On 7/11/25 7:00 AM, James Bottomley wrote:
On Tue, 2025-07-08 at 15:54 +0800, yangge1116@126.com wrote:
From: Ge Yang yangge1116@126.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. To successfully parse the TDX event log header, the check for a pcr_idx value of 0 must be skipped.
According to Table 6 in Section 10.2.1 of the TCG PC Client Specification, the index field does not require the PCR index to be fixed at zero. Therefore, skipping the check for a pcr_idx value of 0 for CC platforms is safe.
This is wrong: the spec does not allow a header EV_ACTION to be recorded with anything other than pcrIndex == 0.
However, the fact that Intel, who practically wrote the TPM spec, can get this wrong shows that others can too. So the best way to fix this is to remove the pcrIndex check for the first event. There's no danger of this causing problems because we check for the TCG_SPECID_SIG signature as the next thing. That means you don't need to thread knowledge of whether this is a CC environment and we're pre-emptively ready for any other spec violators who misread the spec in the same way Intel did.
I agree with James Bottomley's suggestion to remove the pcr_index check without adding any replacement checks.
This check was originally introduced in the following commit to handle a case where certain Dell platforms provided an event log without a valid header:
commit 7dfc06a0f25b593a9f51992f540c0f80a57f3629 Author: Fabian Vogt fvogt@suse.de Date: Mon Jun 15 09:16:36 2020 +0200
efi/tpm: Verify event log header before parsing
At first, I was concerned that the pcr_index check might still be important for this fix. However, after re-reading the commit and reviewing the intent, it appears that relying on the event_type and digest checks should be sufficient for validating the event log header.
Regards,
James