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

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

[yangge1116]

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. There's no danger of this causing problems because we check
for the TCG_SPECID_SIG signature as the next thing.

Link: https://uefi.org/specs/UEFI/2.10/38_Confidential_Computing.html#intel-trust-domain-extension
Fixes: d228814b1913 ("efi/libstub: Add get_event_log() support for CC platforms")
Signed-off-by: Ge Yang <yangge1116@126.com>
Cc: stable@vger.kernel.org
---
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;
-- 
2.7.4

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

[James Bottomley]

On Sat, 2025-07-12 at 10:55 +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.

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

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

[Ge Yang]

在 2025/7/12 11:03, James Bottomley 写道:
> On Sat, 2025-07-12 at 10:55 +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.
> 
> 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.
> 

OK, thanks.


> Regards,
> 
> James