Re: [PATCH RFC 3/3] tsm: Add TVM Measurement Sample Code

[Xing, Cedric]

On 9/14/2024 12:10 PM, James Bottomley wrote:
> On Sat, 2024-09-14 at 11:36 -0500, Xing, Cedric wrote:
> > I have considered this before. But I'm not sure how to
> > (define/describe criteria to) match an MR with its log format.
>
> This is already defined for every existing log format ... why would you
> have to define it again?
>
> >   Also, MRs are arch dependent and may also vary from gen to gen. I'm
> > afraid this might bring in more chaos than order.
>
> I think I understand this. All measurement registers are simply
> equivalent to PCRs in terms of the mathematical definition of how they
> extend.  Exactly what measurements go into a PCR and how they are
> logged is defined in various standards.  The TCG ones are fairly fixed
> now, but if Intel wants to keep redefining the way its measurements
> work, the logical thing to do is tie this to a version number and make
> measuring the version the first log entry so the tools know how to
> differentiate.
I’m not sure if I understand this correctly. Are you suggesting we 
continue using the event definitions from the existing TCG specs with 
just a simple RTMR-to-PCR map? That’s exactly the issue we’re trying to 
address. The current specs don’t cover new applications. For example, 
how to describe the event of launching a container measured to a 
specific SHA-256 digest in CoCo? Defining new event types would require 
revising the specs, which is a high barrier for most applications. While 
TPM has been widely adopted, its use has been mostly limited to pre-boot 
scenarios. The lack of OS applications leveraging TPM is partly due to 
this limitation IMHO.