Message-ID: <CAJwFiGLNh-qu9ezQOmTBh3Dujf=mPRyzKBVXLV-A=GxhwcH-0w@mail.gmail.com>
Date: Sun, 7 Dec 2025 22:01:09 +0800
From: Aristo Chen <jj251510319013@...il.com>
To: Jens Wiklander <jens.wiklander@...aro.org>
Cc: Sumit Garg <sumit.garg@...nel.org>, linux-kernel@...r.kernel.org, 
	op-tee@...ts.trustedfirmware.org, harshal.dev@....qualcomm.com, 
	Aristo Chen <aristo.chen@...onical.com>, mario.limonciello@....com, 
	Rijo Thomas <Rijo-john.Thomas@....com>, 
	Amirreza Zarrabi <amirreza.zarrabi@....qualcomm.com>
Subject: Re: [PATCH v2 1/1] tee: optee: expose OS revision via sysfs

Hi Jens,

Jens Wiklander <jens.wiklander@...aro.org> 於 2025年12月3日週三 下午3:51寫道：
>
> Hi,
>
> On Tue, Dec 2, 2025 at 10:54 AM Aristo Chen <jj251510319013@...il.com> wrote:
> >
> > Hi Jens
> >
> > Jens Wiklander <jens.wiklander@...aro.org> 於 2025年12月1日週一 下午9:06寫道：
> > >
> > > Hi,
> > >
> > > On Mon, Dec 1, 2025 at 12:48 PM Aristo Chen <jj251510319013@...il.com> wrote:
> > > >
> > > > Hi,
> > > >
> > > > Sumit Garg <sumit.garg@...nel.org> 於 2025年11月25日週二 下午3:55寫道：
> > > > >
> > > > > On Tue, Nov 25, 2025 at 01:23:22PM +0530, Sumit Garg via OP-TEE wrote:
> > > > > > On Mon, Nov 24, 2025 at 08:15:04AM +0100, Jens Wiklander wrote:
> > > > > > > Hi,
> > > > > > >
> > > > > > > On Sat, Nov 22, 2025 at 4:00 PM Wei Ming Chen <jj251510319013@...il.com> wrote:
> > > > > > > >
> > > > > > > > From: Aristo Chen <aristo.chen@...onical.com>
> > > > > > > >
> > > > > > > > Today the only way to read the OP-TEE OS version is from dmesg/journal
> > > > > > > > logs, which can be lost as buffers roll over. Capture the OS revision
> > > > > > > > (major/minor/build_id) from secure world for both SMC and FF-A ABIs, store
> > > > > > > > it in the OP-TEE driver, and expose a stable userspace readout via
> > > > > > > > /sys/class/tee/tee*/optee_os_revision.
> > > > > > > >
> > > > > > > > Signed-off-by: Aristo Chen <aristo.chen@...onical.com>
> > > > > > > > ---
> > > > > > > >  drivers/tee/optee/core.c          | 19 +++++++++++++++++++
> > > > > > > >  drivers/tee/optee/ffa_abi.c       | 13 +++++++++++--
> > > > > > > >  drivers/tee/optee/optee_private.h | 17 +++++++++++++++++
> > > > > > > >  drivers/tee/optee/smc_abi.c       | 13 +++++++++++--
> > > > > > > >  4 files changed, 58 insertions(+), 4 deletions(-)
> > > > > > >
> > > > > > > This appears to be a feature that could be useful for all TEEs.
> > > > > >
> > > > > > True, it is something that TEE core should support. Although I would
> > > > > > have preferred to extend TEE_IOC_VERSION since that's the common way the
> > > > > > user-space library get's TEE implementation specific information. But
> > > > > > since it being already a user-space ABI which doesn't offer extension.
> > > > > > Maybe we can consider adding TEE_IOC_REVERSION instead of sysfs.
> > > > >
> > > > > Ah, typo here:
> > > > >
> > > > > s/TEE_IOC_REVERSION/TEE_IOC_REVISION/
> > > > >
> > > > > -Sumit
> > > > >
> > > > > >
> > > > > > But before doing that we need to know who is the actual consumer here
> > > > > > from user-space perspective? Will the client applications also depend on
> > > > > > the TEE implementation revision?
> > > > My current thinking is that if the TEE revision is exposed, users can write a
> > > > script to capture the platform state and record the exact secure OS revision
> > > > even after the dmesg/journalctl logs have rolled over. This would significantly
> > > > improve bug triage and regression tracking.
> > > >
> > > > In my case, I have a package with precompiled xtest binaries for multiple
> > > > releases (from 3.14 to 4.6), and I work with different platforms that run
> > > > different OP-TEE OS versions. Having a reliable way to obtain the TEE
> > > > revision would help a lot, as it would allow me to select the correct xtest
> > > > version when running tests.
> > >
> > > I'm concerned that the ABI might be misused to be part of what the
> > > client expects from the TEE. You even express that as a use case. I'd
> > > rather fix the problem with xtest.
> >
> > Thanks for the feedback! To clarify: currently, the OP-TEE OS revision
> > I expose in
> > sysfs is the same value already printed in dmesg at boot
> >  (e.g., “optee: revision 4.8 (XXXXXX)”).
> >
> > Are your concerns specifically about clients inferring capabilities
> > from a revision
> > string (“rev X.Y implies feature Z”)? If so, I agree that’s fragile
> > and not the intent.
>
> Yes

Thanks for clarifying the concern!

>
> > I’m happy to add a short note in the doc that this is informational
> > only and that
> > feature detection must use proper capability queries.
> >
> > Please let me know if that addresses the worry, or if there’s another
> > concern I’m
> > missing.
>
> Adding APIs that aren't supposed to be used seems odd. Do you know if
> there are examples in the kernel for this kind of thing?
I’ve done some research and, as far as I can tell, the TEE core already
provides an informational-only file at /sys/class/tee/tee0/implementation_id.
My understanding is that it was introduced roughly 10 years ago. However,
I haven’t found any documentation clarifying its intended purpose, so I’m
assuming this may be a similar situation. I’d appreciate it if you could correct
me if I’m wrong.

Also, here are some files with similiar purposes:
- /sys/devices/system/cpu/cpu*/microcode/version
- /sys/devices/virtual/dmi/id/{bios_date,bios_release,bios_vendor,bios_version}
- /sys/kernel/security/apparmor/revision

>
> Cheers,
> Jens

Best Regards,
Aristo

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