On Fri, May 12, 2023 at 08:17:21PM +0200, Thomas Gleixner wrote: > On Fri, May 12 2023 at 17:13, Matthew Garrett wrote: > > On Fri, May 12, 2023 at 03:24:04PM +0200, Thomas Gleixner wrote: > >> On Fri, May 12 2023 at 12:28, Matthew Garrett wrote: > >> > Unless we assert that SHA-1 events are unsupported, it seems a bit odd > >> > to force a policy on people who have both banks enabled. People with > >> > mixed fleets are potentially going to be dealing with SHA-1 measurements > >> > for a while yet, and while there's obviously a security benefit in using > >> > SHA-2 instead it'd be irritating to have to maintain two attestation > >> > policies. > >> > >> Why? > >> > >> If you have a mixed fleet then it's not too much asked to provide two > >> data sets. On a TPM2 system you can enforce SHA-2 and only fallback to > >> SHA-1 on TPM 1.2 hardware. No? > > > > No, beause having TPM2 hardware doesn't guarantee that your firmware > > enables SHA-2 (which also means this is something that could change with > > firmware updates, which means that refusing to support SHA-1 if the > > SHA-2 banks are enabled could result in an entirely different policy > > being required (and plausibly one that isn't implemented in their > > existing tooling) > > It's not rocket science to have both variants supported in tooling, > really. People who are currently using tboot are only getting SHA-1, so there's no obvious reason for them to have added support yet. *My* tooling all supports SHA-2 so I'm completely fine here, but either we refuse to support a bunch of hardware or we have to support SHA-1 anyway, and if we have to support it the only reason not to implement it even in the "SHA-2 is supported" case is because we have opinions about how other people implement their security.
