diff mbox series

[v2] cfi: Use __builtin_function_start

Message ID 20220405221618.633743-1-samitolvanen@google.com (mailing list archive)
State New, archived
Headers show
Series [v2] cfi: Use __builtin_function_start | expand

Commit Message

Sami Tolvanen April 5, 2022, 10:16 p.m. UTC
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: Sami Tolvanen <samitolvanen@google.com>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Reviewed-by: Mark Rutland <mark.rutland@arm.com>
Tested-by: Mark Rutland <mark.rutland@arm.com>
Acked-by: Will Deacon <will@kernel.org> # arm64
---
v2:
- Changed CFI_CLANG to depend on Clang 14 instead of
  __builtin_function_start.
- Squashed all three patches into one.

---
 arch/Kconfig                      |  5 +----
 arch/arm64/include/asm/compiler.h | 16 ----------------
 include/linux/compiler-clang.h    | 10 ++++++++++
 3 files changed, 11 insertions(+), 20 deletions(-)

Comments

Nathan Chancellor April 5, 2022, 10:20 p.m. UTC | #1
On Tue, Apr 05, 2022 at 03:16:18PM -0700, Sami Tolvanen wrote:
> 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: Sami Tolvanen <samitolvanen@google.com>
> Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
> Reviewed-by: Mark Rutland <mark.rutland@arm.com>
> Tested-by: Mark Rutland <mark.rutland@arm.com>
> Acked-by: Will Deacon <will@kernel.org> # arm64

Reviewed-by: Nathan Chancellor <nathan@kernel.org>

> ---
> v2:
> - Changed CFI_CLANG to depend on Clang 14 instead of
>   __builtin_function_start.
> - Squashed all three patches into one.
> 
> ---
>  arch/Kconfig                      |  5 +----
>  arch/arm64/include/asm/compiler.h | 16 ----------------
>  include/linux/compiler-clang.h    | 10 ++++++++++
>  3 files changed, 11 insertions(+), 20 deletions(-)
> 
> diff --git a/arch/Kconfig b/arch/Kconfig
> index 29b0167c088b..c1627bce4a3a 100644
> --- a/arch/Kconfig
> +++ b/arch/Kconfig
> @@ -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
> diff --git a/arch/arm64/include/asm/compiler.h b/arch/arm64/include/asm/compiler.h
> index dc3ea4080e2e..6fb2e6bcc392 100644
> --- a/arch/arm64/include/asm/compiler.h
> +++ b/arch/arm64/include/asm/compiler.h
> @@ -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 */
> diff --git a/include/linux/compiler-clang.h b/include/linux/compiler-clang.h
> index babb1347148c..c84fec767445 100644
> --- a/include/linux/compiler-clang.h
> +++ b/include/linux/compiler-clang.h
> @@ -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.
> -- 
> 2.35.1.1094.g7c7d902a7c-goog
>
Kees Cook April 13, 2022, 7:26 p.m. UTC | #2
On Tue, 5 Apr 2022 15:16:18 -0700, Sami Tolvanen wrote:
> 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.
> 
> [...]

Applied to for-next/hardening, thanks!

[1/1] cfi: Use __builtin_function_start
      https://git.kernel.org/kees/c/e6f3b3c9c109
diff mbox series

Patch

diff --git a/arch/Kconfig b/arch/Kconfig
index 29b0167c088b..c1627bce4a3a 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -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
diff --git a/arch/arm64/include/asm/compiler.h b/arch/arm64/include/asm/compiler.h
index dc3ea4080e2e..6fb2e6bcc392 100644
--- a/arch/arm64/include/asm/compiler.h
+++ b/arch/arm64/include/asm/compiler.h
@@ -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 */
diff --git a/include/linux/compiler-clang.h b/include/linux/compiler-clang.h
index babb1347148c..c84fec767445 100644
--- a/include/linux/compiler-clang.h
+++ b/include/linux/compiler-clang.h
@@ -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.