linux-kernel - Re: [RFC] Second attempt at kernel secure boot support

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Date:	Wed, 31 Oct 2012 13:08:34 -0400
From:	Shea Levy <shea@...alevy.com>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
CC:	Matthew Garrett <mjg59@...f.ucam.org>,
	Josh Boyer <jwboyer@...il.com>, Jiri Kosina <jkosina@...e.cz>,
	linux-kernel@...r.kernel.org,
	linux-security-module@...r.kernel.org, linux-efi@...r.kernel.org
Subject: Re: [RFC] Second attempt at kernel secure boot support

On 10/31/2012 01:08 PM, Alan Cox wrote:
> On Wed, 31 Oct 2012 15:56:35 +0000
> Matthew Garrett <mjg59@...f.ucam.org> wrote:
>
>> 1) Gain root.
>> 2) Modify swap partition directly.
>> 3) Force reboot.
>> 4) Win.
>>
>> Root should not have the ability to elevate themselves to running
>> arbitrary kernel code. Therefore, the above attack needs to be
>> impossible.
> To protect swap you need to basically disallow any unencrypted swap (as
> he OS can't prove any given swap device is local and inside the case) and
> disallow the use of most disk management tools (so you'll need to write a
> few new management interfaces or implement the BPF based command filters
> that have been discussed for years).

Can any kernel memory get swapped? If not all root can do is mess with 
the memory of other userspace processes, which isn't a use-case that 
secure boot cares about from my understanding.

> In addition of course there is no requirement that a device returns
> the data you put on it so subverted removable media is a potential issue.
> Or indeed just cheap memory sticks that do it anyway ;)
>
> Oh and of course the file systems in default mode don't guarantee this so
> you'll need to fix ext3, ext4 8)
>
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