linux-kernel - Re: [PATCH 0/4] tsm: Unified Measurement Register ABI for TVMs

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Message-ID: <01fc0997-a0e7-4086-b0aa-67b4a51b328a@intel.com>
Date: Fri, 14 Feb 2025 08:26:12 -0800
From: Dave Hansen <dave.hansen@...el.com>
To: "Xing, Cedric" <cedric.xing@...el.com>,
 Dan Williams <dan.j.williams@...el.com>,
 "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
 Dave Hansen <dave.hansen@...ux.intel.com>,
 Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
 Borislav Petkov <bp@...en8.de>, x86@...nel.org,
 "H. Peter Anvin" <hpa@...or.com>
Cc: linux-kernel@...r.kernel.org, linux-coco@...ts.linux.dev,
 Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>
Subject: Re: [PATCH 0/4] tsm: Unified Measurement Register ABI for TVMs

On 2/14/25 08:19, Xing, Cedric wrote:
>> But if this is for debug, wouldn't these belong better in debugfs? Do we
>> really want to maintain this interface forever? There's no shame in
>> debugfs.
>>
> There are many other (more important/significant) uses besides debugging.
> 
> For example, any applications that make use of runtime measurements must
> extend RTMRs, and this interface provides that exact functionality.
> 
> Another example, a policy may be associated with a TD (e.g., CoCo) by
> storing its digest in MRCONFIGID, so that the policy could be verified
> against its digest at runtime. This interface allows applications to
> read MRCONFIGID.

The attestation world is horrifically complicated, and I don't
understand the details at _all_. You're going to have to explain this
one to me like I'm five.

Could you also explain how this is different from the hardware and
virtual TPMs and why this doesn't fit into that existing framework? How
are TVMs novel? What justifies all this new stuff?