Commit e6f3b3c9 authored by Sami Tolvanen's avatar Sami Tolvanen Committed by Kees Cook
Browse files

cfi: Use __builtin_function_start 

Clang 14 added support for the __builtin_function_start function,
which allows us to implement the function_nocfi macro without
architecture-specific inline assembly and in a way that also works
with static initializers.

Change CONFIG_CFI_CLANG to depend on Clang >= 14, define
function_nocfi using __builtin_function_start, and remove the arm64
inline assembly implementation.

Link: https://github.com/llvm/llvm-project/commit/ec2e26eaf63558934f5b73a6e530edc453cf9508
Link: https://github.com/ClangBuiltLinux/linux/issues/1353


Signed-off-by: default avatarSami Tolvanen <samitolvanen@google.com>
Reviewed-by: default avatarNick Desaulniers <ndesaulniers@google.com>
Reviewed-by: default avatarMark Rutland <mark.rutland@arm.com>
Tested-by: default avatarMark Rutland <mark.rutland@arm.com>
Acked-by: Will Deacon <will@kernel.org> # arm64
Reviewed-by: default avatarNathan Chancellor <nathan@kernel.org>
Signed-off-by: default avatarKees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20220405221618.633743-1-samitolvanen@google.com
parent 75c1182e

arch/Kconfig

+1 −4
Original line number Diff line number Diff line
@@ -723,10 +723,7 @@ config ARCH_SUPPORTS_CFI_CLANG 
config CFI_CLANG

	bool "Use Clang's Control Flow Integrity (CFI)"

	depends on LTO_CLANG && ARCH_SUPPORTS_CFI_CLANG

	# Clang >= 12:

	# - https://bugs.llvm.org/show_bug.cgi?id=46258

	# - https://bugs.llvm.org/show_bug.cgi?id=47479

	depends on CLANG_VERSION >= 120000

	depends on CLANG_VERSION >= 140000

	select KALLSYMS

	help

	  This option enables Clang’s forward-edge Control Flow Integrity

arch/arm64/include/asm/compiler.h

+0 −16
Original line number Diff line number Diff line
@@ -23,20 +23,4 @@ 
#define __builtin_return_address(val)					\

	(void *)(ptrauth_clear_pac((unsigned long)__builtin_return_address(val)))



#ifdef CONFIG_CFI_CLANG

/*

 * With CONFIG_CFI_CLANG, the compiler replaces function address

 * references with the address of the function's CFI jump table

 * entry. The function_nocfi macro always returns the address of the

 * actual function instead.

 */

#define function_nocfi(x) ({						\

	void *addr;							\

	asm("adrp %0, " __stringify(x) "\n\t"				\

	    "add  %0, %0, :lo12:" __stringify(x)			\

	    : "=r" (addr));						\

	addr;								\

})

#endif



#endif /* __ASM_COMPILER_H */

include/linux/compiler-clang.h

+10 −0
Original line number Diff line number Diff line
@@ -69,6 +69,16 @@ 
#define __nocfi		__attribute__((__no_sanitize__("cfi")))

#define __cficanonical	__attribute__((__cfi_canonical_jump_table__))



#if defined(CONFIG_CFI_CLANG)

/*

 * With CONFIG_CFI_CLANG, the compiler replaces function address

 * references with the address of the function's CFI jump table

 * entry. The function_nocfi macro always returns the address of the

 * actual function instead.

 */

#define function_nocfi(x)	__builtin_function_start(x)

#endif



/*

 * Turn individual warnings and errors on and off locally, depending

 * on version.