Re: Possible race during OP-TEE kernel module device probing

[Sumit Garg via OP-TEE <op-tee@lists.trustedfirmware.org>]

On Mon, Mar 30, 2026 at 11:16:59AM +0200, Jens Wiklander wrote:
> Hi,
> 
> On Mon, Mar 30, 2026 at 6:07 AM Shf Chen (陳少甫) via OP-TEE
> <op-tee@lists.trustedfirmware.org> wrote:
> >
> > On Fri, 2026-03-27 at 15:31 +0530, Sumit Garg wrote:
> > > On Fri, Mar 27, 2026 at 09:01:15AM +0000, Shf Chen (陳少甫) via OP-TEE wrote:
> > > > Hi,
> > > >
> > > > We found a possible race condition issue during OP-TEE kernel driver probing the device.
> > > > A NULL pointer dereference exception can happen when another kernel driver open OP-TEE context
> > > > with tee_client_open_context() then do a SMC call to OP-TEE.
> > > > Below is the exception:
> > >
> > > How is your kernel driver being probed? Have you registered it as a
> > > proper TEE bus driver? Any custom ways to invoke TEE kernel client APIs
> > > are surely susceptible to races like the one you mentioned below.
> > >
> > > -Sumit
> >
> > Hi,
> >
> > Our kernel driver does not registered as a TEE bus driver for some reasons,
> > and we need to use other API to ensure the OP-TEE driver is probed to
> > workaround this issue. But, we think this is error-prone for module developer
> > that need to call to OP-TEE.

The kernel modules API for OP-TEE is via TEE bus only.

> >
> > Although this is not the case, I think that after calling tee_device_register(),
> > the optee device is shown under `/dev/` filesystem. There is a very small chance
> > for userspace program to trigger this race condition, and they don't have clue on
> > whether the device is properly being probed yet.
> 
> I think you're on to something. After calling tee_device_register(),
> the driver must be able to handle requests, at least without crashing.
> optee_enumerate_devices() requires the devices to be registered, so
> that must happen after those calls. But other than that, I think the
> calls to  tee_device_register() should be the last thing in the probe
> function.
> 
> Sumit, do you agree?
> 

Sounds reasonable to me if it's something that can be reproduced via
the user-space client.

-Sumit