Hi James, On Sun, Aug 05, 2018 at 10:47:26AM -0700, James Bottomley wrote: > On Sun, 2018-08-05 at 09:25 +0200, Ard Biesheuvel wrote: > > Hello Chun,yi, > > > > On 5 August 2018 at 05:21, Lee, Chun-Yi <joeyli.kernel@xxxxxxxxx> > > wrote: > > > When secure boot is enabled, only signed EFI binary can access > > > EFI boot service variable before ExitBootService. Which means that > > > the EFI boot service variable is secure. > > > > > > > No it, isn't, and this is a very dangerous assumption to make. > > > > 'Secure' means different things to different people. 'Secure boot' is > > a misnomer, since it is too vague: it should be called 'authenticated > > boot', and the catch is that authentication using public-key crypto > > does not involve secrets at all. > > Hang on, let's not throw the baby out with the bathwater here. > > The design of "secure boot" is to create a boot time environment where > only trusted code may execute. We rely on this trust guarantee when we > pivot from the EFI to the MoK root of trust in shim. > > The reason we in Linux trust this guarantee is that it pertains to the > boot environment only, so any violation would allow Windows boot to be > compromised as well and we trust Microsoft's Business interests in > securing windows far enough to think this would be dealt with very > severely and it's an outcome the ODMs (who also add secure boot keys) > are worried enough about to be very careful. > > The rub (and this is where I'm agreeing with Ard) is that any use case > we come up with where a violation wouldn't cause a problem in windows > is a use case where we cannot rely on the guarantee because Microsoft > no longer has a strong business interest in policing it. This, for > instance, is why we don't populate the Linux trusted keyrings with the > secure boot keys (we may trust them in the boot environment where > compromise would be shared with windows but we can't trust them in the > Linux OS environment where it wouldn't). So this means we have to be > very careful coming up with uses for secure boot that aren't strictly > rooted in the guarantee as enforced by the business interests of > Microsoft and the ODMs. > Thank you for providing the view point from Microsoft bussiness ineterests. I agreed with you. Honestly I didn't think this point before. > > The UEFI variable store was not designed with confidentiality in > > mind, and assuming [given the reputation of EFI on the implementation > > side] that you can use it to keep secrets is rather unwise imho. > > Agree completely here: Microsoft doesn't use UEFI variables for > confidentiality, so we shouldn't either. If you want confidentiality, > use a TPM (like Microsoft does for the bitlocker key). > OK~~ Then I will use TPM trusted key + encrypted key in hibernation encryption/authentication. Thanks for James and Ard's comments. Joey Lee -- To unsubscribe from this list: send the line "unsubscribe linux-efi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
