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Message-ID: <8497d07f-b0e2-4a0f-91b9-9e6ecd1f8b1e@126.com>
Date: Tue, 8 Jul 2025 15:39:38 +0800
From: Ge Yang <yangge1116@....com>
To: Ard Biesheuvel <ardb@...nel.org>
Cc: jarkko@...nel.org, sathyanarayanan.kuppuswamy@...ux.intel.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 V3] efi/tpm: Fix the issue where the CC platforms event
log header can't be correctly identified
在 2025/7/8 9:19, Ard Biesheuvel 写道:
> On Mon, 7 Jul 2025 at 13:15, <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.
>>
>> 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.
>>
>> Link: https://uefi.org/specs/UEFI/2.10/38_Confidential_Computing.html#intel-trust-domain-extension
>> Link: https://trustedcomputinggroup.org/wp-content/uploads/TCG_PCClient_PFP_r1p05_v23_pub.pdf
>> Fixes: d228814b1913 ("efi/libstub: Add get_event_log() support for CC platforms")
>> Signed-off-by: Ge Yang <yangge1116@....com>
>> Cc: stable@...r.kernel.org
>> ---
>>
>> V3:
>> - fix build error
>>
>> V2:
>> - limit the fix for CC only suggested by Jarkko and Sathyanarayanan
>>
>> drivers/char/tpm/eventlog/tpm2.c | 4 +++-
>> drivers/firmware/efi/libstub/tpm.c | 13 +++++++++----
>> drivers/firmware/efi/tpm.c | 4 +++-
>> include/linux/tpm_eventlog.h | 14 +++++++++++---
>> 4 files changed, 26 insertions(+), 9 deletions(-)
>>
>> diff --git a/drivers/char/tpm/eventlog/tpm2.c b/drivers/char/tpm/eventlog/tpm2.c
>> index 37a0580..30ef47c 100644
>> --- a/drivers/char/tpm/eventlog/tpm2.c
>> +++ b/drivers/char/tpm/eventlog/tpm2.c
>> @@ -18,6 +18,7 @@
>> #include <linux/module.h>
>> #include <linux/slab.h>
>> #include <linux/tpm_eventlog.h>
>> +#include <linux/cc_platform.h>
>>
>> #include "../tpm.h"
>> #include "common.h"
>> @@ -36,7 +37,8 @@
>> static size_t calc_tpm2_event_size(struct tcg_pcr_event2_head *event,
>> struct tcg_pcr_event *event_header)
>> {
>> - return __calc_tpm2_event_size(event, event_header, false);
>> + return __calc_tpm2_event_size(event, event_header, false,
>> + cc_platform_has(CC_ATTR_GUEST_STATE_ENCRYPT));
>
>
> This conflates TDX attestation with guest state encryption.
>
> I think there could be meaningful ways for a confidential guest to use
> [emulated] TPM attestation rather than CC specific attestation, so I
> don't think it is a good idea to assume that the fact that we are
> running on a CoCo guest always implies that all the TCG data
> structures are of the CC variety.
>
Okay, thank you. I'll adjust the patch again.
>
>> }
>>
>> static void *tpm2_bios_measurements_start(struct seq_file *m, loff_t *pos)
>> diff --git a/drivers/firmware/efi/libstub/tpm.c b/drivers/firmware/efi/libstub/tpm.c
>> index a5c6c4f..9728060 100644
>> --- a/drivers/firmware/efi/libstub/tpm.c
>> +++ b/drivers/firmware/efi/libstub/tpm.c
>> @@ -50,7 +50,8 @@ void efi_enable_reset_attack_mitigation(void)
>> static void efi_retrieve_tcg2_eventlog(int version, efi_physical_addr_t log_location,
>> efi_physical_addr_t log_last_entry,
>> efi_bool_t truncated,
>> - struct efi_tcg2_final_events_table *final_events_table)
>> + struct efi_tcg2_final_events_table *final_events_table,
>> + bool is_cc_event)
>> {
>> efi_guid_t linux_eventlog_guid = LINUX_EFI_TPM_EVENT_LOG_GUID;
>> efi_status_t status;
>> @@ -87,7 +88,8 @@ static void efi_retrieve_tcg2_eventlog(int version, efi_physical_addr_t log_loca
>> last_entry_size =
>> __calc_tpm2_event_size((void *)last_entry_addr,
>> (void *)(long)log_location,
>> - false);
>> + false,
>> + is_cc_event);
>> } else {
>> last_entry_size = sizeof(struct tcpa_event) +
>> ((struct tcpa_event *) last_entry_addr)->event_size;
>> @@ -123,7 +125,8 @@ static void efi_retrieve_tcg2_eventlog(int version, efi_physical_addr_t log_loca
>> header = data + offset + final_events_size;
>> event_size = __calc_tpm2_event_size(header,
>> (void *)(long)log_location,
>> - false);
>> + false,
>> + is_cc_event);
>> /* If calc fails this is a malformed log */
>> if (!event_size)
>> break;
>> @@ -157,6 +160,7 @@ void efi_retrieve_eventlog(void)
>> efi_tcg2_protocol_t *tpm2 = NULL;
>> efi_bool_t truncated;
>> efi_status_t status;
>> + bool is_cc_event = false;
>>
>> status = efi_bs_call(locate_protocol, &tpm2_guid, NULL, (void **)&tpm2);
>> if (status == EFI_SUCCESS) {
>> @@ -186,11 +190,12 @@ void efi_retrieve_eventlog(void)
>>
>> final_events_table =
>> get_efi_config_table(EFI_CC_FINAL_EVENTS_TABLE_GUID);
>> + is_cc_event = true;
>> }
>>
>> if (status != EFI_SUCCESS || !log_location)
>> return;
>>
>> efi_retrieve_tcg2_eventlog(version, log_location, log_last_entry,
>> - truncated, final_events_table);
>> + truncated, final_events_table, is_cc_event);
>> }
>> diff --git a/drivers/firmware/efi/tpm.c b/drivers/firmware/efi/tpm.c
>> index cdd4310..ca8535d 100644
>> --- a/drivers/firmware/efi/tpm.c
>> +++ b/drivers/firmware/efi/tpm.c
>> @@ -12,6 +12,7 @@
>> #include <linux/init.h>
>> #include <linux/memblock.h>
>> #include <linux/tpm_eventlog.h>
>> +#include <linux/cc_platform.h>
>>
>> int efi_tpm_final_log_size;
>> EXPORT_SYMBOL(efi_tpm_final_log_size);
>> @@ -23,7 +24,8 @@ static int __init tpm2_calc_event_log_size(void *data, int count, void *size_inf
>>
>> while (count > 0) {
>> header = data + size;
>> - event_size = __calc_tpm2_event_size(header, size_info, true);
>> + event_size = __calc_tpm2_event_size(header, size_info, true,
>> + cc_platform_has(CC_ATTR_GUEST_STATE_ENCRYPT));
>> if (event_size == 0)
>> return -1;
>> size += event_size;
>> diff --git a/include/linux/tpm_eventlog.h b/include/linux/tpm_eventlog.h
>> index 891368e..b3380c9 100644
>> --- a/include/linux/tpm_eventlog.h
>> +++ b/include/linux/tpm_eventlog.h
>> @@ -143,6 +143,7 @@ struct tcg_algorithm_info {
>> * @event: Pointer to the event whose size should be calculated
>> * @event_header: Pointer to the initial event containing the digest lengths
>> * @do_mapping: Whether or not the event needs to be mapped
>> + * @is_cc_event: Whether or not the event is from a CC platform
>> *
>> * The TPM2 event log format can contain multiple digests corresponding to
>> * separate PCR banks, and also contains a variable length of the data that
>> @@ -159,7 +160,8 @@ struct tcg_algorithm_info {
>>
>> static __always_inline u32 __calc_tpm2_event_size(struct tcg_pcr_event2_head *event,
>> struct tcg_pcr_event *event_header,
>> - bool do_mapping)
>> + bool do_mapping,
>> + bool is_cc_event)
>> {
>> struct tcg_efi_specid_event_head *efispecid;
>> struct tcg_event_field *event_field;
>> @@ -201,8 +203,14 @@ static __always_inline u32 __calc_tpm2_event_size(struct tcg_pcr_event2_head *ev
>> count = event->count;
>> event_type = event->event_type;
>>
>> - /* Verify that it's the log header */
>> - if (event_header->pcr_idx != 0 ||
>> + /*
>> + * Verify that it's the log header. According to the TCG PC Client
>> + * Specification, when identifying a log header, the check for a
>> + * pcr_idx value of 0 is not required. For CC platforms, skipping
>> + * this check during log header is necessary; otherwise, the CC
>> + * platform's log header may fail to be recognized.
>> + */
>> + if ((!is_cc_event && event_header->pcr_idx != 0) ||
>> event_header->event_type != NO_ACTION ||
>> memcmp(event_header->digest, zero_digest, sizeof(zero_digest))) {
>> size = 0;
>> --
>> 2.7.4
>>
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