linux-kernel - Re: mmap_min_addr and your local LSM (ok, just SELinux)

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Message-ID: <20090728162353.GO15310@basil.fritz.box>
Date:	Tue, 28 Jul 2009 18:23:53 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Kees Cook <kees@...ntu.com>
Cc:	Andi Kleen <andi@...stfloor.org>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	James Morris <jmorris@...ei.org>,
	James Carter <jwcart2@...ho.nsa.gov>,
	Eric Paris <eparis@...hat.com>, linux-kernel@...r.kernel.org,
	linux-security-module@...r.kernel.org, selinux@...ho.nsa.gov,
	Stephen Smalley <sds@...ho.nsa.gov>, spender@...ecurity.net,
	Daniel J Walsh <dwalsh@...hat.com>, cl@...ux-foundation.org,
	Arjan van de Ven <arjan@...radead.org>,
	Chad Sellers <csellers@...sys.com>,
	Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
	mingo@...e.hu
Subject: Re: mmap_min_addr and your local LSM (ok, just SELinux)

> Could the page table flags be used to mask this region?  i.e. force
> PROT_NONE (with the "desired" flags stored elsewhere) and in the segv
> handler check if it is kernel or user space, and then fix-up the flags and
> continue if it's userspace?  (I really don't know the internals on this,
> but it would need to restore PROT_NONE on task-switch or something...)

That's racy with multiple threads.
-Andi

-- 
ak@...ux.intel.com -- Speaking for myself only.
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