linux-kernel - Re: [PATCH] efi: pstore: Support late setup with TEE-backed efivars ops

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Message-ID: <2294ac5b-6977-4f46-964e-b3a30b88efbd@packett.cool>
Date: Thu, 4 Dec 2025 17:57:32 -0300
From: Val Packett <val@...kett.cool>
To: Ilias Apalodimas <ilias.apalodimas@...aro.org>
Cc: Kees Cook <kees@...nel.org>, Tony Luck <tony.luck@...el.com>,
 "Guilherme G. Piccoli" <gpiccoli@...lia.com>,
 Ard Biesheuvel <ardb@...nel.org>, linux-hardening@...r.kernel.org,
 linux-efi@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] efi: pstore: Support late setup with TEE-backed efivars
 ops

On 12/4/25 6:49 AM, Ilias Apalodimas wrote:
> Hi Val,
>
> On Wed, 3 Dec 2025 at 06:29, Val Packett <val@...kett.cool> wrote:
>> On some platforms, EFI variable services only become available when an
>> appropriate TEE driver is initialized such as qseecom, gsmi or stmm.
>>
>> This would work fine when efi_pstore was built as a module and loaded
>> late by userspace, but with CONFIG_EFI_VARS_PSTORE=y this driver would
>> quit due to non-writable efivars before the necessary driver had any
>> chance to load.
> The problem, at least for OP-TEE/StMM, is that writing the variables
> to an RPMB depends on a userspace application If CONFIG_RPMB is not
> selected. We have no guarantees that the app will still be alive.
> I don't know how gsmi or qseecom deal with writing variables. We can
> probably allow it for StMM if CONFIG_RPMB is enabled, but we'll have
> the right trigger to do so.

qseecom/uefisecapp does not have any userspace requirements and works 
fine with efi_pstore.

I don't think complicating efi_pstore with extra logic about which ops 
are fine would be worth it..

Either way, it currently *already* tries to use whatever ops that have 
been registered if it's loaded late as a module by systemd! The only 
thing this patch changes is the CONFIG_EFI_VARS_PSTORE=y case.

Thanks,
~val