[PATCH v2 3/3] tpm: allocate tpm event log if missing

[Ludwig Nussel]

On 6/15/26 15:25, Ilias Apalodimas wrote:
> On Mon, 15 Jun 2026 at 16:09, Ilias Apalodimas
> <ilias.apalodimas at linaro.org> wrote:
>>
>> Hi Ludwig,
>>
>> [...]
>>
>>>>>>
>>>>>> I'd like the eventlog to be initialized before calling this (look below).
>>>>>
>>>>> What if I removed the log parameter from those tcg2_* functions instead?
>>>>> The event log belongs to the tpm device IMO, so should be initialized
>>>>> with the device.
>>>>
>>>> Measured boot EventLogs etc are primarily described by the TCG specs &
>>>> EFI and we only have a specification for it there. The DT describes on
>>>> how to pass it over to linux with sml-base etc.
>>>> However, in the EFI case the Eventlog is allocated as ACPI memory. So
>>>> you cannot allocate the EventLog a priori, until you figure out what
>>>> method you are using to boot. We also have use cases people using it
>>>> only for RNG, due to limited memory, so we can't just allocate it on
>>>> the device bringup. And lastly... Some first stage bootloaders do not
>>>> initialize the TPM & drivers. What they do is prepare an EventLog and
>>>> expect U-Boot to replay it once the TPM is up and running. In that
>>>> case we obviously need to preserve what we have instead of starting
>>>> from scratch.
>>>
>>> Ack, we are on the same page here.
>>>
>>>> My main concern is that I *don't* want the EFI and non-EFI code to
>>>> deviate. I have some patches that I am playing around for quite some
>>>> time and rebased them last week for this reason [1]. If you think
>>>> those help your use case or make your life easier feel free to include
>>>> them.
>>>
>>> Good idea and orthogonal to what I am doing I think. This duplication in
>>> EFI stressed my brain too but I can't care about EFI right now :-)
>>
>> It is, but the deviation in EFI is pretty minimal atm.
>> - EFI calls tcg2_log_prepare_buffer instead of tcg2_measurement_init()
>> -- That's what my patches fix
>> - EFI has it's own version of tcg2_measure_event() -- That's easy to
>> fix as well,.
>>
>>>
>>> IIUC you are centering the change around calling
>>> tcg2_log_prepare_buffer() in efi_init_event_log(). What do you think
>>> about aiming for tcg2_measurement_init() as central starting point
>>> instead?
>>> That would allow to remove even more duplicated code.
>>> It should be sufficient to have tcg2_measurement_init() accept an
>>> optional pointer to pre-allocated log buffer memory. Attached patch
>>> maybe explains the idea better (just as idea, won't compile).
>>
>> I agree. In fact I mistyped the functions names on my previous
>> email.... I really meant tcg2_measurement_init(). The patchset I
>> pointed you to already converts tcg2_log_prepare_buffer() to static.
> 
> Replying to myself here, but.. In order to do that you do need the
> unification patches. tcg2_measurement_init() will need to allocate the
> appropriate buffer depending on EFI or not.

So this is how it would look like with your patches on top:
https://github.com/u-boot/u-boot/compare/master...lnussel:u-boot:tpm-with-ilias-patches

IMO the untangle patch is not needed. Does that look sensible?

cu
Ludwig

-- 
Ludwig Nussel
Siemens AG
www.siemens.com