linux-kernel - Re: [PATCH] x86, x86_64: Fix checks for userspace address limit

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Date:	Wed, 18 May 2011 12:39:19 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Jiri Olsa <jolsa@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>, tglx@...utronix.de,
	mingo@...hat.com, hpa@...or.com, x86@...nel.org,
	linux-kernel@...r.kernel.org,
	Arjan van de Ven <arjan@...radead.org>
Subject: Re: [PATCH] x86, x86_64: Fix checks for userspace address limit


* Linus Torvalds <torvalds@...ux-foundation.org> wrote:

> On Mon, May 16, 2011 at 4:42 AM, Ingo Molnar <mingo@...e.hu> wrote:
> >
> > Hm, something tickles me about this area that we would reintroduce a security
> > hole, that we really wanted to treat the last page of user-space as some sort
> > of guard page but i cannot quite remember it why ...
> >
> > IIRC Linus wrote bits of this so i'm Cc:-ing him just in case he remembers.
> 
> No, I suspect the patch is correct, and it's just a bug. I think it
> comes from the "get_user_X()" cases that afaik use "jae" because they
> add one less than the size (and thus avoid it entirely for the
> single-byte case). See "getuser.S" in the same directory.
> 
> But right now I think I need to do a 2.6.39 release later today (after
> I get some sleep), so doing it as a stable patch (presumably going
> back to pretty much the beginning of time) is probably the right
> thing.

Absolutely - we had this for a long time so it's not a regression and there is 
very little gain from trying to squeeze this fix in so close to v2.6.39 - and 
there are nonzero risks, considering how widely used assembly code this 
changes.

I've queued it up for v2.6.40 with your Acked-by.

Thanks,

	Ingo
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