Re: [PATCH v19 2/6] remoteproc: Add TEE support

[Abdellatif El Khlifi <abdellatif.elkhlifi@arm.com>]

Hi Arnaud,

> Add a remoteproc TEE (Trusted Execution Environment) driver that will be
> probed by the TEE bus. If the associated Trusted application is supported
> on the secure part, this driver offers a client interface to load firmware
> by the secure part.
> This firmware could be authenticated by the secure trusted application.
> 
> A specificity of the implementation is that the firmware has to be
> authenticated and optionally decrypted to access the resource table.
> 
> Consequently, the boot sequence is:
> 
> 1) rproc_parse_fw --> rproc_tee_parse_fw
>    remoteproc TEE:
>    - Requests the TEE application to authenticate and load the firmware
>      in the remote processor memories.
>    - Requests the TEE application for the address of the resource table.
>    - Creates a copy of the resource table stored in rproc->cached_table.
> 
> 2) rproc_load_segments --> rproc_tee_load_fw
>    remoteproc TEE:
>    - Requests the TEE application to load the firmware. Nothing is done
>      at the TEE application as the firmware is already loaded.
>    - In case of recovery, the TEE application has to reload the firmware.
> 
> 3) rproc_tee_get_loaded_rsc_table
>    remoteproc TEE requests the TEE application for the address of the
>    resource table.
> 
> 4) rproc_start --> rproc_tee_start
>    - Requests the TEE application to start the remote processor.
> 
> The shutdown sequence is:
> 
> 5) rproc_stop --> rproc_tee_stop
>    - Requests the TEE application to stop the remote processor.
> 
> 6) rproc_tee_release_fw
>    This function is used to request the TEE application to perform actions
>    to return to the initial state on stop or on error during the boot
>    sequence.
> 
> Signed-off-by: Arnaud Pouliquen <arnaud.pouliquen@foss.st.com>
...
> +
> +static const struct tee_client_device_id rproc_tee_id_table[] = {
> +	{UUID_INIT(0x80a4c275, 0x0a47, 0x4905, 0x82, 0x85, 0x14, 0x86, 0xa9, 0x77, 0x1a, 0x08)},
> +	{}
> +};

Other implementations may use different UUIDs.
What about adding a kernel configuration option which, when enabled, allows
alternative implementations to override this table?

> +/**
> + * rproc_tee_register() - Register a remote processor controlled by the TEE application.
...
> +
> +static int rproc_tee_ctx_match(struct tee_ioctl_version_data *ver, const void *data)
> +{
> +	/* Today we support only the OP-TEE, could be extend to other tees */
> +	return (ver->impl_id == TEE_IMPL_ID_OPTEE);
> +}

Could we make ver->impl_id user-configurable please ? for example, by reading
it from the device tree since it isn’t discoverable at runtime? In our setup, we’d set
it to TEE_IMPL_ID_TSTEE.

> +
> +static int rproc_tee_probe(struct device *dev)
> +{
> +	struct tee_context *tee_ctx;
> +	int ret;
> +
> +	/* Open context with TEE driver */
> +	tee_ctx = tee_client_open_context(NULL, rproc_tee_ctx_match, NULL, NULL);
> +	if (IS_ERR(tee_ctx))
> +		return PTR_ERR(tee_ctx);
> +
> +	ret = mutex_lock_interruptible(&ctx_lock);
> +	if (ret)
> +		return ret;

In some TEEs, the client driver might need to perform extra work during probing.
For example, when using TS TEE, calling tee_shm_alloc_kernel_buf() is required.
Could we introduce an rproc_tee_ops and add a TEE probe operation called by the
remoteproc driver for performing custom TEE setup ?

Kind regards,
Abdellatif