Commit f0202b8c authored Feb 08, 2022 by Kees Cook

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@google.com>
Cc: Nathan Chancellor <nathan@kernel.org>
Cc: llvm@lists.linux.dev
Reviewed-by: Miguel Ojeda <ojeda@kernel.org>
Signed-off-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Link: https://lore.kernel.org/r/20220208225350.1331628-3-keescook@chromium.org

parent f3611431

include/linux/compiler_attributes.h

+14 −0

Original line number	Diff line number	Diff line
		@@ -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
		*/