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Diffstat (limited to 'include/linux/kcsan-checks.h')
| -rw-r--r-- | include/linux/kcsan-checks.h | 430 |
1 files changed, 430 insertions, 0 deletions
diff --git a/include/linux/kcsan-checks.h b/include/linux/kcsan-checks.h new file mode 100644 index 000000000000..7b0b9c44f5f3 --- /dev/null +++ b/include/linux/kcsan-checks.h @@ -0,0 +1,430 @@ +/* SPDX-License-Identifier: GPL-2.0 */ + +#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 TYPE MODIFIERS + * + * <none>: normal read access; + * WRITE : write access; + * ATOMIC: access is atomic; + * ASSERT: access is not a regular access, but an assertion; + * SCOPED: access is a scoped access; + */ +#define KCSAN_ACCESS_WRITE 0x1 +#define KCSAN_ACCESS_ATOMIC 0x2 +#define KCSAN_ACCESS_ASSERT 0x4 +#define KCSAN_ACCESS_SCOPED 0x8 + +/* + * __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); + +/** + * 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 { + struct list_head list; + const volatile void *ptr; + size_t size; + int type; +}; +/* + * 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 \ + __maybe_unused __attribute__((__cleanup__(kcsan_end_scoped_access))) + +/** + * 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_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 __maybe_unused +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 __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 kcsan_disable_current +#define __kcsan_enable_current kcsan_enable_current_nowarn +#else +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 + +/** + * __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_access(ptr, size, 0) + +/** + * __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_access(ptr, size, KCSAN_ACCESS_WRITE) + +/** + * 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_access(ptr, size, 0) + +/** + * 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_access(ptr, size, KCSAN_ACCESS_WRITE) + +/* + * 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(...) do { } while (0) +#define kcsan_check_atomic_write(...) do { } while (0) +#else +#define kcsan_check_atomic_read(ptr, size) \ + kcsan_check_access(ptr, size, KCSAN_ACCESS_ATOMIC) +#define kcsan_check_atomic_write(ptr, size) \ + kcsan_check_access(ptr, size, KCSAN_ACCESS_ATOMIC | KCSAN_ACCESS_WRITE) +#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) \ + __kcsan_check_access(&(var), sizeof(var), KCSAN_ACCESS_ASSERT) + +/* + * 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) __kcsan_scoped_##c##suffix +#define __ASSERT_EXCLUSIVE_SCOPED(var, type, id) \ + struct kcsan_scoped_access __kcsan_scoped_name(id, _) \ + __kcsan_cleanup_scoped; \ + struct kcsan_scoped_access *__kcsan_scoped_name(id, _dummy_p) \ + __maybe_unused = kcsan_begin_scoped_access( \ + &(var), sizeof(var), KCSAN_ACCESS_SCOPED | (type), \ + &__kcsan_scoped_name(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_SCOPED(var, KCSAN_ACCESS_ASSERT, __COUNTER__) + +/** + * 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: ASSERT_EXCLUSIVE_ACCESS_SCOPED(), if applicable, performs more thorough + * checking if a clear scope where no concurrent accesses are expected exists. + * + * Note: 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) \ + __kcsan_check_access(&(var), sizeof(var), KCSAN_ACCESS_WRITE | KCSAN_ACCESS_ASSERT) + +/** + * 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_SCOPED(var, KCSAN_ACCESS_WRITE | KCSAN_ACCESS_ASSERT, __COUNTER__) + +/** + * 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) \ + do { \ + kcsan_set_access_mask(mask); \ + __kcsan_check_access(&(var), sizeof(var), KCSAN_ACCESS_ASSERT);\ + kcsan_set_access_mask(0); \ + kcsan_atomic_next(1); \ + } while (0) + +#endif /* _LINUX_KCSAN_CHECKS_H */ |