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

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Message-ID: <c2cf2184-7753-454e-ac99-8c4f3c9c3d16@intel.com>
Date: Fri, 14 Feb 2025 10:19:49 -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 2/13/2025 5:19 PM, Dave Hansen wrote:
> On 2/13/25 13:50, Xing, Cedric wrote:
>> On 2/13/2025 10:58 AM, Dave Hansen wrote:
> ...
>>> Wait a sec, so there's already ABI for manipulating these? This just
>>> adds a parallel sysfs interface to the existing ABI?
>>>
>> No, this is new. There's no existing ABI for accessing measurement
>> registers from within a TVM (TEE VM). Currently, on TDX for example,
>> reading TDX measurement registers (MRs) must be done by getting a TD
>> quote. And there's no way to extend any RTMRs. Therefore, it would be
>> much easier end users to debug/diagnose measurement related issues
>> (which would almost always require reading MRs) with this patch.
> 
> Ok, that makes sense.
> 
> 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.