Re: [PATCH v6 12/15] arm64: vdso: disable Shadow Call Stack

Will Deacon
2020-01-16T18:35:57Z

On Fri, Dec 06, 2019 at 02:13:48PM -0800, Sami Tolvanen wrote:
> Shadow stacks are only available in the kernel, so disable SCS
> instrumentation for the vDSO.
>
> Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
> Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
> Reviewed-by: Kees Cook <keescook@chromium.org>
> Reviewed-by: Mark Rutland <mark.rutland@arm.com>
> ---
> arch/arm64/kernel/vdso/Makefile | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/arm64/kernel/vdso/Makefile b/arch/arm64/kernel/vdso/Makefile
> index dd2514bb1511..a87a4f11724e 100644
> --- a/arch/arm64/kernel/vdso/Makefile
> +++ b/arch/arm64/kernel/vdso/Makefile
> @@ -25,7 +25,7 @@ ccflags-y += -DDISABLE_BRANCH_PROFILING
>
> VDSO_LDFLAGS := -Bsymbolic
>
> -CFLAGS_REMOVE_vgettimeofday.o = $(CC_FLAGS_FTRACE) -Os
> +CFLAGS_REMOVE_vgettimeofday.o = $(CC_FLAGS_FTRACE) -Os $(CC_FLAGS_SCS)

Should we be removing -ffixed-x18 too, or does that not propagate here
anyway?

Will