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/moduleparam.h>
  18 #include <linux/percpu.h>
  19 #include <linux/preempt.h>
  20 #include <linux/sched.h>
  21 #include <linux/uaccess.h>
  22
  23 #include "encoding.h"
  24 #include "kcsan.h"
  25 #include "permissive.h"
  26
  27 static bool kcsan_early_enable = IS_ENABLED(CONFIG_KCSAN_EARLY_ENABLE);
  28 unsigned int kcsan_udelay_task = CONFIG_KCSAN_UDELAY_TASK;
  29 unsigned int kcsan_udelay_interrupt = CONFIG_KCSAN_UDELAY_INTERRUPT;
  30 static long kcsan_skip_watch = CONFIG_KCSAN_SKIP_WATCH;
  31 static bool kcsan_interrupt_watcher = IS_ENABLED(CONFIG_KCSAN_INTERRUPT_WATCHER);
  32
  33 #ifdef MODULE_PARAM_PREFIX
  34 #undef MODULE_PARAM_PREFIX
  35 #endif
  36 #define MODULE_PARAM_PREFIX "kcsan."
  37 module_param_named(early_enable, kcsan_early_enable, bool, 0);
  38 module_param_named(udelay_task, kcsan_udelay_task, uint, 0644);
  39 module_param_named(udelay_interrupt, kcsan_udelay_interrupt, uint, 0644);
  40 module_param_named(skip_watch, kcsan_skip_watch, long, 0644);
  41 module_param_named(interrupt_watcher, kcsan_interrupt_watcher, bool, 0444);
  42
  43 #ifdef CONFIG_KCSAN_WEAK_MEMORY
  44 static bool kcsan_weak_memory = true;
  45 module_param_named(weak_memory, kcsan_weak_memory, bool, 0644);
  46 #else
  47 #define kcsan_weak_memory false
  48 #endif
  49
  50 bool kcsan_enabled;
  51
  52 /* Per-CPU kcsan_ctx for interrupts */
  53 static DEFINE_PER_CPU(struct kcsan_ctx, kcsan_cpu_ctx) = {
  54         .scoped_accesses        = {LIST_POISON1, NULL},
  55 };
  56
  57 /*
  58  * Helper macros to index into adjacent slots, starting from address slot
  59  * itself, followed by the right and left slots.
  60  *
  61  * The purpose is 2-fold:
  62  *
  63  *      1. if during insertion the address slot is already occupied, check if
  64  *         any adjacent slots are free;
  65  *      2. accesses that straddle a slot boundary due to size that exceeds a
  66  *         slot's range may check adjacent slots if any watchpoint matches.
  67  *
  68  * Note that accesses with very large size may still miss a watchpoint; however,
  69  * given this should be rare, this is a reasonable trade-off to make, since this
  70  * will avoid:
  71  *
  72  *      1. excessive contention between watchpoint checks and setup;
  73  *      2. larger number of simultaneous watchpoints without sacrificing
  74  *         performance.
  75  *
  76  * Example: SLOT_IDX values for KCSAN_CHECK_ADJACENT=1, where i is [0, 1, 2]:
  77  *
  78  *   slot=0:  [ 1,  2,  0]
  79  *   slot=9:  [10, 11,  9]
  80  *   slot=63: [64, 65, 63]
  81  */
  82 #define SLOT_IDX(slot, i) (slot + ((i + KCSAN_CHECK_ADJACENT) % NUM_SLOTS))
  83
  84 /*
  85  * SLOT_IDX_FAST is used in the fast-path. Not first checking the address's primary
  86  * slot (middle) is fine if we assume that races occur rarely. The set of
  87  * indices {SLOT_IDX(slot, i) | i in [0, NUM_SLOTS)} is equivalent to
  88  * {SLOT_IDX_FAST(slot, i) | i in [0, NUM_SLOTS)}.
  89  */
  90 #define SLOT_IDX_FAST(slot, i) (slot + i)
  91
  92 /*
  93  * Watchpoints, with each entry encoded as defined in encoding.h: in order to be
  94  * able to safely update and access a watchpoint without introducing locking
  95  * overhead, we encode each watchpoint as a single atomic long. The initial
  96  * zero-initialized state matches INVALID_WATCHPOINT.
  97  *
  98  * Add NUM_SLOTS-1 entries to account for overflow; this helps avoid having to
  99  * use more complicated SLOT_IDX_FAST calculation with modulo in the fast-path.
 100  */
 101 static atomic_long_t watchpoints[CONFIG_KCSAN_NUM_WATCHPOINTS + NUM_SLOTS-1];
 102
 103 /*
 104  * Instructions to skip watching counter, used in should_watch(). We use a
 105  * per-CPU counter to avoid excessive contention.
 106  */
 107 static DEFINE_PER_CPU(long, kcsan_skip);
 108
 109 /* For kcsan_prandom_u32_max(). */
 110 static DEFINE_PER_CPU(u32, kcsan_rand_state);
 111
 112 static __always_inline atomic_long_t *find_watchpoint(unsigned long addr,
 113                                                       size_t size,
 114                                                       bool expect_write,
 115                                                       long *encoded_watchpoint)
 116 {
 117         const int slot = watchpoint_slot(addr);
 118         const unsigned long addr_masked = addr & WATCHPOINT_ADDR_MASK;
 119         atomic_long_t *watchpoint;
 120         unsigned long wp_addr_masked;
 121         size_t wp_size;
 122         bool is_write;
 123         int i;
 124
 125         BUILD_BUG_ON(CONFIG_KCSAN_NUM_WATCHPOINTS < NUM_SLOTS);
 126
 127         for (i = 0; i < NUM_SLOTS; ++i) {
 128                 watchpoint = &watchpoints[SLOT_IDX_FAST(slot, i)];
 129                 *encoded_watchpoint = atomic_long_read(watchpoint);
 130                 if (!decode_watchpoint(*encoded_watchpoint, &wp_addr_masked,
 131                                        &wp_size, &is_write))
 132                         continue;
 133
 134                 if (expect_write && !is_write)
 135                         continue;
 136
 137                 /* Check if the watchpoint matches the access. */
 138                 if (matching_access(wp_addr_masked, wp_size, addr_masked, size))
 139                         return watchpoint;
 140         }
 141
 142         return NULL;
 143 }
 144
 145 static inline atomic_long_t *
 146 insert_watchpoint(unsigned long addr, size_t size, bool is_write)
 147 {
 148         const int slot = watchpoint_slot(addr);
 149         const long encoded_watchpoint = encode_watchpoint(addr, size, is_write);
 150         atomic_long_t *watchpoint;
 151         int i;
 152
 153         /* Check slot index logic, ensuring we stay within array bounds. */
 154         BUILD_BUG_ON(SLOT_IDX(0, 0) != KCSAN_CHECK_ADJACENT);
 155         BUILD_BUG_ON(SLOT_IDX(0, KCSAN_CHECK_ADJACENT+1) != 0);
 156         BUILD_BUG_ON(SLOT_IDX(CONFIG_KCSAN_NUM_WATCHPOINTS-1, KCSAN_CHECK_ADJACENT) != ARRAY_SIZE(watchpoints)-1);
 157         BUILD_BUG_ON(SLOT_IDX(CONFIG_KCSAN_NUM_WATCHPOINTS-1, KCSAN_CHECK_ADJACENT+1) != ARRAY_SIZE(watchpoints) - NUM_SLOTS);
 158
 159         for (i = 0; i < NUM_SLOTS; ++i) {
 160                 long expect_val = INVALID_WATCHPOINT;
 161
 162                 /* Try to acquire this slot. */
 163                 watchpoint = &watchpoints[SLOT_IDX(slot, i)];
 164                 if (atomic_long_try_cmpxchg_relaxed(watchpoint, &expect_val, encoded_watchpoint))
 165                         return watchpoint;
 166         }
 167
 168         return NULL;
 169 }
 170
 171 /*
 172  * Return true if watchpoint was successfully consumed, false otherwise.
 173  *
 174  * This may return false if:
 175  *
 176  *      1. another thread already consumed the watchpoint;
 177  *      2. the thread that set up the watchpoint already removed it;
 178  *      3. the watchpoint was removed and then re-used.
 179  */
 180 static __always_inline bool
 181 try_consume_watchpoint(atomic_long_t *watchpoint, long encoded_watchpoint)
 182 {
 183         return atomic_long_try_cmpxchg_relaxed(watchpoint, &encoded_watchpoint, CONSUMED_WATCHPOINT);
 184 }
 185
 186 /* Return true if watchpoint was not touched, false if already consumed. */
 187 static inline bool consume_watchpoint(atomic_long_t *watchpoint)
 188 {
 189         return atomic_long_xchg_relaxed(watchpoint, CONSUMED_WATCHPOINT) != CONSUMED_WATCHPOINT;
 190 }
 191
 192 /* Remove the watchpoint -- its slot may be reused after. */
 193 static inline void remove_watchpoint(atomic_long_t *watchpoint)
 194 {
 195         atomic_long_set(watchpoint, INVALID_WATCHPOINT);
 196 }
 197
 198 static __always_inline struct kcsan_ctx *get_ctx(void)
 199 {
 200         /*
 201          * In interrupts, use raw_cpu_ptr to avoid unnecessary checks, that would
 202          * also result in calls that generate warnings in uaccess regions.
 203          */
 204         return in_task() ? &current->kcsan_ctx : raw_cpu_ptr(&kcsan_cpu_ctx);
 205 }
 206
 207 static __always_inline void
 208 check_access(const volatile void *ptr, size_t size, int type, unsigned long ip);
 209
 210 /* Check scoped accesses; never inline because this is a slow-path! */
 211 static noinline void kcsan_check_scoped_accesses(void)
 212 {
 213         struct kcsan_ctx *ctx = get_ctx();
 214         struct kcsan_scoped_access *scoped_access;
 215
 216         if (ctx->disable_scoped)
 217                 return;
 218
 219         ctx->disable_scoped++;
 220         list_for_each_entry(scoped_access, &ctx->scoped_accesses, list) {
 221                 check_access(scoped_access->ptr, scoped_access->size,
 222                              scoped_access->type, scoped_access->ip);
 223         }
 224         ctx->disable_scoped--;
 225 }
 226
 227 /* Rules for generic atomic accesses. Called from fast-path. */
 228 static __always_inline bool
 229 is_atomic(struct kcsan_ctx *ctx, const volatile void *ptr, size_t size, int type)
 230 {
 231         if (type & KCSAN_ACCESS_ATOMIC)
 232                 return true;
 233
 234         /*
 235          * Unless explicitly declared atomic, never consider an assertion access
 236          * as atomic. This allows using them also in atomic regions, such as
 237          * seqlocks, without implicitly changing their semantics.
 238          */
 239         if (type & KCSAN_ACCESS_ASSERT)
 240                 return false;
 241
 242         if (IS_ENABLED(CONFIG_KCSAN_ASSUME_PLAIN_WRITES_ATOMIC) &&
 243             (type & KCSAN_ACCESS_WRITE) && size <= sizeof(long) &&
 244             !(type & KCSAN_ACCESS_COMPOUND) && IS_ALIGNED((unsigned long)ptr, size))
 245                 return true; /* Assume aligned writes up to word size are atomic. */
 246
 247         if (ctx->atomic_next > 0) {
 248                 /*
 249                  * Because we do not have separate contexts for nested
 250                  * interrupts, in case atomic_next is set, we simply assume that
 251                  * the outer interrupt set atomic_next. In the worst case, we
 252                  * will conservatively consider operations as atomic. This is a
 253                  * reasonable trade-off to make, since this case should be
 254                  * extremely rare; however, even if extremely rare, it could
 255                  * lead to false positives otherwise.
 256                  */
 257                 if ((hardirq_count() >> HARDIRQ_SHIFT) < 2)
 258                         --ctx->atomic_next; /* in task, or outer interrupt */
 259                 return true;
 260         }
 261
 262         return ctx->atomic_nest_count > 0 || ctx->in_flat_atomic;
 263 }
 264
 265 static __always_inline bool
 266 should_watch(struct kcsan_ctx *ctx, const volatile void *ptr, size_t size, int type)
 267 {
 268         /*
 269          * Never set up watchpoints when memory operations are atomic.
 270          *
 271          * Need to check this first, before kcsan_skip check below: (1) atomics
 272          * should not count towards skipped instructions, and (2) to actually
 273          * decrement kcsan_atomic_next for consecutive instruction stream.
 274          */
 275         if (is_atomic(ctx, ptr, size, type))
 276                 return false;
 277
 278         if (this_cpu_dec_return(kcsan_skip) >= 0)
 279                 return false;
 280
 281         /*
 282          * NOTE: If we get here, kcsan_skip must always be reset in slow path
 283          * via reset_kcsan_skip() to avoid underflow.
 284          */
 285
 286         /* this operation should be watched */
 287         return true;
 288 }
 289
 290 /*
 291  * Returns a pseudo-random number in interval [0, ep_ro). Simple linear
 292  * congruential generator, using constants from "Numerical Recipes".
 293  */
 294 static u32 kcsan_prandom_u32_max(u32 ep_ro)
 295 {
 296         u32 state = this_cpu_read(kcsan_rand_state);
 297
 298         state = 1664525 * state + 1013904223;
 299         this_cpu_write(kcsan_rand_state, state);
 300
 301         return state % ep_ro;
 302 }
 303
 304 static inline void reset_kcsan_skip(void)
 305 {
 306         long skip_count = kcsan_skip_watch -
 307                           (IS_ENABLED(CONFIG_KCSAN_SKIP_WATCH_RANDOMIZE) ?
 308                                    kcsan_prandom_u32_max(kcsan_skip_watch) :
 309                                    0);
 310         this_cpu_write(kcsan_skip, skip_count);
 311 }
 312
 313 static __always_inline bool kcsan_is_enabled(struct kcsan_ctx *ctx)
 314 {
 315         return READ_ONCE(kcsan_enabled) && !ctx->disable_count;
 316 }
 317
 318 /* Introduce delay depending on context and configuration. */
 319 static void delay_access(int type)
 320 {
 321         unsigned int delay = in_task() ? kcsan_udelay_task : kcsan_udelay_interrupt;
 322         /* For certain access types, skew the random delay to be longer. */
 323         unsigned int skew_delay_order =
 324                 (type & (KCSAN_ACCESS_COMPOUND | KCSAN_ACCESS_ASSERT)) ? 1 : 0;
 325
 326         delay -= IS_ENABLED(CONFIG_KCSAN_DELAY_RANDOMIZE) ?
 327                                kcsan_prandom_u32_max(delay >> skew_delay_order) :
 328                                0;
 329         udelay(delay);
 330 }
 331
 332 /*
 333  * Reads the instrumented memory for value change detection; value change
 334  * detection is currently done for accesses up to a size of 8 bytes.
 335  */
 336 static __always_inline u64 read_instrumented_memory(const volatile void *ptr, size_t size)
 337 {
 338         switch (size) {
 339         case 1:  return READ_ONCE(*(const u8 *)ptr);
 340         case 2:  return READ_ONCE(*(const u16 *)ptr);
 341         case 4:  return READ_ONCE(*(const u32 *)ptr);
 342         case 8:  return READ_ONCE(*(const u64 *)ptr);
 343         default: return 0; /* Ignore; we do not diff the values. */
 344         }
 345 }
 346
 347 void kcsan_save_irqtrace(struct task_struct *task)
 348 {
 349 #ifdef CONFIG_TRACE_IRQFLAGS
 350         task->kcsan_save_irqtrace = task->irqtrace;
 351 #endif
 352 }
 353
 354 void kcsan_restore_irqtrace(struct task_struct *task)
 355 {
 356 #ifdef CONFIG_TRACE_IRQFLAGS
 357         task->irqtrace = task->kcsan_save_irqtrace;
 358 #endif
 359 }
 360
 361 static __always_inline int get_kcsan_stack_depth(void)
 362 {
 363 #ifdef CONFIG_KCSAN_WEAK_MEMORY
 364         return current->kcsan_stack_depth;
 365 #else
 366         BUILD_BUG();
 367         return 0;
 368 #endif
 369 }
 370
 371 static __always_inline void add_kcsan_stack_depth(int val)
 372 {
 373 #ifdef CONFIG_KCSAN_WEAK_MEMORY
 374         current->kcsan_stack_depth += val;
 375 #else
 376         BUILD_BUG();
 377 #endif
 378 }
 379
 380 static __always_inline struct kcsan_scoped_access *get_reorder_access(struct kcsan_ctx *ctx)
 381 {
 382 #ifdef CONFIG_KCSAN_WEAK_MEMORY
 383         return ctx->disable_scoped ? NULL : &ctx->reorder_access;
 384 #else
 385         return NULL;
 386 #endif
 387 }
 388
 389 static __always_inline bool
 390 find_reorder_access(struct kcsan_ctx *ctx, const volatile void *ptr, size_t size,
 391                     int type, unsigned long ip)
 392 {
 393         struct kcsan_scoped_access *reorder_access = get_reorder_access(ctx);
 394
 395         if (!reorder_access)
 396                 return false;
 397
 398         /*
 399          * Note: If accesses are repeated while reorder_access is identical,
 400          * never matches the new access, because !(type & KCSAN_ACCESS_SCOPED).
 401          */
 402         return reorder_access->ptr == ptr && reorder_access->size == size &&
 403                reorder_access->type == type && reorder_access->ip == ip;
 404 }
 405
 406 static inline void
 407 set_reorder_access(struct kcsan_ctx *ctx, const volatile void *ptr, size_t size,
 408                    int type, unsigned long ip)
 409 {
 410         struct kcsan_scoped_access *reorder_access = get_reorder_access(ctx);
 411
 412         if (!reorder_access || !kcsan_weak_memory)
 413                 return;
 414
 415         /*
 416          * To avoid nested interrupts or scheduler (which share kcsan_ctx)
 417          * reading an inconsistent reorder_access, ensure that the below has
 418          * exclusive access to reorder_access by disallowing concurrent use.
 419          */
 420         ctx->disable_scoped++;
 421         barrier();
 422         reorder_access->ptr             = ptr;
 423         reorder_access->size            = size;
 424         reorder_access->type            = type | KCSAN_ACCESS_SCOPED;
 425         reorder_access->ip              = ip;
 426         reorder_access->stack_depth     = get_kcsan_stack_depth();
 427         barrier();
 428         ctx->disable_scoped--;
 429 }
 430
 431 /*
 432  * Pull everything together: check_access() below contains the performance
 433  * critical operations; the fast-path (including check_access) functions should
 434  * all be inlinable by the instrumentation functions.
 435  *
 436  * The slow-path (kcsan_found_watchpoint, kcsan_setup_watchpoint) are
 437  * non-inlinable -- note that, we prefix these with "kcsan_" to ensure they can
 438  * be filtered from the stacktrace, as well as give them unique names for the
 439  * UACCESS whitelist of objtool. Each function uses user_access_save/restore(),
 440  * since they do not access any user memory, but instrumentation is still
 441  * emitted in UACCESS regions.
 442  */
 443
 444 static noinline void kcsan_found_watchpoint(const volatile void *ptr,
 445                                             size_t size,
 446                                             int type,
 447                                             unsigned long ip,
 448                                             atomic_long_t *watchpoint,
 449                                             long encoded_watchpoint)
 450 {
 451         const bool is_assert = (type & KCSAN_ACCESS_ASSERT) != 0;
 452         struct kcsan_ctx *ctx = get_ctx();
 453         unsigned long flags;
 454         bool consumed;
 455
 456         /*
 457          * We know a watchpoint exists. Let's try to keep the race-window
 458          * between here and finally consuming the watchpoint below as small as
 459          * possible -- avoid unneccessarily complex code until consumed.
 460          */
 461
 462         if (!kcsan_is_enabled(ctx))
 463                 return;
 464
 465         /*
 466          * The access_mask check relies on value-change comparison. To avoid
 467          * reporting a race where e.g. the writer set up the watchpoint, but the
 468          * reader has access_mask!=0, we have to ignore the found watchpoint.
 469          *
 470          * reorder_access is never created from an access with access_mask set.
 471          */
 472         if (ctx->access_mask && !find_reorder_access(ctx, ptr, size, type, ip))
 473                 return;
 474
 475         /*
 476          * If the other thread does not want to ignore the access, and there was
 477          * a value change as a result of this thread's operation, we will still
 478          * generate a report of unknown origin.
 479          *
 480          * Use CONFIG_KCSAN_REPORT_RACE_UNKNOWN_ORIGIN=n to filter.
 481          */
 482         if (!is_assert && kcsan_ignore_address(ptr))
 483                 return;
 484
 485         /*
 486          * Consuming the watchpoint must be guarded by kcsan_is_enabled() to
 487          * avoid erroneously triggering reports if the context is disabled.
 488          */
 489         consumed = try_consume_watchpoint(watchpoint, encoded_watchpoint);
 490
 491         /* keep this after try_consume_watchpoint */
 492         flags = user_access_save();
 493
 494         if (consumed) {
 495                 kcsan_save_irqtrace(current);
 496                 kcsan_report_set_info(ptr, size, type, ip, watchpoint - watchpoints);
 497                 kcsan_restore_irqtrace(current);
 498         } else {
 499                 /*
 500                  * The other thread may not print any diagnostics, as it has
 501                  * already removed the watchpoint, or another thread consumed
 502                  * the watchpoint before this thread.
 503                  */
 504                 atomic_long_inc(&kcsan_counters[KCSAN_COUNTER_REPORT_RACES]);
 505         }
 506
 507         if (is_assert)
 508                 atomic_long_inc(&kcsan_counters[KCSAN_COUNTER_ASSERT_FAILURES]);
 509         else
 510                 atomic_long_inc(&kcsan_counters[KCSAN_COUNTER_DATA_RACES]);
 511
 512         user_access_restore(flags);
 513 }
 514
 515 static noinline void
 516 kcsan_setup_watchpoint(const volatile void *ptr, size_t size, int type, unsigned long ip)
 517 {
 518         const bool is_write = (type & KCSAN_ACCESS_WRITE) != 0;
 519         const bool is_assert = (type & KCSAN_ACCESS_ASSERT) != 0;
 520         atomic_long_t *watchpoint;
 521         u64 old, new, diff;
 522         enum kcsan_value_change value_change = KCSAN_VALUE_CHANGE_MAYBE;
 523         bool interrupt_watcher = kcsan_interrupt_watcher;
 524         unsigned long ua_flags = user_access_save();
 525         struct kcsan_ctx *ctx = get_ctx();
 526         unsigned long access_mask = ctx->access_mask;
 527         unsigned long irq_flags = 0;
 528         bool is_reorder_access;
 529
 530         /*
 531          * Always reset kcsan_skip counter in slow-path to avoid underflow; see
 532          * should_watch().
 533          */
 534         reset_kcsan_skip();
 535
 536         if (!kcsan_is_enabled(ctx))
 537                 goto out;
 538
 539         /*
 540          * Check to-ignore addresses after kcsan_is_enabled(), as we may access
 541          * memory that is not yet initialized during early boot.
 542          */
 543         if (!is_assert && kcsan_ignore_address(ptr))
 544                 goto out;
 545
 546         if (!check_encodable((unsigned long)ptr, size)) {
 547                 atomic_long_inc(&kcsan_counters[KCSAN_COUNTER_UNENCODABLE_ACCESSES]);
 548                 goto out;
 549         }
 550
 551         /*
 552          * The local CPU cannot observe reordering of its own accesses, and
 553          * therefore we need to take care of 2 cases to avoid false positives:
 554          *
 555          *      1. Races of the reordered access with interrupts. To avoid, if
 556          *         the current access is reorder_access, disable interrupts.
 557          *      2. Avoid races of scoped accesses from nested interrupts (below).
 558          */
 559         is_reorder_access = find_reorder_access(ctx, ptr, size, type, ip);
 560         if (is_reorder_access)
 561                 interrupt_watcher = false;
 562         /*
 563          * Avoid races of scoped accesses from nested interrupts (or scheduler).
 564          * Assume setting up a watchpoint for a non-scoped (normal) access that
 565          * also conflicts with a current scoped access. In a nested interrupt,
 566          * which shares the context, it would check a conflicting scoped access.
 567          * To avoid, disable scoped access checking.
 568          */
 569         ctx->disable_scoped++;
 570
 571         /*
 572          * Save and restore the IRQ state trace touched by KCSAN, since KCSAN's
 573          * runtime is entered for every memory access, and potentially useful
 574          * information is lost if dirtied by KCSAN.
 575          */
 576         kcsan_save_irqtrace(current);
 577         if (!interrupt_watcher)
 578                 local_irq_save(irq_flags);
 579
 580         watchpoint = insert_watchpoint((unsigned long)ptr, size, is_write);
 581         if (watchpoint == NULL) {
 582                 /*
 583                  * Out of capacity: the size of 'watchpoints', and the frequency
 584                  * with which should_watch() returns true should be tweaked so
 585                  * that this case happens very rarely.
 586                  */
 587                 atomic_long_inc(&kcsan_counters[KCSAN_COUNTER_NO_CAPACITY]);
 588                 goto out_unlock;
 589         }
 590
 591         atomic_long_inc(&kcsan_counters[KCSAN_COUNTER_SETUP_WATCHPOINTS]);
 592         atomic_long_inc(&kcsan_counters[KCSAN_COUNTER_USED_WATCHPOINTS]);
 593
 594         /*
 595          * Read the current value, to later check and infer a race if the data
 596          * was modified via a non-instrumented access, e.g. from a device.
 597          */
 598         old = is_reorder_access ? 0 : read_instrumented_memory(ptr, size);
 599
 600         /*
 601          * Delay this thread, to increase probability of observing a racy
 602          * conflicting access.
 603          */
 604         delay_access(type);
 605
 606         /*
 607          * Re-read value, and check if it is as expected; if not, we infer a
 608          * racy access.
 609          */
 610         if (!is_reorder_access) {
 611                 new = read_instrumented_memory(ptr, size);
 612         } else {
 613                 /*
 614                  * Reordered accesses cannot be used for value change detection,
 615                  * because the memory location may no longer be accessible and
 616                  * could result in a fault.
 617                  */
 618                 new = 0;
 619                 access_mask = 0;
 620         }
 621
 622         diff = old ^ new;
 623         if (access_mask)
 624                 diff &= access_mask;
 625
 626         /*
 627          * Check if we observed a value change.
 628          *
 629          * Also check if the data race should be ignored (the rules depend on
 630          * non-zero diff); if it is to be ignored, the below rules for
 631          * KCSAN_VALUE_CHANGE_MAYBE apply.
 632          */
 633         if (diff && !kcsan_ignore_data_race(size, type, old, new, diff))
 634                 value_change = KCSAN_VALUE_CHANGE_TRUE;
 635
 636         /* Check if this access raced with another. */
 637         if (!consume_watchpoint(watchpoint)) {
 638                 /*
 639                  * Depending on the access type, map a value_change of MAYBE to
 640                  * TRUE (always report) or FALSE (never report).
 641                  */
 642                 if (value_change == KCSAN_VALUE_CHANGE_MAYBE) {
 643                         if (access_mask != 0) {
 644                                 /*
 645                                  * For access with access_mask, we require a
 646                                  * value-change, as it is likely that races on
 647                                  * ~access_mask bits are expected.
 648                                  */
 649                                 value_change = KCSAN_VALUE_CHANGE_FALSE;
 650                         } else if (size > 8 || is_assert) {
 651                                 /* Always assume a value-change. */
 652                                 value_change = KCSAN_VALUE_CHANGE_TRUE;
 653                         }
 654                 }
 655
 656                 /*
 657                  * No need to increment 'data_races' counter, as the racing
 658                  * thread already did.
 659                  *
 660                  * Count 'assert_failures' for each failed ASSERT access,
 661                  * therefore both this thread and the racing thread may
 662                  * increment this counter.
 663                  */
 664                 if (is_assert && value_change == KCSAN_VALUE_CHANGE_TRUE)
 665                         atomic_long_inc(&kcsan_counters[KCSAN_COUNTER_ASSERT_FAILURES]);
 666
 667                 kcsan_report_known_origin(ptr, size, type, ip,
 668                                           value_change, watchpoint - watchpoints,
 669                                           old, new, access_mask);
 670         } else if (value_change == KCSAN_VALUE_CHANGE_TRUE) {
 671                 /* Inferring a race, since the value should not have changed. */
 672
 673                 atomic_long_inc(&kcsan_counters[KCSAN_COUNTER_RACES_UNKNOWN_ORIGIN]);
 674                 if (is_assert)
 675                         atomic_long_inc(&kcsan_counters[KCSAN_COUNTER_ASSERT_FAILURES]);
 676
 677                 if (IS_ENABLED(CONFIG_KCSAN_REPORT_RACE_UNKNOWN_ORIGIN) || is_assert) {
 678                         kcsan_report_unknown_origin(ptr, size, type, ip,
 679                                                     old, new, access_mask);
 680                 }
 681         }
 682
 683         /*
 684          * Remove watchpoint; must be after reporting, since the slot may be
 685          * reused after this point.
 686          */
 687         remove_watchpoint(watchpoint);
 688         atomic_long_dec(&kcsan_counters[KCSAN_COUNTER_USED_WATCHPOINTS]);
 689
 690 out_unlock:
 691         if (!interrupt_watcher)
 692                 local_irq_restore(irq_flags);
 693         kcsan_restore_irqtrace(current);
 694         ctx->disable_scoped--;
 695
 696         /*
 697          * Reordered accesses cannot be used for value change detection,
 698          * therefore never consider for reordering if access_mask is set.
 699          * ASSERT_EXCLUSIVE are not real accesses, ignore them as well.
 700          */
 701         if (!access_mask && !is_assert)
 702                 set_reorder_access(ctx, ptr, size, type, ip);
 703 out:
 704         user_access_restore(ua_flags);
 705 }
 706
 707 static __always_inline void
 708 check_access(const volatile void *ptr, size_t size, int type, unsigned long ip)
 709 {
 710         atomic_long_t *watchpoint;
 711         long encoded_watchpoint;
 712
 713         /*
 714          * Do nothing for 0 sized check; this comparison will be optimized out
 715          * for constant sized instrumentation (__tsan_{read,write}N).
 716          */
 717         if (unlikely(size == 0))
 718                 return;
 719
 720 again:
 721         /*
 722          * Avoid user_access_save in fast-path: find_watchpoint is safe without
 723          * user_access_save, as the address that ptr points to is only used to
 724          * check if a watchpoint exists; ptr is never dereferenced.
 725          */
 726         watchpoint = find_watchpoint((unsigned long)ptr, size,
 727                                      !(type & KCSAN_ACCESS_WRITE),
 728                                      &encoded_watchpoint);
 729         /*
 730          * It is safe to check kcsan_is_enabled() after find_watchpoint in the
 731          * slow-path, as long as no state changes that cause a race to be
 732          * detected and reported have occurred until kcsan_is_enabled() is
 733          * checked.
 734          */
 735
 736         if (unlikely(watchpoint != NULL))
 737                 kcsan_found_watchpoint(ptr, size, type, ip, watchpoint, encoded_watchpoint);
 738         else {
 739                 struct kcsan_ctx *ctx = get_ctx(); /* Call only once in fast-path. */
 740
 741                 if (unlikely(should_watch(ctx, ptr, size, type))) {
 742                         kcsan_setup_watchpoint(ptr, size, type, ip);
 743                         return;
 744                 }
 745
 746                 if (!(type & KCSAN_ACCESS_SCOPED)) {
 747                         struct kcsan_scoped_access *reorder_access = get_reorder_access(ctx);
 748
 749                         if (reorder_access) {
 750                                 /*
 751                                  * reorder_access check: simulates reordering of
 752                                  * the access after subsequent operations.
 753                                  */
 754                                 ptr = reorder_access->ptr;
 755                                 type = reorder_access->type;
 756                                 ip = reorder_access->ip;
 757                                 /*
 758                                  * Upon a nested interrupt, this context's
 759                                  * reorder_access can be modified (shared ctx).
 760                                  * We know that upon return, reorder_access is
 761                                  * always invalidated by setting size to 0 via
 762                                  * __tsan_func_exit(). Therefore we must read
 763                                  * and check size after the other fields.
 764                                  */
 765                                 barrier();
 766                                 size = READ_ONCE(reorder_access->size);
 767                                 if (size)
 768                                         goto again;
 769                         }
 770                 }
 771
 772                 /*
 773                  * Always checked last, right before returning from runtime;
 774                  * if reorder_access is valid, checked after it was checked.
 775                  */
 776                 if (unlikely(ctx->scoped_accesses.prev))
 777                         kcsan_check_scoped_accesses();
 778         }
 779 }
 780
 781 /* === Public interface ===================================================== */
 782
 783 void __init kcsan_init(void)
 784 {
 785         int cpu;
 786
 787         BUG_ON(!in_task());
 788
 789         for_each_possible_cpu(cpu)
 790                 per_cpu(kcsan_rand_state, cpu) = (u32)get_cycles();
 791
 792         /*
 793          * We are in the init task, and no other tasks should be running;
 794          * WRITE_ONCE without memory barrier is sufficient.
 795          */
 796         if (kcsan_early_enable) {
 797                 pr_info("enabled early\n");
 798                 WRITE_ONCE(kcsan_enabled, true);
 799         }
 800
 801         if (IS_ENABLED(CONFIG_KCSAN_REPORT_VALUE_CHANGE_ONLY) ||
 802             IS_ENABLED(CONFIG_KCSAN_ASSUME_PLAIN_WRITES_ATOMIC) ||
 803             IS_ENABLED(CONFIG_KCSAN_PERMISSIVE) ||
 804             IS_ENABLED(CONFIG_KCSAN_IGNORE_ATOMICS)) {
 805                 pr_warn("non-strict mode configured - use CONFIG_KCSAN_STRICT=y to see all data races\n");
 806         } else {
 807                 pr_info("strict mode configured\n");
 808         }
 809 }
 810
 811 /* === Exported interface =================================================== */
 812
 813 void kcsan_disable_current(void)
 814 {
 815         ++get_ctx()->disable_count;
 816 }
 817 EXPORT_SYMBOL(kcsan_disable_current);
 818
 819 void kcsan_enable_current(void)
 820 {
 821         if (get_ctx()->disable_count-- == 0) {
 822                 /*
 823                  * Warn if kcsan_enable_current() calls are unbalanced with
 824                  * kcsan_disable_current() calls, which causes disable_count to
 825                  * become negative and should not happen.
 826                  */
 827                 kcsan_disable_current(); /* restore to 0, KCSAN still enabled */
 828                 kcsan_disable_current(); /* disable to generate warning */
 829                 WARN(1, "Unbalanced %s()", __func__);
 830                 kcsan_enable_current();
 831         }
 832 }
 833 EXPORT_SYMBOL(kcsan_enable_current);
 834
 835 void kcsan_enable_current_nowarn(void)
 836 {
 837         if (get_ctx()->disable_count-- == 0)
 838                 kcsan_disable_current();
 839 }
 840 EXPORT_SYMBOL(kcsan_enable_current_nowarn);
 841
 842 void kcsan_nestable_atomic_begin(void)
 843 {
 844         /*
 845          * Do *not* check and warn if we are in a flat atomic region: nestable
 846          * and flat atomic regions are independent from each other.
 847          * See include/linux/kcsan.h: struct kcsan_ctx comments for more
 848          * comments.
 849          */
 850
 851         ++get_ctx()->atomic_nest_count;
 852 }
 853 EXPORT_SYMBOL(kcsan_nestable_atomic_begin);
 854
 855 void kcsan_nestable_atomic_end(void)
 856 {
 857         if (get_ctx()->atomic_nest_count-- == 0) {
 858                 /*
 859                  * Warn if kcsan_nestable_atomic_end() calls are unbalanced with
 860                  * kcsan_nestable_atomic_begin() calls, which causes
 861                  * atomic_nest_count to become negative and should not happen.
 862                  */
 863                 kcsan_nestable_atomic_begin(); /* restore to 0 */
 864                 kcsan_disable_current(); /* disable to generate warning */
 865                 WARN(1, "Unbalanced %s()", __func__);
 866                 kcsan_enable_current();
 867         }
 868 }
 869 EXPORT_SYMBOL(kcsan_nestable_atomic_end);
 870
 871 void kcsan_flat_atomic_begin(void)
 872 {
 873         get_ctx()->in_flat_atomic = true;
 874 }
 875 EXPORT_SYMBOL(kcsan_flat_atomic_begin);
 876
 877 void kcsan_flat_atomic_end(void)
 878 {
 879         get_ctx()->in_flat_atomic = false;
 880 }
 881 EXPORT_SYMBOL(kcsan_flat_atomic_end);
 882
 883 void kcsan_atomic_next(int n)
 884 {
 885         get_ctx()->atomic_next = n;
 886 }
 887 EXPORT_SYMBOL(kcsan_atomic_next);
 888
 889 void kcsan_set_access_mask(unsigned long mask)
 890 {
 891         get_ctx()->access_mask = mask;
 892 }
 893 EXPORT_SYMBOL(kcsan_set_access_mask);
 894
 895 struct kcsan_scoped_access *
 896 kcsan_begin_scoped_access(const volatile void *ptr, size_t size, int type,
 897                           struct kcsan_scoped_access *sa)
 898 {
 899         struct kcsan_ctx *ctx = get_ctx();
 900
 901         check_access(ptr, size, type, _RET_IP_);
 902
 903         ctx->disable_count++; /* Disable KCSAN, in case list debugging is on. */
 904
 905         INIT_LIST_HEAD(&sa->list);
 906         sa->ptr = ptr;
 907         sa->size = size;
 908         sa->type = type;
 909         sa->ip = _RET_IP_;
 910
 911         if (!ctx->scoped_accesses.prev) /* Lazy initialize list head. */
 912                 INIT_LIST_HEAD(&ctx->scoped_accesses);
 913         list_add(&sa->list, &ctx->scoped_accesses);
 914
 915         ctx->disable_count--;
 916         return sa;
 917 }
 918 EXPORT_SYMBOL(kcsan_begin_scoped_access);
 919
 920 void kcsan_end_scoped_access(struct kcsan_scoped_access *sa)
 921 {
 922         struct kcsan_ctx *ctx = get_ctx();
 923
 924         if (WARN(!ctx->scoped_accesses.prev, "Unbalanced %s()?", __func__))
 925                 return;
 926
 927         ctx->disable_count++; /* Disable KCSAN, in case list debugging is on. */
 928
 929         list_del(&sa->list);
 930         if (list_empty(&ctx->scoped_accesses))
 931                 /*
 932                  * Ensure we do not enter kcsan_check_scoped_accesses()
 933                  * slow-path if unnecessary, and avoids requiring list_empty()
 934                  * in the fast-path (to avoid a READ_ONCE() and potential
 935                  * uaccess warning).
 936                  */
 937                 ctx->scoped_accesses.prev = NULL;
 938
 939         ctx->disable_count--;
 940
 941         check_access(sa->ptr, sa->size, sa->type, sa->ip);
 942 }
 943 EXPORT_SYMBOL(kcsan_end_scoped_access);
 944
 945 void __kcsan_check_access(const volatile void *ptr, size_t size, int type)
 946 {
 947         check_access(ptr, size, type, _RET_IP_);
 948 }
 949 EXPORT_SYMBOL(__kcsan_check_access);
 950
 951 #define DEFINE_MEMORY_BARRIER(name, order_before_cond)                          \
 952         void __kcsan_##name(void)                                               \
 953         {                                                                       \
 954                 struct kcsan_scoped_access *sa = get_reorder_access(get_ctx()); \
 955                 if (!sa)                                                        \
 956                         return;                                                 \
 957                 if (order_before_cond)                                          \
 958                         sa->size = 0;                                           \
 959         }                                                                       \
 960         EXPORT_SYMBOL(__kcsan_##name)
 961
 962 DEFINE_MEMORY_BARRIER(mb, true);
 963 DEFINE_MEMORY_BARRIER(wmb, sa->type & (KCSAN_ACCESS_WRITE | KCSAN_ACCESS_COMPOUND));
 964 DEFINE_MEMORY_BARRIER(rmb, !(sa->type & KCSAN_ACCESS_WRITE) || (sa->type & KCSAN_ACCESS_COMPOUND));
 965 DEFINE_MEMORY_BARRIER(release, true);
 966
 967 /*
 968  * KCSAN uses the same instrumentation that is emitted by supported compilers
 969  * for ThreadSanitizer (TSAN).
 970  *
 971  * When enabled, the compiler emits instrumentation calls (the functions
 972  * prefixed with "__tsan" below) for all loads and stores that it generated;
 973  * inline asm is not instrumented.
 974  *
 975  * Note that, not all supported compiler versions distinguish aligned/unaligned
 976  * accesses, but e.g. recent versions of Clang do. We simply alias the unaligned
 977  * version to the generic version, which can handle both.
 978  */
 979
 980 #define DEFINE_TSAN_READ_WRITE(size)                                           \
 981         void __tsan_read##size(void *ptr);                                     \
 982         void __tsan_read##size(void *ptr)                                      \
 983         {                                                                      \
 984                 check_access(ptr, size, 0, _RET_IP_);                          \
 985         }                                                                      \
 986         EXPORT_SYMBOL(__tsan_read##size);                                      \
 987         void __tsan_unaligned_read##size(void *ptr)                            \
 988                 __alias(__tsan_read##size);                                    \
 989         EXPORT_SYMBOL(__tsan_unaligned_read##size);                            \
 990         void __tsan_write##size(void *ptr);                                    \
 991         void __tsan_write##size(void *ptr)                                     \
 992         {                                                                      \
 993                 check_access(ptr, size, KCSAN_ACCESS_WRITE, _RET_IP_);         \
 994         }                                                                      \
 995         EXPORT_SYMBOL(__tsan_write##size);                                     \
 996         void __tsan_unaligned_write##size(void *ptr)                           \
 997                 __alias(__tsan_write##size);                                   \
 998         EXPORT_SYMBOL(__tsan_unaligned_write##size);                           \
 999         void __tsan_read_write##size(void *ptr);                               \
1000         void __tsan_read_write##size(void *ptr)                                \
1001         {                                                                      \
1002                 check_access(ptr, size,                                        \
1003                              KCSAN_ACCESS_COMPOUND | KCSAN_ACCESS_WRITE,       \
1004                              _RET_IP_);                                        \
1005         }                                                                      \
1006         EXPORT_SYMBOL(__tsan_read_write##size);                                \
1007         void __tsan_unaligned_read_write##size(void *ptr)                      \
1008                 __alias(__tsan_read_write##size);                              \
1009         EXPORT_SYMBOL(__tsan_unaligned_read_write##size)
1010
1011 DEFINE_TSAN_READ_WRITE(1);
1012 DEFINE_TSAN_READ_WRITE(2);
1013 DEFINE_TSAN_READ_WRITE(4);
1014 DEFINE_TSAN_READ_WRITE(8);
1015 DEFINE_TSAN_READ_WRITE(16);
1016
1017 void __tsan_read_range(void *ptr, size_t size);
1018 void __tsan_read_range(void *ptr, size_t size)
1019 {
1020         check_access(ptr, size, 0, _RET_IP_);
1021 }
1022 EXPORT_SYMBOL(__tsan_read_range);
1023
1024 void __tsan_write_range(void *ptr, size_t size);
1025 void __tsan_write_range(void *ptr, size_t size)
1026 {
1027         check_access(ptr, size, KCSAN_ACCESS_WRITE, _RET_IP_);
1028 }
1029 EXPORT_SYMBOL(__tsan_write_range);
1030
1031 /*
1032  * Use of explicit volatile is generally disallowed [1], however, volatile is
1033  * still used in various concurrent context, whether in low-level
1034  * synchronization primitives or for legacy reasons.
1035  * [1] https://lwn.net/Articles/233479/
1036  *
1037  * We only consider volatile accesses atomic if they are aligned and would pass
1038  * the size-check of compiletime_assert_rwonce_type().
1039  */
1040 #define DEFINE_TSAN_VOLATILE_READ_WRITE(size)                                  \
1041         void __tsan_volatile_read##size(void *ptr);                            \
1042         void __tsan_volatile_read##size(void *ptr)                             \
1043         {                                                                      \
1044                 const bool is_atomic = size <= sizeof(long long) &&            \
1045                                        IS_ALIGNED((unsigned long)ptr, size);   \
1046                 if (IS_ENABLED(CONFIG_KCSAN_IGNORE_ATOMICS) && is_atomic)      \
1047                         return;                                                \
1048                 check_access(ptr, size, is_atomic ? KCSAN_ACCESS_ATOMIC : 0,   \
1049                              _RET_IP_);                                        \
1050         }                                                                      \
1051         EXPORT_SYMBOL(__tsan_volatile_read##size);                             \
1052         void __tsan_unaligned_volatile_read##size(void *ptr)                   \
1053                 __alias(__tsan_volatile_read##size);                           \
1054         EXPORT_SYMBOL(__tsan_unaligned_volatile_read##size);                   \
1055         void __tsan_volatile_write##size(void *ptr);                           \
1056         void __tsan_volatile_write##size(void *ptr)                            \
1057         {                                                                      \
1058                 const bool is_atomic = size <= sizeof(long long) &&            \
1059                                        IS_ALIGNED((unsigned long)ptr, size);   \
1060                 if (IS_ENABLED(CONFIG_KCSAN_IGNORE_ATOMICS) && is_atomic)      \
1061                         return;                                                \
1062                 check_access(ptr, size,                                        \
1063                              KCSAN_ACCESS_WRITE |                              \
1064                                      (is_atomic ? KCSAN_ACCESS_ATOMIC : 0),    \
1065                              _RET_IP_);                                        \
1066         }                                                                      \
1067         EXPORT_SYMBOL(__tsan_volatile_write##size);                            \
1068         void __tsan_unaligned_volatile_write##size(void *ptr)                  \
1069                 __alias(__tsan_volatile_write##size);                          \
1070         EXPORT_SYMBOL(__tsan_unaligned_volatile_write##size)
1071
1072 DEFINE_TSAN_VOLATILE_READ_WRITE(1);
1073 DEFINE_TSAN_VOLATILE_READ_WRITE(2);
1074 DEFINE_TSAN_VOLATILE_READ_WRITE(4);
1075 DEFINE_TSAN_VOLATILE_READ_WRITE(8);
1076 DEFINE_TSAN_VOLATILE_READ_WRITE(16);
1077
1078 /*
1079  * Function entry and exit are used to determine the validty of reorder_access.
1080  * Reordering of the access ends at the end of the function scope where the
1081  * access happened. This is done for two reasons:
1082  *
1083  *      1. Artificially limits the scope where missing barriers are detected.
1084  *         This minimizes false positives due to uninstrumented functions that
1085  *         contain the required barriers but were missed.
1086  *
1087  *      2. Simplifies generating the stack trace of the access.
1088  */
1089 void __tsan_func_entry(void *call_pc);
1090 noinline void __tsan_func_entry(void *call_pc)
1091 {
1092         if (!IS_ENABLED(CONFIG_KCSAN_WEAK_MEMORY))
1093                 return;
1094
1095         add_kcsan_stack_depth(1);
1096 }
1097 EXPORT_SYMBOL(__tsan_func_entry);
1098
1099 void __tsan_func_exit(void);
1100 noinline void __tsan_func_exit(void)
1101 {
1102         struct kcsan_scoped_access *reorder_access;
1103
1104         if (!IS_ENABLED(CONFIG_KCSAN_WEAK_MEMORY))
1105                 return;
1106
1107         reorder_access = get_reorder_access(get_ctx());
1108         if (!reorder_access)
1109                 goto out;
1110
1111         if (get_kcsan_stack_depth() <= reorder_access->stack_depth) {
1112                 /*
1113                  * Access check to catch cases where write without a barrier
1114                  * (supposed release) was last access in function: because
1115                  * instrumentation is inserted before the real access, a data
1116                  * race due to the write giving up a c-s would only be caught if
1117                  * we do the conflicting access after.
1118                  */
1119                 check_access(reorder_access->ptr, reorder_access->size,
1120                              reorder_access->type, reorder_access->ip);
1121                 reorder_access->size = 0;
1122                 reorder_access->stack_depth = INT_MIN;
1123         }
1124 out:
1125         add_kcsan_stack_depth(-1);
1126 }
1127 EXPORT_SYMBOL(__tsan_func_exit);
1128
1129 void __tsan_init(void);
1130 void __tsan_init(void)
1131 {
1132 }
1133 EXPORT_SYMBOL(__tsan_init);
1134
1135 /*
1136  * Instrumentation for atomic builtins (__atomic_*, __sync_*).
1137  *
1138  * Normal kernel code _should not_ be using them directly, but some
1139  * architectures may implement some or all atomics using the compilers'
1140  * builtins.
1141  *
1142  * Note: If an architecture decides to fully implement atomics using the
1143  * builtins, because they are implicitly instrumented by KCSAN (and KASAN,
1144  * etc.), implementing the ARCH_ATOMIC interface (to get instrumentation via
1145  * atomic-instrumented) is no longer necessary.
1146  *
1147  * TSAN instrumentation replaces atomic accesses with calls to any of the below
1148  * functions, whose job is to also execute the operation itself.
1149  */
1150
1151 static __always_inline void kcsan_atomic_builtin_memorder(int memorder)
1152 {
1153         if (memorder == __ATOMIC_RELEASE ||
1154             memorder == __ATOMIC_SEQ_CST ||
1155             memorder == __ATOMIC_ACQ_REL)
1156                 __kcsan_release();
1157 }
1158
1159 #define DEFINE_TSAN_ATOMIC_LOAD_STORE(bits)                                                        \
1160         u##bits __tsan_atomic##bits##_load(const u##bits *ptr, int memorder);                      \
1161         u##bits __tsan_atomic##bits##_load(const u##bits *ptr, int memorder)                       \
1162         {                                                                                          \
1163                 kcsan_atomic_builtin_memorder(memorder);                                           \
1164                 if (!IS_ENABLED(CONFIG_KCSAN_IGNORE_ATOMICS)) {                                    \
1165                         check_access(ptr, bits / BITS_PER_BYTE, KCSAN_ACCESS_ATOMIC, _RET_IP_);    \
1166                 }                                                                                  \
1167                 return __atomic_load_n(ptr, memorder);                                             \
1168         }                                                                                          \
1169         EXPORT_SYMBOL(__tsan_atomic##bits##_load);                                                 \
1170         void __tsan_atomic##bits##_store(u##bits *ptr, u##bits v, int memorder);                   \
1171         void __tsan_atomic##bits##_store(u##bits *ptr, u##bits v, int memorder)                    \
1172         {                                                                                          \
1173                 kcsan_atomic_builtin_memorder(memorder);                                           \
1174                 if (!IS_ENABLED(CONFIG_KCSAN_IGNORE_ATOMICS)) {                                    \
1175                         check_access(ptr, bits / BITS_PER_BYTE,                                    \
1176                                      KCSAN_ACCESS_WRITE | KCSAN_ACCESS_ATOMIC, _RET_IP_);          \
1177                 }                                                                                  \
1178                 __atomic_store_n(ptr, v, memorder);                                                \
1179         }                                                                                          \
1180         EXPORT_SYMBOL(__tsan_atomic##bits##_store)
1181
1182 #define DEFINE_TSAN_ATOMIC_RMW(op, bits, suffix)                                                   \
1183         u##bits __tsan_atomic##bits##_##op(u##bits *ptr, u##bits v, int memorder);                 \
1184         u##bits __tsan_atomic##bits##_##op(u##bits *ptr, u##bits v, int memorder)                  \
1185         {                                                                                          \
1186                 kcsan_atomic_builtin_memorder(memorder);                                           \
1187                 if (!IS_ENABLED(CONFIG_KCSAN_IGNORE_ATOMICS)) {                                    \
1188                         check_access(ptr, bits / BITS_PER_BYTE,                                    \
1189                                      KCSAN_ACCESS_COMPOUND | KCSAN_ACCESS_WRITE |                  \
1190                                              KCSAN_ACCESS_ATOMIC, _RET_IP_);                       \
1191                 }                                                                                  \
1192                 return __atomic_##op##suffix(ptr, v, memorder);                                    \
1193         }                                                                                          \
1194         EXPORT_SYMBOL(__tsan_atomic##bits##_##op)
1195
1196 /*
1197  * Note: CAS operations are always classified as write, even in case they
1198  * fail. We cannot perform check_access() after a write, as it might lead to
1199  * false positives, in cases such as:
1200  *
1201  *      T0: __atomic_compare_exchange_n(&p->flag, &old, 1, ...)
1202  *
1203  *      T1: if (__atomic_load_n(&p->flag, ...)) {
1204  *              modify *p;
1205  *              p->flag = 0;
1206  *          }
1207  *
1208  * The only downside is that, if there are 3 threads, with one CAS that
1209  * succeeds, another CAS that fails, and an unmarked racing operation, we may
1210  * point at the wrong CAS as the source of the race. However, if we assume that
1211  * all CAS can succeed in some other execution, the data race is still valid.
1212  */
1213 #define DEFINE_TSAN_ATOMIC_CMPXCHG(bits, strength, weak)                                           \
1214         int __tsan_atomic##bits##_compare_exchange_##strength(u##bits *ptr, u##bits *exp,          \
1215                                                               u##bits val, int mo, int fail_mo);   \
1216         int __tsan_atomic##bits##_compare_exchange_##strength(u##bits *ptr, u##bits *exp,          \
1217                                                               u##bits val, int mo, int fail_mo)    \
1218         {                                                                                          \
1219                 kcsan_atomic_builtin_memorder(mo);                                                 \
1220                 if (!IS_ENABLED(CONFIG_KCSAN_IGNORE_ATOMICS)) {                                    \
1221                         check_access(ptr, bits / BITS_PER_BYTE,                                    \
1222                                      KCSAN_ACCESS_COMPOUND | KCSAN_ACCESS_WRITE |                  \
1223                                              KCSAN_ACCESS_ATOMIC, _RET_IP_);                       \
1224                 }                                                                                  \
1225                 return __atomic_compare_exchange_n(ptr, exp, val, weak, mo, fail_mo);              \
1226         }                                                                                          \
1227         EXPORT_SYMBOL(__tsan_atomic##bits##_compare_exchange_##strength)
1228
1229 #define DEFINE_TSAN_ATOMIC_CMPXCHG_VAL(bits)                                                       \
1230         u##bits __tsan_atomic##bits##_compare_exchange_val(u##bits *ptr, u##bits exp, u##bits val, \
1231                                                            int mo, int fail_mo);                   \
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         {                                                                                          \
1235                 kcsan_atomic_builtin_memorder(mo);                                                 \
1236                 if (!IS_ENABLED(CONFIG_KCSAN_IGNORE_ATOMICS)) {                                    \
1237                         check_access(ptr, bits / BITS_PER_BYTE,                                    \
1238                                      KCSAN_ACCESS_COMPOUND | KCSAN_ACCESS_WRITE |                  \
1239                                              KCSAN_ACCESS_ATOMIC, _RET_IP_);                       \
1240                 }                                                                                  \
1241                 __atomic_compare_exchange_n(ptr, &exp, val, 0, mo, fail_mo);                       \
1242                 return exp;                                                                        \
1243         }                                                                                          \
1244         EXPORT_SYMBOL(__tsan_atomic##bits##_compare_exchange_val)
1245
1246 #define DEFINE_TSAN_ATOMIC_OPS(bits)                                                               \
1247         DEFINE_TSAN_ATOMIC_LOAD_STORE(bits);                                                       \
1248         DEFINE_TSAN_ATOMIC_RMW(exchange, bits, _n);                                                \
1249         DEFINE_TSAN_ATOMIC_RMW(fetch_add, bits, );                                                 \
1250         DEFINE_TSAN_ATOMIC_RMW(fetch_sub, bits, );                                                 \
1251         DEFINE_TSAN_ATOMIC_RMW(fetch_and, bits, );                                                 \
1252         DEFINE_TSAN_ATOMIC_RMW(fetch_or, bits, );                                                  \
1253         DEFINE_TSAN_ATOMIC_RMW(fetch_xor, bits, );                                                 \
1254         DEFINE_TSAN_ATOMIC_RMW(fetch_nand, bits, );                                                \
1255         DEFINE_TSAN_ATOMIC_CMPXCHG(bits, strong, 0);                                               \
1256         DEFINE_TSAN_ATOMIC_CMPXCHG(bits, weak, 1);                                                 \
1257         DEFINE_TSAN_ATOMIC_CMPXCHG_VAL(bits)
1258
1259 DEFINE_TSAN_ATOMIC_OPS(8);
1260 DEFINE_TSAN_ATOMIC_OPS(16);
1261 DEFINE_TSAN_ATOMIC_OPS(32);
1262 DEFINE_TSAN_ATOMIC_OPS(64);
1263
1264 void __tsan_atomic_thread_fence(int memorder);
1265 void __tsan_atomic_thread_fence(int memorder)
1266 {
1267         kcsan_atomic_builtin_memorder(memorder);
1268         __atomic_thread_fence(memorder);
1269 }
1270 EXPORT_SYMBOL(__tsan_atomic_thread_fence);
1271
1272 /*
1273  * In instrumented files, we emit instrumentation for barriers by mapping the
1274  * kernel barriers to an __atomic_signal_fence(), which is interpreted specially
1275  * and otherwise has no relation to a real __atomic_signal_fence(). No known
1276  * kernel code uses __atomic_signal_fence().
1277  *
1278  * Since fsanitize=thread instrumentation handles __atomic_signal_fence(), which
1279  * are turned into calls to __tsan_atomic_signal_fence(), such instrumentation
1280  * can be disabled via the __no_kcsan function attribute (vs. an explicit call
1281  * which could not). When __no_kcsan is requested, __atomic_signal_fence()
1282  * generates no code.
1283  *
1284  * Note: The result of using __atomic_signal_fence() with KCSAN enabled is
1285  * potentially limiting the compiler's ability to reorder operations; however,
1286  * if barriers were instrumented with explicit calls (without LTO), the compiler
1287  * couldn't optimize much anyway. The result of a hypothetical architecture
1288  * using __atomic_signal_fence() in normal code would be KCSAN false negatives.
1289  */
1290 void __tsan_atomic_signal_fence(int memorder);
1291 noinline void __tsan_atomic_signal_fence(int memorder)
1292 {
1293         switch (memorder) {
1294         case __KCSAN_BARRIER_TO_SIGNAL_FENCE_mb:
1295                 __kcsan_mb();
1296                 break;
1297         case __KCSAN_BARRIER_TO_SIGNAL_FENCE_wmb:
1298                 __kcsan_wmb();
1299                 break;
1300         case __KCSAN_BARRIER_TO_SIGNAL_FENCE_rmb:
1301                 __kcsan_rmb();
1302                 break;
1303         case __KCSAN_BARRIER_TO_SIGNAL_FENCE_release:
1304                 __kcsan_release();
1305                 break;
1306         default:
1307                 break;
1308         }
1309 }
1310 EXPORT_SYMBOL(__tsan_atomic_signal_fence);