On 15-05-21 10:02:36, gregkh@xxxxxxxxxxxxxxxxxxx wrote: > On Thu, May 21, 2015 at 04:03:02PM +0000, Woodhouse, David wrote: > > > > In a lot of cases we have loadable firmware precisely to allow us to > > reduce the cost of the hardware. Adding cryptographic capability in the > > 'load firmware' state of the device isn't really compatible with that > > :) > > We do? What devices want this? That's really a bad hardware design to trust > the kernel to get all of this correct. Which means nearly all hardware we use today is badly designed... :) > And I say this as someone who is currently working on a hardware design that > does just this for a very tiny device. It's only a few hundred bytes of > firmware size to be able to do proper key verification that the firmware image > is correct and can be "trusted". And a "few" more bytes for the hash algorithm along the one for asymmetric key computation and management. :) > > In the case where kernel and modules are signed, it *is* useful for a kernel > > device driver also to be able to validate that what it's about to load into > > a device is authentic. Where 'authentic' will originally just mean that it's > > come from the linux-firmware.git repository or the same entity that built > > (and signed) the kernel, but actually I *do* expect vendors who are actively > > maintaining the firmware images in linux-firmware.git to start providing > > detached signatures of their own. > > Again, why have a detached signature and not just part of the firmware blob? > The device needs to be caring about this, not the kernel. In ideal world this is what should be done. However, adding the simplest (read slowest) MD5 implementation requires a few K's of ram on 32bit cpu. MD5 is dead. So we need SHA-something, which isn't smaller in terms of code size. Add the asymmetric cryptography to the picture and we've already put away all vendors. > As the kernel doesn't know/care about what the firmware blob really is, I > don't see why it should be caring about firmware signing as that's a binary > running on a separate "computer". Do we want to take this the next logical > step further and start requiring networked devices to attest their kernels are > signed correctly before we can talk to them? I think it is enough for you to know that your iwlwifi's firmware comes from Intel and not from a random Internet punk. If you trust Intel with your wifi adapter you probably trust them to write good firmware for it. Petko -- 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
