Messages in this thread Patch in this message |  | | From | Kees Cook <> | Subject | [PATCH v2] Compiler Attributes: Introduce __access_*() function attribute | Date | Sat, 24 Sep 2022 08:07:15 -0700 |
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Added in GCC 10.1, the "access" function attribute is used to mark pointer arguments for how they are expected to be accessed in a given function. Both their access type (read/write, read-only, or write-only) and bounds are specified.
These can improve GCC's compile-time diagnostics including -Warray-bounds, -Wstringop-overflow, etc, and can affect __builtin_dynamic_object_size() results.
Cc: Miguel Ojeda <ojeda@kernel.org> Cc: Nick Desaulniers <ndesaulniers@google.com> Cc: Nathan Chancellor <nathan@kernel.org> Cc: Tom Rix <trix@redhat.com> Cc: llvm@lists.linux.dev Signed-off-by: Kees Cook <keescook@chromium.org> --- include/linux/compiler_attributes.h | 30 +++++++++++++++++++++++++++++ 1 file changed, 30 insertions(+)
diff --git a/include/linux/compiler_attributes.h b/include/linux/compiler_attributes.h index 9a9907fad6fd..465be5f072ff 100644 --- a/include/linux/compiler_attributes.h +++ b/include/linux/compiler_attributes.h @@ -20,6 +20,36 @@ * Provide links to the documentation of each supported compiler, if it exists. */ +/* + * Optional: only supported since gcc >= 10 + * Optional: not supported by Clang + * + * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-access-function-attribute + * + * While it is legal to provide only the pointer argument position and + * access type, the kernel macros are designed to require also the bounds + * (element count) argument position; if a function has no bounds argument, + * refactor the code to include one. + * + * These can be used multiple times. For example: + * + * __access_wo(2, 3) __access_ro(4, 5) + * int copy_something(struct context *ctx, u32 *dst, size_t dst_count, + * const u8 *src, int src_len); + * + * If "dst" will also be read from, it could use __access_rw(2, 3) instead. + * + */ +#if __has_attribute(__access__) +# define __access_rw(ptr, count) __attribute__((__access__(read_write, ptr, count))) +# define __access_ro(ptr, count) __attribute__((__access__(read_only, ptr, count))) +# define __access_wo(ptr, count) __attribute__((__access__(write_only, ptr, count))) +#else +# define __access_rw(ptr, count) +# define __access_ro(ptr, count) +# define __access_wo(ptr, count) +#endif + /* * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-alias-function-attribute */ -- 2.34.1
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