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

[yangge1116@126.com]

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.

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@126.com>
Cc: stable@vger.kernel.org
---

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;
-- 
2.7.4