linux-kernel - Re: [PATCHv6 1/3] optee: use uuid for sysfs driver entry

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Date:   Thu, 4 Jun 2020 14:51:03 +0530
From:   Sumit Garg <sumit.garg@...aro.org>
To:     Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
Cc:     Maxim Uvarov <maxim.uvarov@...aro.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "tee-dev @ lists . linaro . org" <tee-dev@...ts.linaro.org>,
        peterhuewe@....de, Jason Gunthorpe <jgg@...pe.ca>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jens Wiklander <jens.wiklander@...aro.org>,
        linux-integrity@...r.kernel.org, Arnd Bergmann <arnd@...aro.org>
Subject: Re: [PATCHv6 1/3] optee: use uuid for sysfs driver entry

On Thu, 4 Jun 2020 at 14:07, Jarkko Sakkinen
<jarkko.sakkinen@...ux.intel.com> wrote:
>
> On Mon, Jun 01, 2020 at 06:06:43PM +0300, Maxim Uvarov wrote:
> > With the evolving use-cases for TEE bus, now it's required to support
> > multi-stage enumeration process. But using a simple index doesn't
> > suffice this requirement and instead leads to duplicate sysfs entries.
> > So instead switch to use more informative device UUID for sysfs entry
> > like:
> > /sys/bus/tee/devices/optee-ta-<uuid>
> >
> > Signed-off-by: Maxim Uvarov <maxim.uvarov@...aro.org>
> > Reviewed-by: Sumit Garg <sumit.garg@...aro.org>
>
> Why do you mean by duplicate sysfs entries?
>

It's just about the device being added with the same name as of the
device which is already present on the TEE bus. So this leads to
duplicate sysfs entry error for device node which is created during
device_register() execution flow.

> > ---
> >  Documentation/ABI/testing/sysfs-bus-optee-devices | 8 ++++++++
> >  MAINTAINERS                                       | 1 +
> >  drivers/tee/optee/device.c                        | 6 +++---
> >  3 files changed, 12 insertions(+), 3 deletions(-)
> >  create mode 100644 Documentation/ABI/testing/sysfs-bus-optee-devices
> >
> > diff --git a/Documentation/ABI/testing/sysfs-bus-optee-devices b/Documentation/ABI/testing/sysfs-bus-optee-devices
> > new file mode 100644
> > index 000000000000..0ae04ae5374a
> > --- /dev/null
> > +++ b/Documentation/ABI/testing/sysfs-bus-optee-devices
> > @@ -0,0 +1,8 @@
> > +What:                /sys/bus/tee/devices/optee-ta-<uuid>/
> > +Date:           May 2020
> > +KernelVersion   5.7
> > +Contact:        tee-dev@...ts.linaro.org
> > +Description:
> > +             OP-TEE bus provides reference to registered drivers under this directory. The <uuid>
> > +             matches Trusted Application (TA) driver and corresponding TA in secure OS. Drivers
> > +             are free to create needed API under optee-ta-<uuid> directory.
> > diff --git a/MAINTAINERS b/MAINTAINERS
> > index ecc0749810b0..6717afef2de3 100644
> > --- a/MAINTAINERS
> > +++ b/MAINTAINERS
> > @@ -12516,6 +12516,7 @@ OP-TEE DRIVER
> >  M:   Jens Wiklander <jens.wiklander@...aro.org>
> >  L:   tee-dev@...ts.linaro.org
> >  S:   Maintained
> > +F:   Documentation/ABI/testing/sysfs-bus-optee-devices
> >  F:   drivers/tee/optee/
> >
> >  OP-TEE RANDOM NUMBER GENERATOR (RNG) DRIVER
> > diff --git a/drivers/tee/optee/device.c b/drivers/tee/optee/device.c
> > index e3a148521ec1..ed3d1ddfa52b 100644
> > --- a/drivers/tee/optee/device.c
> > +++ b/drivers/tee/optee/device.c
> > @@ -65,7 +65,7 @@ static int get_devices(struct tee_context *ctx, u32 session,
> >       return 0;
> >  }
> >
> > -static int optee_register_device(const uuid_t *device_uuid, u32 device_id)
> > +static int optee_register_device(const uuid_t *device_uuid)
> >  {
> >       struct tee_client_device *optee_device = NULL;
> >       int rc;
> > @@ -75,7 +75,7 @@ static int optee_register_device(const uuid_t *device_uuid, u32 device_id)
> >               return -ENOMEM;
> >
> >       optee_device->dev.bus = &tee_bus_type;
> > -     dev_set_name(&optee_device->dev, "optee-clnt%u", device_id);
> > +     dev_set_name(&optee_device->dev, "optee-ta-%pUl", device_uuid);
>
> This code is and already was broken. If dev_set_name() returns -ENOMEM,
> the name will be a null pointer.

Is this an expected error scenario? dev_set_name() is invoked at
numerous places in the kernel without any error check.

>
> Also, I don't get how you can just swap the name without potentially
> breaking the backwards compatiblity towards the user space.

As of now, there isn't any compatibility concerns with user space as
these TEE devices are meant to be used by kernel drivers only. TEE
user-space interface is quite separate (see: Documentation/tee.txt).

-Sumit

>
> /Jarkko