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

On Wed, 25 Sep 2013, James Bottomley wrote:

quoted

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.

James,

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

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
SUSE Labs