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

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Date:	Thu, 26 Sep 2013 16:48:00 +0200 (CEST)
From:	Jiri Kosina <jiri.kosina@...e.com>
To:	James Bottomley <James.Bottomley@...senPartnership.com>
Cc:	Pavel Machek <pavel@....cz>,
	Alan Stern <stern@...land.harvard.edu>,
	David Howells <dhowells@...hat.com>,
	"Lee, Chun-Yi" <joeyli.kernel@...il.com>,
	linux-kernel@...r.kernel.org,
	linux-security-module@...r.kernel.org, linux-efi@...r.kernel.org,
	linux-pm@...r.kernel.org, linux-crypto@...r.kernel.org,
	opensuse-kernel@...nsuse.org, "Rafael J. Wysocki" <rjw@...k.pl>,
	Matthew Garrett <mjg59@...f.ucam.org>,
	Len Brown <len.brown@...el.com>,
	Josh Boyer <jwboyer@...hat.com>,
	Vojtech Pavlik <vojtech@...e.cz>,
	Matt Fleming <matt.fleming@...el.com>,
	Greg KH <gregkh@...uxfoundation.org>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Herbert Xu <herbert@...dor.hengli.com.au>,
	"David S. Miller" <davem@...emloft.net>,
	"H. Peter Anvin" <hpa@...or.com>, Michal Marek <mmarek@...e.cz>,
	Gary Lin <GLin@...e.com>, Vivek Goyal <vgoyal@...hat.com>,
	"Lee, Chun-Yi" <jlee@...e.com>
Subject: Re: [RFC V4 PATCH 00/15] Signature verification of hibernate
 snapshot

On Thu, 26 Sep 2013, James Bottomley wrote:

> > 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
> 
> OK, so the scheme is to keep a symmetric key in BS that is passed into
> the kernel each time (effectively a secret key) for signing and
> validation?

Exactly.

> 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.

>      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.

-- 
Jiri Kosina
SUSE Labs
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