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

From: Kees Cook
Date: Thu Sep 03 2015 - 17:08:46 EST

On Mon, Aug 31, 2015 at 2:23 PM, Andy Lutomirski <luto@xxxxxxxxxxxxxx> wrote:
> On Aug 31, 2015 1:13 PM, "Kees Cook" <keescook@xxxxxxxxxxxx> wrote:
>> On Wed, Aug 12, 2015 at 7:23 PM, Josh Triplett <josh@xxxxxxxxxxxxxxxx> 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@xxxxxxxxxxxx>
>> >
>> > 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?



Kees Cook
Chrome OS Security
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