[RFC PATCH] tee: tstee: Add initial Trusted Services TEE driver

[Balint Dobszay]

Hi Sumit,

On 3 Oct 2023, at 17:42, Sumit Garg wrote:
> On Wed, 27 Sept 2023 at 20:56, Balint Dobszay <balint.dobszay at arm.com> wrote:
>>
>> The Trusted Services project provides a framework for developing and
>> deploying device Root Of Trust services in FF-A Secure Partitions. The
>> FF-A SPs are accessible through the FF-A driver, but this doesn't
>> provide a user space interface. The goal of this TEE driver is to make
>> Trusted Services SPs accessible for user space clients.
>
> I am interested in exploring the user space library/applications. Do
> you have a standard library implementation and some example user-space
> applications leveraging this driver interface?

Yes we have a library reference implementation in Trusted Services using
this driver called libts [1]. There are some test applications that rely
on this library, e.g. ts-service-test [2]. Also, the Parsec project can
use Trusted Services as backend through libts [3] (note, the version of
TS currently integrated in Parsec is not recent, thus the libts in there
still uses an earlier version of this driver).

[snip]

>> +static int tstee_invoke_func(struct tee_context *ctx, struct tee_ioctl_invoke_arg *arg,
>> +                            struct tee_param *param)
>> +{
>> +       struct tstee *tstee = tee_get_drvdata(ctx->teedev);
>> +       struct ffa_device *ffa_dev = tstee->ffa_dev;
>> +       struct ts_context_data *ctxdata = ctx->data;
>> +       struct ffa_send_direct_data ffa_data;
>> +       struct tee_shm *shm = NULL;
>> +       struct ts_session *sess;
>> +       u32 req_len, ffa_args[5] = {};
>> +       int shm_id, rc;
>> +       u8 iface_id;
>> +       u64 handle;
>> +       u16 opcode;
>> +
>> +       mutex_lock(&ctxdata->mutex);
>> +       sess = find_session(ctxdata, arg->session);
>> +
>> +       /* Do this while holding the mutex to make sure that the session wasn't closed meanwhile */
>> +       if (sess)
>> +               iface_id = sess->iface_id;
>> +
>> +       mutex_unlock(&ctxdata->mutex);
>> +       if (!sess)
>> +               return -EINVAL;
>> +
>> +       opcode = lower_16_bits(arg->func);
>> +       shm_id = lower_32_bits(param[0].u.value.a);
>> +       req_len = lower_32_bits(param[0].u.value.b);
>> +
>> +       if (shm_id != 0) {
>> +               shm = tee_shm_get_from_id(ctx, shm_id);
>> +               if (IS_ERR(shm))
>> +                       return PTR_ERR(shm);
>> +
>> +               if (shm->size < req_len) {
>> +                       pr_err("request doesn't fit into shared memory buffer\n");
>> +                       rc = -EINVAL;
>> +                       goto out;
>> +               }
>> +
>> +               handle = shm->sec_world_id;
>> +       } else {
>> +               handle = FFA_INVALID_MEM_HANDLE;
>> +       }
>> +
>> +       ffa_args[TS_RPC_CTRL_REG] = TS_RPC_CTRL_PACK_IFACE_OPCODE(iface_id, opcode);
>> +       ffa_args[TS_RPC_SERVICE_MEM_HANDLE_LSW] = lower_32_bits(handle);
>> +       ffa_args[TS_RPC_SERVICE_MEM_HANDLE_MSW] = upper_32_bits(handle);
>> +       ffa_args[TS_RPC_SERVICE_REQ_LEN] = req_len;
>> +       ffa_args[TS_RPC_SERVICE_CLIENT_ID] = 0;
>> +
>> +       arg_list_to_ffa_data(ffa_args, &ffa_data);
>> +       rc = ffa_dev->ops->msg_ops->sync_send_receive(ffa_dev, &ffa_data);
>
> I haven't dug deeper into the ABI yet, which is something I will look
> into. But these RPC commands caught my attention. Are these RPC calls
> blocking in nature? Is there a possibility that these could cause CPU
> stalls? Do the Linux interrupts remain unhandled until the RPC calls
> return?

Yes, that is correct. We did encounter CPU stalls indeed, our solution
was to enable preemption of S-EL0 SPs in OP-TEE [3] which solved the
issue.

Regards,
Balint

[1] https://git.trustedfirmware.org/TS/trusted-services.git/tree/deployments/libts/arm-linux?h=v1.0.0
[2] https://git.trustedfirmware.org/TS/trusted-services.git/tree/deployments/ts-service-test/arm-linux?h=v1.0.0
[3] https://github.com/parallaxsecond/parsec/tree/3bcd732b92009612109517a6c9075643ef648ca7/src/providers/trusted_service
[4] https://github.com/OP-TEE/optee_os/pull/6002