# Re: \[PATCH v8 12/12\] efi/libstub: disable SCS

- From: Kees Cook \<hidden\>
- Date: 2020-02-19 00:59:25 
- List: linux-arm-kernel
- Page: https://ratatoskr.run/linux-arm-kernel/2020/02/5866916
- Thread: https://ratatoskr.run/linux-arm-kernel/2019/10/5749629/t/5.md

```text
On Tue, Feb 18, 2020 at 04:08:17PM -0800, Sami Tolvanen wrote:
> Disable SCS for the EFI stub and allow x18 to be used.
> 
> Suggested-by: James Morse <james.morse@arm.com>
> Signed-off-by: Sami Tolvanen <samitolvanen@google.com>

Reviewed-by: Kees Cook <redacted>

-Kees

> ---
>  drivers/firmware/efi/libstub/Makefile | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/firmware/efi/libstub/Makefile b/drivers/firmware/efi/libstub/Makefile
> index 98a81576213d..dff9fa5a3f1c 100644
> --- a/drivers/firmware/efi/libstub/Makefile
> +++ b/drivers/firmware/efi/libstub/Makefile
> @@ -30,6 +30,9 @@ KBUILD_CFLAGS			:= $(cflags-y) -DDISABLE_BRANCH_PROFILING \
>  				   $(call cc-option,-fno-stack-protector) \
>  				   -D__DISABLE_EXPORTS
>  
> +#  remove SCS flags from all objects in this directory
> +KBUILD_CFLAGS := $(filter-out -ffixed-x18 $(CC_FLAGS_SCS), $(KBUILD_CFLAGS))
> +
>  GCOV_PROFILE			:= n
>  KASAN_SANITIZE			:= n
>  UBSAN_SANITIZE			:= n
> -- 
> 2.25.0.265.gbab2e86ba0-goog
> 

-- 
Kees Cook

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```