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

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Date:   Tue, 30 Oct 2018 18:39:24 +0900
From:   Masahiro Yamada <yamada.masahiro@...ionext.com>
To:     zhenzhong.duan@...cle.com
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...hat.com>,
        Andy Lutomirski <luto@...nel.org>, konrad.wilk@...cle.com,
        David Woodhouse <dwmw@...zon.co.uk>,
        Thomas Gleixner <tglx@...utronix.de>, srinivas.eeda@...cle.com,
        Borislav Petkov <bp@...e.de>,
        Daniel Borkmann <daniel@...earbox.net>,
        Michal Marek <michal.lkml@...kovi.net>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        "H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH 1/3] retpolines: Only enable retpoline when compiler
 support it

Hi,



On Tue, Oct 30, 2018 at 3:57 PM Zhenzhong Duan
<zhenzhong.duan@...cle.com> 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@...cle.com>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Borislav Petkov <bp@...e.de>
> Cc: Daniel Borkmann <daniel@...earbox.net>
> Cc: David Woodhouse <dwmw@...zon.co.uk>
> Cc: H. Peter Anvin <hpa@...or.com>
> Cc: Ingo Molnar <mingo@...hat.com>
> Cc: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
> Cc: Andy Lutomirski <luto@...nel.org>
> Cc: Masahiro Yamada <yamada.masahiro@...ionext.com>
> Cc: Michal Marek <michal.lkml@...kovi.net>
> ---


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