Re: [PATCH v1 0/2] efi/tpm: Preserve event log without changing x86 E820

[Jasmeet (Jazz) Bhatia]

On Thu Sep 3, 2026 at 7:18 AM PDT, Ard Biesheuvel wrote:
> Hi Jazz,
>
> On Tue, 1 Sep 2026, at 13:34, Jasmeet (Jazz) Bhatia wrote:
>> The EFI stub currently allocates the TPM event log as
>> EFI_ACPI_RECLAIM_MEMORY. On x86, this becomes an ACPI data entry
>> in the E820 map.
>>
>> On a Framework Laptop 16 (AMD Ryzen AI 300 Series), the EFI allocator
>> can place this allocation at different physical addresses across boots.
>> Since x86 hibernation validates architecture-specific data from
>> the firmware E820 map, this causes an otherwise valid hibernation image
>> to be rejected on resume with the following error:
>>
>>   Hibernate inconsistent memory map detected!
>>   PM: hibernation: Image mismatch: architecture specific data
>>
>> Allocating the event log as EFI_LOADER_DATA avoids changing the E820
>> map, but doing that alone would regress the kexec corruption issue fixed
>> by commit 77d48d39e991 ("efistub/tpm: Use ACPI reclaim memory for event
>> log to avoid corruption").
>>
>
> As I replied in the other thread, I am not convinced preserving the TPM
> event log across a kexec makes sense to begin with. This is the firmware's
> view of the state of the TPM PCRs when it handed over the system to the
> first OS.
>
> If the first OS boots, loads a kexec kernel and then boots it without
> measuring any of that into the TPM, the TPM event log will match the
> TPM state, but this is meaningless because of the missing measurements,
> and the attestation chain is broken.
>
> If the first OS does perform TPM measurements, it would need to record
> them into a log and pass that on to the kexec'ed in some implementation
> specific way - it cannot use the existing TPM event log for that.
>
> TL;DR perhaps we should just discard the TPM event log reference from
> the EFI config tables after consuming it. Or add a special case to the
> kexec code to disregard it.
Ok, honestly that makes a lot of sense I see what you are saying and I
tend to agree. I'm treating the copied event log at something that
survives kexec in this patch because of the corruption fix so I'll look
at dropping that LINUX_EFI_TPM_EVENT_LOG_GUID reference and rewrite this
patch. Hopefully, that will avoid that x86 E820 instability as well.

Appreciate the guidance!