linux-kernel - Re: [PATCH V6] efi/tpm: Fix the issue where the CC platforms event log header can't be correctly identified

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Message-ID: <89b6b1ba-4f55-4e54-a49d-7dcaddfd503f@linux.intel.com>
Date: Mon, 14 Jul 2025 06:28:14 -0700
From: Sathyanarayanan Kuppuswamy <sathyanarayanan.kuppuswamy@...ux.intel.com>
To: yangge1116@....com, ardb@...nel.org
Cc: jarkko@...nel.org, James.Bottomley@...senPartnership.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 V6] efi/tpm: Fix the issue where the CC platforms event
 log header can't be correctly identified


On 7/11/25 8:24 PM, 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.
>
> 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. There's no danger of this causing problems because we check for
> the TCG_SPECID_SIG signature as the next thing.
>
> Fixes: d228814b1913 ("efi/libstub: Add get_event_log() support for CC platforms")
> Signed-off-by: Ge Yang <yangge1116@....com>
> Cc: stable@...r.kernel.org
> ---
Reviewed-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>
>
> V6:
> - improve commit message suggested by James
>
> V5:
> - remove the pcr_index check without adding any replacement checks suggested by James and Sathyanarayanan
>
> V4:
> - remove cc_platform_has(CC_ATTR_GUEST_STATE_ENCRYPT) suggested by Ard
>
> V3:
> - fix build error
>
> V2:
> - limit the fix for CC only suggested by Jarkko and Sathyanarayanan
>
>   include/linux/tpm_eventlog.h | 3 +--
>   1 file changed, 1 insertion(+), 2 deletions(-)
>
> diff --git a/include/linux/tpm_eventlog.h b/include/linux/tpm_eventlog.h
> index 891368e..05c0ae5 100644
> --- a/include/linux/tpm_eventlog.h
> +++ b/include/linux/tpm_eventlog.h
> @@ -202,8 +202,7 @@ static __always_inline u32 __calc_tpm2_event_size(struct tcg_pcr_event2_head *ev
>   	event_type = event->event_type;
>   
>   	/* Verify that it's the log header */
> -	if (event_header->pcr_idx != 0 ||
> -	    event_header->event_type != NO_ACTION ||
> +	if (event_header->event_type != NO_ACTION ||
>   	    memcmp(event_header->digest, zero_digest, sizeof(zero_digest))) {
>   		size = 0;
>   		goto out;

-- 
Sathyanarayanan Kuppuswamy
Linux Kernel Developer