[PATCH v2 0/2] hardening: Enable i386 FORTIFY_SOURCE on Clang 16+

[PATCH v2 0/2] hardening: Enable i386 FORTIFY_SOURCE on Clang 16+

[Kees Cook]

Hi,

This drops -ffreestanding for i386 unconditionally for GCC, and on
Clang version 16 and later. FORTIFY_SOURCE depends on the libcall
optimizations made without -ffreestanding on Clang. On GCC, there is no
expected differences. With that done, it's possible to gain Clang
FORTIFY_SOURCE coverage on i386 again, though only for Clang 16+.

-Kees


 v1: https://lore.kernel.org/lkml/20250303214929.work.499-kees@kernel.org/
 v2: drop -ffreestanding (Nathan)

Kees Cook (2):
  x86/build: Remove -ffreestanding on i386 with GCC
  hardening: Enable i386 FORTIFY_SOURCE on Clang 16+

 arch/x86/Makefile          | 2 ++
 security/Kconfig.hardening | 2 +-
 2 files changed, 3 insertions(+), 1 deletion(-)

-- 
2.34.1

[PATCH v2 1/2] x86/build: Remove -ffreestanding on i386 with GCC

[Kees Cook]

The use of -ffreestanding is a leftover that is only needed for certain
versions of Clang. Adjust this to be Clang-only. A later patch will make
this a versioned check.

Signed-off-by: Kees Cook <kees@kernel.org>
---
Cc: Nathan Chancellor <nathan@kernel.org>
Cc: Nick Desaulniers <nick.desaulniers+lkml@gmail.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: x86@kernel.org
Cc: "H. Peter Anvin" <hpa@zytor.com>
---
 arch/x86/Makefile | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/arch/x86/Makefile b/arch/x86/Makefile
index 5b773b34768d..d25ed25fb7d9 100644
--- a/arch/x86/Makefile
+++ b/arch/x86/Makefile
@@ -137,8 +137,10 @@ ifeq ($(CONFIG_X86_32),y)
         include $(srctree)/arch/x86/Makefile_32.cpu
         KBUILD_CFLAGS += $(cflags-y)
 
+    ifeq ($(CONFIG_CC_IS_CLANG),y)
         # temporary until string.h is fixed
         KBUILD_CFLAGS += -ffreestanding
+    endif
 
     ifeq ($(CONFIG_STACKPROTECTOR),y)
         ifeq ($(CONFIG_SMP),y)
-- 
2.34.1

Re: [PATCH v2 1/2] x86/build: Remove -ffreestanding on i386 with GCC

[Ingo Molnar]

* Kees Cook <kees@kernel.org> wrote:

> The use of -ffreestanding is a leftover that is only needed for certain
> versions of Clang. Adjust this to be Clang-only. A later patch will make
> this a versioned check.
> 
> Signed-off-by: Kees Cook <kees@kernel.org>
> ---
> Cc: Nathan Chancellor <nathan@kernel.org>
> Cc: Nick Desaulniers <nick.desaulniers+lkml@gmail.com>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: Borislav Petkov <bp@alien8.de>
> Cc: Dave Hansen <dave.hansen@linux.intel.com>
> Cc: x86@kernel.org
> Cc: "H. Peter Anvin" <hpa@zytor.com>
> ---
>  arch/x86/Makefile | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/arch/x86/Makefile b/arch/x86/Makefile
> index 5b773b34768d..d25ed25fb7d9 100644
> --- a/arch/x86/Makefile
> +++ b/arch/x86/Makefile
> @@ -137,8 +137,10 @@ ifeq ($(CONFIG_X86_32),y)
>          include $(srctree)/arch/x86/Makefile_32.cpu
>          KBUILD_CFLAGS += $(cflags-y)
>  
> +    ifeq ($(CONFIG_CC_IS_CLANG),y)
>          # temporary until string.h is fixed
>          KBUILD_CFLAGS += -ffreestanding
> +    endif

Acked-by: Ingo Molnar <mingo@kernel.org>

	Ingo

Re: [PATCH v2 1/2] x86/build: Remove -ffreestanding on i386 with GCC

[Nathan Chancellor]

On Fri, Mar 07, 2025 at 08:29:25PM -0800, Kees Cook wrote:
> The use of -ffreestanding is a leftover that is only needed for certain
> versions of Clang. Adjust this to be Clang-only. A later patch will make
> this a versioned check.
> 
> Signed-off-by: Kees Cook <kees@kernel.org>

This could also adjust the comment but it is probably not that big of a
deal since the "temporary" is already pretty stale.

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

> ---
> Cc: Nathan Chancellor <nathan@kernel.org>
> Cc: Nick Desaulniers <nick.desaulniers+lkml@gmail.com>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: Borislav Petkov <bp@alien8.de>
> Cc: Dave Hansen <dave.hansen@linux.intel.com>
> Cc: x86@kernel.org
> Cc: "H. Peter Anvin" <hpa@zytor.com>
> ---
>  arch/x86/Makefile | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/arch/x86/Makefile b/arch/x86/Makefile
> index 5b773b34768d..d25ed25fb7d9 100644
> --- a/arch/x86/Makefile
> +++ b/arch/x86/Makefile
> @@ -137,8 +137,10 @@ ifeq ($(CONFIG_X86_32),y)
>          include $(srctree)/arch/x86/Makefile_32.cpu
>          KBUILD_CFLAGS += $(cflags-y)
>  
> +    ifeq ($(CONFIG_CC_IS_CLANG),y)
>          # temporary until string.h is fixed
>          KBUILD_CFLAGS += -ffreestanding
> +    endif
>  
>      ifeq ($(CONFIG_STACKPROTECTOR),y)
>          ifeq ($(CONFIG_SMP),y)
> -- 
> 2.34.1
> 

Re: [PATCH v2 1/2] x86/build: Remove -ffreestanding on i386 with GCC

[Kees Cook]

On Sat, Mar 08, 2025 at 10:17:46AM +0100, Nathan Chancellor wrote:
> On Fri, Mar 07, 2025 at 08:29:25PM -0800, Kees Cook wrote:
> > The use of -ffreestanding is a leftover that is only needed for certain
> > versions of Clang. Adjust this to be Clang-only. A later patch will make
> > this a versioned check.
> > 
> > Signed-off-by: Kees Cook <kees@kernel.org>
> 
> This could also adjust the comment but it is probably not that big of a
> deal since the "temporary" is already pretty stale.

Ah yeah, good call. I'll fix that up locally.

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

Thanks!

-Kees

-- 
Kees Cook

[PATCH v2 2/2] hardening: Enable i386 FORTIFY_SOURCE on Clang 16+

[Kees Cook]

The i386 regparm bug exposed with FORTIFY_SOURCE with Clang was fixed
in Clang 16[1].

Link: https://github.com/llvm/llvm-project/commit/c167c0a4dcdb998affb2756ce76903a12f7d8ca5 [1]
Signed-off-by: Kees Cook <kees@kernel.org>
---
 arch/x86/Makefile          | 2 +-
 security/Kconfig.hardening | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/Makefile b/arch/x86/Makefile
index d25ed25fb7d9..917459d1ad40 100644
--- a/arch/x86/Makefile
+++ b/arch/x86/Makefile
@@ -137,7 +137,7 @@ ifeq ($(CONFIG_X86_32),y)
         include $(srctree)/arch/x86/Makefile_32.cpu
         KBUILD_CFLAGS += $(cflags-y)
 
-    ifeq ($(CONFIG_CC_IS_CLANG),y)
+    ifneq ($(call clang-min-version, 160000),y)
         # temporary until string.h is fixed
         KBUILD_CFLAGS += -ffreestanding
     endif
diff --git a/security/Kconfig.hardening b/security/Kconfig.hardening
index 23ffb0d7c845..c17366ce8224 100644
--- a/security/Kconfig.hardening
+++ b/security/Kconfig.hardening
@@ -286,7 +286,7 @@ config FORTIFY_SOURCE
 	bool "Harden common str/mem functions against buffer overflows"
 	depends on ARCH_HAS_FORTIFY_SOURCE
 	# https://github.com/llvm/llvm-project/issues/53645
-	depends on !CC_IS_CLANG || !X86_32
+	depends on !X86_32 || !CC_IS_CLANG || CLANG_VERSION >= 160000
 	help
 	  Detect overflows of buffers in common string and memory functions
 	  where the compiler can determine and validate the buffer sizes.
-- 
2.34.1

Re: [PATCH v2 2/2] hardening: Enable i386 FORTIFY_SOURCE on Clang 16+

[Nathan Chancellor]

On Fri, Mar 07, 2025 at 08:29:26PM -0800, Kees Cook wrote:
> The i386 regparm bug exposed with FORTIFY_SOURCE with Clang was fixed
> in Clang 16[1].
> 
> Link: https://github.com/llvm/llvm-project/commit/c167c0a4dcdb998affb2756ce76903a12f7d8ca5 [1]
> Signed-off-by: Kees Cook <kees@kernel.org>

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

> ---
>  arch/x86/Makefile          | 2 +-
>  security/Kconfig.hardening | 2 +-
>  2 files changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/Makefile b/arch/x86/Makefile
> index d25ed25fb7d9..917459d1ad40 100644
> --- a/arch/x86/Makefile
> +++ b/arch/x86/Makefile
> @@ -137,7 +137,7 @@ ifeq ($(CONFIG_X86_32),y)
>          include $(srctree)/arch/x86/Makefile_32.cpu
>          KBUILD_CFLAGS += $(cflags-y)
>  
> -    ifeq ($(CONFIG_CC_IS_CLANG),y)
> +    ifneq ($(call clang-min-version, 160000),y)
>          # temporary until string.h is fixed
>          KBUILD_CFLAGS += -ffreestanding
>      endif
> diff --git a/security/Kconfig.hardening b/security/Kconfig.hardening
> index 23ffb0d7c845..c17366ce8224 100644
> --- a/security/Kconfig.hardening
> +++ b/security/Kconfig.hardening
> @@ -286,7 +286,7 @@ config FORTIFY_SOURCE
>  	bool "Harden common str/mem functions against buffer overflows"
>  	depends on ARCH_HAS_FORTIFY_SOURCE
>  	# https://github.com/llvm/llvm-project/issues/53645
> -	depends on !CC_IS_CLANG || !X86_32
> +	depends on !X86_32 || !CC_IS_CLANG || CLANG_VERSION >= 160000
>  	help
>  	  Detect overflows of buffers in common string and memory functions
>  	  where the compiler can determine and validate the buffer sizes.
> -- 
> 2.34.1
>