> From: James Bottomley [mailto:jejb@xxxxxxxxxxxxx] > Sent: Friday, June 12, 2020 7:14 PM > On Fri, 2020-06-12 at 15:11 +0000, Roberto Sassu wrote: > > with recent patches, boot_aggregate can be calculated from non-SHA1 > > PCR banks. I would replace with: > > > > Extend cumulative digest over ... > > > > Given that with this patch boot_aggregate is calculated differently, > > shouldn't we call it boot_aggregate_v2 and enable it with a new > > option? > > So here's the problem: if your current grub doesn't do any TPM > extensions (as most don't), then the two boot aggregates are the same > because PCRs 8 and 9 are zero and there's a test that doesn't add them > to the aggregate if they are zero. For these people its a nop so we > shouldn't force them to choose a different version of the same thing. > > If, however, you're on a distribution where grub is automatically > measuring the kernel and command line into PCRs 8 and 9 (I think Fedora > 32 does this), your boot aggregate will change. It strikes me in that > case we can call this a bug fix, since the boot aggregate isn't > properly binding to the previous measurements without PCRs 8 and 9. In > this case, do we want to allow people to select an option which doesn't > properly bind the IMA log to the boot measurements? That sounds like a > security hole to me. > > However, since it causes a user visible difference in the grub already > measures case, do you have a current use case that would be affected? > As in are lots of people already running a distro with the TPM grub > updates and relying on the old boot aggregate? I don't know how many people would be affected. However, if an attestation tool processes both measurement lists from unpatched kernels and patched kernels, keeping the same name would be a problem as it cannot be determined from the measurement list how boot_aggregate was calculated. Anyway, I agree this should be fixed. At least, I suggest to add a Fixes tag, to ensure that this patch is applied to all stable kernels. Roberto HUAWEI TECHNOLOGIES Duesseldorf GmbH, HRB 56063 Managing Director: Li Peng, Li Jian, Shi Yanli
