// SPDX-License-Identifier: GPL-2.0 /* * KCSAN core runtime. * * Copyright (C) 2019, Google LLC. */ #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);