diff options
Diffstat (limited to 'kernel')
| -rw-r--r-- | kernel/Makefile | 6 | ||||
| -rw-r--r-- | kernel/kcsan/Makefile | 14 | ||||
| -rw-r--r-- | kernel/kcsan/atomic.h | 20 | ||||
| -rw-r--r-- | kernel/kcsan/core.c | 807 | ||||
| -rw-r--r-- | kernel/kcsan/debugfs.c | 349 | ||||
| -rw-r--r-- | kernel/kcsan/encoding.h | 95 | ||||
| -rw-r--r-- | kernel/kcsan/kcsan.h | 142 | ||||
| -rw-r--r-- | kernel/kcsan/report.c | 634 | ||||
| -rw-r--r-- | kernel/kcsan/test.c | 131 | ||||
| -rw-r--r-- | kernel/locking/Makefile | 3 | ||||
| -rw-r--r-- | kernel/sched/Makefile | 6 | ||||
| -rw-r--r-- | kernel/trace/Makefile | 3 |
12 files changed, 2210 insertions, 0 deletions
diff --git a/kernel/Makefile b/kernel/Makefile index c332eb9d4841..ce8716a04d0e 100644 --- a/kernel/Makefile +++ b/kernel/Makefile @@ -23,6 +23,9 @@ endif # Prevents flicker of uninteresting __do_softirq()/__local_bh_disable_ip() # in coverage traces. KCOV_INSTRUMENT_softirq.o := n +# Avoid KCSAN instrumentation in softirq ("No shared variables, all the data +# are CPU local" => assume no data races), to reduce overhead in interrupts. +KCSAN_SANITIZE_softirq.o = n # These are called from save_stack_trace() on slub debug path, # and produce insane amounts of uninteresting coverage. KCOV_INSTRUMENT_module.o := n @@ -31,6 +34,7 @@ KCOV_INSTRUMENT_stacktrace.o := n # Don't self-instrument. KCOV_INSTRUMENT_kcov.o := n KASAN_SANITIZE_kcov.o := n +KCSAN_SANITIZE_kcov.o := n CFLAGS_kcov.o := $(call cc-option, -fno-conserve-stack -fno-stack-protector) # cond_syscall is currently not LTO compatible @@ -103,6 +107,7 @@ obj-$(CONFIG_TRACEPOINTS) += trace/ obj-$(CONFIG_IRQ_WORK) += irq_work.o obj-$(CONFIG_CPU_PM) += cpu_pm.o obj-$(CONFIG_BPF) += bpf/ +obj-$(CONFIG_KCSAN) += kcsan/ obj-$(CONFIG_SHADOW_CALL_STACK) += scs.o obj-$(CONFIG_PERF_EVENTS) += events/ @@ -121,6 +126,7 @@ obj-$(CONFIG_SYSCTL_KUNIT_TEST) += sysctl-test.o obj-$(CONFIG_GCC_PLUGIN_STACKLEAK) += stackleak.o KASAN_SANITIZE_stackleak.o := n +KCSAN_SANITIZE_stackleak.o := n KCOV_INSTRUMENT_stackleak.o := n $(obj)/configs.o: $(obj)/config_data.gz diff --git a/kernel/kcsan/Makefile b/kernel/kcsan/Makefile new file mode 100644 index 000000000000..d4999b38d1be --- /dev/null +++ b/kernel/kcsan/Makefile @@ -0,0 +1,14 @@ +# SPDX-License-Identifier: GPL-2.0 +KCSAN_SANITIZE := n +KCOV_INSTRUMENT := n +UBSAN_SANITIZE := n + +CFLAGS_REMOVE_core.o = $(CC_FLAGS_FTRACE) +CFLAGS_REMOVE_debugfs.o = $(CC_FLAGS_FTRACE) +CFLAGS_REMOVE_report.o = $(CC_FLAGS_FTRACE) + +CFLAGS_core.o := $(call cc-option,-fno-conserve-stack,) \ + $(call cc-option,-fno-stack-protector,) + +obj-y := core.o debugfs.o report.o +obj-$(CONFIG_KCSAN_SELFTEST) += test.o diff --git a/kernel/kcsan/atomic.h b/kernel/kcsan/atomic.h new file mode 100644 index 000000000000..be9e625227f3 --- /dev/null +++ b/kernel/kcsan/atomic.h @@ -0,0 +1,20 @@ +/* SPDX-License-Identifier: GPL-2.0 */ + +#ifndef _KERNEL_KCSAN_ATOMIC_H +#define _KERNEL_KCSAN_ATOMIC_H + +#include <linux/jiffies.h> +#include <linux/sched.h> + +/* + * Special rules for certain memory where concurrent conflicting accesses are + * common, however, the current convention is to not mark them; returns true if + * access to @ptr should be considered atomic. Called from slow-path. + */ +static bool kcsan_is_atomic_special(const volatile void *ptr) +{ + /* volatile globals that have been observed in data races. */ + return ptr == &jiffies || ptr == ¤t->state; +} + +#endif /* _KERNEL_KCSAN_ATOMIC_H */ diff --git a/kernel/kcsan/core.c b/kernel/kcsan/core.c new file mode 100644 index 000000000000..a73a66cf79df --- /dev/null +++ b/kernel/kcsan/core.c @@ -0,0 +1,807 @@ +// SPDX-License-Identifier: GPL-2.0 + +#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/random.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); + +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) && + 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; +} + +static inline void reset_kcsan_skip(void) +{ + long skip_count = kcsan_skip_watch - + (IS_ENABLED(CONFIG_KCSAN_SKIP_WATCH_RANDOMIZE) ? + 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; +} + +static inline unsigned int get_delay(void) +{ + unsigned int delay = in_task() ? kcsan_udelay_task : kcsan_udelay_interrupt; + return delay - (IS_ENABLED(CONFIG_KCSAN_DELAY_RANDOMIZE) ? + prandom_u32_max(delay) : + 0); +} + +/* + * 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_report(ptr, size, type, KCSAN_VALUE_CHANGE_MAYBE, + KCSAN_REPORT_CONSUMED_WATCHPOINT, + watchpoint - watchpoints); + } 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. + */ + kcsan_counter_inc(KCSAN_COUNTER_REPORT_RACES); + } + + if ((type & KCSAN_ACCESS_ASSERT) != 0) + kcsan_counter_inc(KCSAN_COUNTER_ASSERT_FAILURES); + else + kcsan_counter_inc(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)) { + kcsan_counter_inc(KCSAN_COUNTER_UNENCODABLE_ACCESSES); + goto out; + } + + if (!kcsan_interrupt_watcher) + /* Use raw to avoid lockdep recursion via IRQ flags tracing. */ + raw_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. + */ + kcsan_counter_inc(KCSAN_COUNTER_NO_CAPACITY); + goto out_unlock; + } + + kcsan_counter_inc(KCSAN_COUNTER_SETUP_WATCHPOINTS); + kcsan_counter_inc(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("KCSAN: 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. + */ + udelay(get_delay()); + + /* + * 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) + kcsan_counter_inc(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. */ + + kcsan_counter_inc(KCSAN_COUNTER_RACES_UNKNOWN_ORIGIN); + if (is_assert) + kcsan_counter_inc(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); + kcsan_counter_dec(KCSAN_COUNTER_USED_WATCHPOINTS); +out_unlock: + if (!kcsan_interrupt_watcher) + raw_local_irq_restore(irq_flags); +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) +{ + BUG_ON(!in_task()); + + kcsan_debugfs_init(); + + /* + * We are in the init task, and no other tasks should be running; + * WRITE_ONCE without memory barrier is sufficient. + */ + if (kcsan_early_enable) + 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) \ + { \ + 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) \ + { \ + 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) + +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) +{ + check_access(ptr, size, 0); +} +EXPORT_SYMBOL(__tsan_read_range); + +void __tsan_write_range(void *ptr, size_t size) +{ + check_access(ptr, size, KCSAN_ACCESS_WRITE); +} +EXPORT_SYMBOL(__tsan_write_range); + +/* + * The below are not required by KCSAN, but can still be emitted by the + * compiler. + */ +void __tsan_func_entry(void *call_pc) +{ +} +EXPORT_SYMBOL(__tsan_func_entry); +void __tsan_func_exit(void) +{ +} +EXPORT_SYMBOL(__tsan_func_exit); +void __tsan_init(void) +{ +} +EXPORT_SYMBOL(__tsan_init); diff --git a/kernel/kcsan/debugfs.c b/kernel/kcsan/debugfs.c new file mode 100644 index 000000000000..023e49c58d55 --- /dev/null +++ b/kernel/kcsan/debugfs.c @@ -0,0 +1,349 @@ +// SPDX-License-Identifier: GPL-2.0 + +#include <linux/atomic.h> +#include <linux/bsearch.h> +#include <linux/bug.h> +#include <linux/debugfs.h> +#include <linux/init.h> +#include <linux/kallsyms.h> +#include <linux/sched.h> +#include <linux/seq_file.h> +#include <linux/slab.h> +#include <linux/sort.h> +#include <linux/string.h> +#include <linux/uaccess.h> + +#include "kcsan.h" + +/* + * Statistics counters. + */ +static atomic_long_t counters[KCSAN_COUNTER_COUNT]; + +/* + * Addresses for filtering functions from reporting. This list can be used as a + * whitelist or blacklist. + */ +static struct { + unsigned long *addrs; /* array of addresses */ + size_t size; /* current size */ + int used; /* number of elements used */ + bool sorted; /* if elements are sorted */ + bool whitelist; /* if list is a blacklist or whitelist */ +} report_filterlist = { + .addrs = NULL, + .size = 8, /* small initial size */ + .used = 0, + .sorted = false, + .whitelist = false, /* default is blacklist */ +}; +static DEFINE_SPINLOCK(report_filterlist_lock); + +static const char *counter_to_name(enum kcsan_counter_id id) +{ + switch (id) { + case KCSAN_COUNTER_USED_WATCHPOINTS: return "used_watchpoints"; + case KCSAN_COUNTER_SETUP_WATCHPOINTS: return "setup_watchpoints"; + case KCSAN_COUNTER_DATA_RACES: return "data_races"; + case KCSAN_COUNTER_ASSERT_FAILURES: return "assert_failures"; + case KCSAN_COUNTER_NO_CAPACITY: return "no_capacity"; + case KCSAN_COUNTER_REPORT_RACES: return "report_races"; + case KCSAN_COUNTER_RACES_UNKNOWN_ORIGIN: return "races_unknown_origin"; + case KCSAN_COUNTER_UNENCODABLE_ACCESSES: return "unencodable_accesses"; + case KCSAN_COUNTER_ENCODING_FALSE_POSITIVES: return "encoding_false_positives"; + case KCSAN_COUNTER_COUNT: + BUG(); + } + return NULL; +} + +void kcsan_counter_inc(enum kcsan_counter_id id) +{ + atomic_long_inc(&counters[id]); +} + +void kcsan_counter_dec(enum kcsan_counter_id id) +{ + atomic_long_dec(&counters[id]); +} + +/* + * The microbenchmark allows benchmarking KCSAN core runtime only. To run + * multiple threads, pipe 'microbench=<iters>' from multiple tasks into the + * debugfs file. This will not generate any conflicts, and tests fast-path only. + */ +static noinline void microbenchmark(unsigned long iters) +{ + const struct kcsan_ctx ctx_save = current->kcsan_ctx; + const bool was_enabled = READ_ONCE(kcsan_enabled); + cycles_t cycles; + + /* We may have been called from an atomic region; reset context. */ + memset(¤t->kcsan_ctx, 0, sizeof(current->kcsan_ctx)); + /* + * Disable to benchmark fast-path for all accesses, and (expected + * negligible) call into slow-path, but never set up watchpoints. + */ + WRITE_ONCE(kcsan_enabled, false); + + pr_info("KCSAN: %s begin | iters: %lu\n", __func__, iters); + + cycles = get_cycles(); + while (iters--) { + unsigned long addr = iters & ((PAGE_SIZE << 8) - 1); + int type = !(iters & 0x7f) ? KCSAN_ACCESS_ATOMIC : + (!(iters & 0xf) ? KCSAN_ACCESS_WRITE : 0); + __kcsan_check_access((void *)addr, sizeof(long), type); + } + cycles = get_cycles() - cycles; + + pr_info("KCSAN: %s end | cycles: %llu\n", __func__, cycles); + + WRITE_ONCE(kcsan_enabled, was_enabled); + /* restore context */ + current->kcsan_ctx = ctx_save; +} + +/* + * Simple test to create conflicting accesses. Write 'test=<iters>' to KCSAN's + * debugfs file from multiple tasks to generate real conflicts and show reports. + */ +static long test_dummy; +static long test_flags; +static long test_scoped; +static noinline void test_thread(unsigned long iters) +{ + const long CHANGE_BITS = 0xff00ff00ff00ff00L; + const struct kcsan_ctx ctx_save = current->kcsan_ctx; + cycles_t cycles; + + /* We may have been called from an atomic region; reset context. */ + memset(¤t->kcsan_ctx, 0, sizeof(current->kcsan_ctx)); + + pr_info("KCSAN: %s begin | iters: %lu\n", __func__, iters); + pr_info("test_dummy@%px, test_flags@%px, test_scoped@%px,\n", + &test_dummy, &test_flags, &test_scoped); + + cycles = get_cycles(); + while (iters--) { + /* These all should generate reports. */ + __kcsan_check_read(&test_dummy, sizeof(test_dummy)); + ASSERT_EXCLUSIVE_WRITER(test_dummy); + ASSERT_EXCLUSIVE_ACCESS(test_dummy); + + ASSERT_EXCLUSIVE_BITS(test_flags, ~CHANGE_BITS); /* no report */ + __kcsan_check_read(&test_flags, sizeof(test_flags)); /* no report */ + + ASSERT_EXCLUSIVE_BITS(test_flags, CHANGE_BITS); /* report */ + __kcsan_check_read(&test_flags, sizeof(test_flags)); /* no report */ + + /* not actually instrumented */ + WRITE_ONCE(test_dummy, iters); /* to observe value-change */ + __kcsan_check_write(&test_dummy, sizeof(test_dummy)); + + test_flags ^= CHANGE_BITS; /* generate value-change */ + __kcsan_check_write(&test_flags, sizeof(test_flags)); + + BUG_ON(current->kcsan_ctx.scoped_accesses.prev); + { + /* Should generate reports anywhere in this block. */ + ASSERT_EXCLUSIVE_WRITER_SCOPED(test_scoped); + ASSERT_EXCLUSIVE_ACCESS_SCOPED(test_scoped); + BUG_ON(!current->kcsan_ctx.scoped_accesses.prev); + /* Unrelated accesses. */ + __kcsan_check_access(&cycles, sizeof(cycles), 0); + __kcsan_check_access(&cycles, sizeof(cycles), KCSAN_ACCESS_ATOMIC); + } + BUG_ON(current->kcsan_ctx.scoped_accesses.prev); + } + cycles = get_cycles() - cycles; + + pr_info("KCSAN: %s end | cycles: %llu\n", __func__, cycles); + + /* restore context */ + current->kcsan_ctx = ctx_save; +} + +static int cmp_filterlist_addrs(const void *rhs, const void *lhs) +{ + const unsigned long a = *(const unsigned long *)rhs; + const unsigned long b = *(const unsigned long *)lhs; + + return a < b ? -1 : a == b ? 0 : 1; +} + +bool kcsan_skip_report_debugfs(unsigned long func_addr) +{ + unsigned long symbolsize, offset; + unsigned long flags; + bool ret = false; + + if (!kallsyms_lookup_size_offset(func_addr, &symbolsize, &offset)) + return false; + func_addr -= offset; /* Get function start */ + + spin_lock_irqsave(&report_filterlist_lock, flags); + if (report_filterlist.used == 0) + goto out; + + /* Sort array if it is unsorted, and then do a binary search. */ + if (!report_filterlist.sorted) { + sort(report_filterlist.addrs, report_filterlist.used, + sizeof(unsigned long), cmp_filterlist_addrs, NULL); + report_filterlist.sorted = true; + } + ret = !!bsearch(&func_addr, report_filterlist.addrs, + report_filterlist.used, sizeof(unsigned long), + cmp_filterlist_addrs); + if (report_filterlist.whitelist) + ret = !ret; + +out: + spin_unlock_irqrestore(&report_filterlist_lock, flags); + return ret; +} + +static void set_report_filterlist_whitelist(bool whitelist) +{ + unsigned long flags; + + spin_lock_irqsave(&report_filterlist_lock, flags); + report_filterlist.whitelist = whitelist; + spin_unlock_irqrestore(&report_filterlist_lock, flags); +} + +/* Returns 0 on success, error-code otherwise. */ +static ssize_t insert_report_filterlist(const char *func) +{ + unsigned long flags; + unsigned long addr = kallsyms_lookup_name(func); + ssize_t ret = 0; + + if (!addr) { + pr_err("KCSAN: could not find function: '%s'\n", func); + return -ENOENT; + } + + spin_lock_irqsave(&report_filterlist_lock, flags); + + if (report_filterlist.addrs == NULL) { + /* initial allocation */ + report_filterlist.addrs = + kmalloc_array(report_filterlist.size, + sizeof(unsigned long), GFP_ATOMIC); + if (report_filterlist.addrs == NULL) { + ret = -ENOMEM; + goto out; + } + } else if (report_filterlist.used == report_filterlist.size) { + /* resize filterlist */ + size_t new_size = report_filterlist.size * 2; + unsigned long *new_addrs = + krealloc(report_filterlist.addrs, + new_size * sizeof(unsigned long), GFP_ATOMIC); + + if (new_addrs == NULL) { + /* leave filterlist itself untouched */ + ret = -ENOMEM; + goto out; + } + + report_filterlist.size = new_size; + report_filterlist.addrs = new_addrs; + } + + /* Note: deduplicating should be done in userspace. */ + report_filterlist.addrs[report_filterlist.used++] = + kallsyms_lookup_name(func); + report_filterlist.sorted = false; + +out: + spin_unlock_irqrestore(&report_filterlist_lock, flags); + + return ret; +} + +static int show_info(struct seq_file *file, void *v) +{ + int i; + unsigned long flags; + + /* show stats */ + seq_printf(file, "enabled: %i\n", READ_ONCE(kcsan_enabled)); + for (i = 0; i < KCSAN_COUNTER_COUNT; ++i) + seq_printf(file, "%s: %ld\n", counter_to_name(i), + atomic_long_read(&counters[i])); + + /* show filter functions, and filter type */ + spin_lock_irqsave(&report_filterlist_lock, flags); + seq_printf(file, "\n%s functions: %s\n", + report_filterlist.whitelist ? "whitelisted" : "blacklisted", + report_filterlist.used == 0 ? "none" : ""); + for (i = 0; i < report_filterlist.used; ++i) + seq_printf(file, " %ps\n", (void *)report_filterlist.addrs[i]); + spin_unlock_irqrestore(&report_filterlist_lock, flags); + + return 0; +} + +static int debugfs_open(struct inode *inode, struct file *file) +{ + return single_open(file, show_info, NULL); +} + +static ssize_t +debugfs_write(struct file *file, const char __user *buf, size_t count, loff_t *off) +{ + char kbuf[KSYM_NAME_LEN]; + char *arg; + int read_len = count < (sizeof(kbuf) - 1) ? count : (sizeof(kbuf) - 1); + + if (copy_from_user(kbuf, buf, read_len)) + return -EFAULT; + kbuf[read_len] = '\0'; + arg = strstrip(kbuf); + + if (!strcmp(arg, "on")) { + WRITE_ONCE(kcsan_enabled, true); + } else if (!strcmp(arg, "off")) { + WRITE_ONCE(kcsan_enabled, false); + } else if (!strncmp(arg, "microbench=", sizeof("microbench=") - 1)) { + unsigned long iters; + + if (kstrtoul(&arg[sizeof("microbench=") - 1], 0, &iters)) + return -EINVAL; + microbenchmark(iters); + } else if (!strncmp(arg, "test=", sizeof("test=") - 1)) { + unsigned long iters; + + if (kstrtoul(&arg[sizeof("test=") - 1], 0, &iters)) + return -EINVAL; + test_thread(iters); + } else if (!strcmp(arg, "whitelist")) { + set_report_filterlist_whitelist(true); + } else if (!strcmp(arg, "blacklist")) { + set_report_filterlist_whitelist(false); + } else if (arg[0] == '!') { + ssize_t ret = insert_report_filterlist(&arg[1]); + + if (ret < 0) + return ret; + } else { + return -EINVAL; + } + + return count; +} + +static const struct file_operations debugfs_ops = +{ + .read = seq_read, + .open = debugfs_open, + .write = debugfs_write, + .release = single_release +}; + +void __init kcsan_debugfs_init(void) +{ + debugfs_create_file("kcsan", 0644, NULL, NULL, &debugfs_ops); +} diff --git a/kernel/kcsan/encoding.h b/kernel/kcsan/encoding.h new file mode 100644 index 000000000000..f03562aaf2eb --- /dev/null +++ b/kernel/kcsan/encoding.h @@ -0,0 +1,95 @@ +/* SPDX-License-Identifier: GPL-2.0 */ + +#ifndef _KERNEL_KCSAN_ENCODING_H +#define _KERNEL_KCSAN_ENCODING_H + +#include <linux/bits.h> +#include <linux/log2.h> +#include <linux/mm.h> + +#include "kcsan.h" + +#define SLOT_RANGE PAGE_SIZE + +#define INVALID_WATCHPOINT 0 +#define CONSUMED_WATCHPOINT 1 + +/* + * The maximum useful size of accesses for which we set up watchpoints is the + * max range of slots we check on an access. + */ +#define MAX_ENCODABLE_SIZE (SLOT_RANGE * (1 + KCSAN_CHECK_ADJACENT)) + +/* + * Number of bits we use to store size info. + */ +#define WATCHPOINT_SIZE_BITS bits_per(MAX_ENCODABLE_SIZE) +/* + * This encoding for addresses discards the upper (1 for is-write + SIZE_BITS); + * however, most 64-bit architectures do not use the full 64-bit address space. + * Also, in order for a false positive to be observable 2 things need to happen: + * + * 1. different addresses but with the same encoded address race; + * 2. and both map onto the same watchpoint slots; + * + * Both these are assumed to be very unlikely. However, in case it still happens + * happens, the report logic will filter out the false positive (see report.c). + */ +#define WATCHPOINT_ADDR_BITS (BITS_PER_LONG-1 - WATCHPOINT_SIZE_BITS) + +/* + * Masks to set/retrieve the encoded data. + */ +#define WATCHPOINT_WRITE_MASK BIT(BITS_PER_LONG-1) +#define WATCHPOINT_SIZE_MASK \ + GENMASK(BITS_PER_LONG-2, BITS_PER_LONG-2 - WATCHPOINT_SIZE_BITS) +#define WATCHPOINT_ADDR_MASK \ + GENMASK(BITS_PER_LONG-3 - WATCHPOINT_SIZE_BITS, 0) + +static inline bool check_encodable(unsigned long addr, size_t size) +{ + return size <= MAX_ENCODABLE_SIZE; +} + +static inline long +encode_watchpoint(unsigned long addr, size_t size, bool is_write) +{ + return (long)((is_write ? WATCHPOINT_WRITE_MASK : 0) | + (size << WATCHPOINT_ADDR_BITS) | + (addr & WATCHPOINT_ADDR_MASK)); +} + +static __always_inline bool decode_watchpoint(long watchpoint, + unsigned long *addr_masked, + size_t *size, + bool *is_write) +{ + if (watchpoint == INVALID_WATCHPOINT || + watchpoint == CONSUMED_WATCHPOINT) + return false; + + *addr_masked = (unsigned long)watchpoint & WATCHPOINT_ADDR_MASK; + *size = ((unsigned long)watchpoint & WATCHPOINT_SIZE_MASK) >> WATCHPOINT_ADDR_BITS; + *is_write = !!((unsigned long)watchpoint & WATCHPOINT_WRITE_MASK); + + return true; +} + +/* + * Return watchpoint slot for an address. + */ +static __always_inline int watchpoint_slot(unsigned long addr) +{ + return (addr / PAGE_SIZE) % CONFIG_KCSAN_NUM_WATCHPOINTS; +} + +static __always_inline bool matching_access(unsigned long addr1, size_t size1, + unsigned long addr2, size_t size2) +{ + unsigned long end_range1 = addr1 + size1 - 1; + unsigned long end_range2 = addr2 + size2 - 1; + + return addr1 <= end_range2 && addr2 <= end_range1; +} + +#endif /* _KERNEL_KCSAN_ENCODING_H */ diff --git a/kernel/kcsan/kcsan.h b/kernel/kcsan/kcsan.h new file mode 100644 index 000000000000..763d6d08d94b --- /dev/null +++ b/kernel/kcsan/kcsan.h @@ -0,0 +1,142 @@ +/* SPDX-License-Identifier: GPL-2.0 */ + +/* + * The Kernel Concurrency Sanitizer (KCSAN) infrastructure. For more info please + * see Documentation/dev-tools/kcsan.rst. + */ + +#ifndef _KERNEL_KCSAN_KCSAN_H +#define _KERNEL_KCSAN_KCSAN_H + +#include <linux/kcsan.h> + +/* The number of adjacent watchpoints to check. */ +#define KCSAN_CHECK_ADJACENT 1 +#define NUM_SLOTS (1 + 2*KCSAN_CHECK_ADJACENT) + +extern unsigned int kcsan_udelay_task; +extern unsigned int kcsan_udelay_interrupt; + +/* + * Globally enable and disable KCSAN. + */ +extern bool kcsan_enabled; + +/* + * Initialize debugfs file. + */ +void kcsan_debugfs_init(void); + +enum kcsan_counter_id { + /* + * Number of watchpoints currently in use. + */ + KCSAN_COUNTER_USED_WATCHPOINTS, + + /* + * Total number of watchpoints set up. + */ + KCSAN_COUNTER_SETUP_WATCHPOINTS, + + /* + * Total number of data races. + */ + KCSAN_COUNTER_DATA_RACES, + + /* + * Total number of ASSERT failures due to races. If the observed race is + * due to two conflicting ASSERT type accesses, then both will be + * counted. + */ + KCSAN_COUNTER_ASSERT_FAILURES, + + /* + * Number of times no watchpoints were available. + */ + KCSAN_COUNTER_NO_CAPACITY, + + /* + * A thread checking a watchpoint raced with another checking thread; + * only one will be reported. + */ + KCSAN_COUNTER_REPORT_RACES, + + /* + * Observed data value change, but writer thread unknown. + */ + KCSAN_COUNTER_RACES_UNKNOWN_ORIGIN, + + /* + * The access cannot be encoded to a valid watchpoint. + */ + KCSAN_COUNTER_UNENCODABLE_ACCESSES, + + /* + * Watchpoint encoding caused a watchpoint to fire on mismatching + * accesses. + */ + KCSAN_COUNTER_ENCODING_FALSE_POSITIVES, + + KCSAN_COUNTER_COUNT, /* number of counters */ +}; + +/* + * Increment/decrement counter with given id; avoid calling these in fast-path. + */ +extern void kcsan_counter_inc(enum kcsan_counter_id id); +extern void kcsan_counter_dec(enum kcsan_counter_id id); + +/* + * Returns true if data races in the function symbol that maps to func_addr + * (offsets are ignored) should *not* be reported. + */ +extern bool kcsan_skip_report_debugfs(unsigned long func_addr); + +/* + * Value-change states. + */ +enum kcsan_value_change { + /* + * Did not observe a value-change, however, it is valid to report the + * race, depending on preferences. + */ + KCSAN_VALUE_CHANGE_MAYBE, + + /* + * Did not observe a value-change, and it is invalid to report the race. + */ + KCSAN_VALUE_CHANGE_FALSE, + + /* + * The value was observed to change, and the race should be reported. + */ + KCSAN_VALUE_CHANGE_TRUE, +}; + +enum kcsan_report_type { + /* + * The thread that set up the watchpoint and briefly stalled was + * signalled that another thread triggered the watchpoint. + */ + KCSAN_REPORT_RACE_SIGNAL, + + /* + * A thread found and consumed a matching watchpoint. + */ + KCSAN_REPORT_CONSUMED_WATCHPOINT, + + /* + * No other thread was observed to race with the access, but the data + * value before and after the stall differs. + */ + KCSAN_REPORT_RACE_UNKNOWN_ORIGIN, +}; + +/* + * Print a race report from thread that encountered the race. + */ +extern void kcsan_report(const volatile void *ptr, size_t size, int access_type, + enum kcsan_value_change value_change, + enum kcsan_report_type type, int watchpoint_idx); + +#endif /* _KERNEL_KCSAN_KCSAN_H */ diff --git a/kernel/kcsan/report.c b/kernel/kcsan/report.c new file mode 100644 index 000000000000..ac5f8345bae9 --- /dev/null +++ b/kernel/kcsan/report.c @@ -0,0 +1,634 @@ +// SPDX-License-Identifier: GPL-2.0 + +#include <linux/debug_locks.h> +#include <linux/delay.h> +#include <linux/jiffies.h> +#include <linux/kernel.h> +#include <linux/lockdep.h> +#include <linux/preempt.h> +#include <linux/printk.h> +#include <linux/sched.h> +#include <linux/spinlock.h> +#include <linux/stacktrace.h> + +#include "kcsan.h" +#include "encoding.h" + +/* + * Max. number of stack entries to show in the report. + */ +#define NUM_STACK_ENTRIES 64 + +/* Common access info. */ +struct access_info { + const volatile void *ptr; + size_t size; + int access_type; + int task_pid; + int cpu_id; +}; + +/* + * Other thread info: communicated from other racing thread to thread that set + * up the watchpoint, which then prints the complete report atomically. + */ +struct other_info { + struct access_info ai; + unsigned long stack_entries[NUM_STACK_ENTRIES]; + int num_stack_entries; + + /* + * Optionally pass @current. Typically we do not need to pass @current + * via @other_info since just @task_pid is sufficient. Passing @current + * has additional overhead. + * + * To safely pass @current, we must either use get_task_struct/ + * put_task_struct, or stall the thread that populated @other_info. + * + * We cannot rely on get_task_struct/put_task_struct in case + * release_report() races with a task being released, and would have to + * free it in release_report(). This may result in deadlock if we want + * to use KCSAN on the allocators. + * + * Since we also want to reliably print held locks for + * CONFIG_KCSAN_VERBOSE, the current implementation stalls the thread + * that populated @other_info until it has been consumed. + */ + struct task_struct *task; +}; + +/* + * To never block any producers of struct other_info, we need as many elements + * as we have watchpoints (upper bound on concurrent races to report). + */ +static struct other_info other_infos[CONFIG_KCSAN_NUM_WATCHPOINTS + NUM_SLOTS-1]; + +/* + * Information about reported races; used to rate limit reporting. + */ +struct report_time { + /* + * The last time the race was reported. + */ + unsigned long time; + + /* + * The frames of the 2 threads; if only 1 thread is known, one frame + * will be 0. + */ + unsigned long frame1; + unsigned long frame2; +}; + +/* + * Since we also want to be able to debug allocators with KCSAN, to avoid + * deadlock, report_times cannot be dynamically resized with krealloc in + * rate_limit_report. + * + * Therefore, we use a fixed-size array, which at most will occupy a page. This + * still adequately rate limits reports, assuming that a) number of unique data + * races is not excessive, and b) occurrence of unique races within the + * same time window is limited. + */ +#define REPORT_TIMES_MAX (PAGE_SIZE / sizeof(struct report_time)) +#define REPORT_TIMES_SIZE \ + (CONFIG_KCSAN_REPORT_ONCE_IN_MS > REPORT_TIMES_MAX ? \ + REPORT_TIMES_MAX : \ + CONFIG_KCSAN_REPORT_ONCE_IN_MS) +static struct report_time report_times[REPORT_TIMES_SIZE]; + +/* + * Spinlock serializing report generation, and access to @other_infos. Although + * it could make sense to have a finer-grained locking story for @other_infos, + * report generation needs to be serialized either way, so not much is gained. + */ +static DEFINE_RAW_SPINLOCK(report_lock); + +/* + * Checks if the race identified by thread frames frame1 and frame2 has + * been reported since (now - KCSAN_REPORT_ONCE_IN_MS). + */ +static bool rate_limit_report(unsigned long frame1, unsigned long frame2) +{ + struct report_time *use_entry = &report_times[0]; + unsigned long invalid_before; + int i; + + BUILD_BUG_ON(CONFIG_KCSAN_REPORT_ONCE_IN_MS != 0 && REPORT_TIMES_SIZE == 0); + + if (CONFIG_KCSAN_REPORT_ONCE_IN_MS == 0) + return false; + + invalid_before = jiffies - msecs_to_jiffies(CONFIG_KCSAN_REPORT_ONCE_IN_MS); + + /* Check if a matching race report exists. */ + for (i = 0; i < REPORT_TIMES_SIZE; ++i) { + struct report_time *rt = &report_times[i]; + + /* + * Must always select an entry for use to store info as we + * cannot resize report_times; at the end of the scan, use_entry + * will be the oldest entry, which ideally also happened before + * KCSAN_REPORT_ONCE_IN_MS ago. + */ + if (time_before(rt->time, use_entry->time)) + use_entry = rt; + + /* + * Initially, no need to check any further as this entry as well + * as following entries have never been used. + */ + if (rt->time == 0) + break; + + /* Check if entry expired. */ + if (time_before(rt->time, invalid_before)) + continue; /* before KCSAN_REPORT_ONCE_IN_MS ago */ + + /* Reported recently, check if race matches. */ + if ((rt->frame1 == frame1 && rt->frame2 == frame2) || + (rt->frame1 == frame2 && rt->frame2 == frame1)) + return true; + } + + use_entry->time = jiffies; + use_entry->frame1 = frame1; + use_entry->frame2 = frame2; + return false; +} + +/* + * Special rules to skip reporting. + */ +static bool +skip_report(enum kcsan_value_change value_change, unsigned long top_frame) +{ + /* Should never get here if value_change==FALSE. */ + WARN_ON_ONCE(value_change == KCSAN_VALUE_CHANGE_FALSE); + + /* + * The first call to skip_report always has value_change==TRUE, since we + * cannot know the value written of an instrumented access. For the 2nd + * call there are 6 cases with CONFIG_KCSAN_REPORT_VALUE_CHANGE_ONLY: + * + * 1. read watchpoint, conflicting write (value_change==TRUE): report; + * 2. read watchpoint, conflicting write (value_change==MAYBE): skip; + * 3. write watchpoint, conflicting write (value_change==TRUE): report; + * 4. write watchpoint, conflicting write (value_change==MAYBE): skip; + * 5. write watchpoint, conflicting read (value_change==MAYBE): skip; + * 6. write watchpoint, conflicting read (value_change==TRUE): report; + * + * Cases 1-4 are intuitive and expected; case 5 ensures we do not report + * data races where the write may have rewritten the same value; case 6 + * is possible either if the size is larger than what we check value + * changes for or the access type is KCSAN_ACCESS_ASSERT. + */ + if (IS_ENABLED(CONFIG_KCSAN_REPORT_VALUE_CHANGE_ONLY) && + value_change == KCSAN_VALUE_CHANGE_MAYBE) { + /* + * The access is a write, but the data value did not change. + * + * We opt-out of this filter for certain functions at request of + * maintainers. + */ + char buf[64]; + int len = scnprintf(buf, sizeof(buf), "%ps", (void *)top_frame); + + if (!strnstr(buf, "rcu_", len) && + !strnstr(buf, "_rcu", len) && + !strnstr(buf, "_srcu", len)) + return true; + } + + return kcsan_skip_report_debugfs(top_frame); +} + +static const char *get_access_type(int type) +{ + if (type & KCSAN_ACCESS_ASSERT) { + if (type & KCSAN_ACCESS_SCOPED) { + if (type & KCSAN_ACCESS_WRITE) + return "assert no accesses (scoped)"; + else + return "assert no writes (scoped)"; + } else { + if (type & KCSAN_ACCESS_WRITE) + return "assert no accesses"; + else + return "assert no writes"; + } + } + + switch (type) { + case 0: + return "read"; + case KCSAN_ACCESS_ATOMIC: + return "read (marked)"; + case KCSAN_ACCESS_WRITE: + return "write"; + case KCSAN_ACCESS_WRITE | KCSAN_ACCESS_ATOMIC: + return "write (marked)"; + case KCSAN_ACCESS_SCOPED: + return "read (scoped)"; + case KCSAN_ACCESS_SCOPED | KCSAN_ACCESS_ATOMIC: + return "read (marked, scoped)"; + case KCSAN_ACCESS_SCOPED | KCSAN_ACCESS_WRITE: + return "write (scoped)"; + case KCSAN_ACCESS_SCOPED | KCSAN_ACCESS_WRITE | KCSAN_ACCESS_ATOMIC: + return "write (marked, scoped)"; + default: + BUG(); + } +} + +static const char *get_bug_type(int type) +{ + return (type & KCSAN_ACCESS_ASSERT) != 0 ? "assert: race" : "data-race"; +} + +/* Return thread description: in task or interrupt. */ +static const char *get_thread_desc(int task_id) +{ + if (task_id != -1) { + static char buf[32]; /* safe: protected by report_lock */ + + snprintf(buf, sizeof(buf), "task %i", task_id); + return buf; + } + return "interrupt"; +} + +/* Helper to skip KCSAN-related functions in stack-trace. */ +static int get_stack_skipnr(const unsigned long stack_entries[], int num_entries) +{ + char buf[64]; + char *cur; + int len, skip; + + for (skip = 0; skip < num_entries; ++skip) { + len = scnprintf(buf, sizeof(buf), "%ps", (void *)stack_entries[skip]); + + /* Never show tsan_* or {read,write}_once_size. */ + if (strnstr(buf, "tsan_", len) || + strnstr(buf, "_once_size", len)) + continue; + + cur = strnstr(buf, "kcsan_", len); + if (cur) { + cur += sizeof("kcsan_") - 1; + if (strncmp(cur, "test", sizeof("test") - 1)) + continue; /* KCSAN runtime function. */ + /* KCSAN related test. */ + } + + /* + * No match for runtime functions -- @skip entries to skip to + * get to first frame of interest. + */ + break; + } + + return skip; +} + +/* Compares symbolized strings of addr1 and addr2. */ +static int sym_strcmp(void *addr1, void *addr2) +{ + char buf1[64]; + char buf2[64]; + + snprintf(buf1, sizeof(buf1), "%pS", addr1); + snprintf(buf2, sizeof(buf2), "%pS", addr2); + + return strncmp(buf1, buf2, sizeof(buf1)); +} + +static void print_verbose_info(struct task_struct *task) +{ + if (!task) + return; + + pr_err("\n"); + debug_show_held_locks(task); + print_irqtrace_events(task); +} + +/* + * Returns true if a report was generated, false otherwise. + */ +static bool print_report(enum kcsan_value_change value_change, + enum kcsan_report_type type, + const struct access_info *ai, + const struct other_info *other_info) +{ + unsigned long stack_entries[NUM_STACK_ENTRIES] = { 0 }; + int num_stack_entries = stack_trace_save(stack_entries, NUM_STACK_ENTRIES, 1); + int skipnr = get_stack_skipnr(stack_entries, num_stack_entries); + unsigned long this_frame = stack_entries[skipnr]; + unsigned long other_frame = 0; + int other_skipnr = 0; /* silence uninit warnings */ + + /* + * Must check report filter rules before starting to print. + */ + if (skip_report(KCSAN_VALUE_CHANGE_TRUE, stack_entries[skipnr])) + return false; + + if (type == KCSAN_REPORT_RACE_SIGNAL) { + other_skipnr = get_stack_skipnr(other_info->stack_entries, + other_info->num_stack_entries); + other_frame = other_info->stack_entries[other_skipnr]; + + /* @value_change is only known for the other thread */ + if (skip_report(value_change, other_frame)) + return false; + } + + if (rate_limit_report(this_frame, other_frame)) + return false; + + /* Print report header. */ + pr_err("==================================================================\n"); + switch (type) { + case KCSAN_REPORT_RACE_SIGNAL: { + int cmp; + + /* + * Order functions lexographically for consistent bug titles. + * Do not print offset of functions to keep title short. + */ + cmp = sym_strcmp((void *)other_frame, (void *)this_frame); + pr_err("BUG: KCSAN: %s in %ps / %ps\n", + get_bug_type(ai->access_type | other_info->ai.access_type), + (void *)(cmp < 0 ? other_frame : this_frame), + (void *)(cmp < 0 ? this_frame : other_frame)); + } break; + + case KCSAN_REPORT_RACE_UNKNOWN_ORIGIN: + pr_err("BUG: KCSAN: %s in %pS\n", get_bug_type(ai->access_type), + (void *)this_frame); + break; + + default: + BUG(); + } + + pr_err("\n"); + + /* Print information about the racing accesses. */ + switch (type) { + case KCSAN_REPORT_RACE_SIGNAL: + pr_err("%s to 0x%px of %zu bytes by %s on cpu %i:\n", + get_access_type(other_info->ai.access_type), other_info->ai.ptr, + other_info->ai.size, get_thread_desc(other_info->ai.task_pid), + other_info->ai.cpu_id); + + /* Print the other thread's stack trace. */ + stack_trace_print(other_info->stack_entries + other_skipnr, + other_info->num_stack_entries - other_skipnr, + 0); + + if (IS_ENABLED(CONFIG_KCSAN_VERBOSE)) + print_verbose_info(other_info->task); + + pr_err("\n"); + pr_err("%s to 0x%px of %zu bytes by %s on cpu %i:\n", + get_access_type(ai->access_type), ai->ptr, ai->size, + get_thread_desc(ai->task_pid), ai->cpu_id); + break; + + case KCSAN_REPORT_RACE_UNKNOWN_ORIGIN: + pr_err("race at unknown origin, with %s to 0x%px of %zu bytes by %s on cpu %i:\n", + get_access_type(ai->access_type), ai->ptr, ai->size, + get_thread_desc(ai->task_pid), ai->cpu_id); + break; + + default: + BUG(); + } + /* Print stack trace of this thread. */ + stack_trace_print(stack_entries + skipnr, num_stack_entries - skipnr, + 0); + + if (IS_ENABLED(CONFIG_KCSAN_VERBOSE)) + print_verbose_info(current); + + /* Print report footer. */ + pr_err("\n"); + pr_err("Reported by Kernel Concurrency Sanitizer on:\n"); + dump_stack_print_info(KERN_DEFAULT); + pr_err("==================================================================\n"); + + return true; +} + +static void release_report(unsigned long *flags, struct other_info *other_info) +{ + if (other_info) + /* + * Use size to denote valid/invalid, since KCSAN entirely + * ignores 0-sized accesses. + */ + other_info->ai.size = 0; + + raw_spin_unlock_irqrestore(&report_lock, *flags); +} + +/* + * Sets @other_info->task and awaits consumption of @other_info. + * + * Precondition: report_lock is held. + * Postcondition: report_lock is held. + */ +static void set_other_info_task_blocking(unsigned long *flags, + const struct access_info *ai, + struct other_info *other_info) +{ + /* + * We may be instrumenting a code-path where current->state is already + * something other than TASK_RUNNING. + */ + const bool is_running = current->state == TASK_RUNNING; + /* + * To avoid deadlock in case we are in an interrupt here and this is a + * race with a task on the same CPU (KCSAN_INTERRUPT_WATCHER), provide a + * timeout to ensure this works in all contexts. + * + * Await approximately the worst case delay of the reporting thread (if + * we are not interrupted). + */ + int timeout = max(kcsan_udelay_task, kcsan_udelay_interrupt); + + other_info->task = current; + do { + if (is_running) { + /* + * Let lockdep know the real task is sleeping, to print + * the held locks (recall we turned lockdep off, so + * locking/unlocking @report_lock won't be recorded). + */ + set_current_state(TASK_UNINTERRUPTIBLE); + } + raw_spin_unlock_irqrestore(&report_lock, *flags); + /* + * We cannot call schedule() since we also cannot reliably + * determine if sleeping here is permitted -- see in_atomic(). + */ + + udelay(1); + raw_spin_lock_irqsave(&report_lock, *flags); + if (timeout-- < 0) { + /* + * Abort. Reset @other_info->task to NULL, since it + * appears the other thread is still going to consume + * it. It will result in no verbose info printed for + * this task. + */ + other_info->task = NULL; + break; + } + /* + * If invalid, or @ptr nor @current matches, then @other_info + * has been consumed and we may continue. If not, retry. + */ + } while (other_info->ai.size && other_info->ai.ptr == ai->ptr && + other_info->task == current); + if (is_running) + set_current_state(TASK_RUNNING); +} + +/* Populate @other_info; requires that the provided @other_info not in use. */ +static void prepare_report_producer(unsigned long *flags, + const struct access_info *ai, + struct other_info *other_info) +{ + raw_spin_lock_irqsave(&report_lock, *flags); + + /* + * The same @other_infos entry cannot be used concurrently, because + * there is a one-to-one mapping to watchpoint slots (@watchpoints in + * core.c), and a watchpoint is only released for reuse after reporting + * is done by the consumer of @other_info. Therefore, it is impossible + * for another concurrent prepare_report_producer() to set the same + * @other_info, and are guaranteed exclusivity for the @other_infos + * entry pointed to by @other_info. + * + * To check this property holds, size should never be non-zero here, + * because every consumer of struct other_info resets size to 0 in + * release_report(). + */ + WARN_ON(other_info->ai.size); + + other_info->ai = *ai; + other_info->num_stack_entries = stack_trace_save(other_info->stack_entries, NUM_STACK_ENTRIES, 2); + + if (IS_ENABLED(CONFIG_KCSAN_VERBOSE)) + set_other_info_task_blocking(flags, ai, other_info); + + raw_spin_unlock_irqrestore(&report_lock, *flags); +} + +/* Awaits producer to fill @other_info and then returns. */ +static bool prepare_report_consumer(unsigned long *flags, + const struct access_info *ai, + struct other_info *other_info) +{ + + raw_spin_lock_irqsave(&report_lock, *flags); + while (!other_info->ai.size) { /* Await valid @other_info. */ + raw_spin_unlock_irqrestore(&report_lock, *flags); + cpu_relax(); + raw_spin_lock_irqsave(&report_lock, *flags); + } + + /* Should always have a matching access based on watchpoint encoding. */ + if (WARN_ON(!matching_access((unsigned long)other_info->ai.ptr & WATCHPOINT_ADDR_MASK, other_info->ai.size, + (unsigned long)ai->ptr & WATCHPOINT_ADDR_MASK, ai->size))) + goto discard; + + if (!matching_access((unsigned long)other_info->ai.ptr, other_info->ai.size, + (unsigned long)ai->ptr, ai->size)) { + /* + * If the actual accesses to not match, this was a false + * positive due to watchpoint encoding. + */ + kcsan_counter_inc(KCSAN_COUNTER_ENCODING_FALSE_POSITIVES); + goto discard; + } + + return true; + +discard: + release_report(flags, other_info); + return false; +} + +/* + * Depending on the report type either sets @other_info and returns false, or + * awaits @other_info and returns true. If @other_info is not required for the + * report type, simply acquires @report_lock and returns true. + */ +static noinline bool prepare_report(unsigned long *flags, + enum kcsan_report_type type, + const struct access_info *ai, + struct other_info *other_info) +{ + switch (type) { + case KCSAN_REPORT_CONSUMED_WATCHPOINT: + prepare_report_producer(flags, ai, other_info); + return false; + case KCSAN_REPORT_RACE_SIGNAL: + return prepare_report_consumer(flags, ai, other_info); + default: + /* @other_info not required; just acquire @report_lock. */ + raw_spin_lock_irqsave(&report_lock, *flags); + return true; + } +} + +void kcsan_report(const volatile void *ptr, size_t size, int access_type, + enum kcsan_value_change value_change, + enum kcsan_report_type type, int watchpoint_idx) +{ + unsigned long flags = 0; + const struct access_info ai = { + .ptr = ptr, + .size = size, + .access_type = access_type, + .task_pid = in_task() ? task_pid_nr(current) : -1, + .cpu_id = raw_smp_processor_id() + }; + struct other_info *other_info = type == KCSAN_REPORT_RACE_UNKNOWN_ORIGIN + ? NULL : &other_infos[watchpoint_idx]; + + kcsan_disable_current(); + if (WARN_ON(watchpoint_idx < 0 || watchpoint_idx >= ARRAY_SIZE(other_infos))) + goto out; + + /* + * With TRACE_IRQFLAGS, lockdep's IRQ trace state becomes corrupted if + * we do not turn off lockdep here; this could happen due to recursion + * into lockdep via KCSAN if we detect a race in utilities used by + * lockdep. + */ + lockdep_off(); + + if (prepare_report(&flags, type, &ai, other_info)) { + /* + * Never report if value_change is FALSE, only if we it is + * either TRUE or MAYBE. In case of MAYBE, further filtering may + * be done once we know the full stack trace in print_report(). + */ + bool reported = value_change != KCSAN_VALUE_CHANGE_FALSE && + print_report(value_change, type, &ai, other_info); + + if (reported && panic_on_warn) + panic("panic_on_warn set ...\n"); + + release_report(&flags, other_info); + } + + lockdep_on(); +out: + kcsan_enable_current(); +} diff --git a/kernel/kcsan/test.c b/kernel/kcsan/test.c new file mode 100644 index 000000000000..d26a052d3383 --- /dev/null +++ b/kernel/kcsan/test.c @@ -0,0 +1,131 @@ +// SPDX-License-Identifier: GPL-2.0 + +#include <linux/init.h> +#include <linux/kernel.h> +#include <linux/printk.h> +#include <linux/random.h> +#include <linux/types.h> + +#include "encoding.h" + +#define ITERS_PER_TEST 2000 + +/* Test requirements. */ +static bool test_requires(void) +{ + /* random should be initialized for the below tests */ + return prandom_u32() + prandom_u32() != 0; +} + +/* + * Test watchpoint encode and decode: check that encoding some access's info, + * and then subsequent decode preserves the access's info. + */ +static bool test_encode_decode(void) +{ + int i; + + for (i = 0; i < ITERS_PER_TEST; ++i) { + size_t size = prandom_u32_max(MAX_ENCODABLE_SIZE) + 1; + bool is_write = !!prandom_u32_max(2); + unsigned long addr; + + prandom_bytes(&addr, sizeof(addr)); + if (WARN_ON(!check_encodable(addr, size))) + return false; + + /* Encode and decode */ + { + const long encoded_watchpoint = + encode_watchpoint(addr, size, is_write); + unsigned long verif_masked_addr; + size_t verif_size; + bool verif_is_write; + + /* Check special watchpoints */ + if (WARN_ON(decode_watchpoint( + INVALID_WATCHPOINT, &verif_masked_addr, + &verif_size, &verif_is_write))) + return false; + if (WARN_ON(decode_watchpoint( + CONSUMED_WATCHPOINT, &verif_masked_addr, + &verif_size, &verif_is_write))) + return false; + + /* Check decoding watchpoint returns same data */ + if (WARN_ON(!decode_watchpoint( + encoded_watchpoint, &verif_masked_addr, + &verif_size, &verif_is_write))) + return false; + if (WARN_ON(verif_masked_addr != + (addr & WATCHPOINT_ADDR_MASK))) + goto fail; + if (WARN_ON(verif_size != size)) + goto fail; + if (WARN_ON(is_write != verif_is_write)) + goto fail; + + continue; +fail: + pr_err("%s fail: %s %zu bytes @ %lx -> encoded: %lx -> %s %zu bytes @ %lx\n", + __func__, is_write ? "write" : "read", size, + addr, encoded_watchpoint, + verif_is_write ? "write" : "read", verif_size, + verif_masked_addr); + return false; + } + } + + return true; +} + +/* Test access matching function. */ +static bool test_matching_access(void) +{ + if (WARN_ON(!matching_access(10, 1, 10, 1))) + return false; + if (WARN_ON(!matching_access(10, 2, 11, 1))) + return false; + if (WARN_ON(!matching_access(10, 1, 9, 2))) + return false; + if (WARN_ON(matching_access(10, 1, 11, 1))) + return false; + if (WARN_ON(matching_access(9, 1, 10, 1))) + return false; + + /* + * An access of size 0 could match another access, as demonstrated here. + * Rather than add more comparisons to 'matching_access()', which would + * end up in the fast-path for *all* checks, check_access() simply + * returns for all accesses of size 0. + */ + if (WARN_ON(!matching_access(8, 8, 12, 0))) + return false; + + return true; +} + +static int __init kcsan_selftest(void) +{ + int passed = 0; + int total = 0; + +#define RUN_TEST(do_test) \ + do { \ + ++total; \ + if (do_test()) \ + ++passed; \ + else \ + pr_err("KCSAN selftest: " #do_test " failed"); \ + } while (0) + + RUN_TEST(test_requires); + RUN_TEST(test_encode_decode); + RUN_TEST(test_matching_access); + + pr_info("KCSAN selftest: %d/%d tests passed\n", passed, total); + if (passed != total) + panic("KCSAN selftests failed"); + return 0; +} +postcore_initcall(kcsan_selftest); diff --git a/kernel/locking/Makefile b/kernel/locking/Makefile index 45452facff3b..6d11cfb9b41f 100644 --- a/kernel/locking/Makefile +++ b/kernel/locking/Makefile @@ -5,6 +5,9 @@ KCOV_INSTRUMENT := n obj-y += mutex.o semaphore.o rwsem.o percpu-rwsem.o +# Avoid recursion lockdep -> KCSAN -> ... -> lockdep. +KCSAN_SANITIZE_lockdep.o := n + ifdef CONFIG_FUNCTION_TRACER CFLAGS_REMOVE_lockdep.o = $(CC_FLAGS_FTRACE) CFLAGS_REMOVE_lockdep_proc.o = $(CC_FLAGS_FTRACE) diff --git a/kernel/sched/Makefile b/kernel/sched/Makefile index 21fb5a5662b5..5fc9c9b70862 100644 --- a/kernel/sched/Makefile +++ b/kernel/sched/Makefile @@ -7,6 +7,12 @@ endif # that is not a function of syscall inputs. E.g. involuntary context switches. KCOV_INSTRUMENT := n +# There are numerous data races here, however, most of them are due to plain accesses. +# This would make it even harder for syzbot to find reproducers, because these +# bugs trigger without specific input. Disable by default, but should re-enable +# eventually. +KCSAN_SANITIZE := n + ifneq ($(CONFIG_SCHED_OMIT_FRAME_POINTER),y) # According to Alan Modra <alan@linuxcare.com.au>, the -fno-omit-frame-pointer is # needed for x86 only. Why this used to be enabled for all architectures is beyond diff --git a/kernel/trace/Makefile b/kernel/trace/Makefile index 1d8aaa546412..6575bb0a0434 100644 --- a/kernel/trace/Makefile +++ b/kernel/trace/Makefile @@ -6,6 +6,9 @@ ifdef CONFIG_FUNCTION_TRACER ORIG_CFLAGS := $(KBUILD_CFLAGS) KBUILD_CFLAGS = $(subst $(CC_FLAGS_FTRACE),,$(ORIG_CFLAGS)) +# Avoid recursion due to instrumentation. +KCSAN_SANITIZE := n + ifdef CONFIG_FTRACE_SELFTEST # selftest needs instrumentation CFLAGS_trace_selftest_dynamic.o = $(CC_FLAGS_FTRACE) |