From dd06e72e68bcb4070ef211be100d2896e236c8fb Mon Sep 17 00:00:00 2001 From: Kees Cook Date: Wed, 17 May 2023 12:08:44 -0700 Subject: [PATCH] Compiler Attributes: Add __counted_by macro In an effort to annotate all flexible array members with their run-time size information, the "element_count" attribute is being introduced by Clang[1] and GCC[2] in future releases. This annotation will provide the CONFIG_UBSAN_BOUNDS and CONFIG_FORTIFY_SOURCE features the ability to perform run-time bounds checking on otherwise unknown-size flexible arrays. Even though the attribute is under development, we can start the annotation process in the kernel. This requires defining a macro for it, even if we have to change the name of the actual attribute later. Since it is likely that this attribute may change its name to "counted_by" in the future (to better align with a future total bytes "sized_by" attribute), name the wrapper macro "__counted_by", which also reads more clearly (and concisely) in structure definitions. [1] https://reviews.llvm.org/D148381 [2] https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108896 Cc: Bill Wendling Cc: Qing Zhao Cc: Gustavo A. R. Silva Cc: Nick Desaulniers Cc: Nathan Chancellor Cc: Tom Rix Cc: llvm@lists.linux.dev Signed-off-by: Kees Cook Reviewed-by: Gustavo A. R. Silva Reviewed-by: Nathan Chancellor Acked-by: Miguel Ojeda Link: https://lore.kernel.org/r/20230517190841.gonna.796-kees@kernel.org --- include/linux/compiler_attributes.h | 13 +++++++++++++ 1 file changed, 13 insertions(+) diff --git a/include/linux/compiler_attributes.h b/include/linux/compiler_attributes.h index e659cb6..5588bff 100644 --- a/include/linux/compiler_attributes.h +++ b/include/linux/compiler_attributes.h @@ -124,6 +124,19 @@ #endif /* + * Optional: only supported since gcc >= 14 + * Optional: only supported since clang >= 17 + * + * gcc: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108896 + * clang: https://reviews.llvm.org/D148381 + */ +#if __has_attribute(__element_count__) +# define __counted_by(member) __attribute__((__element_count__(#member))) +#else +# define __counted_by(member) +#endif + +/* * Optional: only supported since clang >= 14.0 * * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-error-function-attribute -- 2.7.4