On Wed, May 20, 2015 at 04:08:58PM +0100, David Howells wrote: > Seth Forshee <seth.forshee@xxxxxxxxxxxxx> wrote: > > > > This begs the question on how we'd manage keys for firmware signing on > > > linux-firmare. Since the keys are x509 keys we need a CA. Based on some > > > initial discussions it would seem we'd need the Linux Foundation to create > > > a key, this would be embedded in the kernel and that key would be used to > > > sign Kyle's key. Kyle would in turn use his key for signing > > > linux-firmware files. David, Kyle, did I summarize this correctly ? > > > > I raised the question of key revocation when we discussed this on irc, > > but it wasn't answered to my satisfaction. If a key signed by the > > kernel-embedded key is compromised, how can that key be revoked so that > > it is no longer trusted? > > > > Someone mentioned UEFI blacklists, which I don't know much about, but > > not all systems have UEFI. The only reliable option that comes to mind > > for me is an in-kernel blacklist of keys which should no longer be > > trusted. > > Key revocation is generally an unpleasant problem. How do you inform a system > that a key of any sort is revoked? With PGP, for instance, you might be able > to connect to the net and consult a server. Distros could distribute updates to the blacklist via their usual update mechanisms. That could be a new kernel with an updated blacklist (after all we should expect blacklist updates to be very infrequent). I suppose a database in the initrd which was loaded prior to loading any firmware could work too, then perhaps new blacklists could be loaded into a running kernel without a reboot as well. But that database should probably be signed too, which creates a chicken-and-egg sort of problem. > UEFI has a blacklist that can theoretically be used to prevent both usage of a > key and usage of a particular object. As I understand it, the blacklist in > UEFI is just a table of SHA256 hashes. > > Relying on UEFI presents three problems, though: (1) the system admin has to > manually, as far as I'm aware, inform the BIOS; (2) the UEFI storage is > limited; and (3) not all systems have UEFI. Yeah, that doesn't really sound like a good solution. Not all users are sys admins. > What you do on a non-UEFI system, I'm not sure. If the kernel isn't verified > by the loader or the system firmware then you don't have a 'fully' secure > system anyway and the blacklist may be of questionable value. I think there's still value - compromised firmware could easily be a vector to compromise the kernel. Just because I can't verify my system security doesn't mean that I don't want measures in place to keep it from being compromised. Seth -- To unsubscribe from this list: send the line "unsubscribe linux-wireless" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
