linux-kernel - Re: [PATCH RFC 1/3] firmware: qcom: implement object invoke support

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Message-ID: <CAA8EJpojNj0wB1aG3JWBc3AVGAUH7foShiWsX4MYdkYJLWRn8Q@mail.gmail.com>
Date: Thu, 25 Jul 2024 07:32:49 +0300
From: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To: Amirreza Zarrabi <quic_azarrabi@...cinc.com>
Cc: Bjorn Andersson <andersson@...nel.org>, Konrad Dybcio <konrad.dybcio@...aro.org>, 
	Sumit Semwal <sumit.semwal@...aro.org>, Christian König <christian.koenig@....com>, 
	srinivas.kandagatla@...aro.org, bartosz.golaszewski@...aro.org, 
	linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org, 
	dri-devel@...ts.freedesktop.org, linaro-mm-sig@...ts.linaro.org
Subject: Re: [PATCH RFC 1/3] firmware: qcom: implement object invoke support

On Thu, 25 Jul 2024 at 07:15, Amirreza Zarrabi
<quic_azarrabi@...cinc.com> wrote:
>
>
>
> On 7/25/2024 2:09 PM, Dmitry Baryshkov wrote:
> > On Thu, Jul 25, 2024 at 01:19:07PM GMT, Amirreza Zarrabi wrote:
> >>
> >>
> >> On 7/4/2024 5:34 PM, Dmitry Baryshkov wrote:
> >>> On Thu, 4 Jul 2024 at 00:40, Amirreza Zarrabi <quic_azarrabi@...cinc.com> wrote:
> >>>>
> >>>>
> >>>>
> >>>> On 7/3/2024 10:13 PM, Dmitry Baryshkov wrote:
> >>>>> On Tue, Jul 02, 2024 at 10:57:36PM GMT, Amirreza Zarrabi wrote:
> >>>>>> Qualcomm TEE hosts Trusted Applications and Services that run in the
> >>>>>> secure world. Access to these resources is provided using object
> >>>>>> capabilities. A TEE client with access to the capability can invoke
> >>>>>> the object and request a service. Similarly, TEE can request a service
> >>>>>> from nonsecure world with object capabilities that are exported to secure
> >>>>>> world.
> >>>>>>
> >>>>>> We provide qcom_tee_object which represents an object in both secure
> >>>>>> and nonsecure world. TEE clients can invoke an instance of qcom_tee_object
> >>>>>> to access TEE. TEE can issue a callback request to nonsecure world
> >>>>>> by invoking an instance of qcom_tee_object in nonsecure world.
> >>>>>
> >>>>> Please see Documentation/process/submitting-patches.rst on how to write
> >>>>> commit messages.
> >>>>
> >>>> Ack.
> >>>>
> >>>>>
> >>>>>>
> >>>>>> Any driver in nonsecure world that is interested to export a struct (or a
> >>>>>> service object) to TEE, requires to embed an instance of qcom_tee_object in
> >>>>>> the relevant struct and implements the dispatcher function which is called
> >>>>>> when TEE invoked the service object.
> >>>>>>
> >>>>>> We also provids simplified API which implements the Qualcomm TEE transport
> >>>>>> protocol. The implementation is independent from any services that may
> >>>>>> reside in nonsecure world.
> >>>>>
> >>>>> "also" usually means that it should go to a separate commit.
> >>>>
> >>>> I will split this patch to multiple smaller ones.
> >>>>
> >>>
> >>> [...]
> >>>
> >>>>>
> >>>>>> +    } in, out;
> >>>>>> +};
> >>>>>> +
> >>>>>> +int qcom_tee_object_do_invoke(struct qcom_tee_object_invoke_ctx *oic,
> >>>>>> +    struct qcom_tee_object *object, unsigned long op, struct qcom_tee_arg u[], int *result);
> >>>>>
> >>>>> What's the difference between a result that gets returned by the
> >>>>> function and the result that gets retuned via the pointer?
> >>>>
> >>>> The function result, is local to kernel, for instance memory allocation failure,
> >>>> or failure to issue the smc call. The result in pointer, is the remote result,
> >>>> for instance return value from TA, or the TEE itself.
> >>>>
> >>>> I'll use better name, e.g. 'remote_result'?
> >>>
> >>> See how this is handled by other parties. For example, PSCI. If you
> >>> have a standard set of return codes, translate them to -ESOMETHING in
> >>> your framework and let everybody else see only the standard errors.
> >>>
> >>>
> >>
> >> I can not hide this return value, they are TA dependent. The client to a TA
> >> needs to see it, just knowing that something has failed is not enough in
> >> case they need to do something based on that. I can not even translate them
> >> as they are TA related so the range is unknown.
> >
> > I'd say it a sad design. At least error values should be standard.
> >
>
> Sure. But it is normal. If we finally move to TEE subsystem, this is the value that
> would be copied to struct tee_ioctl_invoke_arg.ret to pass to the caller of
> TEE_IOC_INVOKE.

Ack

-- 
With best wishes
Dmitry