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

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Message-ID: <BANLkTinALOXLa1HYyCQBwYcBo=N0eVcPUg@mail.gmail.com>
Date:	Wed, 18 May 2011 03:08:54 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Ingo Molnar <mingo@...e.hu>
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

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.

              Linus
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