Re: [virtio-dev] [PATCH v2] virtio-tee: Reserve device ID 46 for TEE device

[Rijo Thomas <Rijo-john.Thomas@amd.com>]

On 9/26/2023 12:14 PM, Sumit Garg wrote:
> +cc Alex
> 
> On Tue, 26 Sept 2023 at 08:16, Jens Wiklander <jens.wiklander@linaro.org> wrote:
>>
>> Hi,
>>
>> [+cc Arnd]
>>
>> On Tue, Sep 26, 2023 at 8:00 AM Sumit Garg <sumit.garg@linaro.org> wrote:
>>>
>>> +cc Jens
>>>
>>>> In a virtual environment, an application running in guest VM may want
>>>> to delegate security sensitive tasks to a Trusted Application (TA)
>>>> running within a Trusted Execution Environment (TEE). A TEE is a trusted
>>>> OS running in some secure environment, for example, TrustZone on ARM
>>>> CPUs, or a separate secure co-processor etc.
>>>
>>> I have been exploring this area quite recently with an effort to have a common VIRIO interface which can support different trusted OS implementations. I guess you intend to test it with AMD-TEE, right? Any plans to test it with OP-TEE? As currently we have these two supported upstream.
>>>
Yes, we have tested with AMD-TEE. We have not yet tested with OP-TEE. Sure, we will try it out.

>>> Do you currently have any virtio frontend/backend implementations for this?
Yes, we have. Frontend is a Linux virtio-TEE driver, and backend is virtio-TEE device emulated in QEMU.
We used Xen hypervisor.

>>>
>>>>
>>>> A virtual TEE device emulates a TEE within a guest VM. Such a virtual
>>>> TEE device supports multiple operations such as:
>>>>
>>>> VIRTIO_TEE_CMD_OPEN_DEVICE – Open a communication channel with virtio
>>>>                              TEE device.
>>>> VIRTIO_TEE_CMD_CLOSE_DEVICE – Close communication channel with virtio
>>>>                               TEE device.
>>>> VIRTIO_TEE_CMD_GET_VERSION – Get version of virtio TEE.
>>>> VIRTIO_TEE_CMD_OPEN_SESSION – Open a session to communicate with
>>>>                               trusted application running in TEE.
>>>> VIRTIO_TEE_CMD_CLOSE_SESSION – Close a session to end communication
>>>>                                with trusted application running in TEE.
>>>> VIRTIO_TEE_CMD_INVOKE_FUNC – Invoke a command or function in trusted
>>>>                              application running in TEE.
>>>> VIRTIO_TEE_CMD_CANCEL_REQ – Cancel an ongoing command within TEE.
>>>>
>>>
>>> How about shared memory support? We would like to register guest pages with the trusted OS.
>>
We have a command VIRTIO_TEE_CMD_REGISTER_MEM for registering shared memory buffer with Trusted OS.

In this command, the guest pages are copied into a shadow buffer in the host OS. And this shadow
buffer is mapped with Trusted OS. So, buffer-copy is involved.

One limitation, that we had was that the guest pages were non-contiguous. So, the number of physical
pages that had to be mapped with Trusted OS was exceeding 64 entries when we were testing out the
registering of guest pages. AMD-TEE Trusted OS can map a physically non-contiguous buffer, but the
number of sg entries for such a buffer must be less than 64. So, we resorted to using a shadow buffer
that is allocated within host, and gets mapped with Trusted OS.

Thanks,
Rijo

>> Coincidently Arnd and I (among others) discussed this in person last
>> week and the conclusion was that only temporary shared memory is
>> possible with virtio. So the shared memory has to be set up and torn
>> down by the host during each operation, typically open-session or
>> invoke-func.
> 
> Agree as I was part of those discussions. But I would like to
> understand the reasoning behind it. Is there any restriction by VIRTIO
> specification that we can't register guest page PAs to a device (TEE
> in our case) to allow for zero copy transfers?
> 
> Alex mentioned some references to virtio GPU device. I suppose I need
> to dive into its implementation to see if there are any similarities
> to our use-case.
> 
>> That might not be optimal if trying to maximize
>> performance, but it is portable.
> 
> IMO, the ABI should be flexible enough to support a TEE with optimum
> performance.
> 
> -Sumit
> 
>>
>> Cheers,
>> Jens
>>
>>>
>>> -Sumit
>>>
>>>> We would like to reserve device ID 46 for Virtio-TEE device.
>>>>
>>>> Signed-off-by: Jeshwanth Kumar <jeshwanthkumar.nk@amd.com>
>>>> ---
>>>>  content.tex | 2 ++
>>>>  1 file changed, 2 insertions(+)
>>>>
>>>> diff --git a/content.tex b/content.tex
>>>> index 0a62dce..644aa4a 100644
>>>> --- a/content.tex
>>>> +++ b/content.tex
>>>> @@ -739,6 +739,8 @@ \chapter{Device Types}\label{sec:Device Types}
>>>>  \hline
>>>>  45         &   SPI master \\
>>>>  \hline
>>>> +46         &   TEE device \\
>>>> +\hline
>>>> \end{tabular}
>>>>
>>>>  Some of the devices above are unspecified by this document,

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