kernel/kcsan/core.c

   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() ? &current->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         switch (size) {
 341         case 1:  return READ_ONCE(*(const u8 *)ptr);
 342         case 2:  return READ_ONCE(*(const u16 *)ptr);
 343         case 4:  return READ_ONCE(*(const u32 *)ptr);
 344         case 8:  return READ_ONCE(*(const u64 *)ptr);
 345         default: return 0; /* Ignore; we do not diff the values. */
 346         }
 347 }
 348
 349 void kcsan_save_irqtrace(struct task_struct *task)
 350 {
 351 #ifdef CONFIG_TRACE_IRQFLAGS
 352         task->kcsan_save_irqtrace = task->irqtrace;
 353 #endif
 354 }
 355
 356 void kcsan_restore_irqtrace(struct task_struct *task)
 357 {
 358 #ifdef CONFIG_TRACE_IRQFLAGS
 359         task->irqtrace = task->kcsan_save_irqtrace;
 360 #endif
 361 }
 362
 363 static __always_inline int get_kcsan_stack_depth(void)
 364 {
 365 #ifdef CONFIG_KCSAN_WEAK_MEMORY
 366         return current->kcsan_stack_depth;
 367 #else
 368         BUILD_BUG();
 369         return 0;
 370 #endif
 371 }
 372
 373 static __always_inline void add_kcsan_stack_depth(int val)
 374 {
 375 #ifdef CONFIG_KCSAN_WEAK_MEMORY
 376         current->kcsan_stack_depth += val;
 377 #else
 378         BUILD_BUG();
 379 #endif
 380 }
 381
 382 static __always_inline struct kcsan_scoped_access *get_reorder_access(struct kcsan_ctx *ctx)
 383 {
 384 #ifdef CONFIG_KCSAN_WEAK_MEMORY
 385         return ctx->disable_scoped ? NULL : &ctx->reorder_access;
 386 #else
 387         return NULL;
 388 #endif
 389 }
 390
 391 static __always_inline bool
 392 find_reorder_access(struct kcsan_ctx *ctx, const volatile void *ptr, size_t size,
 393                     int type, unsigned long ip)
 394 {
 395         struct kcsan_scoped_access *reorder_access = get_reorder_access(ctx);
 396
 397         if (!reorder_access)
 398                 return false;
 399
 400         /*
 401          * Note: If accesses are repeated while reorder_access is identical,
 402          * never matches the new access, because !(type & KCSAN_ACCESS_SCOPED).
 403          */
 404         return reorder_access->ptr == ptr && reorder_access->size == size &&
 405                reorder_access->type == type && reorder_access->ip == ip;
 406 }
 407
 408 static inline void
 409 set_reorder_access(struct kcsan_ctx *ctx, const volatile void *ptr, size_t size,
 410                    int type, unsigned long ip)
 411 {
 412         struct kcsan_scoped_access *reorder_access = get_reorder_access(ctx);
 413
 414         if (!reorder_access || !kcsan_weak_memory)
 415                 return;
 416
 417         /*
 418          * To avoid nested interrupts or scheduler (which share kcsan_ctx)
 419          * reading an inconsistent reorder_access, ensure that the below has
 420          * exclusive access to reorder_access by disallowing concurrent use.
 421          */
 422         ctx->disable_scoped++;
 423         barrier();
 424         reorder_access->ptr             = ptr;
 425         reorder_access->size            = size;
 426         reorder_access->type            = type | KCSAN_ACCESS_SCOPED;
 427         reorder_access->ip              = ip;
 428         reorder_access->stack_depth     = get_kcsan_stack_depth();
 429         barrier();
 430         ctx->disable_scoped--;
 431 }
 432
 433 /*
 434  * Pull everything together: check_access() below contains the performance
 435  * critical operations; the fast-path (including check_access) functions should
 436  * all be inlinable by the instrumentation functions.
 437  *
 438  * The slow-path (kcsan_found_watchpoint, kcsan_setup_watchpoint) are
 439  * non-inlinable -- note that, we prefix these with "kcsan_" to ensure they can
 440  * be filtered from the stacktrace, as well as give them unique names for the
 441  * UACCESS whitelist of objtool. Each function uses user_access_save/restore(),
 442  * since they do not access any user memory, but instrumentation is still
 443  * emitted in UACCESS regions.
 444  */
 445
 446 static noinline void kcsan_found_watchpoint(const volatile void *ptr,
 447                                             size_t size,
 448                                             int type,
 449                                             unsigned long ip,
 450                                             atomic_long_t *watchpoint,
 451                                             long encoded_watchpoint)
 452 {
 453         const bool is_assert = (type & KCSAN_ACCESS_ASSERT) != 0;
 454         struct kcsan_ctx *ctx = get_ctx();
 455         unsigned long flags;
 456         bool consumed;
 457
 458         /*
 459          * We know a watchpoint exists. Let's try to keep the race-window
 460          * between here and finally consuming the watchpoint below as small as
 461          * possible -- avoid unneccessarily complex code until consumed.
 462          */
 463
 464         if (!kcsan_is_enabled(ctx))
 465                 return;
 466
 467         /*
 468          * The access_mask check relies on value-change comparison. To avoid
 469          * reporting a race where e.g. the writer set up the watchpoint, but the
 470          * reader has access_mask!=0, we have to ignore the found watchpoint.
 471          *
 472          * reorder_access is never created from an access with access_mask set.
 473          */
 474         if (ctx->access_mask && !find_reorder_access(ctx, ptr, size, type, ip))
 475                 return;
 476
 477         /*
 478          * If the other thread does not want to ignore the access, and there was
 479          * a value change as a result of this thread's operation, we will still
 480          * generate a report of unknown origin.
 481          *
 482          * Use CONFIG_KCSAN_REPORT_RACE_UNKNOWN_ORIGIN=n to filter.
 483          */
 484         if (!is_assert && kcsan_ignore_address(ptr))
 485                 return;
 486
 487         /*
 488          * Consuming the watchpoint must be guarded by kcsan_is_enabled() to
 489          * avoid erroneously triggering reports if the context is disabled.
 490          */
 491         consumed = try_consume_watchpoint(watchpoint, encoded_watchpoint);
 492
 493         /* keep this after try_consume_watchpoint */
 494         flags = user_access_save();
 495
 496         if (consumed) {
 497                 kcsan_save_irqtrace(current);
 498                 kcsan_report_set_info(ptr, size, type, ip, watchpoint - watchpoints);
 499                 kcsan_restore_irqtrace(current);
 500         } else {
 501                 /*
 502                  * The other thread may not print any diagnostics, as it has
 503                  * already removed the watchpoint, or another thread consumed
 504                  * the watchpoint before this thread.
 505                  */
 506                 atomic_long_inc(&kcsan_counters[KCSAN_COUNTER_REPORT_RACES]);
 507         }
 508
 509         if (is_assert)
 510                 atomic_long_inc(&kcsan_counters[KCSAN_COUNTER_ASSERT_FAILURES]);
 511         else
 512                 atomic_long_inc(&kcsan_counters[KCSAN_COUNTER_DATA_RACES]);
 513
 514         user_access_restore(flags);
 515 }
 516
 517 static noinline void
 518 kcsan_setup_watchpoint(const volatile void *ptr, size_t size, int type, unsigned long ip)
 519 {
 520         const bool is_write = (type & KCSAN_ACCESS_WRITE) != 0;
 521         const bool is_assert = (type & KCSAN_ACCESS_ASSERT) != 0;
 522         atomic_long_t *watchpoint;
 523         u64 old, new, diff;
 524         enum kcsan_value_change value_change = KCSAN_VALUE_CHANGE_MAYBE;
 525         bool interrupt_watcher = kcsan_interrupt_watcher;
 526         unsigned long ua_flags = user_access_save();
 527         struct kcsan_ctx *ctx = get_ctx();
 528         unsigned long access_mask = ctx->access_mask;
 529         unsigned long irq_flags = 0;
 530         bool is_reorder_access;
 531
 532         /*
 533          * Always reset kcsan_skip counter in slow-path to avoid underflow; see
 534          * should_watch().
 535          */
 536         reset_kcsan_skip();
 537
 538         if (!kcsan_is_enabled(ctx))
 539                 goto out;
 540
 541         /*
 542          * Check to-ignore addresses after kcsan_is_enabled(), as we may access
 543          * memory that is not yet initialized during early boot.
 544          */
 545         if (!is_assert && kcsan_ignore_address(ptr))
 546                 goto out;
 547
 548         if (!check_encodable((unsigned long)ptr, size)) {
 549                 atomic_long_inc(&kcsan_counters[KCSAN_COUNTER_UNENCODABLE_ACCESSES]);
 550                 goto out;
 551         }
 552
 553         /*
 554          * The local CPU cannot observe reordering of its own accesses, and
 555          * therefore we need to take care of 2 cases to avoid false positives:
 556          *
 557          *      1. Races of the reordered access with interrupts. To avoid, if
 558          *         the current access is reorder_access, disable interrupts.
 559          *      2. Avoid races of scoped accesses from nested interrupts (below).
 560          */
 561         is_reorder_access = find_reorder_access(ctx, ptr, size, type, ip);
 562         if (is_reorder_access)
 563                 interrupt_watcher = false;
 564         /*
 565          * Avoid races of scoped accesses from nested interrupts (or scheduler).
 566          * Assume setting up a watchpoint for a non-scoped (normal) access that
 567          * also conflicts with a current scoped access. In a nested interrupt,
 568          * which shares the context, it would check a conflicting scoped access.
 569          * To avoid, disable scoped access checking.
 570          */
 571         ctx->disable_scoped++;
 572
 573         /*
 574          * Save and restore the IRQ state trace touched by KCSAN, since KCSAN's
 575          * runtime is entered for every memory access, and potentially useful
 576          * information is lost if dirtied by KCSAN.
 577          */
 578         kcsan_save_irqtrace(current);
 579         if (!interrupt_watcher)
 580                 local_irq_save(irq_flags);
 581
 582         watchpoint = insert_watchpoint((unsigned long)ptr, size, is_write);
 583         if (watchpoint == NULL) {
 584                 /*
 585                  * Out of capacity: the size of 'watchpoints', and the frequency
 586                  * with which should_watch() returns true should be tweaked so
 587                  * that this case happens very rarely.
 588                  */
 589                 atomic_long_inc(&kcsan_counters[KCSAN_COUNTER_NO_CAPACITY]);
 590                 goto out_unlock;
 591         }
 592
 593         atomic_long_inc(&kcsan_counters[KCSAN_COUNTER_SETUP_WATCHPOINTS]);
 594         atomic_long_inc(&kcsan_counters[KCSAN_COUNTER_USED_WATCHPOINTS]);
 595
 596         /*
 597          * Read the current value, to later check and infer a race if the data
 598          * was modified via a non-instrumented access, e.g. from a device.
 599          */
 600         old = is_reorder_access ? 0 : read_instrumented_memory(ptr, size);
 601
 602         /*
 603          * Delay this thread, to increase probability of observing a racy
 604          * conflicting access.
 605          */
 606         delay_access(type);
 607
 608         /*
 609          * Re-read value, and check if it is as expected; if not, we infer a
 610          * racy access.
 611          */
 612         if (!is_reorder_access) {
 613                 new = read_instrumented_memory(ptr, size);
 614         } else {
 615                 /*
 616                  * Reordered accesses cannot be used for value change detection,
 617                  * because the memory location may no longer be accessible and
 618                  * could result in a fault.
 619                  */
 620                 new = 0;
 621                 access_mask = 0;
 622         }
 623
 624         diff = old ^ new;
 625         if (access_mask)
 626                 diff &= access_mask;
 627
 628         /*
 629          * Check if we observed a value change.
 630          *
 631          * Also check if the data race should be ignored (the rules depend on
 632          * non-zero diff); if it is to be ignored, the below rules for
 633          * KCSAN_VALUE_CHANGE_MAYBE apply.
 634          */
 635         if (diff && !kcsan_ignore_data_race(size, type, old, new, diff))
 636                 value_change = KCSAN_VALUE_CHANGE_TRUE;
 637
 638         /* Check if this access raced with another. */
 639         if (!consume_watchpoint(watchpoint)) {
 640                 /*
 641                  * Depending on the access type, map a value_change of MAYBE to
 642                  * TRUE (always report) or FALSE (never report).
 643                  */
 644                 if (value_change == KCSAN_VALUE_CHANGE_MAYBE) {
 645                         if (access_mask != 0) {
 646                                 /*
 647                                  * For access with access_mask, we require a
 648                                  * value-change, as it is likely that races on
 649                                  * ~access_mask bits are expected.
 650                                  */
 651                                 value_change = KCSAN_VALUE_CHANGE_FALSE;
 652                         } else if (size > 8 || is_assert) {
 653                                 /* Always assume a value-change. */
 654                                 value_change = KCSAN_VALUE_CHANGE_TRUE;
 655                         }
 656                 }
 657
 658                 /*
 659                  * No need to increment 'data_races' counter, as the racing
 660                  * thread already did.
 661                  *
 662                  * Count 'assert_failures' for each failed ASSERT access,
 663                  * therefore both this thread and the racing thread may
 664                  * increment this counter.
 665                  */
 666                 if (is_assert && value_change == KCSAN_VALUE_CHANGE_TRUE)
 667                         atomic_long_inc(&kcsan_counters[KCSAN_COUNTER_ASSERT_FAILURES]);
 668
 669                 kcsan_report_known_origin(ptr, size, type, ip,
 670                                           value_change, watchpoint - watchpoints,
 671                                           old, new, access_mask);
 672         } else if (value_change == KCSAN_VALUE_CHANGE_TRUE) {
 673                 /* Inferring a race, since the value should not have changed. */
 674
 675                 atomic_long_inc(&kcsan_counters[KCSAN_COUNTER_RACES_UNKNOWN_ORIGIN]);
 676                 if (is_assert)
 677                         atomic_long_inc(&kcsan_counters[KCSAN_COUNTER_ASSERT_FAILURES]);
 678
 679                 if (IS_ENABLED(CONFIG_KCSAN_REPORT_RACE_UNKNOWN_ORIGIN) || is_assert) {
 680                         kcsan_report_unknown_origin(ptr, size, type, ip,
 681                                                     old, new, access_mask);
 682                 }
 683         }
 684
 685         /*
 686          * Remove watchpoint; must be after reporting, since the slot may be
 687          * reused after this point.
 688          */
 689         remove_watchpoint(watchpoint);
 690         atomic_long_dec(&kcsan_counters[KCSAN_COUNTER_USED_WATCHPOINTS]);
 691
 692 out_unlock:
 693         if (!interrupt_watcher)
 694                 local_irq_restore(irq_flags);
 695         kcsan_restore_irqtrace(current);
 696         ctx->disable_scoped--;
 697
 698         /*
 699          * Reordered accesses cannot be used for value change detection,
 700          * therefore never consider for reordering if access_mask is set.
 701          * ASSERT_EXCLUSIVE are not real accesses, ignore them as well.
 702          */
 703         if (!access_mask && !is_assert)
 704                 set_reorder_access(ctx, ptr, size, type, ip);
 705 out:
 706         user_access_restore(ua_flags);
 707 }
 708
 709 static __always_inline void
 710 check_access(const volatile void *ptr, size_t size, int type, unsigned long ip)
 711 {
 712         atomic_long_t *watchpoint;
 713         long encoded_watchpoint;
 714
 715         /*
 716          * Do nothing for 0 sized check; this comparison will be optimized out
 717          * for constant sized instrumentation (__tsan_{read,write}N).
 718          */
 719         if (unlikely(size == 0))
 720                 return;
 721
 722 again:
 723         /*
 724          * Avoid user_access_save in fast-path: find_watchpoint is safe without
 725          * user_access_save, as the address that ptr points to is only used to
 726          * check if a watchpoint exists; ptr is never dereferenced.
 727          */
 728         watchpoint = find_watchpoint((unsigned long)ptr, size,
 729                                      !(type & KCSAN_ACCESS_WRITE),
 730                                      &encoded_watchpoint);
 731         /*
 732          * It is safe to check kcsan_is_enabled() after find_watchpoint in the
 733          * slow-path, as long as no state changes that cause a race to be
 734          * detected and reported have occurred until kcsan_is_enabled() is
 735          * checked.
 736          */
 737
 738         if (unlikely(watchpoint != NULL))
 739                 kcsan_found_watchpoint(ptr, size, type, ip, watchpoint, encoded_watchpoint);
 740         else {
 741                 struct kcsan_ctx *ctx = get_ctx(); /* Call only once in fast-path. */
 742
 743                 if (unlikely(should_watch(ctx, ptr, size, type))) {
 744                         kcsan_setup_watchpoint(ptr, size, type, ip);
 745                         return;
 746                 }
 747
 748                 if (!(type & KCSAN_ACCESS_SCOPED)) {
 749                         struct kcsan_scoped_access *reorder_access = get_reorder_access(ctx);
 750
 751                         if (reorder_access) {
 752                                 /*
 753                                  * reorder_access check: simulates reordering of
 754                                  * the access after subsequent operations.
 755                                  */
 756                                 ptr = reorder_access->ptr;
 757                                 type = reorder_access->type;
 758                                 ip = reorder_access->ip;
 759                                 /*
 760                                  * Upon a nested interrupt, this context's
 761                                  * reorder_access can be modified (shared ctx).
 762                                  * We know that upon return, reorder_access is
 763                                  * always invalidated by setting size to 0 via
 764                                  * __tsan_func_exit(). Therefore we must read
 765                                  * and check size after the other fields.
 766                                  */
 767                                 barrier();
 768                                 size = READ_ONCE(reorder_access->size);
 769                                 if (size)
 770                                         goto again;
 771                         }
 772                 }
 773
 774                 /*
 775                  * Always checked last, right before returning from runtime;
 776                  * if reorder_access is valid, checked after it was checked.
 777                  */
 778                 if (unlikely(ctx->scoped_accesses.prev))
 779                         kcsan_check_scoped_accesses();
 780         }
 781 }
 782
 783 /* === Public interface ===================================================== */
 784
 785 void __init kcsan_init(void)
 786 {
 787         int cpu;
 788
 789         BUG_ON(!in_task());
 790
 791         for_each_possible_cpu(cpu)
 792                 per_cpu(kcsan_rand_state, cpu) = (u32)get_cycles();
 793
 794         /*
 795          * We are in the init task, and no other tasks should be running;
 796          * WRITE_ONCE without memory barrier is sufficient.
 797          */
 798         if (kcsan_early_enable) {
 799                 pr_info("enabled early\n");
 800                 WRITE_ONCE(kcsan_enabled, true);
 801         }
 802
 803         if (IS_ENABLED(CONFIG_KCSAN_REPORT_VALUE_CHANGE_ONLY) ||
 804             IS_ENABLED(CONFIG_KCSAN_ASSUME_PLAIN_WRITES_ATOMIC) ||
 805             IS_ENABLED(CONFIG_KCSAN_PERMISSIVE) ||
 806             IS_ENABLED(CONFIG_KCSAN_IGNORE_ATOMICS)) {
 807                 pr_warn("non-strict mode configured - use CONFIG_KCSAN_STRICT=y to see all data races\n");
 808         } else {
 809                 pr_info("strict mode configured\n");
 810         }
 811 }
 812
 813 /* === Exported interface =================================================== */
 814
 815 void kcsan_disable_current(void)
 816 {
 817         ++get_ctx()->disable_count;
 818 }
 819 EXPORT_SYMBOL(kcsan_disable_current);
 820
 821 void kcsan_enable_current(void)
 822 {
 823         if (get_ctx()->disable_count-- == 0) {
 824                 /*
 825                  * Warn if kcsan_enable_current() calls are unbalanced with
 826                  * kcsan_disable_current() calls, which causes disable_count to
 827                  * become negative and should not happen.
 828                  */
 829                 kcsan_disable_current(); /* restore to 0, KCSAN still enabled */
 830                 kcsan_disable_current(); /* disable to generate warning */
 831                 WARN(1, "Unbalanced %s()", __func__);
 832                 kcsan_enable_current();
 833         }
 834 }
 835 EXPORT_SYMBOL(kcsan_enable_current);
 836
 837 void kcsan_enable_current_nowarn(void)
 838 {
 839         if (get_ctx()->disable_count-- == 0)
 840                 kcsan_disable_current();
 841 }
 842 EXPORT_SYMBOL(kcsan_enable_current_nowarn);
 843
 844 void kcsan_nestable_atomic_begin(void)
 845 {
 846         /*
 847          * Do *not* check and warn if we are in a flat atomic region: nestable
 848          * and flat atomic regions are independent from each other.
 849          * See include/linux/kcsan.h: struct kcsan_ctx comments for more
 850          * comments.
 851          */
 852
 853         ++get_ctx()->atomic_nest_count;
 854 }
 855 EXPORT_SYMBOL(kcsan_nestable_atomic_begin);
 856
 857 void kcsan_nestable_atomic_end(void)
 858 {
 859         if (get_ctx()->atomic_nest_count-- == 0) {
 860                 /*
 861                  * Warn if kcsan_nestable_atomic_end() calls are unbalanced with
 862                  * kcsan_nestable_atomic_begin() calls, which causes
 863                  * atomic_nest_count to become negative and should not happen.
 864                  */
 865                 kcsan_nestable_atomic_begin(); /* restore to 0 */
 866                 kcsan_disable_current(); /* disable to generate warning */
 867                 WARN(1, "Unbalanced %s()", __func__);
 868                 kcsan_enable_current();
 869         }
 870 }
 871 EXPORT_SYMBOL(kcsan_nestable_atomic_end);
 872
 873 void kcsan_flat_atomic_begin(void)
 874 {
 875         get_ctx()->in_flat_atomic = true;
 876 }
 877 EXPORT_SYMBOL(kcsan_flat_atomic_begin);
 878
 879 void kcsan_flat_atomic_end(void)
 880 {
 881         get_ctx()->in_flat_atomic = false;
 882 }
 883 EXPORT_SYMBOL(kcsan_flat_atomic_end);
 884
 885 void kcsan_atomic_next(int n)
 886 {
 887         get_ctx()->atomic_next = n;
 888 }
 889 EXPORT_SYMBOL(kcsan_atomic_next);
 890
 891 void kcsan_set_access_mask(unsigned long mask)
 892 {
 893         get_ctx()->access_mask = mask;
 894 }
 895 EXPORT_SYMBOL(kcsan_set_access_mask);
 896
 897 struct kcsan_scoped_access *
 898 kcsan_begin_scoped_access(const volatile void *ptr, size_t size, int type,
 899                           struct kcsan_scoped_access *sa)
 900 {
 901         struct kcsan_ctx *ctx = get_ctx();
 902
 903         check_access(ptr, size, type, _RET_IP_);
 904
 905         ctx->disable_count++; /* Disable KCSAN, in case list debugging is on. */
 906
 907         INIT_LIST_HEAD(&sa->list);
 908         sa->ptr = ptr;
 909         sa->size = size;
 910         sa->type = type;
 911         sa->ip = _RET_IP_;
 912
 913         if (!ctx->scoped_accesses.prev) /* Lazy initialize list head. */
 914                 INIT_LIST_HEAD(&ctx->scoped_accesses);
 915         list_add(&sa->list, &ctx->scoped_accesses);
 916
 917         ctx->disable_count--;
 918         return sa;
 919 }
 920 EXPORT_SYMBOL(kcsan_begin_scoped_access);
 921
 922 void kcsan_end_scoped_access(struct kcsan_scoped_access *sa)
 923 {
 924         struct kcsan_ctx *ctx = get_ctx();
 925
 926         if (WARN(!ctx->scoped_accesses.prev, "Unbalanced %s()?", __func__))
 927                 return;
 928
 929         ctx->disable_count++; /* Disable KCSAN, in case list debugging is on. */
 930
 931         list_del(&sa->list);
 932         if (list_empty(&ctx->scoped_accesses))
 933                 /*
 934                  * Ensure we do not enter kcsan_check_scoped_accesses()
 935                  * slow-path if unnecessary, and avoids requiring list_empty()
 936                  * in the fast-path (to avoid a READ_ONCE() and potential
 937                  * uaccess warning).
 938                  */
 939                 ctx->scoped_accesses.prev = NULL;
 940
 941         ctx->disable_count--;
 942
 943         check_access(sa->ptr, sa->size, sa->type, sa->ip);
 944 }
 945 EXPORT_SYMBOL(kcsan_end_scoped_access);
 946
 947 void __kcsan_check_access(const volatile void *ptr, size_t size, int type)
 948 {
 949         check_access(ptr, size, type, _RET_IP_);
 950 }
 951 EXPORT_SYMBOL(__kcsan_check_access);
 952
 953 #define DEFINE_MEMORY_BARRIER(name, order_before_cond)                          \
 954         void __kcsan_##name(void)                                               \
 955         {                                                                       \
 956                 struct kcsan_scoped_access *sa = get_reorder_access(get_ctx()); \
 957                 if (!sa)                                                        \
 958                         return;                                                 \
 959                 if (order_before_cond)                                          \
 960                         sa->size = 0;                                           \
 961         }                                                                       \
 962         EXPORT_SYMBOL(__kcsan_##name)
 963
 964 DEFINE_MEMORY_BARRIER(mb, true);
 965 DEFINE_MEMORY_BARRIER(wmb, sa->type & (KCSAN_ACCESS_WRITE | KCSAN_ACCESS_COMPOUND));
 966 DEFINE_MEMORY_BARRIER(rmb, !(sa->type & KCSAN_ACCESS_WRITE) || (sa->type & KCSAN_ACCESS_COMPOUND));
 967 DEFINE_MEMORY_BARRIER(release, true);
 968
 969 /*
 970  * KCSAN uses the same instrumentation that is emitted by supported compilers
 971  * for ThreadSanitizer (TSAN).
 972  *
 973  * When enabled, the compiler emits instrumentation calls (the functions
 974  * prefixed with "__tsan" below) for all loads and stores that it generated;
 975  * inline asm is not instrumented.
 976  *
 977  * Note that, not all supported compiler versions distinguish aligned/unaligned
 978  * accesses, but e.g. recent versions of Clang do. We simply alias the unaligned
 979  * version to the generic version, which can handle both.
 980  */
 981
 982 #define DEFINE_TSAN_READ_WRITE(size)                                           \
 983         void __tsan_read##size(void *ptr);                                     \
 984         void __tsan_read##size(void *ptr)                                      \
 985         {                                                                      \
 986                 check_access(ptr, size, 0, _RET_IP_);                          \
 987         }                                                                      \
 988         EXPORT_SYMBOL(__tsan_read##size);                                      \
 989         void __tsan_unaligned_read##size(void *ptr)                            \
 990                 __alias(__tsan_read##size);                                    \
 991         EXPORT_SYMBOL(__tsan_unaligned_read##size);                            \
 992         void __tsan_write##size(void *ptr);                                    \
 993         void __tsan_write##size(void *ptr)                                     \
 994         {                                                                      \
 995                 check_access(ptr, size, KCSAN_ACCESS_WRITE, _RET_IP_);         \
 996         }                                                                      \
 997         EXPORT_SYMBOL(__tsan_write##size);                                     \
 998         void __tsan_unaligned_write##size(void *ptr)                           \
 999                 __alias(__tsan_write##size);                                   \
1000         EXPORT_SYMBOL(__tsan_unaligned_write##size);                           \
1001         void __tsan_read_write##size(void *ptr);                               \
1002         void __tsan_read_write##size(void *ptr)                                \
1003         {                                                                      \
1004                 check_access(ptr, size,                                        \
1005                              KCSAN_ACCESS_COMPOUND | KCSAN_ACCESS_WRITE,       \
1006                              _RET_IP_);                                        \
1007         }                                                                      \
1008         EXPORT_SYMBOL(__tsan_read_write##size);                                \
1009         void __tsan_unaligned_read_write##size(void *ptr)                      \
1010                 __alias(__tsan_read_write##size);                              \
1011         EXPORT_SYMBOL(__tsan_unaligned_read_write##size)
1012
1013 DEFINE_TSAN_READ_WRITE(1);
1014 DEFINE_TSAN_READ_WRITE(2);
1015 DEFINE_TSAN_READ_WRITE(4);
1016 DEFINE_TSAN_READ_WRITE(8);
1017 DEFINE_TSAN_READ_WRITE(16);
1018
1019 void __tsan_read_range(void *ptr, size_t size);
1020 void __tsan_read_range(void *ptr, size_t size)
1021 {
1022         check_access(ptr, size, 0, _RET_IP_);
1023 }
1024 EXPORT_SYMBOL(__tsan_read_range);
1025
1026 void __tsan_write_range(void *ptr, size_t size);
1027 void __tsan_write_range(void *ptr, size_t size)
1028 {
1029         check_access(ptr, size, KCSAN_ACCESS_WRITE, _RET_IP_);
1030 }
1031 EXPORT_SYMBOL(__tsan_write_range);
1032
1033 /*
1034  * Use of explicit volatile is generally disallowed [1], however, volatile is
1035  * still used in various concurrent context, whether in low-level
1036  * synchronization primitives or for legacy reasons.
1037  * [1] https://lwn.net/Articles/233479/
1038  *
1039  * We only consider volatile accesses atomic if they are aligned and would pass
1040  * the size-check of compiletime_assert_rwonce_type().
1041  */
1042 #define DEFINE_TSAN_VOLATILE_READ_WRITE(size)                                  \
1043         void __tsan_volatile_read##size(void *ptr);                            \
1044         void __tsan_volatile_read##size(void *ptr)                             \
1045         {                                                                      \
1046                 const bool is_atomic = size <= sizeof(long long) &&            \
1047                                        IS_ALIGNED((unsigned long)ptr, size);   \
1048                 if (IS_ENABLED(CONFIG_KCSAN_IGNORE_ATOMICS) && is_atomic)      \
1049                         return;                                                \
1050                 check_access(ptr, size, is_atomic ? KCSAN_ACCESS_ATOMIC : 0,   \
1051                              _RET_IP_);                                        \
1052         }                                                                      \
1053         EXPORT_SYMBOL(__tsan_volatile_read##size);                             \
1054         void __tsan_unaligned_volatile_read##size(void *ptr)                   \
1055                 __alias(__tsan_volatile_read##size);                           \
1056         EXPORT_SYMBOL(__tsan_unaligned_volatile_read##size);                   \
1057         void __tsan_volatile_write##size(void *ptr);                           \
1058         void __tsan_volatile_write##size(void *ptr)                            \
1059         {                                                                      \
1060                 const bool is_atomic = size <= sizeof(long long) &&            \
1061                                        IS_ALIGNED((unsigned long)ptr, size);   \
1062                 if (IS_ENABLED(CONFIG_KCSAN_IGNORE_ATOMICS) && is_atomic)      \
1063                         return;                                                \
1064                 check_access(ptr, size,                                        \
1065                              KCSAN_ACCESS_WRITE |                              \
1066                                      (is_atomic ? KCSAN_ACCESS_ATOMIC : 0),    \
1067                              _RET_IP_);                                        \
1068         }                                                                      \
1069         EXPORT_SYMBOL(__tsan_volatile_write##size);                            \
1070         void __tsan_unaligned_volatile_write##size(void *ptr)                  \
1071                 __alias(__tsan_volatile_write##size);                          \
1072         EXPORT_SYMBOL(__tsan_unaligned_volatile_write##size)
1073
1074 DEFINE_TSAN_VOLATILE_READ_WRITE(1);
1075 DEFINE_TSAN_VOLATILE_READ_WRITE(2);
1076 DEFINE_TSAN_VOLATILE_READ_WRITE(4);
1077 DEFINE_TSAN_VOLATILE_READ_WRITE(8);
1078 DEFINE_TSAN_VOLATILE_READ_WRITE(16);
1079
1080 /*
1081  * Function entry and exit are used to determine the validty of reorder_access.
1082  * Reordering of the access ends at the end of the function scope where the
1083  * access happened. This is done for two reasons:
1084  *
1085  *      1. Artificially limits the scope where missing barriers are detected.
1086  *         This minimizes false positives due to uninstrumented functions that
1087  *         contain the required barriers but were missed.
1088  *
1089  *      2. Simplifies generating the stack trace of the access.
1090  */
1091 void __tsan_func_entry(void *call_pc);
1092 noinline void __tsan_func_entry(void *call_pc)
1093 {
1094         if (!IS_ENABLED(CONFIG_KCSAN_WEAK_MEMORY))
1095                 return;
1096
1097         add_kcsan_stack_depth(1);
1098 }
1099 EXPORT_SYMBOL(__tsan_func_entry);
1100
1101 void __tsan_func_exit(void);
1102 noinline void __tsan_func_exit(void)
1103 {
1104         struct kcsan_scoped_access *reorder_access;
1105
1106         if (!IS_ENABLED(CONFIG_KCSAN_WEAK_MEMORY))
1107                 return;
1108
1109         reorder_access = get_reorder_access(get_ctx());
1110         if (!reorder_access)
1111                 goto out;
1112
1113         if (get_kcsan_stack_depth() <= reorder_access->stack_depth) {
1114                 /*
1115                  * Access check to catch cases where write without a barrier
1116                  * (supposed release) was last access in function: because
1117                  * instrumentation is inserted before the real access, a data
1118                  * race due to the write giving up a c-s would only be caught if
1119                  * we do the conflicting access after.
1120                  */
1121                 check_access(reorder_access->ptr, reorder_access->size,
1122                              reorder_access->type, reorder_access->ip);
1123                 reorder_access->size = 0;
1124                 reorder_access->stack_depth = INT_MIN;
1125         }
1126 out:
1127         add_kcsan_stack_depth(-1);
1128 }
1129 EXPORT_SYMBOL(__tsan_func_exit);
1130
1131 void __tsan_init(void);
1132 void __tsan_init(void)
1133 {
1134 }
1135 EXPORT_SYMBOL(__tsan_init);
1136
1137 /*
1138  * Instrumentation for atomic builtins (__atomic_*, __sync_*).
1139  *
1140  * Normal kernel code _should not_ be using them directly, but some
1141  * architectures may implement some or all atomics using the compilers'
1142  * builtins.
1143  *
1144  * Note: If an architecture decides to fully implement atomics using the
1145  * builtins, because they are implicitly instrumented by KCSAN (and KASAN,
1146  * etc.), implementing the ARCH_ATOMIC interface (to get instrumentation via
1147  * atomic-instrumented) is no longer necessary.
1148  *
1149  * TSAN instrumentation replaces atomic accesses with calls to any of the below
1150  * functions, whose job is to also execute the operation itself.
1151  */
1152
1153 static __always_inline void kcsan_atomic_builtin_memorder(int memorder)
1154 {
1155         if (memorder == __ATOMIC_RELEASE ||
1156             memorder == __ATOMIC_SEQ_CST ||
1157             memorder == __ATOMIC_ACQ_REL)
1158                 __kcsan_release();
1159 }
1160
1161 #define DEFINE_TSAN_ATOMIC_LOAD_STORE(bits)                                                        \
1162         u##bits __tsan_atomic##bits##_load(const u##bits *ptr, int memorder);                      \
1163         u##bits __tsan_atomic##bits##_load(const u##bits *ptr, int memorder)                       \
1164         {                                                                                          \
1165                 kcsan_atomic_builtin_memorder(memorder);                                           \
1166                 if (!IS_ENABLED(CONFIG_KCSAN_IGNORE_ATOMICS)) {                                    \
1167                         check_access(ptr, bits / BITS_PER_BYTE, KCSAN_ACCESS_ATOMIC, _RET_IP_);    \
1168                 }                                                                                  \
1169                 return __atomic_load_n(ptr, memorder);                                             \
1170         }                                                                                          \
1171         EXPORT_SYMBOL(__tsan_atomic##bits##_load);                                                 \
1172         void __tsan_atomic##bits##_store(u##bits *ptr, u##bits v, int memorder);                   \
1173         void __tsan_atomic##bits##_store(u##bits *ptr, u##bits v, int memorder)                    \
1174         {                                                                                          \
1175                 kcsan_atomic_builtin_memorder(memorder);                                           \
1176                 if (!IS_ENABLED(CONFIG_KCSAN_IGNORE_ATOMICS)) {                                    \
1177                         check_access(ptr, bits / BITS_PER_BYTE,                                    \
1178                                      KCSAN_ACCESS_WRITE | KCSAN_ACCESS_ATOMIC, _RET_IP_);          \
1179                 }                                                                                  \
1180                 __atomic_store_n(ptr, v, memorder);                                                \
1181         }                                                                                          \
1182         EXPORT_SYMBOL(__tsan_atomic##bits##_store)
1183
1184 #define DEFINE_TSAN_ATOMIC_RMW(op, bits, suffix)                                                   \
1185         u##bits __tsan_atomic##bits##_##op(u##bits *ptr, u##bits v, int memorder);                 \
1186         u##bits __tsan_atomic##bits##_##op(u##bits *ptr, u##bits v, int memorder)                  \
1187         {                                                                                          \
1188                 kcsan_atomic_builtin_memorder(memorder);                                           \
1189                 if (!IS_ENABLED(CONFIG_KCSAN_IGNORE_ATOMICS)) {                                    \
1190                         check_access(ptr, bits / BITS_PER_BYTE,                                    \
1191                                      KCSAN_ACCESS_COMPOUND | KCSAN_ACCESS_WRITE |                  \
1192                                              KCSAN_ACCESS_ATOMIC, _RET_IP_);                       \
1193                 }                                                                                  \
1194                 return __atomic_##op##suffix(ptr, v, memorder);                                    \
1195         }                                                                                          \
1196         EXPORT_SYMBOL(__tsan_atomic##bits##_##op)
1197
1198 /*
1199  * Note: CAS operations are always classified as write, even in case they
1200  * fail. We cannot perform check_access() after a write, as it might lead to
1201  * false positives, in cases such as:
1202  *
1203  *      T0: __atomic_compare_exchange_n(&p->flag, &old, 1, ...)
1204  *
1205  *      T1: if (__atomic_load_n(&p->flag, ...)) {
1206  *              modify *p;
1207  *              p->flag = 0;
1208  *          }
1209  *
1210  * The only downside is that, if there are 3 threads, with one CAS that
1211  * succeeds, another CAS that fails, and an unmarked racing operation, we may
1212  * point at the wrong CAS as the source of the race. However, if we assume that
1213  * all CAS can succeed in some other execution, the data race is still valid.
1214  */
1215 #define DEFINE_TSAN_ATOMIC_CMPXCHG(bits, strength, weak)                                           \
1216         int __tsan_atomic##bits##_compare_exchange_##strength(u##bits *ptr, u##bits *exp,          \
1217                                                               u##bits val, int mo, int fail_mo);   \
1218         int __tsan_atomic##bits##_compare_exchange_##strength(u##bits *ptr, u##bits *exp,          \
1219                                                               u##bits val, int mo, int fail_mo)    \
1220         {                                                                                          \
1221                 kcsan_atomic_builtin_memorder(mo);                                                 \
1222                 if (!IS_ENABLED(CONFIG_KCSAN_IGNORE_ATOMICS)) {                                    \
1223                         check_access(ptr, bits / BITS_PER_BYTE,                                    \
1224                                      KCSAN_ACCESS_COMPOUND | KCSAN_ACCESS_WRITE |                  \
1225                                              KCSAN_ACCESS_ATOMIC, _RET_IP_);                       \
1226                 }                                                                                  \
1227                 return __atomic_compare_exchange_n(ptr, exp, val, weak, mo, fail_mo);              \
1228         }                                                                                          \
1229         EXPORT_SYMBOL(__tsan_atomic##bits##_compare_exchange_##strength)
1230
1231 #define DEFINE_TSAN_ATOMIC_CMPXCHG_VAL(bits)                                                       \
1232         u##bits __tsan_atomic##bits##_compare_exchange_val(u##bits *ptr, u##bits exp, u##bits val, \
1233                                                            int mo, int fail_mo);                   \
1234         u##bits __tsan_atomic##bits##_compare_exchange_val(u##bits *ptr, u##bits exp, u##bits val, \
1235                                                            int mo, int fail_mo)                    \
1236         {                                                                                          \
1237                 kcsan_atomic_builtin_memorder(mo);                                                 \
1238                 if (!IS_ENABLED(CONFIG_KCSAN_IGNORE_ATOMICS)) {                                    \
1239                         check_access(ptr, bits / BITS_PER_BYTE,                                    \
1240                                      KCSAN_ACCESS_COMPOUND | KCSAN_ACCESS_WRITE |                  \
1241                                              KCSAN_ACCESS_ATOMIC, _RET_IP_);                       \
1242                 }                                                                                  \
1243                 __atomic_compare_exchange_n(ptr, &exp, val, 0, mo, fail_mo);                       \
1244                 return exp;                                                                        \
1245         }                                                                                          \
1246         EXPORT_SYMBOL(__tsan_atomic##bits##_compare_exchange_val)
1247
1248 #define DEFINE_TSAN_ATOMIC_OPS(bits)                                                               \
1249         DEFINE_TSAN_ATOMIC_LOAD_STORE(bits);                                                       \
1250         DEFINE_TSAN_ATOMIC_RMW(exchange, bits, _n);                                                \
1251         DEFINE_TSAN_ATOMIC_RMW(fetch_add, bits, );                                                 \
1252         DEFINE_TSAN_ATOMIC_RMW(fetch_sub, bits, );                                                 \
1253         DEFINE_TSAN_ATOMIC_RMW(fetch_and, bits, );                                                 \
1254         DEFINE_TSAN_ATOMIC_RMW(fetch_or, bits, );                                                  \
1255         DEFINE_TSAN_ATOMIC_RMW(fetch_xor, bits, );                                                 \
1256         DEFINE_TSAN_ATOMIC_RMW(fetch_nand, bits, );                                                \
1257         DEFINE_TSAN_ATOMIC_CMPXCHG(bits, strong, 0);                                               \
1258         DEFINE_TSAN_ATOMIC_CMPXCHG(bits, weak, 1);                                                 \
1259         DEFINE_TSAN_ATOMIC_CMPXCHG_VAL(bits)
1260
1261 DEFINE_TSAN_ATOMIC_OPS(8);
1262 DEFINE_TSAN_ATOMIC_OPS(16);
1263 DEFINE_TSAN_ATOMIC_OPS(32);
1264 DEFINE_TSAN_ATOMIC_OPS(64);
1265
1266 void __tsan_atomic_thread_fence(int memorder);
1267 void __tsan_atomic_thread_fence(int memorder)
1268 {
1269         kcsan_atomic_builtin_memorder(memorder);
1270         __atomic_thread_fence(memorder);
1271 }
1272 EXPORT_SYMBOL(__tsan_atomic_thread_fence);
1273
1274 /*
1275  * In instrumented files, we emit instrumentation for barriers by mapping the
1276  * kernel barriers to an __atomic_signal_fence(), which is interpreted specially
1277  * and otherwise has no relation to a real __atomic_signal_fence(). No known
1278  * kernel code uses __atomic_signal_fence().
1279  *
1280  * Since fsanitize=thread instrumentation handles __atomic_signal_fence(), which
1281  * are turned into calls to __tsan_atomic_signal_fence(), such instrumentation
1282  * can be disabled via the __no_kcsan function attribute (vs. an explicit call
1283  * which could not). When __no_kcsan is requested, __atomic_signal_fence()
1284  * generates no code.
1285  *
1286  * Note: The result of using __atomic_signal_fence() with KCSAN enabled is
1287  * potentially limiting the compiler's ability to reorder operations; however,
1288  * if barriers were instrumented with explicit calls (without LTO), the compiler
1289  * couldn't optimize much anyway. The result of a hypothetical architecture
1290  * using __atomic_signal_fence() in normal code would be KCSAN false negatives.
1291  */
1292 void __tsan_atomic_signal_fence(int memorder);
1293 noinline void __tsan_atomic_signal_fence(int memorder)
1294 {
1295         switch (memorder) {
1296         case __KCSAN_BARRIER_TO_SIGNAL_FENCE_mb:
1297                 __kcsan_mb();
1298                 break;
1299         case __KCSAN_BARRIER_TO_SIGNAL_FENCE_wmb:
1300                 __kcsan_wmb();
1301                 break;
1302         case __KCSAN_BARRIER_TO_SIGNAL_FENCE_rmb:
1303                 __kcsan_rmb();
1304                 break;
1305         case __KCSAN_BARRIER_TO_SIGNAL_FENCE_release:
1306                 __kcsan_release();
1307                 break;
1308         default:
1309                 break;
1310         }
1311 }
1312 EXPORT_SYMBOL(__tsan_atomic_signal_fence);
1313
1314 #ifdef __HAVE_ARCH_MEMSET
1315 void *__tsan_memset(void *s, int c, size_t count);
1316 noinline void *__tsan_memset(void *s, int c, size_t count)
1317 {
1318         /*
1319          * Instead of not setting up watchpoints where accessed size is greater
1320          * than MAX_ENCODABLE_SIZE, truncate checked size to MAX_ENCODABLE_SIZE.
1321          */
1322         size_t check_len = min_t(size_t, count, MAX_ENCODABLE_SIZE);
1323
1324         check_access(s, check_len, KCSAN_ACCESS_WRITE, _RET_IP_);
1325         return memset(s, c, count);
1326 }
1327 #else
1328 void *__tsan_memset(void *s, int c, size_t count) __alias(memset);
1329 #endif
1330 EXPORT_SYMBOL(__tsan_memset);
1331
1332 #ifdef __HAVE_ARCH_MEMMOVE
1333 void *__tsan_memmove(void *dst, const void *src, size_t len);
1334 noinline void *__tsan_memmove(void *dst, const void *src, size_t len)
1335 {
1336         size_t check_len = min_t(size_t, len, MAX_ENCODABLE_SIZE);
1337
1338         check_access(dst, check_len, KCSAN_ACCESS_WRITE, _RET_IP_);
1339         check_access(src, check_len, 0, _RET_IP_);
1340         return memmove(dst, src, len);
1341 }
1342 #else
1343 void *__tsan_memmove(void *dst, const void *src, size_t len) __alias(memmove);
1344 #endif
1345 EXPORT_SYMBOL(__tsan_memmove);
1346
1347 #ifdef __HAVE_ARCH_MEMCPY
1348 void *__tsan_memcpy(void *dst, const void *src, size_t len);
1349 noinline void *__tsan_memcpy(void *dst, const void *src, size_t len)
1350 {
1351         size_t check_len = min_t(size_t, len, MAX_ENCODABLE_SIZE);
1352
1353         check_access(dst, check_len, KCSAN_ACCESS_WRITE, _RET_IP_);
1354         check_access(src, check_len, 0, _RET_IP_);
1355         return memcpy(dst, src, len);
1356 }
1357 #else
1358 void *__tsan_memcpy(void *dst, const void *src, size_t len) __alias(memcpy);
1359 #endif
1360 EXPORT_SYMBOL(__tsan_memcpy);