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. 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. > > Also, are multiple signatures a sensible thing? E.g. regulatory.bin > gets signed by Seth, then Kyle, then $DISTRO and any one key is enough > to validate it. That might further complicate matters. --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
