1 // SPDX-License-Identifier: GPL-2.0 2 3 #include <linux/atomic.h> 4 #include <linux/bug.h> 5 #include <linux/delay.h> 6 #include <linux/export.h> 7 #include <linux/init.h> 8 #include <linux/kernel.h> 9 #include <linux/list.h> 10 #include <linux/moduleparam.h> 11 #include <linux/percpu.h> 12 #include <linux/preempt.h> 13 #include <linux/random.h> 14 #include <linux/sched.h> 15 #include <linux/uaccess.h> 16 17 #include "atomic.h" 18 #include "encoding.h" 19 #include "kcsan.h" 20 21 static bool kcsan_early_enable = IS_ENABLED(CONFIG_KCSAN_EARLY_ENABLE); 22 unsigned int kcsan_udelay_task = CONFIG_KCSAN_UDELAY_TASK; 23 unsigned int kcsan_udelay_interrupt = CONFIG_KCSAN_UDELAY_INTERRUPT; 24 static long kcsan_skip_watch = CONFIG_KCSAN_SKIP_WATCH; 25 static bool kcsan_interrupt_watcher = IS_ENABLED(CONFIG_KCSAN_INTERRUPT_WATCHER); 26 27 #ifdef MODULE_PARAM_PREFIX 28 #undef MODULE_PARAM_PREFIX 29 #endif 30 #define MODULE_PARAM_PREFIX "kcsan." 31 module_param_named(early_enable, kcsan_early_enable, bool, 0); 32 module_param_named(udelay_task, kcsan_udelay_task, uint, 0644); 33 module_param_named(udelay_interrupt, kcsan_udelay_interrupt, uint, 0644); 34 module_param_named(skip_watch, kcsan_skip_watch, long, 0644); 35 module_param_named(interrupt_watcher, kcsan_interrupt_watcher, bool, 0444); 36 37 bool kcsan_enabled; 38 39 /* Per-CPU kcsan_ctx for interrupts */ 40 static DEFINE_PER_CPU(struct kcsan_ctx, kcsan_cpu_ctx) = { 41 .disable_count = 0, 42 .atomic_next = 0, 43 .atomic_nest_count = 0, 44 .in_flat_atomic = false, 45 .access_mask = 0, 46 .scoped_accesses = {LIST_POISON1, NULL}, 47 }; 48 49 /* 50 * Helper macros to index into adjacent slots, starting from address slot 51 * itself, followed by the right and left slots. 52 * 53 * The purpose is 2-fold: 54 * 55 * 1. if during insertion the address slot is already occupied, check if 56 * any adjacent slots are free; 57 * 2. accesses that straddle a slot boundary due to size that exceeds a 58 * slot's range may check adjacent slots if any watchpoint matches. 59 * 60 * Note that accesses with very large size may still miss a watchpoint; however, 61 * given this should be rare, this is a reasonable trade-off to make, since this 62 * will avoid: 63 * 64 * 1. excessive contention between watchpoint checks and setup; 65 * 2. larger number of simultaneous watchpoints without sacrificing 66 * performance. 67 * 68 * Example: SLOT_IDX values for KCSAN_CHECK_ADJACENT=1, where i is [0, 1, 2]: 69 * 70 * slot=0: [ 1, 2, 0] 71 * slot=9: [10, 11, 9] 72 * slot=63: [64, 65, 63] 73 */ 74 #define SLOT_IDX(slot, i) (slot + ((i + KCSAN_CHECK_ADJACENT) % NUM_SLOTS)) 75 76 /* 77 * SLOT_IDX_FAST is used in the fast-path. Not first checking the address's primary 78 * slot (middle) is fine if we assume that races occur rarely. The set of 79 * indices {SLOT_IDX(slot, i) | i in [0, NUM_SLOTS)} is equivalent to 80 * {SLOT_IDX_FAST(slot, i) | i in [0, NUM_SLOTS)}. 81 */ 82 #define SLOT_IDX_FAST(slot, i) (slot + i) 83 84 /* 85 * Watchpoints, with each entry encoded as defined in encoding.h: in order to be 86 * able to safely update and access a watchpoint without introducing locking 87 * overhead, we encode each watchpoint as a single atomic long. The initial 88 * zero-initialized state matches INVALID_WATCHPOINT. 89 * 90 * Add NUM_SLOTS-1 entries to account for overflow; this helps avoid having to 91 * use more complicated SLOT_IDX_FAST calculation with modulo in the fast-path. 92 */ 93 static atomic_long_t watchpoints[CONFIG_KCSAN_NUM_WATCHPOINTS + NUM_SLOTS-1]; 94 95 /* 96 * Instructions to skip watching counter, used in should_watch(). We use a 97 * per-CPU counter to avoid excessive contention. 98 */ 99 static DEFINE_PER_CPU(long, kcsan_skip); 100 101 static __always_inline atomic_long_t *find_watchpoint(unsigned long addr, 102 size_t size, 103 bool expect_write, 104 long *encoded_watchpoint) 105 { 106 const int slot = watchpoint_slot(addr); 107 const unsigned long addr_masked = addr & WATCHPOINT_ADDR_MASK; 108 atomic_long_t *watchpoint; 109 unsigned long wp_addr_masked; 110 size_t wp_size; 111 bool is_write; 112 int i; 113 114 BUILD_BUG_ON(CONFIG_KCSAN_NUM_WATCHPOINTS < NUM_SLOTS); 115 116 for (i = 0; i < NUM_SLOTS; ++i) { 117 watchpoint = &watchpoints[SLOT_IDX_FAST(slot, i)]; 118 *encoded_watchpoint = atomic_long_read(watchpoint); 119 if (!decode_watchpoint(*encoded_watchpoint, &wp_addr_masked, 120 &wp_size, &is_write)) 121 continue; 122 123 if (expect_write && !is_write) 124 continue; 125 126 /* Check if the watchpoint matches the access. */ 127 if (matching_access(wp_addr_masked, wp_size, addr_masked, size)) 128 return watchpoint; 129 } 130 131 return NULL; 132 } 133 134 static inline atomic_long_t * 135 insert_watchpoint(unsigned long addr, size_t size, bool is_write) 136 { 137 const int slot = watchpoint_slot(addr); 138 const long encoded_watchpoint = encode_watchpoint(addr, size, is_write); 139 atomic_long_t *watchpoint; 140 int i; 141 142 /* Check slot index logic, ensuring we stay within array bounds. */ 143 BUILD_BUG_ON(SLOT_IDX(0, 0) != KCSAN_CHECK_ADJACENT); 144 BUILD_BUG_ON(SLOT_IDX(0, KCSAN_CHECK_ADJACENT+1) != 0); 145 BUILD_BUG_ON(SLOT_IDX(CONFIG_KCSAN_NUM_WATCHPOINTS-1, KCSAN_CHECK_ADJACENT) != ARRAY_SIZE(watchpoints)-1); 146 BUILD_BUG_ON(SLOT_IDX(CONFIG_KCSAN_NUM_WATCHPOINTS-1, KCSAN_CHECK_ADJACENT+1) != ARRAY_SIZE(watchpoints) - NUM_SLOTS); 147 148 for (i = 0; i < NUM_SLOTS; ++i) { 149 long expect_val = INVALID_WATCHPOINT; 150 151 /* Try to acquire this slot. */ 152 watchpoint = &watchpoints[SLOT_IDX(slot, i)]; 153 if (atomic_long_try_cmpxchg_relaxed(watchpoint, &expect_val, encoded_watchpoint)) 154 return watchpoint; 155 } 156 157 return NULL; 158 } 159 160 /* 161 * Return true if watchpoint was successfully consumed, false otherwise. 162 * 163 * This may return false if: 164 * 165 * 1. another thread already consumed the watchpoint; 166 * 2. the thread that set up the watchpoint already removed it; 167 * 3. the watchpoint was removed and then re-used. 168 */ 169 static __always_inline bool 170 try_consume_watchpoint(atomic_long_t *watchpoint, long encoded_watchpoint) 171 { 172 return atomic_long_try_cmpxchg_relaxed(watchpoint, &encoded_watchpoint, CONSUMED_WATCHPOINT); 173 } 174 175 /* Return true if watchpoint was not touched, false if already consumed. */ 176 static inline bool consume_watchpoint(atomic_long_t *watchpoint) 177 { 178 return atomic_long_xchg_relaxed(watchpoint, CONSUMED_WATCHPOINT) != CONSUMED_WATCHPOINT; 179 } 180 181 /* Remove the watchpoint -- its slot may be reused after. */ 182 static inline void remove_watchpoint(atomic_long_t *watchpoint) 183 { 184 atomic_long_set(watchpoint, INVALID_WATCHPOINT); 185 } 186 187 static __always_inline struct kcsan_ctx *get_ctx(void) 188 { 189 /* 190 * In interrupts, use raw_cpu_ptr to avoid unnecessary checks, that would 191 * also result in calls that generate warnings in uaccess regions. 192 */ 193 return in_task() ? ¤t->kcsan_ctx : raw_cpu_ptr(&kcsan_cpu_ctx); 194 } 195 196 /* Check scoped accesses; never inline because this is a slow-path! */ 197 static noinline void kcsan_check_scoped_accesses(void) 198 { 199 struct kcsan_ctx *ctx = get_ctx(); 200 struct list_head *prev_save = ctx->scoped_accesses.prev; 201 struct kcsan_scoped_access *scoped_access; 202 203 ctx->scoped_accesses.prev = NULL; /* Avoid recursion. */ 204 list_for_each_entry(scoped_access, &ctx->scoped_accesses, list) 205 __kcsan_check_access(scoped_access->ptr, scoped_access->size, scoped_access->type); 206 ctx->scoped_accesses.prev = prev_save; 207 } 208 209 /* Rules for generic atomic accesses. Called from fast-path. */ 210 static __always_inline bool 211 is_atomic(const volatile void *ptr, size_t size, int type, struct kcsan_ctx *ctx) 212 { 213 if (type & KCSAN_ACCESS_ATOMIC) 214 return true; 215 216 /* 217 * Unless explicitly declared atomic, never consider an assertion access 218 * as atomic. This allows using them also in atomic regions, such as 219 * seqlocks, without implicitly changing their semantics. 220 */ 221 if (type & KCSAN_ACCESS_ASSERT) 222 return false; 223 224 if (IS_ENABLED(CONFIG_KCSAN_ASSUME_PLAIN_WRITES_ATOMIC) && 225 (type & KCSAN_ACCESS_WRITE) && size <= sizeof(long) && 226 IS_ALIGNED((unsigned long)ptr, size)) 227 return true; /* Assume aligned writes up to word size are atomic. */ 228 229 if (ctx->atomic_next > 0) { 230 /* 231 * Because we do not have separate contexts for nested 232 * interrupts, in case atomic_next is set, we simply assume that 233 * the outer interrupt set atomic_next. In the worst case, we 234 * will conservatively consider operations as atomic. This is a 235 * reasonable trade-off to make, since this case should be 236 * extremely rare; however, even if extremely rare, it could 237 * lead to false positives otherwise. 238 */ 239 if ((hardirq_count() >> HARDIRQ_SHIFT) < 2) 240 --ctx->atomic_next; /* in task, or outer interrupt */ 241 return true; 242 } 243 244 return ctx->atomic_nest_count > 0 || ctx->in_flat_atomic; 245 } 246 247 static __always_inline bool 248 should_watch(const volatile void *ptr, size_t size, int type, struct kcsan_ctx *ctx) 249 { 250 /* 251 * Never set up watchpoints when memory operations are atomic. 252 * 253 * Need to check this first, before kcsan_skip check below: (1) atomics 254 * should not count towards skipped instructions, and (2) to actually 255 * decrement kcsan_atomic_next for consecutive instruction stream. 256 */ 257 if (is_atomic(ptr, size, type, ctx)) 258 return false; 259 260 if (this_cpu_dec_return(kcsan_skip) >= 0) 261 return false; 262 263 /* 264 * NOTE: If we get here, kcsan_skip must always be reset in slow path 265 * via reset_kcsan_skip() to avoid underflow. 266 */ 267 268 /* this operation should be watched */ 269 return true; 270 } 271 272 static inline void reset_kcsan_skip(void) 273 { 274 long skip_count = kcsan_skip_watch - 275 (IS_ENABLED(CONFIG_KCSAN_SKIP_WATCH_RANDOMIZE) ? 276 prandom_u32_max(kcsan_skip_watch) : 277 0); 278 this_cpu_write(kcsan_skip, skip_count); 279 } 280 281 static __always_inline bool kcsan_is_enabled(void) 282 { 283 return READ_ONCE(kcsan_enabled) && get_ctx()->disable_count == 0; 284 } 285 286 static inline unsigned int get_delay(void) 287 { 288 unsigned int delay = in_task() ? kcsan_udelay_task : kcsan_udelay_interrupt; 289 return delay - (IS_ENABLED(CONFIG_KCSAN_DELAY_RANDOMIZE) ? 290 prandom_u32_max(delay) : 291 0); 292 } 293 294 /* 295 * Pull everything together: check_access() below contains the performance 296 * critical operations; the fast-path (including check_access) functions should 297 * all be inlinable by the instrumentation functions. 298 * 299 * The slow-path (kcsan_found_watchpoint, kcsan_setup_watchpoint) are 300 * non-inlinable -- note that, we prefix these with "kcsan_" to ensure they can 301 * be filtered from the stacktrace, as well as give them unique names for the 302 * UACCESS whitelist of objtool. Each function uses user_access_save/restore(), 303 * since they do not access any user memory, but instrumentation is still 304 * emitted in UACCESS regions. 305 */ 306 307 static noinline void kcsan_found_watchpoint(const volatile void *ptr, 308 size_t size, 309 int type, 310 atomic_long_t *watchpoint, 311 long encoded_watchpoint) 312 { 313 unsigned long flags; 314 bool consumed; 315 316 if (!kcsan_is_enabled()) 317 return; 318 319 /* 320 * The access_mask check relies on value-change comparison. To avoid 321 * reporting a race where e.g. the writer set up the watchpoint, but the 322 * reader has access_mask!=0, we have to ignore the found watchpoint. 323 */ 324 if (get_ctx()->access_mask != 0) 325 return; 326 327 /* 328 * Consume the watchpoint as soon as possible, to minimize the chances 329 * of !consumed. Consuming the watchpoint must always be guarded by 330 * kcsan_is_enabled() check, as otherwise we might erroneously 331 * triggering reports when disabled. 332 */ 333 consumed = try_consume_watchpoint(watchpoint, encoded_watchpoint); 334 335 /* keep this after try_consume_watchpoint */ 336 flags = user_access_save(); 337 338 if (consumed) { 339 kcsan_report(ptr, size, type, KCSAN_VALUE_CHANGE_MAYBE, 340 KCSAN_REPORT_CONSUMED_WATCHPOINT, 341 watchpoint - watchpoints); 342 } else { 343 /* 344 * The other thread may not print any diagnostics, as it has 345 * already removed the watchpoint, or another thread consumed 346 * the watchpoint before this thread. 347 */ 348 kcsan_counter_inc(KCSAN_COUNTER_REPORT_RACES); 349 } 350 351 if ((type & KCSAN_ACCESS_ASSERT) != 0) 352 kcsan_counter_inc(KCSAN_COUNTER_ASSERT_FAILURES); 353 else 354 kcsan_counter_inc(KCSAN_COUNTER_DATA_RACES); 355 356 user_access_restore(flags); 357 } 358 359 static noinline void 360 kcsan_setup_watchpoint(const volatile void *ptr, size_t size, int type) 361 { 362 const bool is_write = (type & KCSAN_ACCESS_WRITE) != 0; 363 const bool is_assert = (type & KCSAN_ACCESS_ASSERT) != 0; 364 atomic_long_t *watchpoint; 365 union { 366 u8 _1; 367 u16 _2; 368 u32 _4; 369 u64 _8; 370 } expect_value; 371 unsigned long access_mask; 372 enum kcsan_value_change value_change = KCSAN_VALUE_CHANGE_MAYBE; 373 unsigned long ua_flags = user_access_save(); 374 unsigned long irq_flags = 0; 375 376 /* 377 * Always reset kcsan_skip counter in slow-path to avoid underflow; see 378 * should_watch(). 379 */ 380 reset_kcsan_skip(); 381 382 if (!kcsan_is_enabled()) 383 goto out; 384 385 /* 386 * Special atomic rules: unlikely to be true, so we check them here in 387 * the slow-path, and not in the fast-path in is_atomic(). Call after 388 * kcsan_is_enabled(), as we may access memory that is not yet 389 * initialized during early boot. 390 */ 391 if (!is_assert && kcsan_is_atomic_special(ptr)) 392 goto out; 393 394 if (!check_encodable((unsigned long)ptr, size)) { 395 kcsan_counter_inc(KCSAN_COUNTER_UNENCODABLE_ACCESSES); 396 goto out; 397 } 398 399 if (!kcsan_interrupt_watcher) 400 /* Use raw to avoid lockdep recursion via IRQ flags tracing. */ 401 raw_local_irq_save(irq_flags); 402 403 watchpoint = insert_watchpoint((unsigned long)ptr, size, is_write); 404 if (watchpoint == NULL) { 405 /* 406 * Out of capacity: the size of 'watchpoints', and the frequency 407 * with which should_watch() returns true should be tweaked so 408 * that this case happens very rarely. 409 */ 410 kcsan_counter_inc(KCSAN_COUNTER_NO_CAPACITY); 411 goto out_unlock; 412 } 413 414 kcsan_counter_inc(KCSAN_COUNTER_SETUP_WATCHPOINTS); 415 kcsan_counter_inc(KCSAN_COUNTER_USED_WATCHPOINTS); 416 417 /* 418 * Read the current value, to later check and infer a race if the data 419 * was modified via a non-instrumented access, e.g. from a device. 420 */ 421 expect_value._8 = 0; 422 switch (size) { 423 case 1: 424 expect_value._1 = READ_ONCE(*(const u8 *)ptr); 425 break; 426 case 2: 427 expect_value._2 = READ_ONCE(*(const u16 *)ptr); 428 break; 429 case 4: 430 expect_value._4 = READ_ONCE(*(const u32 *)ptr); 431 break; 432 case 8: 433 expect_value._8 = READ_ONCE(*(const u64 *)ptr); 434 break; 435 default: 436 break; /* ignore; we do not diff the values */ 437 } 438 439 if (IS_ENABLED(CONFIG_KCSAN_DEBUG)) { 440 kcsan_disable_current(); 441 pr_err("KCSAN: watching %s, size: %zu, addr: %px [slot: %d, encoded: %lx]\n", 442 is_write ? "write" : "read", size, ptr, 443 watchpoint_slot((unsigned long)ptr), 444 encode_watchpoint((unsigned long)ptr, size, is_write)); 445 kcsan_enable_current(); 446 } 447 448 /* 449 * Delay this thread, to increase probability of observing a racy 450 * conflicting access. 451 */ 452 udelay(get_delay()); 453 454 /* 455 * Re-read value, and check if it is as expected; if not, we infer a 456 * racy access. 457 */ 458 access_mask = get_ctx()->access_mask; 459 switch (size) { 460 case 1: 461 expect_value._1 ^= READ_ONCE(*(const u8 *)ptr); 462 if (access_mask) 463 expect_value._1 &= (u8)access_mask; 464 break; 465 case 2: 466 expect_value._2 ^= READ_ONCE(*(const u16 *)ptr); 467 if (access_mask) 468 expect_value._2 &= (u16)access_mask; 469 break; 470 case 4: 471 expect_value._4 ^= READ_ONCE(*(const u32 *)ptr); 472 if (access_mask) 473 expect_value._4 &= (u32)access_mask; 474 break; 475 case 8: 476 expect_value._8 ^= READ_ONCE(*(const u64 *)ptr); 477 if (access_mask) 478 expect_value._8 &= (u64)access_mask; 479 break; 480 default: 481 break; /* ignore; we do not diff the values */ 482 } 483 484 /* Were we able to observe a value-change? */ 485 if (expect_value._8 != 0) 486 value_change = KCSAN_VALUE_CHANGE_TRUE; 487 488 /* Check if this access raced with another. */ 489 if (!consume_watchpoint(watchpoint)) { 490 /* 491 * Depending on the access type, map a value_change of MAYBE to 492 * TRUE (always report) or FALSE (never report). 493 */ 494 if (value_change == KCSAN_VALUE_CHANGE_MAYBE) { 495 if (access_mask != 0) { 496 /* 497 * For access with access_mask, we require a 498 * value-change, as it is likely that races on 499 * ~access_mask bits are expected. 500 */ 501 value_change = KCSAN_VALUE_CHANGE_FALSE; 502 } else if (size > 8 || is_assert) { 503 /* Always assume a value-change. */ 504 value_change = KCSAN_VALUE_CHANGE_TRUE; 505 } 506 } 507 508 /* 509 * No need to increment 'data_races' counter, as the racing 510 * thread already did. 511 * 512 * Count 'assert_failures' for each failed ASSERT access, 513 * therefore both this thread and the racing thread may 514 * increment this counter. 515 */ 516 if (is_assert && value_change == KCSAN_VALUE_CHANGE_TRUE) 517 kcsan_counter_inc(KCSAN_COUNTER_ASSERT_FAILURES); 518 519 kcsan_report(ptr, size, type, value_change, KCSAN_REPORT_RACE_SIGNAL, 520 watchpoint - watchpoints); 521 } else if (value_change == KCSAN_VALUE_CHANGE_TRUE) { 522 /* Inferring a race, since the value should not have changed. */ 523 524 kcsan_counter_inc(KCSAN_COUNTER_RACES_UNKNOWN_ORIGIN); 525 if (is_assert) 526 kcsan_counter_inc(KCSAN_COUNTER_ASSERT_FAILURES); 527 528 if (IS_ENABLED(CONFIG_KCSAN_REPORT_RACE_UNKNOWN_ORIGIN) || is_assert) 529 kcsan_report(ptr, size, type, KCSAN_VALUE_CHANGE_TRUE, 530 KCSAN_REPORT_RACE_UNKNOWN_ORIGIN, 531 watchpoint - watchpoints); 532 } 533 534 /* 535 * Remove watchpoint; must be after reporting, since the slot may be 536 * reused after this point. 537 */ 538 remove_watchpoint(watchpoint); 539 kcsan_counter_dec(KCSAN_COUNTER_USED_WATCHPOINTS); 540 out_unlock: 541 if (!kcsan_interrupt_watcher) 542 raw_local_irq_restore(irq_flags); 543 out: 544 user_access_restore(ua_flags); 545 } 546 547 static __always_inline void check_access(const volatile void *ptr, size_t size, 548 int type) 549 { 550 const bool is_write = (type & KCSAN_ACCESS_WRITE) != 0; 551 atomic_long_t *watchpoint; 552 long encoded_watchpoint; 553 554 /* 555 * Do nothing for 0 sized check; this comparison will be optimized out 556 * for constant sized instrumentation (__tsan_{read,write}N). 557 */ 558 if (unlikely(size == 0)) 559 return; 560 561 /* 562 * Avoid user_access_save in fast-path: find_watchpoint is safe without 563 * user_access_save, as the address that ptr points to is only used to 564 * check if a watchpoint exists; ptr is never dereferenced. 565 */ 566 watchpoint = find_watchpoint((unsigned long)ptr, size, !is_write, 567 &encoded_watchpoint); 568 /* 569 * It is safe to check kcsan_is_enabled() after find_watchpoint in the 570 * slow-path, as long as no state changes that cause a race to be 571 * detected and reported have occurred until kcsan_is_enabled() is 572 * checked. 573 */ 574 575 if (unlikely(watchpoint != NULL)) 576 kcsan_found_watchpoint(ptr, size, type, watchpoint, 577 encoded_watchpoint); 578 else { 579 struct kcsan_ctx *ctx = get_ctx(); /* Call only once in fast-path. */ 580 581 if (unlikely(should_watch(ptr, size, type, ctx))) 582 kcsan_setup_watchpoint(ptr, size, type); 583 else if (unlikely(ctx->scoped_accesses.prev)) 584 kcsan_check_scoped_accesses(); 585 } 586 } 587 588 /* === Public interface ===================================================== */ 589 590 void __init kcsan_init(void) 591 { 592 BUG_ON(!in_task()); 593 594 kcsan_debugfs_init(); 595 596 /* 597 * We are in the init task, and no other tasks should be running; 598 * WRITE_ONCE without memory barrier is sufficient. 599 */ 600 if (kcsan_early_enable) 601 WRITE_ONCE(kcsan_enabled, true); 602 } 603 604 /* === Exported interface =================================================== */ 605 606 void kcsan_disable_current(void) 607 { 608 ++get_ctx()->disable_count; 609 } 610 EXPORT_SYMBOL(kcsan_disable_current); 611 612 void kcsan_enable_current(void) 613 { 614 if (get_ctx()->disable_count-- == 0) { 615 /* 616 * Warn if kcsan_enable_current() calls are unbalanced with 617 * kcsan_disable_current() calls, which causes disable_count to 618 * become negative and should not happen. 619 */ 620 kcsan_disable_current(); /* restore to 0, KCSAN still enabled */ 621 kcsan_disable_current(); /* disable to generate warning */ 622 WARN(1, "Unbalanced %s()", __func__); 623 kcsan_enable_current(); 624 } 625 } 626 EXPORT_SYMBOL(kcsan_enable_current); 627 628 void kcsan_enable_current_nowarn(void) 629 { 630 if (get_ctx()->disable_count-- == 0) 631 kcsan_disable_current(); 632 } 633 EXPORT_SYMBOL(kcsan_enable_current_nowarn); 634 635 void kcsan_nestable_atomic_begin(void) 636 { 637 /* 638 * Do *not* check and warn if we are in a flat atomic region: nestable 639 * and flat atomic regions are independent from each other. 640 * See include/linux/kcsan.h: struct kcsan_ctx comments for more 641 * comments. 642 */ 643 644 ++get_ctx()->atomic_nest_count; 645 } 646 EXPORT_SYMBOL(kcsan_nestable_atomic_begin); 647 648 void kcsan_nestable_atomic_end(void) 649 { 650 if (get_ctx()->atomic_nest_count-- == 0) { 651 /* 652 * Warn if kcsan_nestable_atomic_end() calls are unbalanced with 653 * kcsan_nestable_atomic_begin() calls, which causes 654 * atomic_nest_count to become negative and should not happen. 655 */ 656 kcsan_nestable_atomic_begin(); /* restore to 0 */ 657 kcsan_disable_current(); /* disable to generate warning */ 658 WARN(1, "Unbalanced %s()", __func__); 659 kcsan_enable_current(); 660 } 661 } 662 EXPORT_SYMBOL(kcsan_nestable_atomic_end); 663 664 void kcsan_flat_atomic_begin(void) 665 { 666 get_ctx()->in_flat_atomic = true; 667 } 668 EXPORT_SYMBOL(kcsan_flat_atomic_begin); 669 670 void kcsan_flat_atomic_end(void) 671 { 672 get_ctx()->in_flat_atomic = false; 673 } 674 EXPORT_SYMBOL(kcsan_flat_atomic_end); 675 676 void kcsan_atomic_next(int n) 677 { 678 get_ctx()->atomic_next = n; 679 } 680 EXPORT_SYMBOL(kcsan_atomic_next); 681 682 void kcsan_set_access_mask(unsigned long mask) 683 { 684 get_ctx()->access_mask = mask; 685 } 686 EXPORT_SYMBOL(kcsan_set_access_mask); 687 688 struct kcsan_scoped_access * 689 kcsan_begin_scoped_access(const volatile void *ptr, size_t size, int type, 690 struct kcsan_scoped_access *sa) 691 { 692 struct kcsan_ctx *ctx = get_ctx(); 693 694 __kcsan_check_access(ptr, size, type); 695 696 ctx->disable_count++; /* Disable KCSAN, in case list debugging is on. */ 697 698 INIT_LIST_HEAD(&sa->list); 699 sa->ptr = ptr; 700 sa->size = size; 701 sa->type = type; 702 703 if (!ctx->scoped_accesses.prev) /* Lazy initialize list head. */ 704 INIT_LIST_HEAD(&ctx->scoped_accesses); 705 list_add(&sa->list, &ctx->scoped_accesses); 706 707 ctx->disable_count--; 708 return sa; 709 } 710 EXPORT_SYMBOL(kcsan_begin_scoped_access); 711 712 void kcsan_end_scoped_access(struct kcsan_scoped_access *sa) 713 { 714 struct kcsan_ctx *ctx = get_ctx(); 715 716 if (WARN(!ctx->scoped_accesses.prev, "Unbalanced %s()?", __func__)) 717 return; 718 719 ctx->disable_count++; /* Disable KCSAN, in case list debugging is on. */ 720 721 list_del(&sa->list); 722 if (list_empty(&ctx->scoped_accesses)) 723 /* 724 * Ensure we do not enter kcsan_check_scoped_accesses() 725 * slow-path if unnecessary, and avoids requiring list_empty() 726 * in the fast-path (to avoid a READ_ONCE() and potential 727 * uaccess warning). 728 */ 729 ctx->scoped_accesses.prev = NULL; 730 731 ctx->disable_count--; 732 733 __kcsan_check_access(sa->ptr, sa->size, sa->type); 734 } 735 EXPORT_SYMBOL(kcsan_end_scoped_access); 736 737 void __kcsan_check_access(const volatile void *ptr, size_t size, int type) 738 { 739 check_access(ptr, size, type); 740 } 741 EXPORT_SYMBOL(__kcsan_check_access); 742 743 /* 744 * KCSAN uses the same instrumentation that is emitted by supported compilers 745 * for ThreadSanitizer (TSAN). 746 * 747 * When enabled, the compiler emits instrumentation calls (the functions 748 * prefixed with "__tsan" below) for all loads and stores that it generated; 749 * inline asm is not instrumented. 750 * 751 * Note that, not all supported compiler versions distinguish aligned/unaligned 752 * accesses, but e.g. recent versions of Clang do. We simply alias the unaligned 753 * version to the generic version, which can handle both. 754 */ 755 756 #define DEFINE_TSAN_READ_WRITE(size) \ 757 void __tsan_read##size(void *ptr) \ 758 { \ 759 check_access(ptr, size, 0); \ 760 } \ 761 EXPORT_SYMBOL(__tsan_read##size); \ 762 void __tsan_unaligned_read##size(void *ptr) \ 763 __alias(__tsan_read##size); \ 764 EXPORT_SYMBOL(__tsan_unaligned_read##size); \ 765 void __tsan_write##size(void *ptr) \ 766 { \ 767 check_access(ptr, size, KCSAN_ACCESS_WRITE); \ 768 } \ 769 EXPORT_SYMBOL(__tsan_write##size); \ 770 void __tsan_unaligned_write##size(void *ptr) \ 771 __alias(__tsan_write##size); \ 772 EXPORT_SYMBOL(__tsan_unaligned_write##size) 773 774 DEFINE_TSAN_READ_WRITE(1); 775 DEFINE_TSAN_READ_WRITE(2); 776 DEFINE_TSAN_READ_WRITE(4); 777 DEFINE_TSAN_READ_WRITE(8); 778 DEFINE_TSAN_READ_WRITE(16); 779 780 void __tsan_read_range(void *ptr, size_t size) 781 { 782 check_access(ptr, size, 0); 783 } 784 EXPORT_SYMBOL(__tsan_read_range); 785 786 void __tsan_write_range(void *ptr, size_t size) 787 { 788 check_access(ptr, size, KCSAN_ACCESS_WRITE); 789 } 790 EXPORT_SYMBOL(__tsan_write_range); 791 792 /* 793 * Use of explicit volatile is generally disallowed [1], however, volatile is 794 * still used in various concurrent context, whether in low-level 795 * synchronization primitives or for legacy reasons. 796 * [1] https://lwn.net/Articles/233479/ 797 * 798 * We only consider volatile accesses atomic if they are aligned and would pass 799 * the size-check of compiletime_assert_rwonce_type(). 800 */ 801 #define DEFINE_TSAN_VOLATILE_READ_WRITE(size) \ 802 void __tsan_volatile_read##size(void *ptr) \ 803 { \ 804 const bool is_atomic = size <= sizeof(long long) && \ 805 IS_ALIGNED((unsigned long)ptr, size); \ 806 if (IS_ENABLED(CONFIG_KCSAN_IGNORE_ATOMICS) && is_atomic) \ 807 return; \ 808 check_access(ptr, size, is_atomic ? KCSAN_ACCESS_ATOMIC : 0); \ 809 } \ 810 EXPORT_SYMBOL(__tsan_volatile_read##size); \ 811 void __tsan_unaligned_volatile_read##size(void *ptr) \ 812 __alias(__tsan_volatile_read##size); \ 813 EXPORT_SYMBOL(__tsan_unaligned_volatile_read##size); \ 814 void __tsan_volatile_write##size(void *ptr) \ 815 { \ 816 const bool is_atomic = size <= sizeof(long long) && \ 817 IS_ALIGNED((unsigned long)ptr, size); \ 818 if (IS_ENABLED(CONFIG_KCSAN_IGNORE_ATOMICS) && is_atomic) \ 819 return; \ 820 check_access(ptr, size, \ 821 KCSAN_ACCESS_WRITE | \ 822 (is_atomic ? KCSAN_ACCESS_ATOMIC : 0)); \ 823 } \ 824 EXPORT_SYMBOL(__tsan_volatile_write##size); \ 825 void __tsan_unaligned_volatile_write##size(void *ptr) \ 826 __alias(__tsan_volatile_write##size); \ 827 EXPORT_SYMBOL(__tsan_unaligned_volatile_write##size) 828 829 DEFINE_TSAN_VOLATILE_READ_WRITE(1); 830 DEFINE_TSAN_VOLATILE_READ_WRITE(2); 831 DEFINE_TSAN_VOLATILE_READ_WRITE(4); 832 DEFINE_TSAN_VOLATILE_READ_WRITE(8); 833 DEFINE_TSAN_VOLATILE_READ_WRITE(16); 834 835 /* 836 * The below are not required by KCSAN, but can still be emitted by the 837 * compiler. 838 */ 839 void __tsan_func_entry(void *call_pc) 840 { 841 } 842 EXPORT_SYMBOL(__tsan_func_entry); 843 void __tsan_func_exit(void) 844 { 845 } 846 EXPORT_SYMBOL(__tsan_func_exit); 847 void __tsan_init(void) 848 { 849 } 850 EXPORT_SYMBOL(__tsan_init); 851