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 void kcsan_save_irqtrace(struct task_struct *task) 295 { 296 #ifdef CONFIG_TRACE_IRQFLAGS 297 task->kcsan_save_irqtrace = task->irqtrace; 298 #endif 299 } 300 301 void kcsan_restore_irqtrace(struct task_struct *task) 302 { 303 #ifdef CONFIG_TRACE_IRQFLAGS 304 task->irqtrace = task->kcsan_save_irqtrace; 305 #endif 306 } 307 308 /* 309 * Pull everything together: check_access() below contains the performance 310 * critical operations; the fast-path (including check_access) functions should 311 * all be inlinable by the instrumentation functions. 312 * 313 * The slow-path (kcsan_found_watchpoint, kcsan_setup_watchpoint) are 314 * non-inlinable -- note that, we prefix these with "kcsan_" to ensure they can 315 * be filtered from the stacktrace, as well as give them unique names for the 316 * UACCESS whitelist of objtool. Each function uses user_access_save/restore(), 317 * since they do not access any user memory, but instrumentation is still 318 * emitted in UACCESS regions. 319 */ 320 321 static noinline void kcsan_found_watchpoint(const volatile void *ptr, 322 size_t size, 323 int type, 324 atomic_long_t *watchpoint, 325 long encoded_watchpoint) 326 { 327 unsigned long flags; 328 bool consumed; 329 330 if (!kcsan_is_enabled()) 331 return; 332 333 /* 334 * The access_mask check relies on value-change comparison. To avoid 335 * reporting a race where e.g. the writer set up the watchpoint, but the 336 * reader has access_mask!=0, we have to ignore the found watchpoint. 337 */ 338 if (get_ctx()->access_mask != 0) 339 return; 340 341 /* 342 * Consume the watchpoint as soon as possible, to minimize the chances 343 * of !consumed. Consuming the watchpoint must always be guarded by 344 * kcsan_is_enabled() check, as otherwise we might erroneously 345 * triggering reports when disabled. 346 */ 347 consumed = try_consume_watchpoint(watchpoint, encoded_watchpoint); 348 349 /* keep this after try_consume_watchpoint */ 350 flags = user_access_save(); 351 352 if (consumed) { 353 kcsan_save_irqtrace(current); 354 kcsan_report(ptr, size, type, KCSAN_VALUE_CHANGE_MAYBE, 355 KCSAN_REPORT_CONSUMED_WATCHPOINT, 356 watchpoint - watchpoints); 357 kcsan_restore_irqtrace(current); 358 } else { 359 /* 360 * The other thread may not print any diagnostics, as it has 361 * already removed the watchpoint, or another thread consumed 362 * the watchpoint before this thread. 363 */ 364 kcsan_counter_inc(KCSAN_COUNTER_REPORT_RACES); 365 } 366 367 if ((type & KCSAN_ACCESS_ASSERT) != 0) 368 kcsan_counter_inc(KCSAN_COUNTER_ASSERT_FAILURES); 369 else 370 kcsan_counter_inc(KCSAN_COUNTER_DATA_RACES); 371 372 user_access_restore(flags); 373 } 374 375 static noinline void 376 kcsan_setup_watchpoint(const volatile void *ptr, size_t size, int type) 377 { 378 const bool is_write = (type & KCSAN_ACCESS_WRITE) != 0; 379 const bool is_assert = (type & KCSAN_ACCESS_ASSERT) != 0; 380 atomic_long_t *watchpoint; 381 union { 382 u8 _1; 383 u16 _2; 384 u32 _4; 385 u64 _8; 386 } expect_value; 387 unsigned long access_mask; 388 enum kcsan_value_change value_change = KCSAN_VALUE_CHANGE_MAYBE; 389 unsigned long ua_flags = user_access_save(); 390 unsigned long irq_flags = 0; 391 392 /* 393 * Always reset kcsan_skip counter in slow-path to avoid underflow; see 394 * should_watch(). 395 */ 396 reset_kcsan_skip(); 397 398 if (!kcsan_is_enabled()) 399 goto out; 400 401 /* 402 * Special atomic rules: unlikely to be true, so we check them here in 403 * the slow-path, and not in the fast-path in is_atomic(). Call after 404 * kcsan_is_enabled(), as we may access memory that is not yet 405 * initialized during early boot. 406 */ 407 if (!is_assert && kcsan_is_atomic_special(ptr)) 408 goto out; 409 410 if (!check_encodable((unsigned long)ptr, size)) { 411 kcsan_counter_inc(KCSAN_COUNTER_UNENCODABLE_ACCESSES); 412 goto out; 413 } 414 415 /* 416 * Save and restore the IRQ state trace touched by KCSAN, since KCSAN's 417 * runtime is entered for every memory access, and potentially useful 418 * information is lost if dirtied by KCSAN. 419 */ 420 kcsan_save_irqtrace(current); 421 if (!kcsan_interrupt_watcher) 422 local_irq_save(irq_flags); 423 424 watchpoint = insert_watchpoint((unsigned long)ptr, size, is_write); 425 if (watchpoint == NULL) { 426 /* 427 * Out of capacity: the size of 'watchpoints', and the frequency 428 * with which should_watch() returns true should be tweaked so 429 * that this case happens very rarely. 430 */ 431 kcsan_counter_inc(KCSAN_COUNTER_NO_CAPACITY); 432 goto out_unlock; 433 } 434 435 kcsan_counter_inc(KCSAN_COUNTER_SETUP_WATCHPOINTS); 436 kcsan_counter_inc(KCSAN_COUNTER_USED_WATCHPOINTS); 437 438 /* 439 * Read the current value, to later check and infer a race if the data 440 * was modified via a non-instrumented access, e.g. from a device. 441 */ 442 expect_value._8 = 0; 443 switch (size) { 444 case 1: 445 expect_value._1 = READ_ONCE(*(const u8 *)ptr); 446 break; 447 case 2: 448 expect_value._2 = READ_ONCE(*(const u16 *)ptr); 449 break; 450 case 4: 451 expect_value._4 = READ_ONCE(*(const u32 *)ptr); 452 break; 453 case 8: 454 expect_value._8 = READ_ONCE(*(const u64 *)ptr); 455 break; 456 default: 457 break; /* ignore; we do not diff the values */ 458 } 459 460 if (IS_ENABLED(CONFIG_KCSAN_DEBUG)) { 461 kcsan_disable_current(); 462 pr_err("KCSAN: watching %s, size: %zu, addr: %px [slot: %d, encoded: %lx]\n", 463 is_write ? "write" : "read", size, ptr, 464 watchpoint_slot((unsigned long)ptr), 465 encode_watchpoint((unsigned long)ptr, size, is_write)); 466 kcsan_enable_current(); 467 } 468 469 /* 470 * Delay this thread, to increase probability of observing a racy 471 * conflicting access. 472 */ 473 udelay(get_delay()); 474 475 /* 476 * Re-read value, and check if it is as expected; if not, we infer a 477 * racy access. 478 */ 479 access_mask = get_ctx()->access_mask; 480 switch (size) { 481 case 1: 482 expect_value._1 ^= READ_ONCE(*(const u8 *)ptr); 483 if (access_mask) 484 expect_value._1 &= (u8)access_mask; 485 break; 486 case 2: 487 expect_value._2 ^= READ_ONCE(*(const u16 *)ptr); 488 if (access_mask) 489 expect_value._2 &= (u16)access_mask; 490 break; 491 case 4: 492 expect_value._4 ^= READ_ONCE(*(const u32 *)ptr); 493 if (access_mask) 494 expect_value._4 &= (u32)access_mask; 495 break; 496 case 8: 497 expect_value._8 ^= READ_ONCE(*(const u64 *)ptr); 498 if (access_mask) 499 expect_value._8 &= (u64)access_mask; 500 break; 501 default: 502 break; /* ignore; we do not diff the values */ 503 } 504 505 /* Were we able to observe a value-change? */ 506 if (expect_value._8 != 0) 507 value_change = KCSAN_VALUE_CHANGE_TRUE; 508 509 /* Check if this access raced with another. */ 510 if (!consume_watchpoint(watchpoint)) { 511 /* 512 * Depending on the access type, map a value_change of MAYBE to 513 * TRUE (always report) or FALSE (never report). 514 */ 515 if (value_change == KCSAN_VALUE_CHANGE_MAYBE) { 516 if (access_mask != 0) { 517 /* 518 * For access with access_mask, we require a 519 * value-change, as it is likely that races on 520 * ~access_mask bits are expected. 521 */ 522 value_change = KCSAN_VALUE_CHANGE_FALSE; 523 } else if (size > 8 || is_assert) { 524 /* Always assume a value-change. */ 525 value_change = KCSAN_VALUE_CHANGE_TRUE; 526 } 527 } 528 529 /* 530 * No need to increment 'data_races' counter, as the racing 531 * thread already did. 532 * 533 * Count 'assert_failures' for each failed ASSERT access, 534 * therefore both this thread and the racing thread may 535 * increment this counter. 536 */ 537 if (is_assert && value_change == KCSAN_VALUE_CHANGE_TRUE) 538 kcsan_counter_inc(KCSAN_COUNTER_ASSERT_FAILURES); 539 540 kcsan_report(ptr, size, type, value_change, KCSAN_REPORT_RACE_SIGNAL, 541 watchpoint - watchpoints); 542 } else if (value_change == KCSAN_VALUE_CHANGE_TRUE) { 543 /* Inferring a race, since the value should not have changed. */ 544 545 kcsan_counter_inc(KCSAN_COUNTER_RACES_UNKNOWN_ORIGIN); 546 if (is_assert) 547 kcsan_counter_inc(KCSAN_COUNTER_ASSERT_FAILURES); 548 549 if (IS_ENABLED(CONFIG_KCSAN_REPORT_RACE_UNKNOWN_ORIGIN) || is_assert) 550 kcsan_report(ptr, size, type, KCSAN_VALUE_CHANGE_TRUE, 551 KCSAN_REPORT_RACE_UNKNOWN_ORIGIN, 552 watchpoint - watchpoints); 553 } 554 555 /* 556 * Remove watchpoint; must be after reporting, since the slot may be 557 * reused after this point. 558 */ 559 remove_watchpoint(watchpoint); 560 kcsan_counter_dec(KCSAN_COUNTER_USED_WATCHPOINTS); 561 out_unlock: 562 if (!kcsan_interrupt_watcher) 563 local_irq_restore(irq_flags); 564 kcsan_restore_irqtrace(current); 565 out: 566 user_access_restore(ua_flags); 567 } 568 569 static __always_inline void check_access(const volatile void *ptr, size_t size, 570 int type) 571 { 572 const bool is_write = (type & KCSAN_ACCESS_WRITE) != 0; 573 atomic_long_t *watchpoint; 574 long encoded_watchpoint; 575 576 /* 577 * Do nothing for 0 sized check; this comparison will be optimized out 578 * for constant sized instrumentation (__tsan_{read,write}N). 579 */ 580 if (unlikely(size == 0)) 581 return; 582 583 /* 584 * Avoid user_access_save in fast-path: find_watchpoint is safe without 585 * user_access_save, as the address that ptr points to is only used to 586 * check if a watchpoint exists; ptr is never dereferenced. 587 */ 588 watchpoint = find_watchpoint((unsigned long)ptr, size, !is_write, 589 &encoded_watchpoint); 590 /* 591 * It is safe to check kcsan_is_enabled() after find_watchpoint in the 592 * slow-path, as long as no state changes that cause a race to be 593 * detected and reported have occurred until kcsan_is_enabled() is 594 * checked. 595 */ 596 597 if (unlikely(watchpoint != NULL)) 598 kcsan_found_watchpoint(ptr, size, type, watchpoint, 599 encoded_watchpoint); 600 else { 601 struct kcsan_ctx *ctx = get_ctx(); /* Call only once in fast-path. */ 602 603 if (unlikely(should_watch(ptr, size, type, ctx))) 604 kcsan_setup_watchpoint(ptr, size, type); 605 else if (unlikely(ctx->scoped_accesses.prev)) 606 kcsan_check_scoped_accesses(); 607 } 608 } 609 610 /* === Public interface ===================================================== */ 611 612 void __init kcsan_init(void) 613 { 614 BUG_ON(!in_task()); 615 616 kcsan_debugfs_init(); 617 618 /* 619 * We are in the init task, and no other tasks should be running; 620 * WRITE_ONCE without memory barrier is sufficient. 621 */ 622 if (kcsan_early_enable) 623 WRITE_ONCE(kcsan_enabled, true); 624 } 625 626 /* === Exported interface =================================================== */ 627 628 void kcsan_disable_current(void) 629 { 630 ++get_ctx()->disable_count; 631 } 632 EXPORT_SYMBOL(kcsan_disable_current); 633 634 void kcsan_enable_current(void) 635 { 636 if (get_ctx()->disable_count-- == 0) { 637 /* 638 * Warn if kcsan_enable_current() calls are unbalanced with 639 * kcsan_disable_current() calls, which causes disable_count to 640 * become negative and should not happen. 641 */ 642 kcsan_disable_current(); /* restore to 0, KCSAN still enabled */ 643 kcsan_disable_current(); /* disable to generate warning */ 644 WARN(1, "Unbalanced %s()", __func__); 645 kcsan_enable_current(); 646 } 647 } 648 EXPORT_SYMBOL(kcsan_enable_current); 649 650 void kcsan_enable_current_nowarn(void) 651 { 652 if (get_ctx()->disable_count-- == 0) 653 kcsan_disable_current(); 654 } 655 EXPORT_SYMBOL(kcsan_enable_current_nowarn); 656 657 void kcsan_nestable_atomic_begin(void) 658 { 659 /* 660 * Do *not* check and warn if we are in a flat atomic region: nestable 661 * and flat atomic regions are independent from each other. 662 * See include/linux/kcsan.h: struct kcsan_ctx comments for more 663 * comments. 664 */ 665 666 ++get_ctx()->atomic_nest_count; 667 } 668 EXPORT_SYMBOL(kcsan_nestable_atomic_begin); 669 670 void kcsan_nestable_atomic_end(void) 671 { 672 if (get_ctx()->atomic_nest_count-- == 0) { 673 /* 674 * Warn if kcsan_nestable_atomic_end() calls are unbalanced with 675 * kcsan_nestable_atomic_begin() calls, which causes 676 * atomic_nest_count to become negative and should not happen. 677 */ 678 kcsan_nestable_atomic_begin(); /* restore to 0 */ 679 kcsan_disable_current(); /* disable to generate warning */ 680 WARN(1, "Unbalanced %s()", __func__); 681 kcsan_enable_current(); 682 } 683 } 684 EXPORT_SYMBOL(kcsan_nestable_atomic_end); 685 686 void kcsan_flat_atomic_begin(void) 687 { 688 get_ctx()->in_flat_atomic = true; 689 } 690 EXPORT_SYMBOL(kcsan_flat_atomic_begin); 691 692 void kcsan_flat_atomic_end(void) 693 { 694 get_ctx()->in_flat_atomic = false; 695 } 696 EXPORT_SYMBOL(kcsan_flat_atomic_end); 697 698 void kcsan_atomic_next(int n) 699 { 700 get_ctx()->atomic_next = n; 701 } 702 EXPORT_SYMBOL(kcsan_atomic_next); 703 704 void kcsan_set_access_mask(unsigned long mask) 705 { 706 get_ctx()->access_mask = mask; 707 } 708 EXPORT_SYMBOL(kcsan_set_access_mask); 709 710 struct kcsan_scoped_access * 711 kcsan_begin_scoped_access(const volatile void *ptr, size_t size, int type, 712 struct kcsan_scoped_access *sa) 713 { 714 struct kcsan_ctx *ctx = get_ctx(); 715 716 __kcsan_check_access(ptr, size, type); 717 718 ctx->disable_count++; /* Disable KCSAN, in case list debugging is on. */ 719 720 INIT_LIST_HEAD(&sa->list); 721 sa->ptr = ptr; 722 sa->size = size; 723 sa->type = type; 724 725 if (!ctx->scoped_accesses.prev) /* Lazy initialize list head. */ 726 INIT_LIST_HEAD(&ctx->scoped_accesses); 727 list_add(&sa->list, &ctx->scoped_accesses); 728 729 ctx->disable_count--; 730 return sa; 731 } 732 EXPORT_SYMBOL(kcsan_begin_scoped_access); 733 734 void kcsan_end_scoped_access(struct kcsan_scoped_access *sa) 735 { 736 struct kcsan_ctx *ctx = get_ctx(); 737 738 if (WARN(!ctx->scoped_accesses.prev, "Unbalanced %s()?", __func__)) 739 return; 740 741 ctx->disable_count++; /* Disable KCSAN, in case list debugging is on. */ 742 743 list_del(&sa->list); 744 if (list_empty(&ctx->scoped_accesses)) 745 /* 746 * Ensure we do not enter kcsan_check_scoped_accesses() 747 * slow-path if unnecessary, and avoids requiring list_empty() 748 * in the fast-path (to avoid a READ_ONCE() and potential 749 * uaccess warning). 750 */ 751 ctx->scoped_accesses.prev = NULL; 752 753 ctx->disable_count--; 754 755 __kcsan_check_access(sa->ptr, sa->size, sa->type); 756 } 757 EXPORT_SYMBOL(kcsan_end_scoped_access); 758 759 void __kcsan_check_access(const volatile void *ptr, size_t size, int type) 760 { 761 check_access(ptr, size, type); 762 } 763 EXPORT_SYMBOL(__kcsan_check_access); 764 765 /* 766 * KCSAN uses the same instrumentation that is emitted by supported compilers 767 * for ThreadSanitizer (TSAN). 768 * 769 * When enabled, the compiler emits instrumentation calls (the functions 770 * prefixed with "__tsan" below) for all loads and stores that it generated; 771 * inline asm is not instrumented. 772 * 773 * Note that, not all supported compiler versions distinguish aligned/unaligned 774 * accesses, but e.g. recent versions of Clang do. We simply alias the unaligned 775 * version to the generic version, which can handle both. 776 */ 777 778 #define DEFINE_TSAN_READ_WRITE(size) \ 779 void __tsan_read##size(void *ptr); \ 780 void __tsan_read##size(void *ptr) \ 781 { \ 782 check_access(ptr, size, 0); \ 783 } \ 784 EXPORT_SYMBOL(__tsan_read##size); \ 785 void __tsan_unaligned_read##size(void *ptr) \ 786 __alias(__tsan_read##size); \ 787 EXPORT_SYMBOL(__tsan_unaligned_read##size); \ 788 void __tsan_write##size(void *ptr); \ 789 void __tsan_write##size(void *ptr) \ 790 { \ 791 check_access(ptr, size, KCSAN_ACCESS_WRITE); \ 792 } \ 793 EXPORT_SYMBOL(__tsan_write##size); \ 794 void __tsan_unaligned_write##size(void *ptr) \ 795 __alias(__tsan_write##size); \ 796 EXPORT_SYMBOL(__tsan_unaligned_write##size) 797 798 DEFINE_TSAN_READ_WRITE(1); 799 DEFINE_TSAN_READ_WRITE(2); 800 DEFINE_TSAN_READ_WRITE(4); 801 DEFINE_TSAN_READ_WRITE(8); 802 DEFINE_TSAN_READ_WRITE(16); 803 804 void __tsan_read_range(void *ptr, size_t size); 805 void __tsan_read_range(void *ptr, size_t size) 806 { 807 check_access(ptr, size, 0); 808 } 809 EXPORT_SYMBOL(__tsan_read_range); 810 811 void __tsan_write_range(void *ptr, size_t size); 812 void __tsan_write_range(void *ptr, size_t size) 813 { 814 check_access(ptr, size, KCSAN_ACCESS_WRITE); 815 } 816 EXPORT_SYMBOL(__tsan_write_range); 817 818 /* 819 * Use of explicit volatile is generally disallowed [1], however, volatile is 820 * still used in various concurrent context, whether in low-level 821 * synchronization primitives or for legacy reasons. 822 * [1] https://lwn.net/Articles/233479/ 823 * 824 * We only consider volatile accesses atomic if they are aligned and would pass 825 * the size-check of compiletime_assert_rwonce_type(). 826 */ 827 #define DEFINE_TSAN_VOLATILE_READ_WRITE(size) \ 828 void __tsan_volatile_read##size(void *ptr); \ 829 void __tsan_volatile_read##size(void *ptr) \ 830 { \ 831 const bool is_atomic = size <= sizeof(long long) && \ 832 IS_ALIGNED((unsigned long)ptr, size); \ 833 if (IS_ENABLED(CONFIG_KCSAN_IGNORE_ATOMICS) && is_atomic) \ 834 return; \ 835 check_access(ptr, size, is_atomic ? KCSAN_ACCESS_ATOMIC : 0); \ 836 } \ 837 EXPORT_SYMBOL(__tsan_volatile_read##size); \ 838 void __tsan_unaligned_volatile_read##size(void *ptr) \ 839 __alias(__tsan_volatile_read##size); \ 840 EXPORT_SYMBOL(__tsan_unaligned_volatile_read##size); \ 841 void __tsan_volatile_write##size(void *ptr); \ 842 void __tsan_volatile_write##size(void *ptr) \ 843 { \ 844 const bool is_atomic = size <= sizeof(long long) && \ 845 IS_ALIGNED((unsigned long)ptr, size); \ 846 if (IS_ENABLED(CONFIG_KCSAN_IGNORE_ATOMICS) && is_atomic) \ 847 return; \ 848 check_access(ptr, size, \ 849 KCSAN_ACCESS_WRITE | \ 850 (is_atomic ? KCSAN_ACCESS_ATOMIC : 0)); \ 851 } \ 852 EXPORT_SYMBOL(__tsan_volatile_write##size); \ 853 void __tsan_unaligned_volatile_write##size(void *ptr) \ 854 __alias(__tsan_volatile_write##size); \ 855 EXPORT_SYMBOL(__tsan_unaligned_volatile_write##size) 856 857 DEFINE_TSAN_VOLATILE_READ_WRITE(1); 858 DEFINE_TSAN_VOLATILE_READ_WRITE(2); 859 DEFINE_TSAN_VOLATILE_READ_WRITE(4); 860 DEFINE_TSAN_VOLATILE_READ_WRITE(8); 861 DEFINE_TSAN_VOLATILE_READ_WRITE(16); 862 863 /* 864 * The below are not required by KCSAN, but can still be emitted by the 865 * compiler. 866 */ 867 void __tsan_func_entry(void *call_pc); 868 void __tsan_func_entry(void *call_pc) 869 { 870 } 871 EXPORT_SYMBOL(__tsan_func_entry); 872 void __tsan_func_exit(void); 873 void __tsan_func_exit(void) 874 { 875 } 876 EXPORT_SYMBOL(__tsan_func_exit); 877 void __tsan_init(void); 878 void __tsan_init(void) 879 { 880 } 881 EXPORT_SYMBOL(__tsan_init); 882