Re: [PATCH v6 06/14] x86: Add early SHA support for Secure Launch early measurements

[Thomas Gleixner]

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.

What a mess.