linux-kernel - Re: [PATCH] x86/efi: pull NV+BS variables out before we exit boot services

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Date:	Tue, 19 Mar 2013 18:40:56 +0000
From:	James Bottomley <James.Bottomley@...senPartnership.com>
To:	Matthew Garrett <mjg59@...f.ucam.org>
Cc:	linux-efi@...r.kernel.org,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] x86/efi: pull NV+BS variables out before we exit boot
 services

On Tue, 2013-03-19 at 18:28 +0000, Matthew Garrett wrote:
> On Tue, Mar 19, 2013 at 06:23:31PM +0000, James Bottomley wrote:
> 
> > The scheme we discussed, unless something radically changed, was to
> > convey a temporary key pair via a mechanism to later verify the
> > hybernate kernel on a resume.  That only requires reboot safe knowledge
> > of the public key.  The private key can be conveyed in BS only (not NV),
> > and should be consumed (as in deleted) by the OS when it receives it, so
> > it wouldn't be exposed by this patch.
> 
> It requires the key to survive the system being entirely powered down, 
> which means it needs to be BS+NV. It shouldn't be possible for userspace 
> to access this key.

It requires the *public* key to survive power down, certainly.  The
private key can be thrown away once the hibernate image is signed.  I
think the scheme can be constructed so the private key is never in NV
storage ... that also makes it more secure against tampering.

James



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