Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752510AbbETAjZ (ORCPT ); Tue, 19 May 2015 20:39:25 -0400 Received: from cantor2.suse.de ([195.135.220.15]:59607 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751650AbbETAjW (ORCPT ); Tue, 19 May 2015 20:39:22 -0400 Date: Wed, 20 May 2015 02:39:17 +0200 From: "Luis R. Rodriguez" To: Andy Lutomirski , Mimi Zohar , Matthew Garrett , Casey Schaufler Cc: Julian Calaby , Andy Lutomirski , LSM List , James Morris , "Serge E. Hallyn" , "linux-kernel@vger.kernel.org" , linux-wireless , David Howells , Kyle McMartin , David Woodhouse , Seth Forshee , Greg Kroah-Hartman , Mimi Zohar , Konstantin Ryabitsev , Michal Marek , Abelardo Ricart III , Sedat Dilek , keyrings@linux-nfs.org, Borislav Petkov , Jiri Kosina , Linus Torvalds Subject: Re: [RFD] linux-firmware key arrangement for firmware signing Message-ID: <20150520003917.GV23057@wotan.suse.de> References: <20150519200232.GM23057@wotan.suse.de> <555BA438.2070802@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4260 Lines: 91 On Tue, May 19, 2015 at 04:42:05PM -0700, Andy Lutomirski wrote: > On Tue, May 19, 2015 at 4:30 PM, Julian Calaby wrote: > > Hi All, > > > > On Wed, May 20, 2015 at 6:59 AM, Andy Lutomirski wrote: > >> [added cc's from the other thread] > >> > >> On 05/19/2015 01:02 PM, Luis R. Rodriguez wrote: > >>> > >>> David Howells has posted v4 of his series of supporting PKCS#7 for module > >>> signing. I'm in my v3 series now on RFCs for firmware PKCS#7 support, and > >>> after > >>> some review and patch shuffling I think this is ready for patch form. My > >>> own > >>> series however depend on quite a bit of other pending changes, one series > >>> which > >>> will go through Rusty's tree, another series of fixes on firmware_class > >>> which > >>> should go through Greg's tree. I'll wait until all this and David's own > >>> patches > >>> get merged before posting firmware PKCS#7 support. Before all this though > >>> in > >>> preparation for fw signing one thing we should start to talk about more > >>> broadly > >>> however is how linux-firmware binary file signing would work in practice > >>> and > >>> what we need, and make sure folks are OK with all this. > >>> > >>> First, firmware signing will be completely optional as with module > >>> signing. > >>> > >> > >> ... > >> > >>> Other than this last nitpick, any other concerns or recommendations ? > >> > >> > >> A couple. Some of these are general concerns with the existing > >> infrastructure, but #1 is a specific problem that gets much worse if we add > >> firmware signing. Feel free to ignore 2-4. > >> > >> 1. We should get the signature semantics right. I think that, for modules, > >> we currently sign literally the module payload. For modules, in my > >> semi-amateurish crypto universe [1], this is fine *as long as the key in > >> question is used for no other purpose*. For firmware, it's dangerous, since > >> it would be vulnerable to substitution attacks in which the adversary > >> convinces us to interpret one firmware file as firmware for another device > >> or purpose entirely. > >> > >> We should be signing something that's semantically equivalent to "This is a > >> valid module: xyz", "This is a valid 'regulatory.bin': xyz", or "This is a > >> valid kexec image: xyz". > > > > Something that occurred to me (as a complete bystander) was: would it > > make sense to have keys able to be restricted to particular "types" of > > signable data? I.e. the key that can sign a valid regulatory.bin file > > cannot be used to sign a module or a kexec image. - This could remove > > the need to have multiple keyrings. (Also, UEFI keys unless otherwise > > tagged could be restricted to only signing bootloaders or kernels) > > Seems sensible to me. As for having keys for fw signing be specific to fw data without a keyring, if that is desirable I think we can devise a way to do that. For instance if we wanted to we can have FW_SIG by default trust first keys on system_trusted_keyring just as module signature works -- or if we wanted to just trust, say a Kyle key. Not sure if the later is possible yet, but htat would require some changes. Then as an evolution if we wanted to enable a specific request fw to be mapped to a specific fw file the new APIs I was looking to add could easily enable this provided that we first decide we do want to trust say one key perhaps not on system_trusted_keyring for fw signing. That'd need to be decided first. As for the UEFI stuff -- from what I gather its too late there. We could certainly go with something else for fw signing though, just lemme hear it hard and clear. > FWIW, I'm starting to think that UEFI-based validation of kexec images > should be totally separate. It uses a nasty PE format with a hideous > PKCS #7 formatted signature. Maybe that should be a completely > separate piece of code. LSM'ify it I guess? Again, if that's reasonable then I think we'll need stacking and that's still not merged. Luis -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/