linux-kernel - Re: Security fix for remapping of page 0 (was [PATCH] Change ZERO_SIZE

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Message-ID: <20090607102910.GA1592@ucw.cz>
Date:	Sun, 7 Jun 2009 12:29:11 +0200
From:	Pavel Machek <pavel@....cz>
To:	Christoph Lameter <cl@...ux-foundation.org>
Cc:	"Larry H." <research@...reption.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-mm@...ck.org, Alan Cox <alan@...rguk.ukuu.org.uk>,
	Rik van Riel <riel@...hat.com>, linux-kernel@...r.kernel.org,
	pageexec@...email.hu
Subject: Re: Security fix for remapping of page 0 (was [PATCH] Change
	ZERO_SIZE_PTR to point at unmapped space)

Hi!

> Ok. So what we need to do is stop this toying around with remapping of
> page 0. The following patch contains a fix and a test program that
> demonstrates the issue.
> 
> 
> Subject: [Security] Do not allow remapping of page 0 via MAP_FIXED
> 
> If one remaps page 0 then the kernel checks for NULL pointers of various
> flavors are bypassed and this may be exploited in various creative ways
> to transfer data from kernel space to user space.

Yes, mmap() at page zero 0 makes exploits harder; and yes disabling it
may be useful (but we tried that before, see Alan's comment). But that
does not it mean it deserves _security_ label. Call it robustness or
something....
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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