Re: [PATCH v7 06/11] firmware: qcom: scm: add support for object invocation

[Amirreza Zarrabi <amirreza.zarrabi@oss.qualcomm.com>]

On 8/13/2025 7:53 PM, Konrad Dybcio wrote:
> On 8/13/25 2:35 AM, Amirreza Zarrabi wrote:
>> Qualcomm TEE (QTEE) hosts Trusted Applications (TAs) and services in
>> the secure world, accessed via objects. A QTEE client can invoke these
>> objects to request services. Similarly, QTEE can request services from
>> the nonsecure world using objects exported to the secure world.
>>
>> Add low-level primitives to facilitate the invocation of objects hosted
>> in QTEE, as well as those hosted in the nonsecure world.
>>
>> If support for object invocation is available, the qcom_scm allocates
>> a dedicated child platform device. The driver for this device communicates
>> with QTEE using low-level primitives.
>>
>> Tested-by: Neil Armstrong <neil.armstrong@linaro.org>
>> Tested-by: Harshal Dev <quic_hdev@quicinc.com>
>> Signed-off-by: Amirreza Zarrabi <amirreza.zarrabi@oss.qualcomm.com>
>> ---
> 
> [...]
> 
>> +int qcom_scm_qtee_invoke_smc(phys_addr_t inbuf, size_t inbuf_size,
>> +			     phys_addr_t outbuf, size_t outbuf_size,
>> +			     u64 *result, u64 *response_type)
>> +{
>> +	struct qcom_scm_desc desc = {
>> +		.svc = QCOM_SCM_SVC_SMCINVOKE,
>> +		.cmd = QCOM_SCM_SMCINVOKE_INVOKE,
>> +		.owner = ARM_SMCCC_OWNER_TRUSTED_OS,
>> +		.args[0] = inbuf,
>> +		.args[1] = inbuf_size,
>> +		.args[2] = outbuf,
>> +		.args[3] = outbuf_size,
>> +		.arginfo = QCOM_SCM_ARGS(4, QCOM_SCM_RW, QCOM_SCM_VAL,
>> +					 QCOM_SCM_RW, QCOM_SCM_VAL),
>> +	};
>> +	struct qcom_scm_res res;
>> +	int ret;
>> +
>> +	ret = qcom_scm_call(__scm->dev, &desc, &res);
>> +	if (ret)
>> +		return ret;
>> +
>> +	*response_type = res.result[0];
>> +	*result = res.result[1];
> 
> These are dereferenced without checking, which will surely upset static
> checkers (and users)
> 

There is no consistency in qcom_scm.c; I see multiple instances where
similar dereferencing is already happening in this file. However, I'll
add the if (...) check to be sure. The reason I initially skipped it
is that this API has a single user -- the TEE subsystem.

> I see that res.result[2] should also return some (aptly named) "data"
> which you handled in v1, but dropped in v2 (without a comment AFAICT)
> 
> Looking at it, we could probably wrap it in qcom_scm_qseecom_call()
> which this seems to be fit for
> 

I cannot use qcom_scm_qseecom_call() because this is not a qseecom
transport. It's a new transport called smcinvoke, which, for instance,
does not require a lock.

The data field is intended for qseecom over smcinvoke, which we will
never support -- so there's no reason to return it.

>> +
>> +	return 0;
>> +}
>> +EXPORT_SYMBOL(qcom_scm_qtee_invoke_smc);
>> +
>> +/**
>> + * qcom_scm_qtee_callback_response() - Submit response for callback request.
>> + * @buf: start address of memory area used for outbound buffer.
>> + * @buf_size: size of the memory area used for outbound buffer.
>> + * @result: Result of QTEE object invocation.
>> + * @response_type: Response type returned by QTEE.
>> + *
>> + * @response_type determines how the contents of @buf should be processed.
>> + *
>> + * Return: On success, return 0 or <0 on failure.
>> + */
>> +int qcom_scm_qtee_callback_response(phys_addr_t buf, size_t buf_size,
>> +				    u64 *result, u64 *response_type)
> 
> These should be aligned

Ack.

> 
>> +{
>> +	struct qcom_scm_desc desc = {
>> +		.svc = QCOM_SCM_SVC_SMCINVOKE,
>> +		.cmd = QCOM_SCM_SMCINVOKE_CB_RSP,
>> +		.owner = ARM_SMCCC_OWNER_TRUSTED_OS,
>> +		.args[0] = buf,
>> +		.args[1] = buf_size,
>> +		.arginfo = QCOM_SCM_ARGS(2, QCOM_SCM_RW, QCOM_SCM_VAL),
>> +	};
>> +	struct qcom_scm_res res;
>> +	int ret;
>> +
>> +	ret = qcom_scm_call(__scm->dev, &desc, &res);
>> +	if (ret)
>> +		return ret;
>> +
>> +	*response_type = res.result[0];
>> +	*result = res.result[1];
> 
> this also seems like a good candidate for qcom_scm_qseecom_call()
> 

ditto.

> [...]
> 
>>  /**
>>   * qcom_scm_is_available() - Checks if SCM is available
>>   */
>> @@ -2326,6 +2444,16 @@ static int qcom_scm_probe(struct platform_device *pdev)
>>  	ret = qcom_scm_qseecom_init(scm);
>>  	WARN(ret < 0, "failed to initialize qseecom: %d\n", ret);
>>  
>> +	/*
>> +	 * Initialize the QTEE object interface.
>> +	 *
>> +	 * This only represents the availability for QTEE object invocation
>> +	 * and callback support. On failure, ignore the result. Any subsystem
>> +	 * depending on it may fail if it tries to access this interface.
>> +	 */
>> +	ret = qcom_scm_qtee_init(scm);
>> +	WARN(ret < 0, "failed to initialize qcomtee: %d\n", ret);
> 
> This will throw a WARN on *a lot* of platforms, ranging from
> Chromebooks running TF-A (with a reduced SMC handler), through
> platforms requiring QCOM_SCM_SMCINVOKE_INVOKE_LEGACY (0x00) cmd
> 

Are you suggesting I remove the WARN? If so, how should the user be notified?
Should the error simply be ignored?

> Konrad

Thanks,
Amir