From mboxrd@z Thu Jan 1 00:00:00 1970 From: Matthew Garrett Subject: Re: [PATCH] x86/efi: pull NV+BS variables out before we exit boot services Date: Tue, 19 Mar 2013 23:17:56 +0000 Message-ID: <20130319231756.GA21071@srcf.ucam.org> References: <20130319014850.GA28934@srcf.ucam.org> <1363680885.2377.11.camel@dabdike.int.hansenpartnership.com> <20130319163531.GA10879@srcf.ucam.org> <1363713447.2377.60.camel@dabdike.int.hansenpartnership.com> <20130319172506.GA11969@srcf.ucam.org> <1363717411.2377.68.camel@dabdike.int.hansenpartnership.com> <20130319182810.GA13003@srcf.ucam.org> <1363718456.2377.71.camel@dabdike.int.hansenpartnership.com> <20130319185003.GA13301@srcf.ucam.org> <1363734031.2377.77.camel@dabdike.int.hansenpartnership.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <1363734031.2377.77.camel-sFMDBYUN5F8GjUHQrlYNx2Wm91YjaHnnhRte9Li2A+AAvxtiuMwx3w@public.gmane.org> Sender: linux-efi-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: James Bottomley Cc: linux-efi-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-kernel List-Id: linux-efi@vger.kernel.org On Tue, Mar 19, 2013 at 11:00:31PM +0000, James Bottomley wrote: > On Tue, 2013-03-19 at 18:50 +0000, Matthew Garrett wrote: > > Well, that somewhat complicates implementation - we'd be encrypting the > > entire contents of memory except for the key that we're using to encrypt > > memory. Keeping the public key away from userspace avoids having to care > > about that. > > I don't quite understand what you're getting at: the principle of public > key cryptography is that you can make the public key, well public. You > only need to guard the private key. Ok, so let's just rephrase it as asymmetric cryptography. The aim is to ensure that there's never a situation where userspace can decrypt a hibernation file, modify it and reencrypt it. So, shim (or whatever) generates a keypair. The encryption key is passed to the kernel being booted. The decryption key is stashed in a variable in order to be passed to the resume kernel. If the decryption key is available to userspace then the kernel needs to discard the encryption key during image write-out - otherwise the encryption key will be in the encrypted image. If the decryption key isn't available to userspace then this isn't a concern. If the decryption key *is* available to userspace (as it would be in your case), there's a requirement to discard the encryption key during the hibernation process. This isn't impossible, but it does add a little to the complexity. -- Matthew Garrett | mjg59-1xO5oi07KQx4cg9Nei1l7Q@public.gmane.org