linux-kernel - Re: [PATCH] x86, vsyscall: add CONFIG to control default

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Date:	Thu, 3 Sep 2015 14:08:40 -0700
From:	Kees Cook <keescook@...omium.org>
To:	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>
Cc:	Josh Triplett <josh@...htriplett.org>,
	Andy Lutomirski <luto@...capital.net>,
	"x86@...nel.org" <x86@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] x86, vsyscall: add CONFIG to control default

On Mon, Aug 31, 2015 at 2:23 PM, Andy Lutomirski <luto@...capital.net> wrote:
> On Aug 31, 2015 1:13 PM, "Kees Cook" <keescook@...omium.org> wrote:
>>
>> On Wed, Aug 12, 2015 at 7:23 PM, Josh Triplett <josh@...htriplett.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@...omium.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.
>
> Native adds almost no code and almost no maintenance burden -- it's
> really just a PTE bit.
>
>>
>> Can someone from the x86 tree take this patch, or are there other
>> things to improve?
>
> It looks good to me.

tglx, hpa, ingo? Can this go into -tip?

Thanks!

-Kees

-- 
Kees Cook
Chrome OS Security
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