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

["Jasmeet (Jazz) Bhatia" <jasmeet.bhatia.us@gmail.com>]

On Mon Sep 7, 2026 at 8:57 AM PDT, Ilias Apalodimas wrote:
> Hi Ard,
>
> On Fri, 4 Sept 2026 at 19:39, Ard Biesheuvel <ardb@kernel.org> wrote:
>>
>>
>>
>> On Fri, 4 Sep 2026, at 17:45, Jasmeet (Jazz) Bhatia wrote:
>> > 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.
>
> It doesn't make sense imho. The only thing you prove is that you
> kexeced from a 'previous good OS', but without knowledge of what that
> OS did before kexecing.
>
>> >>
>> >> 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.
>
> Hrmm, that might be problematic. The EventLog needs to illustrate the
> state of the TPM PCRs. IOW replaying the EventLog in memory should
> match the current TPM PCRs. But that also means we'll have to teach
> kexec how to properly extend the PCRs and update the EventLog.
>
>> >>
>> >> 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.

Assuming we drop the LINUX_EFI_TPM_EVENT_LOG_GUID reference after the
kernel consumes the log, is that going to impact any in-kernel kexec
path that expects that efi.tpm_log to remain valid? Or is that reference
only needed during the initial TPM event log import?

I'm trying to understand whether removing that reference is just for
stopping the next kernel from re-importing the stale firmware log, or
whether other there exists other users of that reference.

>
> I can't decide what's best here. IIRC we don't expose the final event
> log config table in systab right? So we won't break any user-space app
> that depends on it.  We just copy it in
> /sys/kernel/security/tpm0/binary_bios_measurements. In that case
> getting rid of it would work.
>
> Cheers
> /Ilias
>
>> > 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!
>>
>> Please don't send any patches yet - I'd like to get some input from other
>> folks as well.
>>