linux-kernel - Re: [PATCH V3] efi/tpm: Fix the issue where the CC platforms event log header can't be correctly identified

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Message-ID: <bed58d57f3d2aa2a5a3c1498d24d109be5717612.camel@HansenPartnership.com>
Date: Fri, 11 Jul 2025 05:32:00 -0700
From: James Bottomley <James.Bottomley@...senPartnership.com>
To: Ge Yang <yangge1116@....com>, ardb@...nel.org
Cc: jarkko@...nel.org, sathyanarayanan.kuppuswamy@...ux.intel.com, 
	ilias.apalodimas@...aro.org, jgg@...pe.ca, linux-efi@...r.kernel.org, 
	linux-kernel@...r.kernel.org, stable@...r.kernel.org, liuzixing@...on.cn
Subject: Re: [PATCH V3] efi/tpm: Fix the issue where the CC platforms event
 log header can't be correctly identified

On Fri, 2025-07-11 at 09:23 +0800, Ge Yang wrote:
> 在 2025/7/11 5:58, James Bottomley 写道:
[...]
> > I think someone has misread the spec.  EV_NO_ACTION events produce
> > no PCR extension.  So the PCR value zero is conventional (and
> > required by the TCG) since nothing gets logged.  Therefore even if
> > you're technically using PCR0 for something else EV_NO_ACTION
> > events should still have the conventional PCR = 0 value to conform
> > to the TCG spec. I assume it's too late to correct this in the
> > implementation?
> > 
> 
> According to Table 14 in Section 10.4.1 of the TCG PC Client 
> Specification, for EV_NO_ACTION events, the PCR (Platform
> Configuration Register) value can be 0 or other values, such as 6.
> 
> Link: 
> https://trustedcomputinggroup.org/wp-content/uploads/TCG_PCClient_PFP_r1p05_v23_pub.pdf

You're selectively quoting one part of the spec out of context. 
Section 10.4.5 (which is the normative one about EV_NO_ACTION events)
says:

   1. All EV_NO_ACTION events SHALL set TCG_PCR_EVENT2.pcrIndex = 0,
   unless otherwise specified.

And the only update to this is in 10.4.5.4 where it says a vendor
specific EV_NO_ACTION event may set pcrIndex to 6.  Since the log
header is not vendor specific, it must have pcr = 0.

Regards,

James