Re: [Tee-dev] [PATCHv8 1/3] optee: use uuid for sysfs driver entry

[Jerome Forissier]

On 6/18/20 6:59 AM, Sumit Garg wrote:
> Hi Jerome,
> 
> On Wed, 17 Jun 2020 at 20:46, Jerome Forissier <jerome@xxxxxxxxxxxxx> wrote:
>>
>>
>>
>> On 6/17/20 3:58 PM, Sumit Garg wrote:
>>> Hi Maxim,
>>>
>>> On Thu, 4 Jun 2020 at 23:28, Maxim Uvarov <maxim.uvarov@xxxxxxxxxx> 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@xxxxxxxxxx>
>>>> Reviewed-by: Sumit Garg <sumit.garg@xxxxxxxxxx>
>>>> ---
>>>>  Documentation/ABI/testing/sysfs-bus-optee-devices | 8 ++++++++
>>>>  MAINTAINERS                                       | 1 +
>>>>  drivers/tee/optee/device.c                        | 9 ++++++---
>>>>  3 files changed, 15 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@xxxxxxxxxxxxxxxx
>>>> +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@xxxxxxxxxx>
>>>>  L:     tee-dev@xxxxxxxxxxxxxxxx
>>>>  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..23d264c8146e 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 +75,10 @@ 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);
>>>> +       if (dev_set_name(&optee_device->dev, "optee-ta-%pUl", device_uuid)) {
>>>
>>> You should be using format specifier as: "%pUb" instead of "%pUl" as
>>> UUID representation for TAs is in big endian format. See below:
>>
>> Where does device_uuid come from? If it comes directly from OP-TEE, then
>> it should be a pointer to the following struct:
>>
>> typedef struct
>> {
>>         uint32_t timeLow;
>>         uint16_t timeMid;
>>         uint16_t timeHiAndVersion;
>>         uint8_t clockSeqAndNode[8];
>> } TEE_UUID;
>>
>> (GlobalPlatform TEE Internal Core API spec v1.2.1 section 3.2.4)
>>
>> - The spec does not mandate any particular endianness and simply warns
>> about possible issues if secure and non-secure worlds differ in endianness.
>> - OP-TEE uses %pUl assuming that host order is little endian (that is
>> true for the Arm platforms that run OP-TEE currently). By the same logic
>> %pUl should be fine in the kernel.
>> - On the other hand, the UUID in a Trusted App header is always encoded
>> big endian by the Python script that signs and optionally encrypts the
>> TA. This should not have any visible impact on UUIDs exchanged between
>> the secure and non-secure world though.
>>
>> So I am wondering why you had to use %pUb. There must be some
>> inconsistency somewhere :-/
> 
> Yes there is. Linux stores UUID in big endian format (16 byte octets)
> and OP-TEE stores UUID in little endian format (in form of struct you
> referenced above).
> 
> And format conversion APIs [1] in OP-TEE OS are used while passing
> UUID among Linux and OP-TEE.
> 
> So we need to use %pUb in case of Linux and %pUl in case of OP-TEE.
> 
> [1] https://github.com/OP-TEE/optee_os/blob/master/core/tee/uuid.c


Got it now. The TA enumeration function in OP-TEE performs  the
conversion here:
https://github.com/OP-TEE/optee_os/blob/3.9.0/core/pta/device.c#L34

Thanks for clarifying.

-- 
Jerome