linux-kernel - Re: [PATCH V5] efi/tpm: Fix the issue where the CC platforms event log header can't be correctly identified

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Message-ID: <31d1da85f3ec863d16f4bcb173dab687efd6ceed.camel@HansenPartnership.com>
Date: Fri, 11 Jul 2025 23:03:46 -0400
From: James Bottomley <James.Bottomley@...senPartnership.com>
To: 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 V5] efi/tpm: Fix the issue where the CC platforms event
 log header can't be correctly identified

On Sat, 2025-07-12 at 10:55 +0800, yangge1116@....com wrote:
> From: Ge Yang <yangge1116@....com>
> 
> Since commit d228814b1913 ("efi/libstub: Add get_event_log() support
> for CC platforms") reuses TPM2 support code for the CC platforms,
> when launching a TDX virtual machine with coco measurement enabled,
> the following error log is generated:
> 
> [Firmware Bug]: Failed to parse event in TPM Final Events Log
> 
> Call Trace:
> efi_config_parse_tables()
>   efi_tpm_eventlog_init()
>     tpm2_calc_event_log_size()
>       __calc_tpm2_event_size()
> 
> The pcr_idx value in the Intel TDX log header is 1, causing the
> function __calc_tpm2_event_size() to fail to recognize the log
> header, ultimately leading to the "Failed to parse event in TPM Final
> Events Log" error.
> 
> According to UEFI Specification 2.10, Section 38.4.1: For TDX, TPM
> PCR 0 maps to MRTD, so the log header uses TPM PCR 1 instead.

This isn't a justification ... Intel just screwed up.  Whatever the
UEFI spec says about PCR mapping, the log spec the TCG produces
requires the header event to have a pcrIndex of 0 and, since it isn't
recorded in a PCR, it doesn't matter what the mapping is.

Just say Intel misread the spec and wrongly sets pcrIndex to 1 in the
header and since they did this, we fear others might, so we're relaxing
the header check.

Regards,

James