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Date: Tue, 8 Feb 2022 14:53:44 -0800 From: Kees Cook <keescook@...omium.org> To: Kees Cook <keescook@...omium.org> Cc: Nick Desaulniers <ndesaulniers@...gle.com>, Nathan Chancellor <nathan@...nel.org>, llvm@...ts.linux.dev, Miguel Ojeda <ojeda@...nel.org>, George Burgess IV <gbiv@...gle.com>, linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org Subject: [PATCH v7 2/8] Compiler Attributes: Add __pass_object_size for Clang In order to gain greater visibility to type information when using __builtin_object_size(), Clang has a function attribute "pass_object_size" that will make size information available for marked arguments in a function by way of implicit additional function arguments that are then wired up the __builtin_object_size(). This is needed to implement FORTIFY_SOURCE in Clang, as a workaround to Clang's __builtin_object_size() having limited visibility[1] into types across function calls (even inlines). This attribute has an additional benefit that it can be used even on non-inline functions to gain argument size information. [1] https://github.com/llvm/llvm-project/issues/53516 Cc: Nick Desaulniers <ndesaulniers@...gle.com> Cc: Nathan Chancellor <nathan@...nel.org> Cc: llvm@...ts.linux.dev Reviewed-by: Miguel Ojeda <ojeda@...nel.org> Signed-off-by: Kees Cook <keescook@...omium.org> --- include/linux/compiler_attributes.h | 14 ++++++++++++++ 1 file changed, 14 insertions(+) diff --git a/include/linux/compiler_attributes.h b/include/linux/compiler_attributes.h index 37e260020221..d0c503772061 100644 --- a/include/linux/compiler_attributes.h +++ b/include/linux/compiler_attributes.h @@ -263,6 +263,20 @@ */ #define __packed __attribute__((__packed__)) +/* + * Note: the "type" argument should match any __builtin_object_size(p, type) usage. + * + * Optional: not supported by gcc. + * Optional: not supported by icc. + * + * clang: https://clang.llvm.org/docs/AttributeReference.html#pass-object-size-pass-dynamic-object-size + */ +#if __has_attribute(__pass_object_size__) +# define __pass_object_size(type) __attribute__((__pass_object_size__(type))) +#else +# define __pass_object_size(type) +#endif + /* * gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-pure-function-attribute */ -- 2.30.2
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