linux-kernel - Re: [PATCH] efi/libstub: Only disable stackleak plugin for arm64

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Date:   Tue, 31 Jul 2018 09:51:21 +0100
From:   Will Deacon <will.deacon@....com>
To:     Laura Abbott <labbott@...hat.com>
Cc:     Stephen Rothwell <sfr@...b.auug.org.au>,
        Kees Cook <keescook@...gle.com>,
        Linux-Next Mailing List <linux-next@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Alexander Popov <alex.popov@...ux.com>,
        Catalin Marinas <catalin.marinas@....com>
Subject: Re: [PATCH] efi/libstub: Only disable stackleak plugin for arm64

On Mon, Jul 30, 2018 at 11:31:18AM -0700, Laura Abbott wrote:
> arm64 uses the full KBUILD_CFLAGS for building libstub as opposed
> to x86 which doesn't. This means that x86 doesn't pick up
> the gcc-plugins. We need to disable the stackleak plugin but
> doing this unconditionally breaks x86 build since it doesn't
> have any plugins. Switch to disabling the stackleak plugin for
> arm64 only.
> 
> Signed-off-by: Laura Abbott <labbott@...hat.com>
> ---
>  drivers/firmware/efi/libstub/Makefile | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)

Cheers, Laura, I'll pick this up today. I think we'll need the same thing
for 32-bit ARM if/when they enable support for the plugin.

Will

> diff --git a/drivers/firmware/efi/libstub/Makefile b/drivers/firmware/efi/libstub/Makefile
> index 25dd2a14560d..88c322d7c71e 100644
> --- a/drivers/firmware/efi/libstub/Makefile
> +++ b/drivers/firmware/efi/libstub/Makefile
> @@ -11,7 +11,10 @@ cflags-$(CONFIG_X86)		+= -m$(BITS) -D__KERNEL__ -O2 \
>  				   -fPIC -fno-strict-aliasing -mno-red-zone \
>  				   -mno-mmx -mno-sse -fshort-wchar
>  
> -cflags-$(CONFIG_ARM64)		:= $(subst -pg,,$(KBUILD_CFLAGS)) -fpie
> +# arm64 uses the full KBUILD_CFLAGS so it's necessary to explicitly
> +# disable the stackleak plugin
> +cflags-$(CONFIG_ARM64)		:= $(subst -pg,,$(KBUILD_CFLAGS)) -fpie \
> +				   $(DISABLE_STACKLEAK_PLUGIN)
>  cflags-$(CONFIG_ARM)		:= $(subst -pg,,$(KBUILD_CFLAGS)) \
>  				   -fno-builtin -fpic -mno-single-pic-base
>  
> @@ -21,7 +24,6 @@ KBUILD_CFLAGS			:= $(cflags-y) -DDISABLE_BRANCH_PROFILING \
>  				   -D__NO_FORTIFY \
>  				   $(call cc-option,-ffreestanding) \
>  				   $(call cc-option,-fno-stack-protector) \
> -				   $(DISABLE_STACKLEAK_PLUGIN)
>  
>  GCOV_PROFILE			:= n
>  KASAN_SANITIZE			:= n
> -- 
> 2.17.1
>