Messages in this thread | | | Date | Thu, 26 Sep 2013 16:56:33 +0200 | From | Vojtech Pavlik <> | Subject | Re: [RFC V4 PATCH 00/15] Signature verification of hibernate snapshot |
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On Thu, Sep 26, 2013 at 04:48:00PM +0200, Jiri Kosina wrote:
> > The only two problems I see are > > > > 1. The key isn't generational (any compromise obtains it). This > > can be fixed by using a set of keys generated on each boot and > > passing in both K_{N-1} and K_N > > I think this could be easily made optional, leaving the user with choice > of faster or "safer" boot.
Ideally, the key should be regenerated on each true reboot and kept the same if it is just a resume. Unfortunately, I don't see a way to distinguish those before we call ExitBootServices().
The reasoning behind that is that in the case of a kernel compromise, a suspended-and-resumed kernel will still be compromised, so there is no value in passing it a new key. A freshly booted kernel, though, should get a new key, exactly because the attacker could have obtained a key from the previous, compromised one.
This speeds up the ususal suspend-and-resume cycle, but provides full security once the user performs a full reboot.
The question that remains is how to tell in advance.
> > 2. No external agency other than the next kernel can do the > > validation since the validating key has to be secret > > This is true, but as you said, the relevance of this seems to be rather > questionable.
Indeed, it's hard to imagine a scenario that is also valid within the secure boot threat model.
-- Vojtech Pavlik Director SUSE Labs
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