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

[Sumit Garg]

On Tue, 10 Oct 2023 at 21:11, Balint Dobszay <balint.dobszay at arm.com> wrote:
>
> 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).

Although I am currently exploring the user-space interface, I would
like to give it a hands-on. Is it possible to run this trusted
services setup on Qemu? If yes then can you share instructions how to
test them?

>
> [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.

I would have preferred to unite FFA_INTERRUPT and
OPTEE_FFA_YIELDING_CALL_RETURN_INTERRUPT since underneath both are
using FFA ABI.

Jens,

Can we change OP-TEE to use FFA_INTERRUPT as well when using FFA ABI?

-Sumit

>
> 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