Re: [PATCH 1/3] retpolines: Only enable retpoline when compiler support it

[Masahiro Yamada]

Hi,



On Tue, Oct 30, 2018 at 3:57 PM Zhenzhong Duan
<zhenzhong.duan@xxxxxxxxxx> wrote:
>
> Since retpoline capable compilers are widely available, make
> CONFIG_RETPOLINE hard depend on it.
>
> Change KBUILD to use CONFIG_RETPOLINE_SUPPORT to avoid conflict with
> CONFIG_RETPOLINE which is used by kernel.
>
> With all that stuff, the check of RETPOLINE is changed to
> CONFIG_RETPOLINE.
>
> This change is based on suggestion in https://lkml.org/lkml/2018/9/18/1016
>
> Signed-off-by: Zhenzhong Duan <zhenzhong.duan@xxxxxxxxxx>
> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> Cc: Borislav Petkov <bp@xxxxxxx>
> Cc: Daniel Borkmann <daniel@xxxxxxxxxxxxx>
> Cc: David Woodhouse <dwmw@xxxxxxxxxxxx>
> Cc: H. Peter Anvin <hpa@xxxxxxxxx>
> Cc: Ingo Molnar <mingo@xxxxxxxxxx>
> Cc: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
> Cc: Andy Lutomirski <luto@xxxxxxxxxx>
> Cc: Masahiro Yamada <yamada.masahiro@xxxxxxxxxxxxx>
> Cc: Michal Marek <michal.lkml@xxxxxxxxxxx>
> ---


Instead of adding another CONFIG option,
does it make sense to add compiler support checks
to 'depends on' syntax ?


config RETPOLINE
         bool "Avoid speculative indirect branches in kernel"
         depends on $(cc-option,-mindirect-branch=thunk-extern
-mindirect-branch-register) || \
                    $(cc-option,-mretpoline-external-thunk)
         default y
         select STACK_VALIDATION if HAVE_STACK_VALIDATION






-- 
Best Regards
Masahiro Yamada