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

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Message-ID: <50913CDB.4030107@shealevy.com>
Date:	Wed, 31 Oct 2012 10:59:39 -0400
From:	Shea Levy <shea@...alevy.com>
To:	Josh Boyer <jwboyer@...il.com>
CC:	Jiri Kosina <jkosina@...e.cz>, Matthew Garrett <mjg@...hat.com>,
	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 10:54 AM, Josh Boyer wrote:
> On Wed, Oct 31, 2012 at 10:50 AM, Jiri Kosina <jkosina@...e.cz> wrote:
>> On Mon, 29 Oct 2012, Matthew Garrett wrote:
>>
>>>>> This is pretty much identical to the first patchset, but with the capability
>>>>> renamed (CAP_COMPROMISE_KERNEL) and the kexec patch dropped. If anyone wants
>>>>> to deploy these then they should disable kexec until support for signed
>>>>> kexec payloads has been merged.
>>>> Apparently your patchset currently doesn't handle device firmware loading,
>>>> nor do you seem to mention in in the comments.
>>> Correct.
>>>
>>>> I believe signed firmware loading should be put on plate as well, right?
>>> I think that's definitely something that should be covered. I hadn't
>>> worried about it immediately as any attack would be limited to machines
>>> with a specific piece of hardware, and the attacker would need to expend
>>> a significant amount of reverse engineering work on the firmware - and
>>> we'd probably benefit from them doing that in the long run...
>> Now -- how about resuming from S4?
>>
>> Reading stored memory image (potentially tampered before reboot) from disk
>> is basically DMA-ing arbitrary data over the whole RAM. I am currently not
>> able to imagine a scenario how this could be made "secure" (without
>> storing private keys to sign the hibernation image on the machine itself
>> which, well, doesn't sound secure either).
> I have a patch that disables that.  I imagine it will be included in the
> next submission of the patchset.
>
> You can find it here in the meantime:
>
> http://jwboyer.fedorapeople.org/pub/0001-hibernate-Disable-in-a-Secure-Boot-environment.patch
>
> josh
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Perhaps this is overkill and too efi-specific, but on systems (like efi) 
where there is firmware-manged storage that is protected from unsigned 
access (e.g. efi vars), couldn't the kernel store a hash of the 
hibernation image in that storage?
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