linux-kernel - Re: [tip:x86/security] x86: Add NX protection for kernel data

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Message-ID: <20110111233135.GL4979@outflux.net>
Date:	Tue, 11 Jan 2011 15:31:35 -0800
From:	Kees Cook <kees.cook@...onical.com>
To:	mingo@...hat.com, hpa@...or.com, sliakh.lkml@...il.com,
	jmorris@...ei.org, linux-kernel@...r.kernel.org,
	rusty@...tcorp.com.au, torvalds@...ux-foundation.org, ak@....de,
	davej@...hat.com, jiang@...ncsu.edu, arjan@...radead.org,
	castet.matthieu@...e.fr, tglx@...utronix.de, sfr@...b.auug.org.au,
	mingo@...e.hu, Stefan Bader <stefan.bader@...onical.com>
Subject: Re: [tip:x86/security] x86: Add NX protection for kernel data

On Thu, Nov 18, 2010 at 02:08:22PM +0000, tip-bot for Matthieu Castet wrote:
> Commit-ID:  5bd5a452662bc37c54fb6828db1a3faf87e6511c
> Gitweb:     http://git.kernel.org/tip/5bd5a452662bc37c54fb6828db1a3faf87e6511c
> Author:     Matthieu Castet <castet.matthieu@...e.fr>
> AuthorDate: Tue, 16 Nov 2010 22:31:26 +0100
> Committer:  Ingo Molnar <mingo@...e.hu>
> CommitDate: Thu, 18 Nov 2010 12:52:04 +0100
> 
> x86: Add NX protection for kernel data

[I'd sent this in reply to the wrong patch before, resending now...]

Hi,

I was just shown this[1] on Xen from an Ubuntu bug report[2].

[    1.230382] NX-protecting the kernel data: 3884k
[    1.231002] BUG: unable to handle kernel paging request at c1782ae0
...
[    1.231145] Call Trace:
[    1.231152]  [<c0138481>] ? __change_page_attr+0x2c1/0x370
[    1.231161]  [<c02163a1>] ? __purge_vmap_area_lazy+0xc1/0x180
[    1.231169]  [<c013857c>] ? __change_page_attr_set_clr+0x4c/0xb0
[    1.231176]  [<c0138838>] ? change_page_attr_set_clr+0x128/0x300
[    1.231183]  [<c010798e>] ? __raw_callee_save_xen_restore_fl+0x6/0x8
[    1.231192]  [<c0159ca1>] ? vprintk+0x171/0x3f0
[    1.231198]  [<c0138bdf>] ? set_memory_nx+0x5f/0x70


Does Xen have different size page table allocations or something weird?

-Kees

[1] http://launchpadlibrarian.net/61853131/natty-failed-boot-ec2.txt
[2] https://bugs.launchpad.net/ubuntu/+source/linux/+bug/699828

-- 
Kees Cook
Ubuntu Security Team
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