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

[Jerome Forissier <jerome@forissier.org>]

On 6/17/20 9:52 PM, Maxim Uvarov wrote:
> On Wed, 17 Jun 2020 at 18:16, Jerome Forissier <jerome@forissier.org> 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@linaro.org> 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@linaro.org>
>>>> Reviewed-by: Sumit Garg <sumit.garg@linaro.org>
>>>> ---
>>>>  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@lists.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@linaro.org>
>>>>  L:     tee-dev@lists.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..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 :-/
>>
>> --
>> Jerome
> 
> From  linux side it is for example:
> 
> static const struct tee_client_device_id optee_ftpm_id_table[] = {
>         {UUID_INIT(0xbc50d971, 0xd4c9, 0x42c4,
>                    0x82, 0xcb, 0x34, 0x3f, 0xb7, 0xf3, 0x78, 0x96)},
>         {}
> };
> 
> static struct tee_client_driver ftpm_tee_driver = {
>         .id_table       = optee_ftpm_id_table,
>         .driver         = {
> 
> So sysfs name has to be the same as the driver has. And  UUD is simple
> 16 bytes:#define UUID_SIZE 16
> typedef struct {
>         __u8 b[UUID_SIZE];
> } uuid_t;
> 
> From TA it also:
> #define TA_UUID  { 0xBC50D971, 0xD4C9, 0x42C4, \
>         {0x82, 0xCB, 0x34, 0x3F, 0xB7, 0xF3, 0x78, 0x96}}
> 
> Compare uuid from optee and kernel driver version is simple:
> static inline bool uuid_equal(const uuid_t *u1, const uuid_t *u2)
> {
>         return memcmp(u1, u2, sizeof(uuid_t)) == 0;
> }
> 
> So to support better code navigation. For example grep sources for
> 0xBC50D971, or find in sysfs  "*bc50d971-*" I would say we need to use
> BE format.
> optee might also need to switch to BE prints for the same reason.


Sorry but this does not make much sense to me :-/

All I want to say is, if you ever need to use %pUb for things to work as
expected then it is *very* suspect and you should try to understand why,
because as I said and as far as I can tell OP-TEE stores all it's UUIDs
in memory in little endian format (more precisely, host endian with all
platforms being little endian currently), and %pUb is not even
implemented in OP-TEE.

-- 
Jerome