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Linux kernel mirror (for testing) git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
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#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/minmax.h>#include <linux/moduleparam.h>#include <linux/percpu.h>#include <linux/preempt.h>#include <linux/sched.h>#include <linux/string.h>#include <linux/uaccess.h>
#include "encoding.h"#include "kcsan.h"#include "permissive.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);
#ifdef CONFIG_KCSAN_WEAK_MEMORYstatic bool kcsan_weak_memory = true;module_param_named(weak_memory, kcsan_weak_memory, bool, 0644);#else#define kcsan_weak_memory false#endif
bool kcsan_enabled;
/* Per-CPU kcsan_ctx for interrupts */static DEFINE_PER_CPU(struct kcsan_ctx, kcsan_cpu_ctx) = { .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 booltry_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);}
static __always_inline voidcheck_access(const volatile void *ptr, size_t size, int type, unsigned long ip);
/* 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 kcsan_scoped_access *scoped_access;
if (ctx->disable_scoped) return;
ctx->disable_scoped++; list_for_each_entry(scoped_access, &ctx->scoped_accesses, list) { check_access(scoped_access->ptr, scoped_access->size, scoped_access->type, scoped_access->ip); } ctx->disable_scoped--;}
/* Rules for generic atomic accesses. Called from fast-path. */static __always_inline boolis_atomic(struct kcsan_ctx *ctx, const volatile void *ptr, size_t size, int type){ 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 boolshould_watch(struct kcsan_ctx *ctx, const volatile void *ptr, size_t size, int type){ /* * 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(ctx, ptr, size, type)) 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(struct kcsan_ctx *ctx){ return READ_ONCE(kcsan_enabled) && !ctx->disable_count;}
/* 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);}
/* * Reads the instrumented memory for value change detection; value change * detection is currently done for accesses up to a size of 8 bytes. */static __always_inline u64 read_instrumented_memory(const volatile void *ptr, size_t size){ /* * In the below we don't necessarily need the read of the location to * be atomic, and we don't use READ_ONCE(), since all we need for race * detection is to observe 2 different values. * * Furthermore, on certain architectures (such as arm64), READ_ONCE() * may turn into more complex instructions than a plain load that cannot * do unaligned accesses. */ switch (size) { case 1: return *(const volatile u8 *)ptr; case 2: return *(const volatile u16 *)ptr; case 4: return *(const volatile u32 *)ptr; case 8: return *(const volatile u64 *)ptr; default: return 0; /* Ignore; we do not diff the values. */ }}
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}
static __always_inline int get_kcsan_stack_depth(void){#ifdef CONFIG_KCSAN_WEAK_MEMORY return current->kcsan_stack_depth;#else BUILD_BUG(); return 0;#endif}
static __always_inline void add_kcsan_stack_depth(int val){#ifdef CONFIG_KCSAN_WEAK_MEMORY current->kcsan_stack_depth += val;#else BUILD_BUG();#endif}
static __always_inline struct kcsan_scoped_access *get_reorder_access(struct kcsan_ctx *ctx){#ifdef CONFIG_KCSAN_WEAK_MEMORY return ctx->disable_scoped ? NULL : &ctx->reorder_access;#else return NULL;#endif}
static __always_inline boolfind_reorder_access(struct kcsan_ctx *ctx, const volatile void *ptr, size_t size, int type, unsigned long ip){ struct kcsan_scoped_access *reorder_access = get_reorder_access(ctx);
if (!reorder_access) return false;
/* * Note: If accesses are repeated while reorder_access is identical, * never matches the new access, because !(type & KCSAN_ACCESS_SCOPED). */ return reorder_access->ptr == ptr && reorder_access->size == size && reorder_access->type == type && reorder_access->ip == ip;}
static inline voidset_reorder_access(struct kcsan_ctx *ctx, const volatile void *ptr, size_t size, int type, unsigned long ip){ struct kcsan_scoped_access *reorder_access = get_reorder_access(ctx);
if (!reorder_access || !kcsan_weak_memory) return;
/* * To avoid nested interrupts or scheduler (which share kcsan_ctx) * reading an inconsistent reorder_access, ensure that the below has * exclusive access to reorder_access by disallowing concurrent use. */ ctx->disable_scoped++; barrier(); reorder_access->ptr = ptr; reorder_access->size = size; reorder_access->type = type | KCSAN_ACCESS_SCOPED; reorder_access->ip = ip; reorder_access->stack_depth = get_kcsan_stack_depth(); barrier(); ctx->disable_scoped--;}
/* * 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, unsigned long ip, atomic_long_t *watchpoint, long encoded_watchpoint){ const bool is_assert = (type & KCSAN_ACCESS_ASSERT) != 0; struct kcsan_ctx *ctx = get_ctx(); unsigned long flags; bool consumed;
/* * We know a watchpoint exists. Let's try to keep the race-window * between here and finally consuming the watchpoint below as small as * possible -- avoid unneccessarily complex code until consumed. */
if (!kcsan_is_enabled(ctx)) 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. * * reorder_access is never created from an access with access_mask set. */ if (ctx->access_mask && !find_reorder_access(ctx, ptr, size, type, ip)) return;
/* * If the other thread does not want to ignore the access, and there was * a value change as a result of this thread's operation, we will still * generate a report of unknown origin. * * Use CONFIG_KCSAN_REPORT_RACE_UNKNOWN_ORIGIN=n to filter. */ if (!is_assert && kcsan_ignore_address(ptr)) return;
/* * Consuming the watchpoint must be guarded by kcsan_is_enabled() to * avoid erroneously triggering reports if the context is 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_set_info(ptr, size, type, ip, 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 (is_assert) 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 voidkcsan_setup_watchpoint(const volatile void *ptr, size_t size, int type, unsigned long ip){ const bool is_write = (type & KCSAN_ACCESS_WRITE) != 0; const bool is_assert = (type & KCSAN_ACCESS_ASSERT) != 0; atomic_long_t *watchpoint; u64 old, new, diff; enum kcsan_value_change value_change = KCSAN_VALUE_CHANGE_MAYBE; bool interrupt_watcher = kcsan_interrupt_watcher; unsigned long ua_flags = user_access_save(); struct kcsan_ctx *ctx = get_ctx(); unsigned long access_mask = ctx->access_mask; unsigned long irq_flags = 0; bool is_reorder_access;
/* * Always reset kcsan_skip counter in slow-path to avoid underflow; see * should_watch(). */ reset_kcsan_skip();
if (!kcsan_is_enabled(ctx)) goto out;
/* * Check to-ignore addresses after kcsan_is_enabled(), as we may access * memory that is not yet initialized during early boot. */ if (!is_assert && kcsan_ignore_address(ptr)) goto out;
if (!check_encodable((unsigned long)ptr, size)) { atomic_long_inc(&kcsan_counters[KCSAN_COUNTER_UNENCODABLE_ACCESSES]); goto out; }
/* * The local CPU cannot observe reordering of its own accesses, and * therefore we need to take care of 2 cases to avoid false positives: * * 1. Races of the reordered access with interrupts. To avoid, if * the current access is reorder_access, disable interrupts. * 2. Avoid races of scoped accesses from nested interrupts (below). */ is_reorder_access = find_reorder_access(ctx, ptr, size, type, ip); if (is_reorder_access) interrupt_watcher = false; /* * Avoid races of scoped accesses from nested interrupts (or scheduler). * Assume setting up a watchpoint for a non-scoped (normal) access that * also conflicts with a current scoped access. In a nested interrupt, * which shares the context, it would check a conflicting scoped access. * To avoid, disable scoped access checking. */ ctx->disable_scoped++;
/* * 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 (!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. */ old = is_reorder_access ? 0 : read_instrumented_memory(ptr, size);
/* * 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. */ if (!is_reorder_access) { new = read_instrumented_memory(ptr, size); } else { /* * Reordered accesses cannot be used for value change detection, * because the memory location may no longer be accessible and * could result in a fault. */ new = 0; access_mask = 0; }
diff = old ^ new; if (access_mask) diff &= access_mask;
/* * Check if we observed a value change. * * Also check if the data race should be ignored (the rules depend on * non-zero diff); if it is to be ignored, the below rules for * KCSAN_VALUE_CHANGE_MAYBE apply. */ if (diff && !kcsan_ignore_data_race(size, type, old, new, diff)) 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_known_origin(ptr, size, type, ip, value_change, watchpoint - watchpoints, old, new, access_mask); } 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_unknown_origin(ptr, size, type, ip, old, new, access_mask); } }
/* * 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 (!interrupt_watcher) local_irq_restore(irq_flags); kcsan_restore_irqtrace(current); ctx->disable_scoped--;
/* * Reordered accesses cannot be used for value change detection, * therefore never consider for reordering if access_mask is set. * ASSERT_EXCLUSIVE are not real accesses, ignore them as well. */ if (!access_mask && !is_assert) set_reorder_access(ctx, ptr, size, type, ip);out: user_access_restore(ua_flags);}
static __always_inline voidcheck_access(const volatile void *ptr, size_t size, int type, unsigned long ip){ 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;
again: /* * 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, !(type & KCSAN_ACCESS_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, ip, watchpoint, encoded_watchpoint); else { struct kcsan_ctx *ctx = get_ctx(); /* Call only once in fast-path. */
if (unlikely(should_watch(ctx, ptr, size, type))) { kcsan_setup_watchpoint(ptr, size, type, ip); return; }
if (!(type & KCSAN_ACCESS_SCOPED)) { struct kcsan_scoped_access *reorder_access = get_reorder_access(ctx);
if (reorder_access) { /* * reorder_access check: simulates reordering of * the access after subsequent operations. */ ptr = reorder_access->ptr; type = reorder_access->type; ip = reorder_access->ip; /* * Upon a nested interrupt, this context's * reorder_access can be modified (shared ctx). * We know that upon return, reorder_access is * always invalidated by setting size to 0 via * __tsan_func_exit(). Therefore we must read * and check size after the other fields. */ barrier(); size = READ_ONCE(reorder_access->size); if (size) goto again; } }
/* * Always checked last, right before returning from runtime; * if reorder_access is valid, checked after it was checked. */ 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); }
if (IS_ENABLED(CONFIG_KCSAN_REPORT_VALUE_CHANGE_ONLY) || IS_ENABLED(CONFIG_KCSAN_ASSUME_PLAIN_WRITES_ATOMIC) || IS_ENABLED(CONFIG_KCSAN_PERMISSIVE) || IS_ENABLED(CONFIG_KCSAN_IGNORE_ATOMICS)) { pr_warn("non-strict mode configured - use CONFIG_KCSAN_STRICT=y to see all data races\n"); } else { pr_info("strict mode configured\n"); }}
/* === 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();
check_access(ptr, size, type, _RET_IP_);
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; sa->ip = _RET_IP_;
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--;
check_access(sa->ptr, sa->size, sa->type, sa->ip);}EXPORT_SYMBOL(kcsan_end_scoped_access);
void __kcsan_check_access(const volatile void *ptr, size_t size, int type){ check_access(ptr, size, type, _RET_IP_);}EXPORT_SYMBOL(__kcsan_check_access);
#define DEFINE_MEMORY_BARRIER(name, order_before_cond) \ void __kcsan_##name(void) \ { \ struct kcsan_scoped_access *sa = get_reorder_access(get_ctx()); \ if (!sa) \ return; \ if (order_before_cond) \ sa->size = 0; \ } \ EXPORT_SYMBOL(__kcsan_##name)
DEFINE_MEMORY_BARRIER(mb, true);DEFINE_MEMORY_BARRIER(wmb, sa->type & (KCSAN_ACCESS_WRITE | KCSAN_ACCESS_COMPOUND));DEFINE_MEMORY_BARRIER(rmb, !(sa->type & KCSAN_ACCESS_WRITE) || (sa->type & KCSAN_ACCESS_COMPOUND));DEFINE_MEMORY_BARRIER(release, true);
/* * 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, _RET_IP_); \ } \ 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, _RET_IP_); \ } \ 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, \ _RET_IP_); \ } \ 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, _RET_IP_);}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, _RET_IP_);}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, \ _RET_IP_); \ } \ 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), \ _RET_IP_); \ } \ 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);
/* * Function entry and exit are used to determine the validty of reorder_access. * Reordering of the access ends at the end of the function scope where the * access happened. This is done for two reasons: * * 1. Artificially limits the scope where missing barriers are detected. * This minimizes false positives due to uninstrumented functions that * contain the required barriers but were missed. * * 2. Simplifies generating the stack trace of the access. */void __tsan_func_entry(void *call_pc);noinline void __tsan_func_entry(void *call_pc){ if (!IS_ENABLED(CONFIG_KCSAN_WEAK_MEMORY)) return;
add_kcsan_stack_depth(1);}EXPORT_SYMBOL(__tsan_func_entry);
void __tsan_func_exit(void);noinline void __tsan_func_exit(void){ struct kcsan_scoped_access *reorder_access;
if (!IS_ENABLED(CONFIG_KCSAN_WEAK_MEMORY)) return;
reorder_access = get_reorder_access(get_ctx()); if (!reorder_access) goto out;
if (get_kcsan_stack_depth() <= reorder_access->stack_depth) { /* * Access check to catch cases where write without a barrier * (supposed release) was last access in function: because * instrumentation is inserted before the real access, a data * race due to the write giving up a c-s would only be caught if * we do the conflicting access after. */ check_access(reorder_access->ptr, reorder_access->size, reorder_access->type, reorder_access->ip); reorder_access->size = 0; reorder_access->stack_depth = INT_MIN; }out: add_kcsan_stack_depth(-1);}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. */
static __always_inline void kcsan_atomic_builtin_memorder(int memorder){ if (memorder == __ATOMIC_RELEASE || memorder == __ATOMIC_SEQ_CST || memorder == __ATOMIC_ACQ_REL) __kcsan_release();}
#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) \ { \ kcsan_atomic_builtin_memorder(memorder); \ if (!IS_ENABLED(CONFIG_KCSAN_IGNORE_ATOMICS)) { \ check_access(ptr, bits / BITS_PER_BYTE, KCSAN_ACCESS_ATOMIC, _RET_IP_); \ } \ 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) \ { \ kcsan_atomic_builtin_memorder(memorder); \ if (!IS_ENABLED(CONFIG_KCSAN_IGNORE_ATOMICS)) { \ check_access(ptr, bits / BITS_PER_BYTE, \ KCSAN_ACCESS_WRITE | KCSAN_ACCESS_ATOMIC, _RET_IP_); \ } \ __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) \ { \ kcsan_atomic_builtin_memorder(memorder); \ if (!IS_ENABLED(CONFIG_KCSAN_IGNORE_ATOMICS)) { \ check_access(ptr, bits / BITS_PER_BYTE, \ KCSAN_ACCESS_COMPOUND | KCSAN_ACCESS_WRITE | \ KCSAN_ACCESS_ATOMIC, _RET_IP_); \ } \ 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) \ { \ kcsan_atomic_builtin_memorder(mo); \ if (!IS_ENABLED(CONFIG_KCSAN_IGNORE_ATOMICS)) { \ check_access(ptr, bits / BITS_PER_BYTE, \ KCSAN_ACCESS_COMPOUND | KCSAN_ACCESS_WRITE | \ KCSAN_ACCESS_ATOMIC, _RET_IP_); \ } \ 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) \ { \ kcsan_atomic_builtin_memorder(mo); \ if (!IS_ENABLED(CONFIG_KCSAN_IGNORE_ATOMICS)) { \ check_access(ptr, bits / BITS_PER_BYTE, \ KCSAN_ACCESS_COMPOUND | KCSAN_ACCESS_WRITE | \ KCSAN_ACCESS_ATOMIC, _RET_IP_); \ } \ __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);#ifdef CONFIG_64BITDEFINE_TSAN_ATOMIC_OPS(64);#endif
void __tsan_atomic_thread_fence(int memorder);void __tsan_atomic_thread_fence(int memorder){ kcsan_atomic_builtin_memorder(memorder); __atomic_thread_fence(memorder);}EXPORT_SYMBOL(__tsan_atomic_thread_fence);
/* * In instrumented files, we emit instrumentation for barriers by mapping the * kernel barriers to an __atomic_signal_fence(), which is interpreted specially * and otherwise has no relation to a real __atomic_signal_fence(). No known * kernel code uses __atomic_signal_fence(). * * Since fsanitize=thread instrumentation handles __atomic_signal_fence(), which * are turned into calls to __tsan_atomic_signal_fence(), such instrumentation * can be disabled via the __no_kcsan function attribute (vs. an explicit call * which could not). When __no_kcsan is requested, __atomic_signal_fence() * generates no code. * * Note: The result of using __atomic_signal_fence() with KCSAN enabled is * potentially limiting the compiler's ability to reorder operations; however, * if barriers were instrumented with explicit calls (without LTO), the compiler * couldn't optimize much anyway. The result of a hypothetical architecture * using __atomic_signal_fence() in normal code would be KCSAN false negatives. */void __tsan_atomic_signal_fence(int memorder);noinline void __tsan_atomic_signal_fence(int memorder){ switch (memorder) { case __KCSAN_BARRIER_TO_SIGNAL_FENCE_mb: __kcsan_mb(); break; case __KCSAN_BARRIER_TO_SIGNAL_FENCE_wmb: __kcsan_wmb(); break; case __KCSAN_BARRIER_TO_SIGNAL_FENCE_rmb: __kcsan_rmb(); break; case __KCSAN_BARRIER_TO_SIGNAL_FENCE_release: __kcsan_release(); break; default: break; }}EXPORT_SYMBOL(__tsan_atomic_signal_fence);
#ifdef __HAVE_ARCH_MEMSETvoid *__tsan_memset(void *s, int c, size_t count);noinline void *__tsan_memset(void *s, int c, size_t count){ /* * Instead of not setting up watchpoints where accessed size is greater * than MAX_ENCODABLE_SIZE, truncate checked size to MAX_ENCODABLE_SIZE. */ size_t check_len = min_t(size_t, count, MAX_ENCODABLE_SIZE);
check_access(s, check_len, KCSAN_ACCESS_WRITE, _RET_IP_); return memset(s, c, count);}#elsevoid *__tsan_memset(void *s, int c, size_t count) __alias(memset);#endifEXPORT_SYMBOL(__tsan_memset);
#ifdef __HAVE_ARCH_MEMMOVEvoid *__tsan_memmove(void *dst, const void *src, size_t len);noinline void *__tsan_memmove(void *dst, const void *src, size_t len){ size_t check_len = min_t(size_t, len, MAX_ENCODABLE_SIZE);
check_access(dst, check_len, KCSAN_ACCESS_WRITE, _RET_IP_); check_access(src, check_len, 0, _RET_IP_); return memmove(dst, src, len);}#elsevoid *__tsan_memmove(void *dst, const void *src, size_t len) __alias(memmove);#endifEXPORT_SYMBOL(__tsan_memmove);
#ifdef __HAVE_ARCH_MEMCPYvoid *__tsan_memcpy(void *dst, const void *src, size_t len);noinline void *__tsan_memcpy(void *dst, const void *src, size_t len){ size_t check_len = min_t(size_t, len, MAX_ENCODABLE_SIZE);
check_access(dst, check_len, KCSAN_ACCESS_WRITE, _RET_IP_); check_access(src, check_len, 0, _RET_IP_); return memcpy(dst, src, len);}#elsevoid *__tsan_memcpy(void *dst, const void *src, size_t len) __alias(memcpy);#endifEXPORT_SYMBOL(__tsan_memcpy);