Re: [RFC V4 PATCH 00/15] Signature verification of hibernatesnapshot

From: Jiri Kosina
Date: Thu Sep 26 2013 - 02:24:58 EST

On Wed, 25 Sep 2013, James Bottomley wrote:

> > I don't get this. Why is it important that current kernel can't
> > recreate the signature?
> The thread model is an attack on the saved information (i.e. the suspend
> image) between it being saved by the old kernel and used by the new one.
> The important point isn't that the new kernel doesn't have access to
> K_{N-1} it's that no-one does: the key is destroyed as soon as the old
> kernel terminates however the verification public part P_{N-1} survives.


could you please describe the exact scenario you think that the symmetric
keys aproach doesn't protect against, while the assymetric key aproach

The crucial points, which I believe make the symmetric key aproach work
(and I feel quite embarassed by the fact that I haven't realized this
initially when coming up with the assymetric keys aproach) are:

- the kernel that is performing the actual resumption is trusted in the
secure boot model, i.e. you trust it to perform proper verification

- potentially malicious userspace (which is what we are protecting against
-- malicious root creating fake hibernation image and issuing reboot)
doesn't have access to the symmetric key

Jiri Kosina
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