651 void kcsan_disable_current(void) 652 { 653 ++get_ctx()->disable_count; 654 } 655 EXPORT_SYMBOL(kcsan_disable_current); 656 657 void kcsan_enable_current(void) 658 { 659 if (get_ctx()->disable_count-- == 0) { 660 /* 661 * Warn if kcsan_enable_current() calls are unbalanced with 662 * kcsan_disable_current() calls, which causes disable_count to 663 * become negative and should not happen. 664 */ 665 kcsan_disable_current(); /* restore to 0, KCSAN still enabled */ 666 kcsan_disable_current(); /* disable to generate warning */ 667 WARN(1, "Unbalanced %s()", __func__); 668 kcsan_enable_current(); 669 } 670 } 671 EXPORT_SYMBOL(kcsan_enable_current); 672 673 void kcsan_enable_current_nowarn(void) 674 { 675 if (get_ctx()->disable_count-- == 0) 676 kcsan_disable_current(); 677 } 678 EXPORT_SYMBOL(kcsan_enable_current_nowarn); 679 680 void kcsan_nestable_atomic_begin(void) 681 { 682 /* 683 * Do *not* check and warn if we are in a flat atomic region: nestable 684 * and flat atomic regions are independent from each other. 685 * See include/linux/kcsan.h: struct kcsan_ctx comments for more 686 * comments. 687 */ 688 689 ++get_ctx()->atomic_nest_count; 690 } 691 EXPORT_SYMBOL(kcsan_nestable_atomic_begin); 692 693 void kcsan_nestable_atomic_end(void) 694 { 695 if (get_ctx()->atomic_nest_count-- == 0) { 696 /* 697 * Warn if kcsan_nestable_atomic_end() calls are unbalanced with 698 * kcsan_nestable_atomic_begin() calls, which causes 699 * atomic_nest_count to become negative and should not happen. 700 */ 701 kcsan_nestable_atomic_begin(); /* restore to 0 */ 702 kcsan_disable_current(); /* disable to generate warning */ 703 WARN(1, "Unbalanced %s()", __func__); 704 kcsan_enable_current(); 705 } 706 } 707 EXPORT_SYMBOL(kcsan_nestable_atomic_end); 708 709 void kcsan_flat_atomic_begin(void) 710 { 711 get_ctx()->in_flat_atomic = true; 712 } 713 EXPORT_SYMBOL(kcsan_flat_atomic_begin); 714 715 void kcsan_flat_atomic_end(void) 716 { 717 get_ctx()->in_flat_atomic = false; 718 } 719 EXPORT_SYMBOL(kcsan_flat_atomic_end); 720 721 void kcsan_atomic_next(int n) 722 { 723 get_ctx()->atomic_next = n; 724 } 725 EXPORT_SYMBOL(kcsan_atomic_next); 726 727 void kcsan_set_access_mask(unsigned long mask) 728 { 729 get_ctx()->access_mask = mask; 730 } 731 EXPORT_SYMBOL(kcsan_set_access_mask); 732 733 struct kcsan_scoped_access * 734 kcsan_begin_scoped_access(const volatile void *ptr, size_t size, int type, 735 struct kcsan_scoped_access *sa) 736 { 737 struct kcsan_ctx *ctx = get_ctx(); 738 739 __kcsan_check_access(ptr, size, type); 740 741 ctx->disable_count++; /* Disable KCSAN, in case list debugging is on. */ 742 743 INIT_LIST_HEAD(&sa->list); 744 sa->ptr = ptr; 745 sa->size = size; 746 sa->type = type; 747 748 if (!ctx->scoped_accesses.prev) /* Lazy initialize list head. */ 749 INIT_LIST_HEAD(&ctx->scoped_accesses); 750 list_add(&sa->list, &ctx->scoped_accesses); 751 752 ctx->disable_count--; 753 return sa; 754 } 755 EXPORT_SYMBOL(kcsan_begin_scoped_access); 756 757 void kcsan_end_scoped_access(struct kcsan_scoped_access *sa) 758 { 759 struct kcsan_ctx *ctx = get_ctx(); 760 761 if (WARN(!ctx->scoped_accesses.prev, "Unbalanced %s()?", __func__)) 762 return; 763 764 ctx->disable_count++; /* Disable KCSAN, in case list debugging is on. */ 765 766 list_del(&sa->list); 767 if (list_empty(&ctx->scoped_accesses)) 768 /* 769 * Ensure we do not enter kcsan_check_scoped_accesses() 770 * slow-path if unnecessary, and avoids requiring list_empty() 771 * in the fast-path (to avoid a READ_ONCE() and potential 772 * uaccess warning). 773 */ 774 ctx->scoped_accesses.prev = NULL; 775 776 ctx->disable_count--; 777 778 __kcsan_check_access(sa->ptr, sa->size, sa->type); 779 } 780 EXPORT_SYMBOL(kcsan_end_scoped_access); 781 782 void __kcsan_check_access(const volatile void *ptr, size_t size, int type) 783 { 784 check_access(ptr, size, type); 785 } 786 EXPORT_SYMBOL(__kcsan_check_access); 787 788 /* 789 * KCSAN uses the same instrumentation that is emitted by supported compilers 790 * for ThreadSanitizer (TSAN). 791 * 792 * When enabled, the compiler emits instrumentation calls (the functions 793 * prefixed with "__tsan" below) for all loads and stores that it generated; 794 * inline asm is not instrumented. 795 * 796 * Note that, not all supported compiler versions distinguish aligned/unaligned 797 * accesses, but e.g. recent versions of Clang do. We simply alias the unaligned 798 * version to the generic version, which can handle both. 799 */ 800 801 #define DEFINE_TSAN_READ_WRITE(size) \ 802 void __tsan_read##size(void *ptr); \ 803 void __tsan_read##size(void *ptr) \ 804 { \ 805 check_access(ptr, size, 0); \ 806 } \ 807 EXPORT_SYMBOL(__tsan_read##size); \ 808 void __tsan_unaligned_read##size(void *ptr) \ 809 __alias(__tsan_read##size); \ 810 EXPORT_SYMBOL(__tsan_unaligned_read##size); \ 811 void __tsan_write##size(void *ptr); \ 812 void __tsan_write##size(void *ptr) \ 813 { \ 814 check_access(ptr, size, KCSAN_ACCESS_WRITE); \ 815 } \ 816 EXPORT_SYMBOL(__tsan_write##size); \ 817 void __tsan_unaligned_write##size(void *ptr) \ 818 __alias(__tsan_write##size); \ 819 EXPORT_SYMBOL(__tsan_unaligned_write##size); \ 820 void __tsan_read_write##size(void *ptr); \ 821 void __tsan_read_write##size(void *ptr) \ 822 { \ 823 check_access(ptr, size, \ 824 KCSAN_ACCESS_COMPOUND | KCSAN_ACCESS_WRITE); \ 825 } \ 826 EXPORT_SYMBOL(__tsan_read_write##size); \ 827 void __tsan_unaligned_read_write##size(void *ptr) \ 828 __alias(__tsan_read_write##size); \ 829 EXPORT_SYMBOL(__tsan_unaligned_read_write##size) 830 831 DEFINE_TSAN_READ_WRITE(1); 832 DEFINE_TSAN_READ_WRITE(2); 833 DEFINE_TSAN_READ_WRITE(4); 834 DEFINE_TSAN_READ_WRITE(8); 835 DEFINE_TSAN_READ_WRITE(16); 836 837 void __tsan_read_range(void *ptr, size_t size); 838 void __tsan_read_range(void *ptr, size_t size) 839 { 840 check_access(ptr, size, 0); 841 } 842 EXPORT_SYMBOL(__tsan_read_range); 843 844 void __tsan_write_range(void *ptr, size_t size); 845 void __tsan_write_range(void *ptr, size_t size) 846 { 847 check_access(ptr, size, KCSAN_ACCESS_WRITE); 848 } 849 EXPORT_SYMBOL(__tsan_write_range); 850 851 /* 852 * Use of explicit volatile is generally disallowed [1], however, volatile is 853 * still used in various concurrent context, whether in low-level 854 * synchronization primitives or for legacy reasons. 855 * [1] https://lwn.net/Articles/233479/ 856 * 857 * We only consider volatile accesses atomic if they are aligned and would pass 858 * the size-check of compiletime_assert_rwonce_type(). 859 */ 860 #define DEFINE_TSAN_VOLATILE_READ_WRITE(size) \ 861 void __tsan_volatile_read##size(void *ptr); \ 862 void __tsan_volatile_read##size(void *ptr) \ 863 { \ 864 const bool is_atomic = size <= sizeof(long long) && \ 865 IS_ALIGNED((unsigned long)ptr, size); \ 866 if (IS_ENABLED(CONFIG_KCSAN_IGNORE_ATOMICS) && is_atomic) \ 867 return; \ 868 check_access(ptr, size, is_atomic ? KCSAN_ACCESS_ATOMIC : 0); \ 869 } \ 870 EXPORT_SYMBOL(__tsan_volatile_read##size); \ 871 void __tsan_unaligned_volatile_read##size(void *ptr) \ 872 __alias(__tsan_volatile_read##size); \ 873 EXPORT_SYMBOL(__tsan_unaligned_volatile_read##size); \ 874 void __tsan_volatile_write##size(void *ptr); \ 875 void __tsan_volatile_write##size(void *ptr) \ 876 { \ 877 const bool is_atomic = size <= sizeof(long long) && \ 878 IS_ALIGNED((unsigned long)ptr, size); \ 879 if (IS_ENABLED(CONFIG_KCSAN_IGNORE_ATOMICS) && is_atomic) \ 880 return; \ 881 check_access(ptr, size, \ 882 KCSAN_ACCESS_WRITE | \ 883 (is_atomic ? KCSAN_ACCESS_ATOMIC : 0)); \ 884 } \ 885 EXPORT_SYMBOL(__tsan_volatile_write##size); \ 886 void __tsan_unaligned_volatile_write##size(void *ptr) \ 887 __alias(__tsan_volatile_write##size); \ 888 EXPORT_SYMBOL(__tsan_unaligned_volatile_write##size) 889 890 DEFINE_TSAN_VOLATILE_READ_WRITE(1); 891 DEFINE_TSAN_VOLATILE_READ_WRITE(2); 892 DEFINE_TSAN_VOLATILE_READ_WRITE(4); 893 DEFINE_TSAN_VOLATILE_READ_WRITE(8); 894 DEFINE_TSAN_VOLATILE_READ_WRITE(16); 895 896 /* 897 * The below are not required by KCSAN, but can still be emitted by the 898 * compiler. 899 */ 900 void __tsan_func_entry(void *call_pc); 901 void __tsan_func_entry(void *call_pc) 902 { 903 } 904 EXPORT_SYMBOL(__tsan_func_entry); 905 void __tsan_func_exit(void); 906 void __tsan_func_exit(void) 907 { 908 } 909 EXPORT_SYMBOL(__tsan_func_exit); 910 void __tsan_init(void); 911 void __tsan_init(void) 912 { 913 } 914 EXPORT_SYMBOL(__tsan_init); 915 916 /* 917 * Instrumentation for atomic builtins (__atomic_*, __sync_*). 918 * 919 * Normal kernel code _should not_ be using them directly, but some 920 * architectures may implement some or all atomics using the compilers' 921 * builtins. 922 * 923 * Note: If an architecture decides to fully implement atomics using the 924 * builtins, because they are implicitly instrumented by KCSAN (and KASAN, 925 * etc.), implementing the ARCH_ATOMIC interface (to get instrumentation via 926 * atomic-instrumented) is no longer necessary. 927 * 928 * TSAN instrumentation replaces atomic accesses with calls to any of the below 929 * functions, whose job is to also execute the operation itself. 930 */ 931 932 #define DEFINE_TSAN_ATOMIC_LOAD_STORE(bits) \ 933 u##bits __tsan_atomic##bits##_load(const u##bits *ptr, int memorder); \ 934 u##bits __tsan_atomic##bits##_load(const u##bits *ptr, int memorder) \ 935 { \ 936 if (!IS_ENABLED(CONFIG_KCSAN_IGNORE_ATOMICS)) { \ 937 check_access(ptr, bits / BITS_PER_BYTE, KCSAN_ACCESS_ATOMIC); \ 938 } \ 939 return __atomic_load_n(ptr, memorder); \ 940 } \ 941 EXPORT_SYMBOL(__tsan_atomic##bits##_load); \ 942 void __tsan_atomic##bits##_store(u##bits *ptr, u##bits v, int memorder); \ 943 void __tsan_atomic##bits##_store(u##bits *ptr, u##bits v, int memorder) \ 944 { \ 945 if (!IS_ENABLED(CONFIG_KCSAN_IGNORE_ATOMICS)) { \ 946 check_access(ptr, bits / BITS_PER_BYTE, \ 947 KCSAN_ACCESS_WRITE | KCSAN_ACCESS_ATOMIC); \ 948 } \ 949 __atomic_store_n(ptr, v, memorder); \ 950 } \ 951 EXPORT_SYMBOL(__tsan_atomic##bits##_store) 952 953 #define DEFINE_TSAN_ATOMIC_RMW(op, bits, suffix) \ 954 u##bits __tsan_atomic##bits##_##op(u##bits *ptr, u##bits v, int memorder); \ 955 u##bits __tsan_atomic##bits##_##op(u##bits *ptr, u##bits v, int memorder) \ 956 { \ 957 if (!IS_ENABLED(CONFIG_KCSAN_IGNORE_ATOMICS)) { \ 958 check_access(ptr, bits / BITS_PER_BYTE, \ 959 KCSAN_ACCESS_COMPOUND | KCSAN_ACCESS_WRITE | \ 960 KCSAN_ACCESS_ATOMIC); \ 961 } \ 962 return __atomic_##op##suffix(ptr, v, memorder); \ 963 } \ 964 EXPORT_SYMBOL(__tsan_atomic##bits##_##op) 965 966 /* 967 * Note: CAS operations are always classified as write, even in case they 968 * fail. We cannot perform check_access() after a write, as it might lead to 969 * false positives, in cases such as: 970 * 971 * T0: __atomic_compare_exchange_n(&p->flag, &old, 1, ...) 972 * 973 * T1: if (__atomic_load_n(&p->flag, ...)) { 974 * modify *p; 975 * p->flag = 0; 976 * } 977 * 978 * The only downside is that, if there are 3 threads, with one CAS that 979 * succeeds, another CAS that fails, and an unmarked racing operation, we may 980 * point at the wrong CAS as the source of the race. However, if we assume that 981 * all CAS can succeed in some other execution, the data race is still valid. 982 */ 983 #define DEFINE_TSAN_ATOMIC_CMPXCHG(bits, strength, weak) \ 984 int __tsan_atomic##bits##_compare_exchange_##strength(u##bits *ptr, u##bits *exp, \ 985 u##bits val, int mo, int fail_mo); \ 986 int __tsan_atomic##bits##_compare_exchange_##strength(u##bits *ptr, u##bits *exp, \ 987 u##bits val, int mo, int fail_mo) \ 988 { \ 989 if (!IS_ENABLED(CONFIG_KCSAN_IGNORE_ATOMICS)) { \ 990 check_access(ptr, bits / BITS_PER_BYTE, \ 991 KCSAN_ACCESS_COMPOUND | KCSAN_ACCESS_WRITE | \ 992 KCSAN_ACCESS_ATOMIC); \ 993 } \ 994 return __atomic_compare_exchange_n(ptr, exp, val, weak, mo, fail_mo); \ 995 } \ 996 EXPORT_SYMBOL(__tsan_atomic##bits##_compare_exchange_##strength) 997 998 #define DEFINE_TSAN_ATOMIC_CMPXCHG_VAL(bits) \ 999 u##bits __tsan_atomic##bits##_compare_exchange_val(u##bits *ptr, u##bits exp, u##bits val, \ 1000 int mo, int fail_mo); \ 1001 u##bits __tsan_atomic##bits##_compare_exchange_val(u##bits *ptr, u##bits exp, u##bits val, \ 1002 int mo, int fail_mo) \ 1003 { \ 1004 if (!IS_ENABLED(CONFIG_KCSAN_IGNORE_ATOMICS)) { \ 1005 check_access(ptr, bits / BITS_PER_BYTE, \ 1006 KCSAN_ACCESS_COMPOUND | KCSAN_ACCESS_WRITE | \ 1007 KCSAN_ACCESS_ATOMIC); \ 1008 } \ 1009 __atomic_compare_exchange_n(ptr, &exp, val, 0, mo, fail_mo); \ 1010 return exp; \ 1011 } \ 1012 EXPORT_SYMBOL(__tsan_atomic##bits##_compare_exchange_val) 1013 1014 #define DEFINE_TSAN_ATOMIC_OPS(bits) \ 1015 DEFINE_TSAN_ATOMIC_LOAD_STORE(bits); \ 1016 DEFINE_TSAN_ATOMIC_RMW(exchange, bits, _n); \ 1017 DEFINE_TSAN_ATOMIC_RMW(fetch_add, bits, ); \ 1018 DEFINE_TSAN_ATOMIC_RMW(fetch_sub, bits, ); \ 1019 DEFINE_TSAN_ATOMIC_RMW(fetch_and, bits, ); \ 1020 DEFINE_TSAN_ATOMIC_RMW(fetch_or, bits, ); \ 1021 DEFINE_TSAN_ATOMIC_RMW(fetch_xor, bits, ); \ 1022 DEFINE_TSAN_ATOMIC_RMW(fetch_nand, bits, ); \ 1023 DEFINE_TSAN_ATOMIC_CMPXCHG(bits, strong, 0); \ 1024 DEFINE_TSAN_ATOMIC_CMPXCHG(bits, weak, 1); \ 1025 DEFINE_TSAN_ATOMIC_CMPXCHG_VAL(bits) 1026 1027 DEFINE_TSAN_ATOMIC_OPS(8); 1028 DEFINE_TSAN_ATOMIC_OPS(16); 1029 DEFINE_TSAN_ATOMIC_OPS(32); 1030 DEFINE_TSAN_ATOMIC_OPS(64); 1031 1032 void __tsan_atomic_thread_fence(int memorder); 1033 void __tsan_atomic_thread_fence(int memorder) 1034 { 1035 __atomic_thread_fence(memorder); 1036 } 1037 EXPORT_SYMBOL(__tsan_atomic_thread_fence); 1038 1039 void __tsan_atomic_signal_fence(int memorder); 1040 void __tsan_atomic_signal_fence(int memorder) { } 1041 EXPORT_SYMBOL(__tsan_atomic_signal_fence); 1042