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kcsan: Add core memory barrier instrumentation functions 

Add the core memory barrier instrumentation functions. These invalidate
the current in-flight reordered access based on the rules for the
respective barrier types and in-flight access type.

To obtain barrier instrumentation that can be disabled via __no_kcsan
with appropriate compiler-support (and not just with objtool help),
barrier instrumentation repurposes __atomic_signal_fence(), instead of
inserting explicit calls. Crucially, __atomic_signal_fence() normally
does not map to any real instructions, but is still intercepted by
fsanitize=thread. As a result, like any other instrumentation done by
the compiler, barrier instrumentation can be disabled with __no_kcsan.

Unfortunately Clang and GCC currently differ in their __no_kcsan aka
__no_sanitize_thread behaviour with respect to builtin atomics (and
__tsan_func_{entry,exit}) instrumentation. This is already reflected in
Kconfig.kcsan's dependencies for KCSAN_WEAK_MEMORY. A later change will
introduce support for newer versions of Clang that can implement
__no_kcsan to also remove the additional instrumentation introduced by
KCSAN_WEAK_MEMORY.

Signed-off-by: Marco Elver <elver@google.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit is contained in:
Marco Elver 2021-11-30 12:44:13 +01:00 committed by Paul E. McKenney
parent 69562e4983
commit 0b8b0830ac
2 changed files with 136 additions and 3 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

71
include/linux/kcsan-checks.h
View File

@ -36,6 +36,36 @@
*/
void __kcsan_check_access(const volatile void *ptr, size_t size, int type);
/*
* See definition of __tsan_atomic_signal_fence() in kernel/kcsan/core.c.
* Note: The mappings are arbitrary, and do not reflect any real mappings of C11
* memory orders to the LKMM memory orders and vice-versa!
*/
#define __KCSAN_BARRIER_TO_SIGNAL_FENCE_mb __ATOMIC_SEQ_CST
#define __KCSAN_BARRIER_TO_SIGNAL_FENCE_wmb __ATOMIC_ACQ_REL
#define __KCSAN_BARRIER_TO_SIGNAL_FENCE_rmb __ATOMIC_ACQUIRE
#define __KCSAN_BARRIER_TO_SIGNAL_FENCE_release __ATOMIC_RELEASE
/**
* __kcsan_mb - full memory barrier instrumentation
*/
void __kcsan_mb(void);
/**
* __kcsan_wmb - write memory barrier instrumentation
*/
void __kcsan_wmb(void);
/**
* __kcsan_rmb - read memory barrier instrumentation
*/
void __kcsan_rmb(void);
/**
* __kcsan_release - release barrier instrumentation
*/
void __kcsan_release(void);
/**
* kcsan_disable_current - disable KCSAN for the current context
*
@ -159,6 +189,10 @@ void kcsan_end_scoped_access(struct kcsan_scoped_access *sa);
static inline void __kcsan_check_access(const volatile void *ptr, size_t size,
int type) { }
static inline void __kcsan_mb(void) { }
static inline void __kcsan_wmb(void) { }
static inline void __kcsan_rmb(void) { }
static inline void __kcsan_release(void) { }
static inline void kcsan_disable_current(void) { }
static inline void kcsan_enable_current(void) { }
static inline void kcsan_enable_current_nowarn(void) { }
@ -191,12 +225,45 @@ static inline void kcsan_end_scoped_access(struct kcsan_scoped_access *sa) { }
*/
#define __kcsan_disable_current kcsan_disable_current
#define __kcsan_enable_current kcsan_enable_current_nowarn
#else
#else /* __SANITIZE_THREAD__ */
static inline void kcsan_check_access(const volatile void *ptr, size_t size,
int type) { }
static inline void __kcsan_enable_current(void) { }
static inline void __kcsan_disable_current(void) { }
#endif
#endif /* __SANITIZE_THREAD__ */
#if defined(CONFIG_KCSAN_WEAK_MEMORY) && defined(__SANITIZE_THREAD__)
/*
* Normal barrier instrumentation is not done via explicit calls, but by mapping
* to a repurposed __atomic_signal_fence(), which normally does not generate any
* real instructions, but is still intercepted by fsanitize=thread. This means,
* like any other compile-time instrumentation, barrier instrumentation can be
* disabled with the __no_kcsan function attribute.
*
* Also see definition of __tsan_atomic_signal_fence() in kernel/kcsan/core.c.
*/
#define __KCSAN_BARRIER_TO_SIGNAL_FENCE(name) \
static __always_inline void kcsan_##name(void) \
{ \
barrier(); \
__atomic_signal_fence(__KCSAN_BARRIER_TO_SIGNAL_FENCE_##name); \
barrier(); \
}
__KCSAN_BARRIER_TO_SIGNAL_FENCE(mb)
__KCSAN_BARRIER_TO_SIGNAL_FENCE(wmb)
__KCSAN_BARRIER_TO_SIGNAL_FENCE(rmb)
__KCSAN_BARRIER_TO_SIGNAL_FENCE(release)
#elif defined(CONFIG_KCSAN_WEAK_MEMORY) && defined(__KCSAN_INSTRUMENT_BARRIERS__)
#define kcsan_mb __kcsan_mb
#define kcsan_wmb __kcsan_wmb
#define kcsan_rmb __kcsan_rmb
#define kcsan_release __kcsan_release
#else /* CONFIG_KCSAN_WEAK_MEMORY && ... */
static inline void kcsan_mb(void) { }
static inline void kcsan_wmb(void) { }
static inline void kcsan_rmb(void) { }
static inline void kcsan_release(void) { }
#endif /* CONFIG_KCSAN_WEAK_MEMORY && ... */
/**
* __kcsan_check_read - check regular read access for races

68
kernel/kcsan/core.c
View File

@ -939,6 +939,22 @@ void __kcsan_check_access(const volatile void *ptr, size_t size, int type)
}
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).
@ -1123,10 +1139,19 @@ EXPORT_SYMBOL(__tsan_init);
* 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_); \
} \
@ -1136,6 +1161,7 @@ EXPORT_SYMBOL(__tsan_init);
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_); \
@ -1148,6 +1174,7 @@ EXPORT_SYMBOL(__tsan_init);
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 | \
@ -1180,6 +1207,7 @@ EXPORT_SYMBOL(__tsan_init);
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 | \
@ -1195,6 +1223,7 @@ EXPORT_SYMBOL(__tsan_init);
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 | \
@ -1226,10 +1255,47 @@ DEFINE_TSAN_ATOMIC_OPS(64);
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);
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);