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- // SPDX-License-Identifier: GPL-2.0
- #define pr_fmt(fmt) "kcsan: " fmt
- #include <linux/atomic.h>
- #include <linux/bug.h>
- #include <linux/delay.h>
- #include <linux/export.h>
- #include <linux/init.h>
- #include <linux/kernel.h>
- #include <linux/list.h>
- #include <linux/moduleparam.h>
- #include <linux/percpu.h>
- #include <linux/preempt.h>
- #include <linux/sched.h>
- #include <linux/uaccess.h>
- #include "atomic.h"
- #include "encoding.h"
- #include "kcsan.h"
- static bool kcsan_early_enable = IS_ENABLED(CONFIG_KCSAN_EARLY_ENABLE);
- unsigned int kcsan_udelay_task = CONFIG_KCSAN_UDELAY_TASK;
- unsigned int kcsan_udelay_interrupt = CONFIG_KCSAN_UDELAY_INTERRUPT;
- static long kcsan_skip_watch = CONFIG_KCSAN_SKIP_WATCH;
- static bool kcsan_interrupt_watcher = IS_ENABLED(CONFIG_KCSAN_INTERRUPT_WATCHER);
- #ifdef MODULE_PARAM_PREFIX
- #undef MODULE_PARAM_PREFIX
- #endif
- #define MODULE_PARAM_PREFIX "kcsan."
- module_param_named(early_enable, kcsan_early_enable, bool, 0);
- module_param_named(udelay_task, kcsan_udelay_task, uint, 0644);
- module_param_named(udelay_interrupt, kcsan_udelay_interrupt, uint, 0644);
- module_param_named(skip_watch, kcsan_skip_watch, long, 0644);
- module_param_named(interrupt_watcher, kcsan_interrupt_watcher, bool, 0444);
- bool kcsan_enabled;
- /* Per-CPU kcsan_ctx for interrupts */
- static DEFINE_PER_CPU(struct kcsan_ctx, kcsan_cpu_ctx) = {
- .disable_count = 0,
- .atomic_next = 0,
- .atomic_nest_count = 0,
- .in_flat_atomic = false,
- .access_mask = 0,
- .scoped_accesses = {LIST_POISON1, NULL},
- };
- /*
- * Helper macros to index into adjacent slots, starting from address slot
- * itself, followed by the right and left slots.
- *
- * The purpose is 2-fold:
- *
- * 1. if during insertion the address slot is already occupied, check if
- * any adjacent slots are free;
- * 2. accesses that straddle a slot boundary due to size that exceeds a
- * slot's range may check adjacent slots if any watchpoint matches.
- *
- * Note that accesses with very large size may still miss a watchpoint; however,
- * given this should be rare, this is a reasonable trade-off to make, since this
- * will avoid:
- *
- * 1. excessive contention between watchpoint checks and setup;
- * 2. larger number of simultaneous watchpoints without sacrificing
- * performance.
- *
- * Example: SLOT_IDX values for KCSAN_CHECK_ADJACENT=1, where i is [0, 1, 2]:
- *
- * slot=0: [ 1, 2, 0]
- * slot=9: [10, 11, 9]
- * slot=63: [64, 65, 63]
- */
- #define SLOT_IDX(slot, i) (slot + ((i + KCSAN_CHECK_ADJACENT) % NUM_SLOTS))
- /*
- * SLOT_IDX_FAST is used in the fast-path. Not first checking the address's primary
- * slot (middle) is fine if we assume that races occur rarely. The set of
- * indices {SLOT_IDX(slot, i) | i in [0, NUM_SLOTS)} is equivalent to
- * {SLOT_IDX_FAST(slot, i) | i in [0, NUM_SLOTS)}.
- */
- #define SLOT_IDX_FAST(slot, i) (slot + i)
- /*
- * Watchpoints, with each entry encoded as defined in encoding.h: in order to be
- * able to safely update and access a watchpoint without introducing locking
- * overhead, we encode each watchpoint as a single atomic long. The initial
- * zero-initialized state matches INVALID_WATCHPOINT.
- *
- * Add NUM_SLOTS-1 entries to account for overflow; this helps avoid having to
- * use more complicated SLOT_IDX_FAST calculation with modulo in the fast-path.
- */
- static atomic_long_t watchpoints[CONFIG_KCSAN_NUM_WATCHPOINTS + NUM_SLOTS-1];
- /*
- * Instructions to skip watching counter, used in should_watch(). We use a
- * per-CPU counter to avoid excessive contention.
- */
- static DEFINE_PER_CPU(long, kcsan_skip);
- /* For kcsan_prandom_u32_max(). */
- static DEFINE_PER_CPU(u32, kcsan_rand_state);
- static __always_inline atomic_long_t *find_watchpoint(unsigned long addr,
- size_t size,
- bool expect_write,
- long *encoded_watchpoint)
- {
- const int slot = watchpoint_slot(addr);
- const unsigned long addr_masked = addr & WATCHPOINT_ADDR_MASK;
- atomic_long_t *watchpoint;
- unsigned long wp_addr_masked;
- size_t wp_size;
- bool is_write;
- int i;
- BUILD_BUG_ON(CONFIG_KCSAN_NUM_WATCHPOINTS < NUM_SLOTS);
- for (i = 0; i < NUM_SLOTS; ++i) {
- watchpoint = &watchpoints[SLOT_IDX_FAST(slot, i)];
- *encoded_watchpoint = atomic_long_read(watchpoint);
- if (!decode_watchpoint(*encoded_watchpoint, &wp_addr_masked,
- &wp_size, &is_write))
- continue;
- if (expect_write && !is_write)
- continue;
- /* Check if the watchpoint matches the access. */
- if (matching_access(wp_addr_masked, wp_size, addr_masked, size))
- return watchpoint;
- }
- return NULL;
- }
- static inline atomic_long_t *
- insert_watchpoint(unsigned long addr, size_t size, bool is_write)
- {
- const int slot = watchpoint_slot(addr);
- const long encoded_watchpoint = encode_watchpoint(addr, size, is_write);
- atomic_long_t *watchpoint;
- int i;
- /* Check slot index logic, ensuring we stay within array bounds. */
- BUILD_BUG_ON(SLOT_IDX(0, 0) != KCSAN_CHECK_ADJACENT);
- BUILD_BUG_ON(SLOT_IDX(0, KCSAN_CHECK_ADJACENT+1) != 0);
- BUILD_BUG_ON(SLOT_IDX(CONFIG_KCSAN_NUM_WATCHPOINTS-1, KCSAN_CHECK_ADJACENT) != ARRAY_SIZE(watchpoints)-1);
- BUILD_BUG_ON(SLOT_IDX(CONFIG_KCSAN_NUM_WATCHPOINTS-1, KCSAN_CHECK_ADJACENT+1) != ARRAY_SIZE(watchpoints) - NUM_SLOTS);
- for (i = 0; i < NUM_SLOTS; ++i) {
- long expect_val = INVALID_WATCHPOINT;
- /* Try to acquire this slot. */
- watchpoint = &watchpoints[SLOT_IDX(slot, i)];
- if (atomic_long_try_cmpxchg_relaxed(watchpoint, &expect_val, encoded_watchpoint))
- return watchpoint;
- }
- return NULL;
- }
- /*
- * Return true if watchpoint was successfully consumed, false otherwise.
- *
- * This may return false if:
- *
- * 1. another thread already consumed the watchpoint;
- * 2. the thread that set up the watchpoint already removed it;
- * 3. the watchpoint was removed and then re-used.
- */
- static __always_inline bool
- try_consume_watchpoint(atomic_long_t *watchpoint, long encoded_watchpoint)
- {
- return atomic_long_try_cmpxchg_relaxed(watchpoint, &encoded_watchpoint, CONSUMED_WATCHPOINT);
- }
- /* Return true if watchpoint was not touched, false if already consumed. */
- static inline bool consume_watchpoint(atomic_long_t *watchpoint)
- {
- return atomic_long_xchg_relaxed(watchpoint, CONSUMED_WATCHPOINT) != CONSUMED_WATCHPOINT;
- }
- /* Remove the watchpoint -- its slot may be reused after. */
- static inline void remove_watchpoint(atomic_long_t *watchpoint)
- {
- atomic_long_set(watchpoint, INVALID_WATCHPOINT);
- }
- static __always_inline struct kcsan_ctx *get_ctx(void)
- {
- /*
- * In interrupts, use raw_cpu_ptr to avoid unnecessary checks, that would
- * also result in calls that generate warnings in uaccess regions.
- */
- return in_task() ? ¤t->kcsan_ctx : raw_cpu_ptr(&kcsan_cpu_ctx);
- }
- /* Check scoped accesses; never inline because this is a slow-path! */
- static noinline void kcsan_check_scoped_accesses(void)
- {
- struct kcsan_ctx *ctx = get_ctx();
- struct list_head *prev_save = ctx->scoped_accesses.prev;
- struct kcsan_scoped_access *scoped_access;
- ctx->scoped_accesses.prev = NULL; /* Avoid recursion. */
- list_for_each_entry(scoped_access, &ctx->scoped_accesses, list)
- __kcsan_check_access(scoped_access->ptr, scoped_access->size, scoped_access->type);
- ctx->scoped_accesses.prev = prev_save;
- }
- /* Rules for generic atomic accesses. Called from fast-path. */
- static __always_inline bool
- is_atomic(const volatile void *ptr, size_t size, int type, struct kcsan_ctx *ctx)
- {
- if (type & KCSAN_ACCESS_ATOMIC)
- return true;
- /*
- * Unless explicitly declared atomic, never consider an assertion access
- * as atomic. This allows using them also in atomic regions, such as
- * seqlocks, without implicitly changing their semantics.
- */
- if (type & KCSAN_ACCESS_ASSERT)
- return false;
- if (IS_ENABLED(CONFIG_KCSAN_ASSUME_PLAIN_WRITES_ATOMIC) &&
- (type & KCSAN_ACCESS_WRITE) && size <= sizeof(long) &&
- !(type & KCSAN_ACCESS_COMPOUND) && IS_ALIGNED((unsigned long)ptr, size))
- return true; /* Assume aligned writes up to word size are atomic. */
- if (ctx->atomic_next > 0) {
- /*
- * Because we do not have separate contexts for nested
- * interrupts, in case atomic_next is set, we simply assume that
- * the outer interrupt set atomic_next. In the worst case, we
- * will conservatively consider operations as atomic. This is a
- * reasonable trade-off to make, since this case should be
- * extremely rare; however, even if extremely rare, it could
- * lead to false positives otherwise.
- */
- if ((hardirq_count() >> HARDIRQ_SHIFT) < 2)
- --ctx->atomic_next; /* in task, or outer interrupt */
- return true;
- }
- return ctx->atomic_nest_count > 0 || ctx->in_flat_atomic;
- }
- static __always_inline bool
- should_watch(const volatile void *ptr, size_t size, int type, struct kcsan_ctx *ctx)
- {
- /*
- * Never set up watchpoints when memory operations are atomic.
- *
- * Need to check this first, before kcsan_skip check below: (1) atomics
- * should not count towards skipped instructions, and (2) to actually
- * decrement kcsan_atomic_next for consecutive instruction stream.
- */
- if (is_atomic(ptr, size, type, ctx))
- return false;
- if (this_cpu_dec_return(kcsan_skip) >= 0)
- return false;
- /*
- * NOTE: If we get here, kcsan_skip must always be reset in slow path
- * via reset_kcsan_skip() to avoid underflow.
- */
- /* this operation should be watched */
- return true;
- }
- /*
- * Returns a pseudo-random number in interval [0, ep_ro). Simple linear
- * congruential generator, using constants from "Numerical Recipes".
- */
- static u32 kcsan_prandom_u32_max(u32 ep_ro)
- {
- u32 state = this_cpu_read(kcsan_rand_state);
- state = 1664525 * state + 1013904223;
- this_cpu_write(kcsan_rand_state, state);
- return state % ep_ro;
- }
- static inline void reset_kcsan_skip(void)
- {
- long skip_count = kcsan_skip_watch -
- (IS_ENABLED(CONFIG_KCSAN_SKIP_WATCH_RANDOMIZE) ?
- kcsan_prandom_u32_max(kcsan_skip_watch) :
- 0);
- this_cpu_write(kcsan_skip, skip_count);
- }
- static __always_inline bool kcsan_is_enabled(void)
- {
- return READ_ONCE(kcsan_enabled) && get_ctx()->disable_count == 0;
- }
- /* Introduce delay depending on context and configuration. */
- static void delay_access(int type)
- {
- unsigned int delay = in_task() ? kcsan_udelay_task : kcsan_udelay_interrupt;
- /* For certain access types, skew the random delay to be longer. */
- unsigned int skew_delay_order =
- (type & (KCSAN_ACCESS_COMPOUND | KCSAN_ACCESS_ASSERT)) ? 1 : 0;
- delay -= IS_ENABLED(CONFIG_KCSAN_DELAY_RANDOMIZE) ?
- kcsan_prandom_u32_max(delay >> skew_delay_order) :
- 0;
- udelay(delay);
- }
- void kcsan_save_irqtrace(struct task_struct *task)
- {
- #ifdef CONFIG_TRACE_IRQFLAGS
- task->kcsan_save_irqtrace = task->irqtrace;
- #endif
- }
- void kcsan_restore_irqtrace(struct task_struct *task)
- {
- #ifdef CONFIG_TRACE_IRQFLAGS
- task->irqtrace = task->kcsan_save_irqtrace;
- #endif
- }
- /*
- * Pull everything together: check_access() below contains the performance
- * critical operations; the fast-path (including check_access) functions should
- * all be inlinable by the instrumentation functions.
- *
- * The slow-path (kcsan_found_watchpoint, kcsan_setup_watchpoint) are
- * non-inlinable -- note that, we prefix these with "kcsan_" to ensure they can
- * be filtered from the stacktrace, as well as give them unique names for the
- * UACCESS whitelist of objtool. Each function uses user_access_save/restore(),
- * since they do not access any user memory, but instrumentation is still
- * emitted in UACCESS regions.
- */
- static noinline void kcsan_found_watchpoint(const volatile void *ptr,
- size_t size,
- int type,
- atomic_long_t *watchpoint,
- long encoded_watchpoint)
- {
- unsigned long flags;
- bool consumed;
- if (!kcsan_is_enabled())
- return;
- /*
- * The access_mask check relies on value-change comparison. To avoid
- * reporting a race where e.g. the writer set up the watchpoint, but the
- * reader has access_mask!=0, we have to ignore the found watchpoint.
- */
- if (get_ctx()->access_mask != 0)
- return;
- /*
- * Consume the watchpoint as soon as possible, to minimize the chances
- * of !consumed. Consuming the watchpoint must always be guarded by
- * kcsan_is_enabled() check, as otherwise we might erroneously
- * triggering reports when disabled.
- */
- consumed = try_consume_watchpoint(watchpoint, encoded_watchpoint);
- /* keep this after try_consume_watchpoint */
- flags = user_access_save();
- if (consumed) {
- kcsan_save_irqtrace(current);
- kcsan_report(ptr, size, type, KCSAN_VALUE_CHANGE_MAYBE,
- KCSAN_REPORT_CONSUMED_WATCHPOINT,
- watchpoint - watchpoints);
- kcsan_restore_irqtrace(current);
- } else {
- /*
- * The other thread may not print any diagnostics, as it has
- * already removed the watchpoint, or another thread consumed
- * the watchpoint before this thread.
- */
- atomic_long_inc(&kcsan_counters[KCSAN_COUNTER_REPORT_RACES]);
- }
- if ((type & KCSAN_ACCESS_ASSERT) != 0)
- atomic_long_inc(&kcsan_counters[KCSAN_COUNTER_ASSERT_FAILURES]);
- else
- atomic_long_inc(&kcsan_counters[KCSAN_COUNTER_DATA_RACES]);
- user_access_restore(flags);
- }
- static noinline void
- kcsan_setup_watchpoint(const volatile void *ptr, size_t size, int type)
- {
- const bool is_write = (type & KCSAN_ACCESS_WRITE) != 0;
- const bool is_assert = (type & KCSAN_ACCESS_ASSERT) != 0;
- atomic_long_t *watchpoint;
- union {
- u8 _1;
- u16 _2;
- u32 _4;
- u64 _8;
- } expect_value;
- unsigned long access_mask;
- enum kcsan_value_change value_change = KCSAN_VALUE_CHANGE_MAYBE;
- unsigned long ua_flags = user_access_save();
- unsigned long irq_flags = 0;
- /*
- * Always reset kcsan_skip counter in slow-path to avoid underflow; see
- * should_watch().
- */
- reset_kcsan_skip();
- if (!kcsan_is_enabled())
- goto out;
- /*
- * Special atomic rules: unlikely to be true, so we check them here in
- * the slow-path, and not in the fast-path in is_atomic(). Call after
- * kcsan_is_enabled(), as we may access memory that is not yet
- * initialized during early boot.
- */
- if (!is_assert && kcsan_is_atomic_special(ptr))
- goto out;
- if (!check_encodable((unsigned long)ptr, size)) {
- atomic_long_inc(&kcsan_counters[KCSAN_COUNTER_UNENCODABLE_ACCESSES]);
- goto out;
- }
- /*
- * Save and restore the IRQ state trace touched by KCSAN, since KCSAN's
- * runtime is entered for every memory access, and potentially useful
- * information is lost if dirtied by KCSAN.
- */
- kcsan_save_irqtrace(current);
- if (!kcsan_interrupt_watcher)
- local_irq_save(irq_flags);
- watchpoint = insert_watchpoint((unsigned long)ptr, size, is_write);
- if (watchpoint == NULL) {
- /*
- * Out of capacity: the size of 'watchpoints', and the frequency
- * with which should_watch() returns true should be tweaked so
- * that this case happens very rarely.
- */
- atomic_long_inc(&kcsan_counters[KCSAN_COUNTER_NO_CAPACITY]);
- goto out_unlock;
- }
- atomic_long_inc(&kcsan_counters[KCSAN_COUNTER_SETUP_WATCHPOINTS]);
- atomic_long_inc(&kcsan_counters[KCSAN_COUNTER_USED_WATCHPOINTS]);
- /*
- * Read the current value, to later check and infer a race if the data
- * was modified via a non-instrumented access, e.g. from a device.
- */
- expect_value._8 = 0;
- switch (size) {
- case 1:
- expect_value._1 = READ_ONCE(*(const u8 *)ptr);
- break;
- case 2:
- expect_value._2 = READ_ONCE(*(const u16 *)ptr);
- break;
- case 4:
- expect_value._4 = READ_ONCE(*(const u32 *)ptr);
- break;
- case 8:
- expect_value._8 = READ_ONCE(*(const u64 *)ptr);
- break;
- default:
- break; /* ignore; we do not diff the values */
- }
- if (IS_ENABLED(CONFIG_KCSAN_DEBUG)) {
- kcsan_disable_current();
- pr_err("watching %s, size: %zu, addr: %px [slot: %d, encoded: %lx]\n",
- is_write ? "write" : "read", size, ptr,
- watchpoint_slot((unsigned long)ptr),
- encode_watchpoint((unsigned long)ptr, size, is_write));
- kcsan_enable_current();
- }
- /*
- * Delay this thread, to increase probability of observing a racy
- * conflicting access.
- */
- delay_access(type);
- /*
- * Re-read value, and check if it is as expected; if not, we infer a
- * racy access.
- */
- access_mask = get_ctx()->access_mask;
- switch (size) {
- case 1:
- expect_value._1 ^= READ_ONCE(*(const u8 *)ptr);
- if (access_mask)
- expect_value._1 &= (u8)access_mask;
- break;
- case 2:
- expect_value._2 ^= READ_ONCE(*(const u16 *)ptr);
- if (access_mask)
- expect_value._2 &= (u16)access_mask;
- break;
- case 4:
- expect_value._4 ^= READ_ONCE(*(const u32 *)ptr);
- if (access_mask)
- expect_value._4 &= (u32)access_mask;
- break;
- case 8:
- expect_value._8 ^= READ_ONCE(*(const u64 *)ptr);
- if (access_mask)
- expect_value._8 &= (u64)access_mask;
- break;
- default:
- break; /* ignore; we do not diff the values */
- }
- /* Were we able to observe a value-change? */
- if (expect_value._8 != 0)
- value_change = KCSAN_VALUE_CHANGE_TRUE;
- /* Check if this access raced with another. */
- if (!consume_watchpoint(watchpoint)) {
- /*
- * Depending on the access type, map a value_change of MAYBE to
- * TRUE (always report) or FALSE (never report).
- */
- if (value_change == KCSAN_VALUE_CHANGE_MAYBE) {
- if (access_mask != 0) {
- /*
- * For access with access_mask, we require a
- * value-change, as it is likely that races on
- * ~access_mask bits are expected.
- */
- value_change = KCSAN_VALUE_CHANGE_FALSE;
- } else if (size > 8 || is_assert) {
- /* Always assume a value-change. */
- value_change = KCSAN_VALUE_CHANGE_TRUE;
- }
- }
- /*
- * No need to increment 'data_races' counter, as the racing
- * thread already did.
- *
- * Count 'assert_failures' for each failed ASSERT access,
- * therefore both this thread and the racing thread may
- * increment this counter.
- */
- if (is_assert && value_change == KCSAN_VALUE_CHANGE_TRUE)
- atomic_long_inc(&kcsan_counters[KCSAN_COUNTER_ASSERT_FAILURES]);
- kcsan_report(ptr, size, type, value_change, KCSAN_REPORT_RACE_SIGNAL,
- watchpoint - watchpoints);
- } else if (value_change == KCSAN_VALUE_CHANGE_TRUE) {
- /* Inferring a race, since the value should not have changed. */
- atomic_long_inc(&kcsan_counters[KCSAN_COUNTER_RACES_UNKNOWN_ORIGIN]);
- if (is_assert)
- atomic_long_inc(&kcsan_counters[KCSAN_COUNTER_ASSERT_FAILURES]);
- if (IS_ENABLED(CONFIG_KCSAN_REPORT_RACE_UNKNOWN_ORIGIN) || is_assert)
- kcsan_report(ptr, size, type, KCSAN_VALUE_CHANGE_TRUE,
- KCSAN_REPORT_RACE_UNKNOWN_ORIGIN,
- watchpoint - watchpoints);
- }
- /*
- * Remove watchpoint; must be after reporting, since the slot may be
- * reused after this point.
- */
- remove_watchpoint(watchpoint);
- atomic_long_dec(&kcsan_counters[KCSAN_COUNTER_USED_WATCHPOINTS]);
- out_unlock:
- if (!kcsan_interrupt_watcher)
- local_irq_restore(irq_flags);
- kcsan_restore_irqtrace(current);
- out:
- user_access_restore(ua_flags);
- }
- static __always_inline void check_access(const volatile void *ptr, size_t size,
- int type)
- {
- const bool is_write = (type & KCSAN_ACCESS_WRITE) != 0;
- atomic_long_t *watchpoint;
- long encoded_watchpoint;
- /*
- * Do nothing for 0 sized check; this comparison will be optimized out
- * for constant sized instrumentation (__tsan_{read,write}N).
- */
- if (unlikely(size == 0))
- return;
- /*
- * Avoid user_access_save in fast-path: find_watchpoint is safe without
- * user_access_save, as the address that ptr points to is only used to
- * check if a watchpoint exists; ptr is never dereferenced.
- */
- watchpoint = find_watchpoint((unsigned long)ptr, size, !is_write,
- &encoded_watchpoint);
- /*
- * It is safe to check kcsan_is_enabled() after find_watchpoint in the
- * slow-path, as long as no state changes that cause a race to be
- * detected and reported have occurred until kcsan_is_enabled() is
- * checked.
- */
- if (unlikely(watchpoint != NULL))
- kcsan_found_watchpoint(ptr, size, type, watchpoint,
- encoded_watchpoint);
- else {
- struct kcsan_ctx *ctx = get_ctx(); /* Call only once in fast-path. */
- if (unlikely(should_watch(ptr, size, type, ctx)))
- kcsan_setup_watchpoint(ptr, size, type);
- else if (unlikely(ctx->scoped_accesses.prev))
- kcsan_check_scoped_accesses();
- }
- }
- /* === Public interface ===================================================== */
- void __init kcsan_init(void)
- {
- int cpu;
- BUG_ON(!in_task());
- for_each_possible_cpu(cpu)
- per_cpu(kcsan_rand_state, cpu) = (u32)get_cycles();
- /*
- * We are in the init task, and no other tasks should be running;
- * WRITE_ONCE without memory barrier is sufficient.
- */
- if (kcsan_early_enable) {
- pr_info("enabled early\n");
- WRITE_ONCE(kcsan_enabled, true);
- }
- }
- /* === Exported interface =================================================== */
- void kcsan_disable_current(void)
- {
- ++get_ctx()->disable_count;
- }
- EXPORT_SYMBOL(kcsan_disable_current);
- void kcsan_enable_current(void)
- {
- if (get_ctx()->disable_count-- == 0) {
- /*
- * Warn if kcsan_enable_current() calls are unbalanced with
- * kcsan_disable_current() calls, which causes disable_count to
- * become negative and should not happen.
- */
- kcsan_disable_current(); /* restore to 0, KCSAN still enabled */
- kcsan_disable_current(); /* disable to generate warning */
- WARN(1, "Unbalanced %s()", __func__);
- kcsan_enable_current();
- }
- }
- EXPORT_SYMBOL(kcsan_enable_current);
- void kcsan_enable_current_nowarn(void)
- {
- if (get_ctx()->disable_count-- == 0)
- kcsan_disable_current();
- }
- EXPORT_SYMBOL(kcsan_enable_current_nowarn);
- void kcsan_nestable_atomic_begin(void)
- {
- /*
- * Do *not* check and warn if we are in a flat atomic region: nestable
- * and flat atomic regions are independent from each other.
- * See include/linux/kcsan.h: struct kcsan_ctx comments for more
- * comments.
- */
- ++get_ctx()->atomic_nest_count;
- }
- EXPORT_SYMBOL(kcsan_nestable_atomic_begin);
- void kcsan_nestable_atomic_end(void)
- {
- if (get_ctx()->atomic_nest_count-- == 0) {
- /*
- * Warn if kcsan_nestable_atomic_end() calls are unbalanced with
- * kcsan_nestable_atomic_begin() calls, which causes
- * atomic_nest_count to become negative and should not happen.
- */
- kcsan_nestable_atomic_begin(); /* restore to 0 */
- kcsan_disable_current(); /* disable to generate warning */
- WARN(1, "Unbalanced %s()", __func__);
- kcsan_enable_current();
- }
- }
- EXPORT_SYMBOL(kcsan_nestable_atomic_end);
- void kcsan_flat_atomic_begin(void)
- {
- get_ctx()->in_flat_atomic = true;
- }
- EXPORT_SYMBOL(kcsan_flat_atomic_begin);
- void kcsan_flat_atomic_end(void)
- {
- get_ctx()->in_flat_atomic = false;
- }
- EXPORT_SYMBOL(kcsan_flat_atomic_end);
- void kcsan_atomic_next(int n)
- {
- get_ctx()->atomic_next = n;
- }
- EXPORT_SYMBOL(kcsan_atomic_next);
- void kcsan_set_access_mask(unsigned long mask)
- {
- get_ctx()->access_mask = mask;
- }
- EXPORT_SYMBOL(kcsan_set_access_mask);
- struct kcsan_scoped_access *
- kcsan_begin_scoped_access(const volatile void *ptr, size_t size, int type,
- struct kcsan_scoped_access *sa)
- {
- struct kcsan_ctx *ctx = get_ctx();
- __kcsan_check_access(ptr, size, type);
- ctx->disable_count++; /* Disable KCSAN, in case list debugging is on. */
- INIT_LIST_HEAD(&sa->list);
- sa->ptr = ptr;
- sa->size = size;
- sa->type = type;
- if (!ctx->scoped_accesses.prev) /* Lazy initialize list head. */
- INIT_LIST_HEAD(&ctx->scoped_accesses);
- list_add(&sa->list, &ctx->scoped_accesses);
- ctx->disable_count--;
- return sa;
- }
- EXPORT_SYMBOL(kcsan_begin_scoped_access);
- void kcsan_end_scoped_access(struct kcsan_scoped_access *sa)
- {
- struct kcsan_ctx *ctx = get_ctx();
- if (WARN(!ctx->scoped_accesses.prev, "Unbalanced %s()?", __func__))
- return;
- ctx->disable_count++; /* Disable KCSAN, in case list debugging is on. */
- list_del(&sa->list);
- if (list_empty(&ctx->scoped_accesses))
- /*
- * Ensure we do not enter kcsan_check_scoped_accesses()
- * slow-path if unnecessary, and avoids requiring list_empty()
- * in the fast-path (to avoid a READ_ONCE() and potential
- * uaccess warning).
- */
- ctx->scoped_accesses.prev = NULL;
- ctx->disable_count--;
- __kcsan_check_access(sa->ptr, sa->size, sa->type);
- }
- EXPORT_SYMBOL(kcsan_end_scoped_access);
- void __kcsan_check_access(const volatile void *ptr, size_t size, int type)
- {
- check_access(ptr, size, type);
- }
- EXPORT_SYMBOL(__kcsan_check_access);
- /*
- * KCSAN uses the same instrumentation that is emitted by supported compilers
- * for ThreadSanitizer (TSAN).
- *
- * When enabled, the compiler emits instrumentation calls (the functions
- * prefixed with "__tsan" below) for all loads and stores that it generated;
- * inline asm is not instrumented.
- *
- * Note that, not all supported compiler versions distinguish aligned/unaligned
- * accesses, but e.g. recent versions of Clang do. We simply alias the unaligned
- * version to the generic version, which can handle both.
- */
- #define DEFINE_TSAN_READ_WRITE(size) \
- void __tsan_read##size(void *ptr); \
- void __tsan_read##size(void *ptr) \
- { \
- check_access(ptr, size, 0); \
- } \
- EXPORT_SYMBOL(__tsan_read##size); \
- void __tsan_unaligned_read##size(void *ptr) \
- __alias(__tsan_read##size); \
- EXPORT_SYMBOL(__tsan_unaligned_read##size); \
- void __tsan_write##size(void *ptr); \
- void __tsan_write##size(void *ptr) \
- { \
- check_access(ptr, size, KCSAN_ACCESS_WRITE); \
- } \
- EXPORT_SYMBOL(__tsan_write##size); \
- void __tsan_unaligned_write##size(void *ptr) \
- __alias(__tsan_write##size); \
- EXPORT_SYMBOL(__tsan_unaligned_write##size); \
- void __tsan_read_write##size(void *ptr); \
- void __tsan_read_write##size(void *ptr) \
- { \
- check_access(ptr, size, \
- KCSAN_ACCESS_COMPOUND | KCSAN_ACCESS_WRITE); \
- } \
- EXPORT_SYMBOL(__tsan_read_write##size); \
- void __tsan_unaligned_read_write##size(void *ptr) \
- __alias(__tsan_read_write##size); \
- EXPORT_SYMBOL(__tsan_unaligned_read_write##size)
- DEFINE_TSAN_READ_WRITE(1);
- DEFINE_TSAN_READ_WRITE(2);
- DEFINE_TSAN_READ_WRITE(4);
- DEFINE_TSAN_READ_WRITE(8);
- DEFINE_TSAN_READ_WRITE(16);
- void __tsan_read_range(void *ptr, size_t size);
- void __tsan_read_range(void *ptr, size_t size)
- {
- check_access(ptr, size, 0);
- }
- EXPORT_SYMBOL(__tsan_read_range);
- void __tsan_write_range(void *ptr, size_t size);
- void __tsan_write_range(void *ptr, size_t size)
- {
- check_access(ptr, size, KCSAN_ACCESS_WRITE);
- }
- EXPORT_SYMBOL(__tsan_write_range);
- /*
- * Use of explicit volatile is generally disallowed [1], however, volatile is
- * still used in various concurrent context, whether in low-level
- * synchronization primitives or for legacy reasons.
- * [1] https://lwn.net/Articles/233479/
- *
- * We only consider volatile accesses atomic if they are aligned and would pass
- * the size-check of compiletime_assert_rwonce_type().
- */
- #define DEFINE_TSAN_VOLATILE_READ_WRITE(size) \
- void __tsan_volatile_read##size(void *ptr); \
- void __tsan_volatile_read##size(void *ptr) \
- { \
- const bool is_atomic = size <= sizeof(long long) && \
- IS_ALIGNED((unsigned long)ptr, size); \
- if (IS_ENABLED(CONFIG_KCSAN_IGNORE_ATOMICS) && is_atomic) \
- return; \
- check_access(ptr, size, is_atomic ? KCSAN_ACCESS_ATOMIC : 0); \
- } \
- EXPORT_SYMBOL(__tsan_volatile_read##size); \
- void __tsan_unaligned_volatile_read##size(void *ptr) \
- __alias(__tsan_volatile_read##size); \
- EXPORT_SYMBOL(__tsan_unaligned_volatile_read##size); \
- void __tsan_volatile_write##size(void *ptr); \
- void __tsan_volatile_write##size(void *ptr) \
- { \
- const bool is_atomic = size <= sizeof(long long) && \
- IS_ALIGNED((unsigned long)ptr, size); \
- if (IS_ENABLED(CONFIG_KCSAN_IGNORE_ATOMICS) && is_atomic) \
- return; \
- check_access(ptr, size, \
- KCSAN_ACCESS_WRITE | \
- (is_atomic ? KCSAN_ACCESS_ATOMIC : 0)); \
- } \
- EXPORT_SYMBOL(__tsan_volatile_write##size); \
- void __tsan_unaligned_volatile_write##size(void *ptr) \
- __alias(__tsan_volatile_write##size); \
- EXPORT_SYMBOL(__tsan_unaligned_volatile_write##size)
- DEFINE_TSAN_VOLATILE_READ_WRITE(1);
- DEFINE_TSAN_VOLATILE_READ_WRITE(2);
- DEFINE_TSAN_VOLATILE_READ_WRITE(4);
- DEFINE_TSAN_VOLATILE_READ_WRITE(8);
- DEFINE_TSAN_VOLATILE_READ_WRITE(16);
- /*
- * The below are not required by KCSAN, but can still be emitted by the
- * compiler.
- */
- void __tsan_func_entry(void *call_pc);
- void __tsan_func_entry(void *call_pc)
- {
- }
- EXPORT_SYMBOL(__tsan_func_entry);
- void __tsan_func_exit(void);
- void __tsan_func_exit(void)
- {
- }
- EXPORT_SYMBOL(__tsan_func_exit);
- void __tsan_init(void);
- void __tsan_init(void)
- {
- }
- EXPORT_SYMBOL(__tsan_init);
- /*
- * Instrumentation for atomic builtins (__atomic_*, __sync_*).
- *
- * Normal kernel code _should not_ be using them directly, but some
- * architectures may implement some or all atomics using the compilers'
- * builtins.
- *
- * Note: If an architecture decides to fully implement atomics using the
- * builtins, because they are implicitly instrumented by KCSAN (and KASAN,
- * etc.), implementing the ARCH_ATOMIC interface (to get instrumentation via
- * atomic-instrumented) is no longer necessary.
- *
- * TSAN instrumentation replaces atomic accesses with calls to any of the below
- * functions, whose job is to also execute the operation itself.
- */
- #define DEFINE_TSAN_ATOMIC_LOAD_STORE(bits) \
- u##bits __tsan_atomic##bits##_load(const u##bits *ptr, int memorder); \
- u##bits __tsan_atomic##bits##_load(const u##bits *ptr, int memorder) \
- { \
- if (!IS_ENABLED(CONFIG_KCSAN_IGNORE_ATOMICS)) { \
- check_access(ptr, bits / BITS_PER_BYTE, KCSAN_ACCESS_ATOMIC); \
- } \
- return __atomic_load_n(ptr, memorder); \
- } \
- EXPORT_SYMBOL(__tsan_atomic##bits##_load); \
- void __tsan_atomic##bits##_store(u##bits *ptr, u##bits v, int memorder); \
- void __tsan_atomic##bits##_store(u##bits *ptr, u##bits v, int memorder) \
- { \
- if (!IS_ENABLED(CONFIG_KCSAN_IGNORE_ATOMICS)) { \
- check_access(ptr, bits / BITS_PER_BYTE, \
- KCSAN_ACCESS_WRITE | KCSAN_ACCESS_ATOMIC); \
- } \
- __atomic_store_n(ptr, v, memorder); \
- } \
- EXPORT_SYMBOL(__tsan_atomic##bits##_store)
- #define DEFINE_TSAN_ATOMIC_RMW(op, bits, suffix) \
- u##bits __tsan_atomic##bits##_##op(u##bits *ptr, u##bits v, int memorder); \
- u##bits __tsan_atomic##bits##_##op(u##bits *ptr, u##bits v, int memorder) \
- { \
- if (!IS_ENABLED(CONFIG_KCSAN_IGNORE_ATOMICS)) { \
- check_access(ptr, bits / BITS_PER_BYTE, \
- KCSAN_ACCESS_COMPOUND | KCSAN_ACCESS_WRITE | \
- KCSAN_ACCESS_ATOMIC); \
- } \
- return __atomic_##op##suffix(ptr, v, memorder); \
- } \
- EXPORT_SYMBOL(__tsan_atomic##bits##_##op)
- /*
- * Note: CAS operations are always classified as write, even in case they
- * fail. We cannot perform check_access() after a write, as it might lead to
- * false positives, in cases such as:
- *
- * T0: __atomic_compare_exchange_n(&p->flag, &old, 1, ...)
- *
- * T1: if (__atomic_load_n(&p->flag, ...)) {
- * modify *p;
- * p->flag = 0;
- * }
- *
- * The only downside is that, if there are 3 threads, with one CAS that
- * succeeds, another CAS that fails, and an unmarked racing operation, we may
- * point at the wrong CAS as the source of the race. However, if we assume that
- * all CAS can succeed in some other execution, the data race is still valid.
- */
- #define DEFINE_TSAN_ATOMIC_CMPXCHG(bits, strength, weak) \
- int __tsan_atomic##bits##_compare_exchange_##strength(u##bits *ptr, u##bits *exp, \
- u##bits val, int mo, int fail_mo); \
- int __tsan_atomic##bits##_compare_exchange_##strength(u##bits *ptr, u##bits *exp, \
- u##bits val, int mo, int fail_mo) \
- { \
- if (!IS_ENABLED(CONFIG_KCSAN_IGNORE_ATOMICS)) { \
- check_access(ptr, bits / BITS_PER_BYTE, \
- KCSAN_ACCESS_COMPOUND | KCSAN_ACCESS_WRITE | \
- KCSAN_ACCESS_ATOMIC); \
- } \
- return __atomic_compare_exchange_n(ptr, exp, val, weak, mo, fail_mo); \
- } \
- EXPORT_SYMBOL(__tsan_atomic##bits##_compare_exchange_##strength)
- #define DEFINE_TSAN_ATOMIC_CMPXCHG_VAL(bits) \
- u##bits __tsan_atomic##bits##_compare_exchange_val(u##bits *ptr, u##bits exp, u##bits val, \
- int mo, int fail_mo); \
- u##bits __tsan_atomic##bits##_compare_exchange_val(u##bits *ptr, u##bits exp, u##bits val, \
- int mo, int fail_mo) \
- { \
- if (!IS_ENABLED(CONFIG_KCSAN_IGNORE_ATOMICS)) { \
- check_access(ptr, bits / BITS_PER_BYTE, \
- KCSAN_ACCESS_COMPOUND | KCSAN_ACCESS_WRITE | \
- KCSAN_ACCESS_ATOMIC); \
- } \
- __atomic_compare_exchange_n(ptr, &exp, val, 0, mo, fail_mo); \
- return exp; \
- } \
- EXPORT_SYMBOL(__tsan_atomic##bits##_compare_exchange_val)
- #define DEFINE_TSAN_ATOMIC_OPS(bits) \
- DEFINE_TSAN_ATOMIC_LOAD_STORE(bits); \
- DEFINE_TSAN_ATOMIC_RMW(exchange, bits, _n); \
- DEFINE_TSAN_ATOMIC_RMW(fetch_add, bits, ); \
- DEFINE_TSAN_ATOMIC_RMW(fetch_sub, bits, ); \
- DEFINE_TSAN_ATOMIC_RMW(fetch_and, bits, ); \
- DEFINE_TSAN_ATOMIC_RMW(fetch_or, bits, ); \
- DEFINE_TSAN_ATOMIC_RMW(fetch_xor, bits, ); \
- DEFINE_TSAN_ATOMIC_RMW(fetch_nand, bits, ); \
- DEFINE_TSAN_ATOMIC_CMPXCHG(bits, strong, 0); \
- DEFINE_TSAN_ATOMIC_CMPXCHG(bits, weak, 1); \
- DEFINE_TSAN_ATOMIC_CMPXCHG_VAL(bits)
- DEFINE_TSAN_ATOMIC_OPS(8);
- DEFINE_TSAN_ATOMIC_OPS(16);
- DEFINE_TSAN_ATOMIC_OPS(32);
- DEFINE_TSAN_ATOMIC_OPS(64);
- void __tsan_atomic_thread_fence(int memorder);
- void __tsan_atomic_thread_fence(int memorder)
- {
- __atomic_thread_fence(memorder);
- }
- EXPORT_SYMBOL(__tsan_atomic_thread_fence);
- void __tsan_atomic_signal_fence(int memorder);
- void __tsan_atomic_signal_fence(int memorder) { }
- EXPORT_SYMBOL(__tsan_atomic_signal_fence);
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