On Tue, May 19, 2015 at 05:41:37PM -0700, Andy Lutomirski wrote: > On Tue, May 19, 2015 at 5:39 PM, Luis R. Rodriguez <mcgrof@xxxxxxxx> wrote: > > On Tue, May 19, 2015 at 04:42:05PM -0700, Andy Lutomirski wrote: > >> On Tue, May 19, 2015 at 4:30 PM, Julian Calaby <julian.calaby@xxxxxxxxx> wrote: > >> > Hi All, > >> > > >> > On Wed, May 20, 2015 at 6:59 AM, Andy Lutomirski <luto@xxxxxxxxxx> 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. > > Isn't stacking backwards for this, though? The semantics we'd want is > accept if any verifiers accept, not accept if all verifiers accept, > right? That can be added, and if stacking is not yet merged perhaps Casey can consider it? Luis -- 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
