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Subject: Re: [PATCH] x86, vsyscall: add CONFIG to control default
From: Kees Cook <keescook@chromium.org>
To: Josh Triplett <josh@joshtriplett.org>
Cc: Andy Lutomirski <luto@amacapital.net>,
        Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@redhat.com>,
        "H. Peter Anvin" <hpa@zytor.com>, "x86@kernel.org" <x86@kernel.org>,
        LKML <linux-kernel@vger.kernel.org>
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On Wed, Aug 12, 2015 at 7:23 PM, Josh Triplett <josh@joshtriplett.org> wrote:
> On Wed, Aug 12, 2015 at 05:55:19PM -0700, Kees Cook wrote:
>> Most modern systems can run with vsyscall=none. In an effort to provide
>> a way for build-time defaults to lack legacy settings, this adds a new
>> CONFIG to select the type of vsyscall mapping to use, similar to the
>> existing "vsyscall" command line parameter.
>>
>> Signed-off-by: Kees Cook <keescook@chromium.org>
>
> Seems reasonable to me.  One question, though: is there *any* reason to
> choose "native" over "emulate"?  (Does "emulate" have a sufficient
> performance penalty to matter, and do people running old glibc really
> care about that performance while still not wanting to upgrade?)
> If there is a reason, could you please document it in the
> descriptions of the "native" and "emulate" options (as an upside and a
> downside, respectively)?  If there isn't, you might consider a patch to
> remove "native".

I think "native" is available out of an abundance of caution. Andy
left it available, though I'm not sure if he had plans to remove
"native" entirely.

Can someone from the x86 tree take this patch, or are there other
things to improve?

Thanks!

-Kees

-- 
Kees Cook
Chrome OS Security