[PATCH] efi/tpm: Fix the issue where the CC platforms event log header can't be correctly identified
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 Spec 2.10 Section 38.4.1: For Tdx, TPM PCR 0 maps to MRTD, so the log header uses TPM PCR 1. To successfully parse the TDX event log header, the check for a pcr_idx value of 0 has been removed here, and it appears that this will not affect other functionalities.
Link: https://uefi.org/specs/UEFI/2.10/38_Confidential_Computing.html#intel-trust-... 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 --- 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;
On Thu, Jul 03, 2025 at 10:38:37AM +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 Spec 2.10 Section 38.4.1: For Tdx, TPM PCR 0 maps to MRTD, so the log header uses TPM PCR 1. To successfully parse the TDX event log header, the check for a pcr_idx value of 0 has been removed here, and it appears that this will not affect other functionalities.
I'm not familiar with the original change but with a quick check it did not change __calc_tpm2_event_size(). Your change is changing semantics to two types of callers:
1. Those that caused the bug. 2. Those that nothing to do with this bug.
I'm not seeing anything explaining that your change is guaranteed not to have any consequences to "innocent" callers, which have no relation to the bug.
Link: https://uefi.org/specs/UEFI/2.10/38_Confidential_Computing.html#intel-trust-... 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
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
BR, Jarkko
在 2025/7/4 9:50, Jarkko Sakkinen 写道:
On Thu, Jul 03, 2025 at 10:38:37AM +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 Spec 2.10 Section 38.4.1: For Tdx, TPM PCR 0 maps to MRTD, so the log header uses TPM PCR 1. To successfully parse the TDX event log header, the check for a pcr_idx value of 0 has been removed here, and it appears that this will not affect other functionalities.
I'm not familiar with the original change but with a quick check it did not change __calc_tpm2_event_size(). Your change is changing semantics to two types of callers:
- Those that caused the bug.
- Those that nothing to do with this bug.
I'm not seeing anything explaining that your change is guaranteed not to have any consequences to "innocent" callers, which have no relation to the bug.
Thank you for your response.
According to Section 10.2.1, Table 6 (TCG_PCClientPCREvent Structure) in the TCG PC Client Platform Firmware Profile Specification, determining whether an event is an event log header does not require checking the pcrIndex field. The identification can be made based on other fields alone. Therefore, removing the pcrIndex check here is considered safe for "innocent" callers.
Reference Link: https://trustedcomputinggroup.org/wp-content/uploads/TCG_PCClient_PFP_r1p05_...
Link: https://uefi.org/specs/UEFI/2.10/38_Confidential_Computing.html#intel-trust-... 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
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
BR, Jarkko
On Fri, Jul 04, 2025 at 10:53:54AM +0800, Ge Yang wrote:
在 2025/7/4 9:50, Jarkko Sakkinen 写道:
On Thu, Jul 03, 2025 at 10:38:37AM +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 Spec 2.10 Section 38.4.1: For Tdx, TPM PCR 0 maps to MRTD, so the log header uses TPM PCR 1. To successfully parse the TDX event log header, the check for a pcr_idx value of 0 has been removed here, and it appears that this will not affect other functionalities.
I'm not familiar with the original change but with a quick check it did not change __calc_tpm2_event_size(). Your change is changing semantics to two types of callers:
- Those that caused the bug.
- Those that nothing to do with this bug.
I'm not seeing anything explaining that your change is guaranteed not to have any consequences to "innocent" callers, which have no relation to the bug.
Thank you for your response.
According to Section 10.2.1, Table 6 (TCG_PCClientPCREvent Structure) in the TCG PC Client Platform Firmware Profile Specification, determining whether an event is an event log header does not require checking the pcrIndex field. The identification can be made based on other fields alone. Therefore, removing the pcrIndex check here is considered safe for "innocent" callers.
Thanks for digging that out. Can you add something to the commit message? That spec is common knowledge if you are "into the topic" in the first palace so something along the lines of this would be perfectly fine:
"The check can be safely removed, as ccording to table 6 at section 10.2.1 of TCG PC client specification the index field does not require fixing the PCR index to zero."
But then: we still have that constraint there and we cannot predict the side-effects of removing a constraint, even if it is incorrectly defined constraint. For comparison, it's much less risky situation when adding additional constraints, as possible side-effects in the worst case scenarios can be even theoretically much lighter than in the opposite situation.
For this reasons it would be perhaps better to limit the fix for the CC only, and not change the semantics across the board.
BR, Jarkko
在 2025/7/4 23:13, Jarkko Sakkinen 写道:
On Fri, Jul 04, 2025 at 10:53:54AM +0800, Ge Yang wrote:
在 2025/7/4 9:50, Jarkko Sakkinen 写道:
On Thu, Jul 03, 2025 at 10:38:37AM +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 Spec 2.10 Section 38.4.1: For Tdx, TPM PCR 0 maps to MRTD, so the log header uses TPM PCR 1. To successfully parse the TDX event log header, the check for a pcr_idx value of 0 has been removed here, and it appears that this will not affect other functionalities.
I'm not familiar with the original change but with a quick check it did not change __calc_tpm2_event_size(). Your change is changing semantics to two types of callers:
- Those that caused the bug.
- Those that nothing to do with this bug.
I'm not seeing anything explaining that your change is guaranteed not to have any consequences to "innocent" callers, which have no relation to the bug.
Thank you for your response.
According to Section 10.2.1, Table 6 (TCG_PCClientPCREvent Structure) in the TCG PC Client Platform Firmware Profile Specification, determining whether an event is an event log header does not require checking the pcrIndex field. The identification can be made based on other fields alone. Therefore, removing the pcrIndex check here is considered safe for "innocent" callers.
Thanks for digging that out. Can you add something to the commit message? That spec is common knowledge if you are "into the topic" in the first palace so something along the lines of this would be perfectly fine:
"The check can be safely removed, as ccording to table 6 at section 10.2.1 of TCG PC client specification the index field does not require fixing the PCR index to zero."
Ok, thanks.
But then: we still have that constraint there and we cannot predict the side-effects of removing a constraint, even if it is incorrectly defined constraint. For comparison, it's much less risky situation when adding additional constraints, as possible side-effects in the worst case scenarios can be even theoretically much lighter than in the opposite situation.
For this reasons it would be perhaps better to limit the fix for the CC only, and not change the semantics across the board.
Ok, thanks.
I originally intended to add a cc_platform_has(CC_ATTR_GUEST_STATE_ENCRYPT) check inside the __calc_tpm2_event_size() function to limit the fix to Confidential Computing (CC) platforms only. However, this function is also used during the EFI stub phase, where the cc_platform_has() function is not defined.
Call Trace: efi_pe_entry() efi_stub_entry() efi_retrieve_eventlog() efi_retrieve_tcg2_eventlog() __calc_tpm2_event_size()
Therefore, I plan to modify __calc_tpm2_event_size() to accept an additional parameter indicating whether the event originates from a CC platform.
BR, Jarkko
On 7/3/25 7:53 PM, Ge Yang wrote:
在 2025/7/4 9:50, Jarkko Sakkinen 写道:
On Thu, Jul 03, 2025 at 10:38:37AM +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 Spec 2.10 Section 38.4.1: For Tdx, TPM PCR 0 maps to MRTD, so the log header uses TPM PCR 1. To successfully parse the TDX event log header, the check for a pcr_idx value of 0 has been removed here, and it appears that this will not affect other functionalities.
I'm not familiar with the original change but with a quick check it did not change __calc_tpm2_event_size(). Your change is changing semantics to two types of callers:
- Those that caused the bug.
- Those that nothing to do with this bug.
I'm not seeing anything explaining that your change is guaranteed not to have any consequences to "innocent" callers, which have no relation to the bug.
Thank you for your response.
According to Section 10.2.1, Table 6 (TCG_PCClientPCREvent Structure) in the TCG PC Client Platform Firmware Profile Specification, determining whether an event is an event log header does not require checking the pcrIndex field. The identification can be made based on other fields alone. Therefore, removing the pcrIndex check here is considered safe for "innocent" callers.
Reference Link: https://trustedcomputinggroup.org/wp-content/uploads/TCG_PCClient_PFP_r1p05_...
It looks like this check was originally added to handle a case which does not align with the TCG spec. So removing it directly may have some impact to these older platform. Can we make this conditional to CC platform?
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
It is possible that the first event in the event log is not actually a log header at all, but rather a normal event. This leads to the cast in __calc_tpm2_event_size being an invalid conversion, which means that the values read are effectively garbage. Depending on the first event's contents, this leads either to apparently normal behaviour, a crash or a freeze.
While this behaviour of the firmware is not in accordance with the TCG Client EFI Specification, this happens on a Dell Precision 5510 with the TPM enabled but hidden from the OS ("TPM On" disabled, state otherwise untouched). The EFI firmware claims that the TPM is present and active and that it supports the TCG 2.0 event log format.
Fortunately, this can be worked around by simply checking the header of the first event and the event log header signature itself.
Commit b4f1874c6216 ("tpm: check event log version before reading final events") addressed a similar issue also found on Dell models.
Fixes: 6b0326190205 ("efi: Attempt to get the TCG2 event log in the boot stub") Signed-off-by: Fabian Vogt fvogt@suse.de Link: https://lore.kernel.org/r/1927248.evlx2EsYKh@linux-e202.suse.de Bugzilla: https://bugzilla.suse.com/show_bug.cgi?id=1165773 Signed-off-by: Ard Biesheuvel ardb@kernel.org
Link: https://uefi.org/specs/UEFI/2.10/38_Confidential_Computing.html#intel-trust-... 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
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
BR, Jarkko
在 2025/7/5 6:27, Sathyanarayanan Kuppuswamy 写道:
On 7/3/25 7:53 PM, Ge Yang wrote:
在 2025/7/4 9:50, Jarkko Sakkinen 写道:
On Thu, Jul 03, 2025 at 10:38:37AM +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 Spec 2.10 Section 38.4.1: For Tdx, TPM PCR 0 maps to MRTD, so the log header uses TPM PCR 1. To successfully parse the TDX event log header, the check for a pcr_idx value of 0 has been removed here, and it appears that this will not affect other functionalities.
I'm not familiar with the original change but with a quick check it did not change __calc_tpm2_event_size(). Your change is changing semantics to two types of callers:
- Those that caused the bug.
- Those that nothing to do with this bug.
I'm not seeing anything explaining that your change is guaranteed not to have any consequences to "innocent" callers, which have no relation to the bug.
Thank you for your response.
According to Section 10.2.1, Table 6 (TCG_PCClientPCREvent Structure) in the TCG PC Client Platform Firmware Profile Specification, determining whether an event is an event log header does not require checking the pcrIndex field. The identification can be made based on other fields alone. Therefore, removing the pcrIndex check here is considered safe for "innocent" callers.
Reference Link: https://trustedcomputinggroup.org/wp-content/uploads/ TCG_PCClient_PFP_r1p05_v23_pub.pdf
It looks like this check was originally added to handle a case which does not align with the TCG spec. So removing it directly may have some impact to these older platform. Can we make this conditional to CC platform?
Ok, thanks.
I originally intended to add a cc_platform_has(CC_ATTR_GUEST_STATE_ENCRYPT) check inside the __calc_tpm2_event_size() function to limit the fix to Confidential Computing (CC) platforms only. However, this function is also used during the EFI stub phase, where the cc_platform_has() function is not defined.
Call Trace: efi_pe_entry() efi_stub_entry() efi_retrieve_eventlog() efi_retrieve_tcg2_eventlog() __calc_tpm2_event_size()
Therefore, I plan to modify __calc_tpm2_event_size() to accept an additional parameter indicating whether the event originates from a CC platform.
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
It is possible that the first event in the event log is not actually a log header at all, but rather a normal event. This leads to the cast in __calc_tpm2_event_size being an invalid conversion, which means that the values read are effectively garbage. Depending on the first event's contents, this leads either to apparently normal behaviour, a crash or a freeze.
While this behaviour of the firmware is not in accordance with the TCG Client EFI Specification, this happens on a Dell Precision 5510 with the TPM enabled but hidden from the OS ("TPM On" disabled, state otherwise untouched). The EFI firmware claims that the TPM is present and active and that it supports the TCG 2.0 event log format.
Fortunately, this can be worked around by simply checking the header of the first event and the event log header signature itself.
Commit b4f1874c6216 ("tpm: check event log version before reading final events") addressed a similar issue also found on Dell models.
Fixes: 6b0326190205 ("efi: Attempt to get the TCG2 event log in the boot stub") Signed-off-by: Fabian Vogt fvogt@suse.de Link: https://lore.kernel.org/r/1927248.evlx2EsYKh@linux-e202.suse.de Bugzilla: https://bugzilla.suse.com/show_bug.cgi?id=1165773 Signed-off-by: Ard Biesheuvel ardb@kernel.org
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
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
BR, Jarkko
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