aboutsummaryrefslogtreecommitdiffstats
path: root/include/linux/kcsan-checks.h
diff options
context:
space:
mode:
Diffstat (limited to 'include/linux/kcsan-checks.h')
-rw-r--r--include/linux/kcsan-checks.h430
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 */

Privacy Policy