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? --Andy -- 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
