/* SPDX-License-Identifier: GPL-2.0 */ /* * KCSAN access checks and modifiers. These can be used to explicitly check * uninstrumented accesses, or change KCSAN checking behaviour of accesses. * * Copyright (C) 2019, Google LLC. */ #ifndef _LINUX_KCSAN_CHECKS_H #define _LINUX_KCSAN_CHECKS_H /* Note: Only include what is already included by compiler.h. */ #include <linux/compiler_attributes.h> #include <linux/types.h> /* Access types -- if KCSAN_ACCESS_WRITE is not set, the access is a read. */ #define KCSAN_ACCESS_WRITE … #define KCSAN_ACCESS_COMPOUND … #define KCSAN_ACCESS_ATOMIC … /* The following are special, and never due to compiler instrumentation. */ #define KCSAN_ACCESS_ASSERT … #define KCSAN_ACCESS_SCOPED … /* * __kcsan_*: Always calls into the runtime when KCSAN is enabled. This may be used * even in compilation units that selectively disable KCSAN, but must use KCSAN * to validate access to an address. Never use these in header files! */ #ifdef CONFIG_KCSAN /** * __kcsan_check_access - check generic access for races * * @ptr: address of access * @size: size of access * @type: access type modifier */ 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 … #define __KCSAN_BARRIER_TO_SIGNAL_FENCE_wmb … #define __KCSAN_BARRIER_TO_SIGNAL_FENCE_rmb … #define __KCSAN_BARRIER_TO_SIGNAL_FENCE_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 * * Supports nesting. */ void kcsan_disable_current(void); /** * kcsan_enable_current - re-enable KCSAN for the current context * * Supports nesting. */ void kcsan_enable_current(void); void kcsan_enable_current_nowarn(void); /* Safe in uaccess regions. */ /** * kcsan_nestable_atomic_begin - begin nestable atomic region * * Accesses within the atomic region may appear to race with other accesses but * should be considered atomic. */ void kcsan_nestable_atomic_begin(void); /** * kcsan_nestable_atomic_end - end nestable atomic region */ void kcsan_nestable_atomic_end(void); /** * kcsan_flat_atomic_begin - begin flat atomic region * * Accesses within the atomic region may appear to race with other accesses but * should be considered atomic. */ void kcsan_flat_atomic_begin(void); /** * kcsan_flat_atomic_end - end flat atomic region */ void kcsan_flat_atomic_end(void); /** * kcsan_atomic_next - consider following accesses as atomic * * Force treating the next n memory accesses for the current context as atomic * operations. * * @n: number of following memory accesses to treat as atomic. */ void kcsan_atomic_next(int n); /** * kcsan_set_access_mask - set access mask * * Set the access mask for all accesses for the current context if non-zero. * Only value changes to bits set in the mask will be reported. * * @mask: bitmask */ void kcsan_set_access_mask(unsigned long mask); /* Scoped access information. */ struct kcsan_scoped_access { … }; /* * Automatically call kcsan_end_scoped_access() when kcsan_scoped_access goes * out of scope; relies on attribute "cleanup", which is supported by all * compilers that support KCSAN. */ #define __kcsan_cleanup_scoped … /** * kcsan_begin_scoped_access - begin scoped access * * Begin scoped access and initialize @sa, which will cause KCSAN to * continuously check the memory range in the current thread until * kcsan_end_scoped_access() is called for @sa. * * Scoped accesses are implemented by appending @sa to an internal list for the * current execution context, and then checked on every call into the KCSAN * runtime. * * @ptr: address of access * @size: size of access * @type: access type modifier * @sa: struct kcsan_scoped_access to use for the scope of the access */ struct kcsan_scoped_access * kcsan_begin_scoped_access(const volatile void *ptr, size_t size, int type, struct kcsan_scoped_access *sa); /** * kcsan_end_scoped_access - end scoped access * * End a scoped access, which will stop KCSAN checking the memory range. * Requires that kcsan_begin_scoped_access() was previously called once for @sa. * * @sa: a previously initialized struct kcsan_scoped_access */ void kcsan_end_scoped_access(struct kcsan_scoped_access *sa); #else /* CONFIG_KCSAN */ 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) { } static inline void kcsan_nestable_atomic_begin(void) { } static inline void kcsan_nestable_atomic_end(void) { } static inline void kcsan_flat_atomic_begin(void) { } static inline void kcsan_flat_atomic_end(void) { } static inline void kcsan_atomic_next(int n) { } static inline void kcsan_set_access_mask(unsigned long mask) { } struct kcsan_scoped_access { }; #define __kcsan_cleanup_scoped … static inline struct kcsan_scoped_access * kcsan_begin_scoped_access(const volatile void *ptr, size_t size, int type, struct kcsan_scoped_access *sa) { return sa; } static inline void kcsan_end_scoped_access(struct kcsan_scoped_access *sa) { } #endif /* CONFIG_KCSAN */ #ifdef __SANITIZE_THREAD__ /* * Only calls into the runtime when the particular compilation unit has KCSAN * instrumentation enabled. May be used in header files. */ #define kcsan_check_access … /* * Only use these to disable KCSAN for accesses in the current compilation unit; * calls into libraries may still perform KCSAN checks. */ #define __kcsan_disable_current … #define __kcsan_enable_current … #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 /* __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. * * These are all macros, like <asm/barrier.h>, since some architectures use them * in non-static inline functions. */ #define __KCSAN_BARRIER_TO_SIGNAL_FENCE … #define kcsan_mb … #define kcsan_wmb … #define kcsan_rmb … #define kcsan_release … #elif defined(CONFIG_KCSAN_WEAK_MEMORY) && defined(__KCSAN_INSTRUMENT_BARRIERS__) #define kcsan_mb … #define kcsan_wmb … #define kcsan_rmb … #define kcsan_release … #else /* CONFIG_KCSAN_WEAK_MEMORY && ... */ #define kcsan_mb() … #define kcsan_wmb() … #define kcsan_rmb() … #define kcsan_release() … #endif /* CONFIG_KCSAN_WEAK_MEMORY && ... */ /** * __kcsan_check_read - check regular read access for races * * @ptr: address of access * @size: size of access */ #define __kcsan_check_read(ptr, size) … /** * __kcsan_check_write - check regular write access for races * * @ptr: address of access * @size: size of access */ #define __kcsan_check_write(ptr, size) … /** * __kcsan_check_read_write - check regular read-write access for races * * @ptr: address of access * @size: size of access */ #define __kcsan_check_read_write(ptr, size) … /** * kcsan_check_read - check regular read access for races * * @ptr: address of access * @size: size of access */ #define kcsan_check_read(ptr, size) … /** * kcsan_check_write - check regular write access for races * * @ptr: address of access * @size: size of access */ #define kcsan_check_write(ptr, size) … /** * kcsan_check_read_write - check regular read-write access for races * * @ptr: address of access * @size: size of access */ #define kcsan_check_read_write(ptr, size) … /* * Check for atomic accesses: if atomic accesses are not ignored, this simply * aliases to kcsan_check_access(), otherwise becomes a no-op. */ #ifdef CONFIG_KCSAN_IGNORE_ATOMICS #define kcsan_check_atomic_read … #define kcsan_check_atomic_write … #define kcsan_check_atomic_read_write … #else #define kcsan_check_atomic_read(ptr, size) … #define kcsan_check_atomic_write(ptr, size) … #define kcsan_check_atomic_read_write(ptr, size) … #endif /** * ASSERT_EXCLUSIVE_WRITER - assert no concurrent writes to @var * * Assert that there are no concurrent writes to @var; other readers are * allowed. This assertion can be used to specify properties of concurrent code, * where violation cannot be detected as a normal data race. * * For example, if we only have a single writer, but multiple concurrent * readers, to avoid data races, all these accesses must be marked; even * concurrent marked writes racing with the single writer are bugs. * Unfortunately, due to being marked, they are no longer data races. For cases * like these, we can use the macro as follows: * * .. code-block:: c * * void writer(void) { * spin_lock(&update_foo_lock); * ASSERT_EXCLUSIVE_WRITER(shared_foo); * WRITE_ONCE(shared_foo, ...); * spin_unlock(&update_foo_lock); * } * void reader(void) { * // update_foo_lock does not need to be held! * ... = READ_ONCE(shared_foo); * } * * Note: ASSERT_EXCLUSIVE_WRITER_SCOPED(), if applicable, performs more thorough * checking if a clear scope where no concurrent writes are expected exists. * * @var: variable to assert on */ #define ASSERT_EXCLUSIVE_WRITER(var) … /* * Helper macros for implementation of for ASSERT_EXCLUSIVE_*_SCOPED(). @id is * expected to be unique for the scope in which instances of kcsan_scoped_access * are declared. */ #define __kcsan_scoped_name(c, suffix) … #define __ASSERT_EXCLUSIVE_SCOPED(var, type, id) … /** * ASSERT_EXCLUSIVE_WRITER_SCOPED - assert no concurrent writes to @var in scope * * Scoped variant of ASSERT_EXCLUSIVE_WRITER(). * * Assert that there are no concurrent writes to @var for the duration of the * scope in which it is introduced. This provides a better way to fully cover * the enclosing scope, compared to multiple ASSERT_EXCLUSIVE_WRITER(), and * increases the likelihood for KCSAN to detect racing accesses. * * For example, it allows finding race-condition bugs that only occur due to * state changes within the scope itself: * * .. code-block:: c * * void writer(void) { * spin_lock(&update_foo_lock); * { * ASSERT_EXCLUSIVE_WRITER_SCOPED(shared_foo); * WRITE_ONCE(shared_foo, 42); * ... * // shared_foo should still be 42 here! * } * spin_unlock(&update_foo_lock); * } * void buggy(void) { * if (READ_ONCE(shared_foo) == 42) * WRITE_ONCE(shared_foo, 1); // bug! * } * * @var: variable to assert on */ #define ASSERT_EXCLUSIVE_WRITER_SCOPED(var) … /** * ASSERT_EXCLUSIVE_ACCESS - assert no concurrent accesses to @var * * Assert that there are no concurrent accesses to @var (no readers nor * writers). This assertion can be used to specify properties of concurrent * code, where violation cannot be detected as a normal data race. * * For example, where exclusive access is expected after determining no other * users of an object are left, but the object is not actually freed. We can * check that this property actually holds as follows: * * .. code-block:: c * * if (refcount_dec_and_test(&obj->refcnt)) { * ASSERT_EXCLUSIVE_ACCESS(*obj); * do_some_cleanup(obj); * release_for_reuse(obj); * } * * Note: * * 1. ASSERT_EXCLUSIVE_ACCESS_SCOPED(), if applicable, performs more thorough * checking if a clear scope where no concurrent accesses are expected exists. * * 2. For cases where the object is freed, `KASAN <kasan.html>`_ is a better * fit to detect use-after-free bugs. * * @var: variable to assert on */ #define ASSERT_EXCLUSIVE_ACCESS(var) … /** * ASSERT_EXCLUSIVE_ACCESS_SCOPED - assert no concurrent accesses to @var in scope * * Scoped variant of ASSERT_EXCLUSIVE_ACCESS(). * * Assert that there are no concurrent accesses to @var (no readers nor writers) * for the entire duration of the scope in which it is introduced. This provides * a better way to fully cover the enclosing scope, compared to multiple * ASSERT_EXCLUSIVE_ACCESS(), and increases the likelihood for KCSAN to detect * racing accesses. * * @var: variable to assert on */ #define ASSERT_EXCLUSIVE_ACCESS_SCOPED(var) … /** * ASSERT_EXCLUSIVE_BITS - assert no concurrent writes to subset of bits in @var * * Bit-granular variant of ASSERT_EXCLUSIVE_WRITER(). * * Assert that there are no concurrent writes to a subset of bits in @var; * concurrent readers are permitted. This assertion captures more detailed * bit-level properties, compared to the other (word granularity) assertions. * Only the bits set in @mask are checked for concurrent modifications, while * ignoring the remaining bits, i.e. concurrent writes (or reads) to ~mask bits * are ignored. * * Use this for variables, where some bits must not be modified concurrently, * yet other bits are expected to be modified concurrently. * * For example, variables where, after initialization, some bits are read-only, * but other bits may still be modified concurrently. A reader may wish to * assert that this is true as follows: * * .. code-block:: c * * ASSERT_EXCLUSIVE_BITS(flags, READ_ONLY_MASK); * foo = (READ_ONCE(flags) & READ_ONLY_MASK) >> READ_ONLY_SHIFT; * * Note: The access that immediately follows ASSERT_EXCLUSIVE_BITS() is assumed * to access the masked bits only, and KCSAN optimistically assumes it is * therefore safe, even in the presence of data races, and marking it with * READ_ONCE() is optional from KCSAN's point-of-view. We caution, however, that * it may still be advisable to do so, since we cannot reason about all compiler * optimizations when it comes to bit manipulations (on the reader and writer * side). If you are sure nothing can go wrong, we can write the above simply * as: * * .. code-block:: c * * ASSERT_EXCLUSIVE_BITS(flags, READ_ONLY_MASK); * foo = (flags & READ_ONLY_MASK) >> READ_ONLY_SHIFT; * * Another example, where this may be used, is when certain bits of @var may * only be modified when holding the appropriate lock, but other bits may still * be modified concurrently. Writers, where other bits may change concurrently, * could use the assertion as follows: * * .. code-block:: c * * spin_lock(&foo_lock); * ASSERT_EXCLUSIVE_BITS(flags, FOO_MASK); * old_flags = flags; * new_flags = (old_flags & ~FOO_MASK) | (new_foo << FOO_SHIFT); * if (cmpxchg(&flags, old_flags, new_flags) != old_flags) { ... } * spin_unlock(&foo_lock); * * @var: variable to assert on * @mask: only check for modifications to bits set in @mask */ #define ASSERT_EXCLUSIVE_BITS(var, mask) … #endif /* _LINUX_KCSAN_CHECKS_H */
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