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

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Message-ID: <20090603171409.5c60422c@lxorguk.ukuu.org.uk>
Date:	Wed, 3 Jun 2009 17:14:09 +0100
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Christoph Lameter <cl@...ux-foundation.org>,
	"Larry H." <research@...reption.com>, linux-mm@...ck.org,
	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)

> It defaults to 64kB in at least the x86 defconfig files, but to 0 in the 
> Kconfig defaults. Also, for some reason it has a "depends on SECURITY", 
> which means that if you just default to the old-style unix security you'll 
> lose it.
> 
> So there are several ways to disable it by mistake. I don't know what 
> distros do.

Fedora at least uses SELinux to manage it. You need some kind of security
policy engine running as a few apps really need to map low space (mostly
for vm86)

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