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

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Message-ID: <12ed2ab1-e97d-4a20-8370-8c60cabffc77@intel.com>
Date: Fri, 14 Feb 2025 15:59:52 -0600
From: "Xing, Cedric" <cedric.xing@...el.com>
To: Dave Hansen <dave.hansen@...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 2/14/2025 10:26 AM, Dave Hansen wrote:
> 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?
TVM (TEE VM) is a broad term referring to encrypted/protected VMs on 
various confidential computing (CC) architectures, such as AMD SEV, Arm 
CCA, Intel TDX, etc. Each of these architectures includes hardware 
components for storing software measurements, known as measurement 
registers (MRs). This patch series aims to provide the necessary 
functionality for applications that need to access these MRs.

There are no real/hardware TPMs but only virtual ones in TVMs. Virtual 
TPMs can be built upon the native MRs provided by the underlying CC 
architectures.

If you need more detailed information, I'd be happy to discuss it 
further offline to avoid cluttering the mailing list.