Message-ID: <c3d14f64-bf04-46b9-ac7b-af7ef9014335@xs4all.nl>
Date:   Wed, 20 Sep 2023 09:20:50 +0200
From:   Hans Verkuil <hverkuil-cisco@...all.nl>
To:     Nicolas Dufresne <nicolas.dufresne@...labora.com>,
        Jeffrey Kardatzke <jkardatzke@...gle.com>
Cc:     Yunfei Dong (董云飞) 
        <Yunfei.Dong@...iatek.com>,
        "nhebert@...omium.org" <nhebert@...omium.org>,
        "benjamin.gaignard@...labora.com" <benjamin.gaignard@...labora.com>,
        "nfraprado@...labora.com" <nfraprado@...labora.com>,
        "angelogioacchino.delregno@...labora.com" 
        <angelogioacchino.delregno@...labora.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-mediatek@...ts.infradead.org" 
        <linux-mediatek@...ts.infradead.org>,
        "frkoenig@...omium.org" <frkoenig@...omium.org>,
        "stevecho@...omium.org" <stevecho@...omium.org>,
        "wenst@...omium.org" <wenst@...omium.org>,
        "linux-media@...r.kernel.org" <linux-media@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "daniel@...ll.ch" <daniel@...ll.ch>,
        Project_Global_Chrome_Upstream_Group 
        <Project_Global_Chrome_Upstream_Group@...iatek.com>,
        "hsinyi@...omium.org" <hsinyi@...omium.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 12/14] media: medkatek: vcodec: set secure mode to decoder
 driver

On 19/09/2023 20:51, Nicolas Dufresne wrote:
> Le mardi 19 septembre 2023 à 10:53 +0200, Hans Verkuil a écrit :
>> On 18/09/2023 22:57, Jeffrey Kardatzke wrote:
>>> On Fri, Sep 15, 2023 at 1:56 AM Hans Verkuil <hverkuil-cisco@...all.nl> wrote:
>>>>
>>>> On 15/09/2023 10:25, Yunfei Dong (董云飞) wrote:
>>>>> Hi Hans & Nicolas,
>>>>>
>>>>> Thanks for your advice.
>>>>>
>>>>> On Tue, 2023-09-12 at 11:30 +0200, Hans Verkuil wrote:
>>>>>>
>>>>>> External email : Please do not click links or open attachments until
>>>>>> you have verified the sender or the content.
>>>>>>  Hi,
>>>>>>
>>>>>> On 9/11/23 17:54, Nicolas Dufresne wrote:
>>>>>>> Hi,
>>>>>>>
>>>>>>> Le lundi 11 septembre 2023 à 20:59 +0800, Yunfei Dong a écrit :
>>>>>>>> Setting secure mode flag to kernel when trying to play secure
>>>>>>
>>>>>> video,
>>>>>>>> then decoder driver will initialize tee related interface to
>>>>>>
>>>>>> support
>>>>>>>> svp.
>>>>>>>
>>>>>>>
>>>>>>> This is not what the patch is doing, please rework. This patch is
>>>>>>
>>>>>> an vendor API
>>>>>>> addition introducing V4L2_CID_MPEG_MTK_SET_SECURE_MODE. I should
>>>>>>
>>>>>> not have to
>>>>>>> read your patch to understand this.
>>>>>>>
>>>>>>>>
>>>>>>>> Signed-off-by: Yunfei Dong <yunfei.dong@...iatek.com>
>>>>>>>> ---
>>>>>>>>  .../vcodec/decoder/mtk_vcodec_dec_stateless.c     | 15
>>>>>>
>>>>>> ++++++++++++++-
>>>>>>>>  drivers/media/v4l2-core/v4l2-ctrls-defs.c         |  5 +++++
>>>>>>>>  include/uapi/linux/v4l2-controls.h                |  1 +
>>>>>>>>  3 files changed, 20 insertions(+), 1 deletion(-)
>>>>>>>>
>>>>>>>> diff --git
>>>>>>
>>>>>> a/drivers/media/platform/mediatek/vcodec/decoder/mtk_vcodec_dec_state
>>>>>> less.c
>>>>>> b/drivers/media/platform/mediatek/vcodec/decoder/mtk_vcodec_dec_state
>>>>>> less.c
>>>>>>>> index d2b09ce9f1cf..a981178c25d9 100644
>>>>>>>> ---
>>>>>>
>>>>>> a/drivers/media/platform/mediatek/vcodec/decoder/mtk_vcodec_dec_state
>>>>>> less.c
>>>>>>>> +++
>>>>>>
>>>>>> b/drivers/media/platform/mediatek/vcodec/decoder/mtk_vcodec_dec_state
>>>>>> less.c
>>>>>>>> @@ -535,6 +535,17 @@ static int mtk_vdec_s_ctrl(struct v4l2_ctrl
>>>>>>
>>>>>> *ctrl)
>>>>>>>>  ctrl->val = mtk_dma_contig_get_secure_handle(ctx, ctrl->val);
>>>>>>>>  mtk_v4l2_vdec_dbg(3, ctx, "get secure handle: %d => 0x%x",
>>>>>>
>>>>>> sec_fd, ctrl->val);
>>>>>>>>  break;
>>>>>>>> +case V4L2_CID_MPEG_MTK_SET_SECURE_MODE:
>>>>>>>
>>>>>>> Stepping back a little and focusing on the API, what makes your
>>>>>>
>>>>>> driver so
>>>>>>> special that it should be the only one having a "secure mode" ? We
>>>>>>
>>>>>> are touching
>>>>>>> in gap in the media pipeline in Linux, and this should come with
>>>>>>
>>>>>> consideration
>>>>>>> of the global API.
>>>>>>>
>>>>>>> Why is this API better then let's say Google Android one, were they
>>>>>>
>>>>>> expose 2
>>>>>>> device nodes in their fork of the MFC driver (a secure and a non
>>>>>>
>>>>>> secure one) ?
>>>>>>
>>>>>> Perhaps it is a good idea to first post an RFC with an uAPI proposal
>>>>>> on how to
>>>>>> handle secure video. I suspect this isn't mediatek specific, other
>>>>>> SoCs with
>>>>>> tee support could use this as well.
>>>>>>
>>>>>> As Nicolas said, it's long known to be a gap in our media support, so
>>>>>> it is
>>>>>> really great that you started work on this, but you need to look at
>>>>>> this from
>>>>>> a more generic point-of-view, and not mediatek-specific.
>>>>>>
>>>>>
>>>>> Whether your have any advice about how to do a more generic driver to
>>>>> handle secure video playback?
>>>>>
>>>>> There are several kind of buffer: output queue buffer/capture queue
>>>>> buffer/working buffer.
>>>>>
>>>>> output and capture queue buffer: user space will call tee related
>>>>> interface to allocate secure handle. Will convert to secure handle with
>>>>> v4l2 framework, then send secure handle to optee-os.
>>>>>
>>>>> working buffer: calling dma_heap and dma_buf to get secure memory
>>>>> handle, then covert secure iova in optee-os.
>>>>>
>>>>> Using the same kernel driver for svp and non-svp playback, just the
>>>>> buffer type are different. Normal is iova and secure is secure handle.
>>>>>
>>>>> User driver will tell the kernel driver with CID control whether the
>>>>> current playback is svp or non-svp.
>>>>
>>>> My understanding is that when you switch to secure mode, the driver makes
>>>> some optee calls to set everything up. And userspace needs a way convert a
>>>> dmabuf fd to a 'secure handle', which appears to be the DMA address of the
>>>> buffer. Who uses that handle?
>>>
>>> The only user space usage for getting the 'secure handle' from an fd
>>> is when that memory is written to. This is done when the TEE decrypts
>>> the video contents. User space sends the encrypted video + 'secure
>>> handle' to the TEE, and the TEE decrypts the contents to the memory
>>> associated with the 'secure handle'. Then the 'secure handle' is
>>> passed into the TEE again with the v4l2 driver to use as the source
>>> for video decoding (but w/ v4l2, user space is passing in fds).
>>
>> I think I need some more background. This series is to support a 'Secure Video
>> Processor' (at least, that's what svp stands for I believe, something that
>> is not mentioned anywhere in this series, BTW) which is used to decode an
>> encrypted h264 stream.
>>
>> First question: how is that stream encrypted? Is that according to some standard?
>> Nothing is mentioned about that.
>>
>> I gather that the encrypted stream is fed to the codec as usual (i.e. just put it
>> in the output buffer and queue it to the codec), nothing special is needed for that.
>> Except, how does the hardware know it is encrypted? I guess that's where the
>> control comes in, you have to turn on SVP mode first.
> 
> Decryption takes place before the decoder. I suspect there is no dedicated
> driver for that, the TEE driver API is similar to smart card API and fits well
> this task. So the decrytor consume normal memory that is encrypted and is only
> allowed to decrypt into secure memory. All this is happening before the decoder,
> so is out of scope for this patchset.
> 
> Just a correction :-D.
> 
>>
>> For the capture buffers you need to provide buffers from secure/trusted memory.
>> That's a dmabuf fd, but where does that come from?
>>
>> I saw this message:
>>
>> https://lore.kernel.org/linux-media/CAPj87rOHctwHJM-7HiQpt8Q0b09x0WWw_T4XsL0qT=dS+XzyZQ@mail.gmail.com/T/#u
>>
>> so I expect that's where it comes from. But I agree that getting this from dma-heaps
>> seems more natural.
>>
>> I assume that those capture buffers are inaccessible from the CPU? (Hence 'secure')
>>
>> For actually displaying these secure buffers you would use drm, and I assume that
>> the hardware would mix in the contents of the secure buffer into the video output
>> pipeline? I.e., the actual contents remain inaccessible. And that the video output
>> (HDMI or DisplayPort) is using HDCP?
>>
>>>
>>>>
>>>> In any case, using a control to switch to secure mode and using a control
>>>> to convert a dmabuf fd to a secure handle seems a poor choice to me.
>>>>
>>>> I was wondering if it wouldn't be better to create a new V4L2_MEMORY_ type,
>>>> e.g. V4L2_MEMORY_DMABUF_SECURE (or perhaps _DMABUF_OPTEE). That ensures that
>>>> once you create buffers for the first time, the driver can switch into secure
>>>> mode, and until all buffers are released again you know that the driver will
>>>> stay in secure mode.
>>>
>>> Why do you think the control for setting secure mode is a poor choice?
>>> There's various places in the driver code where functionality changes
>>> based on being secure/non-secure mode, so this is very much a 'global'
>>> setting for the driver. It could be inferred based off a new memory
>>> type for the queues...which then sets that flag in the driver; but
>>> that seems like it would be more fragile and would require checking
>>> for incompatible output/capture memory types. I'm not against another
>>> way of doing this; but didn't see why you think the proposed method is
>>> a poor choice.
>>
>> I assume you are either decoding to secure memory all the time, or not
>> at all. That's something you would want to select the moment you allocate
>> the first buffer. Using the V4L2_MEMORY_ value would be the natural place
>> for that. A control can typically be toggled at any time, and it makes
>> no sense to do that for secure streaming.
>>
>> Related to that: if you pass a dmabuf fd you will need to check somewhere
>> if the fd points to secure memory or not. You don't want to mix the two
>> but you want to check that at VIDIOC_QBUF time.
>>
>> Note that the V4L2_MEMORY_ value is already checked in the v4l2 core,
>> drivers do not need to do that.
> 
> Just to clarify a bit, and make sure I understand this too. You are proposing to
> introduce something like:
> 
>    V4L2_MEMORY_SECURE_DMABUF
> 
> Which like V4L2_MEMORY_DMABUF is meant to import dmabuf, while telling the
> driver that the memory is secure according to the definition of "secure" for the
> platform its running on.
> 
> This drivers also allocate secure SHM (a standard tee concept) and have internal
> allocation for reconstruction buffer and some hw specific reference metadata. So
> the idea would be that it would keep allocation using the dmabuf heap internal
> APIs ? And decide which type of memory based on the memory type found in the
> queue?

Yes. Once you request the first buffer you basically tell the driver whether it
will operate in secure or non-secure mode, and that stays that way until all
buffers are freed. I think that makes sense.

If there is a need in the future to have V4L2 allocate the secure buffers, then
a similar V4L2_MEMORY_MMAP_SECURE type can be added. I think using v4l2_memory
to select secure or non-secure mode is logical and fits well with the V4L2 API.

> Stepping back a little, why can't we have a way for drivers to detect that
> dmabuf are secure ? I'm wondering if its actually useful to impose to all
> userspace component to know that a dmabuf is secure ?

I was wondering the same thing: there should be a simple way for drivers and
userspace to check if a dmabuf fd is secure or not. That will certainly help
the vb2 framework verify that you don't mix secure and non-secure dmabuf fds.

> 
> Also, regarding MTK, these are stateless decoders. I think it would be nice to
> show use example code that can properly parse the un-encrypted header, pass the
> data to the decryptor and decode. There is a bit of mechanic in there that lacks
> clarification, a reference implementation would clearly help. Finally, does this
> platform offers some clearkey implementation (or other alternative) so we can do
> validation and regression testing? It would be very unfortunate to add feature
> upstream that can only be tested by proprietary CDM software.

Good points.

	Hans

> 
> Nicolas
> 
>>
>>>
>>>>
>>>> For converting the dmabuf fd into a secure handle: a new ioctl similar to
>>>> VIDIOC_EXPBUF might be more suited for that.
>>>
>>> I actually think the best way for converting the dmabuf fd into a
>>> secure handle would be another ioctl in the dma-heap driver...since
>>> that's where the memory is actually allocated from. But this really
>>> depends on upstream maintainers and what they are comfortable with.
>>
>> That feels like a more natural place of doing this.
>>
>> Regards,
>>
>> 	Hans
>>
>>>
>>>>
>>>> Note that I am the first to admit that I have no experience with secure
>>>> video pipelines or optee-os, so I am looking at this purely from an uAPI
>>>> perspective.
>>>>
>>>> Regards,
>>>>
>>>>         Hans
>>>>
>>>>>
>>>>> Best Regards,
>>>>> Yunfei Dong
>>>>>> Regards,
>>>>>>
>>>>>> Hans
>>>>>>
>>>>>>>
>>>>>>> regards,
>>>>>>> Nicolas
>>>>>>>
>>>>>>> p.s. you forgot to document your control in the RST doc, please do
>>>>>>
>>>>>> in following
>>>>>>> release.
>>>>>>>
>>>>>>>> +ctx->is_svp_mode = ctrl->val;
>>>>>>>> +
>>>>>>>> +if (ctx->is_svp_mode) {
>>>>>>>> +ret = mtk_vcodec_dec_optee_open(ctx->dev->optee_private);
>>>>>>>> +if (ret)
>>>>>>>> +mtk_v4l2_vdec_err(ctx, "open secure mode failed.");
>>>>>>>> +else
>>>>>>>> +mtk_v4l2_vdec_dbg(3, ctx, "decoder in secure mode: %d", ctrl-
>>>>>>>
>>>>>>> val);
>>>>>>>> +}
>>>>>>>> +break;
>>>>>>>>  default:
>>>>>>>>  mtk_v4l2_vdec_dbg(3, ctx, "Not supported to set ctrl id:
>>>>>>>> 0x%x\n",
>>>>>>
>>>>>> hdr_ctrl->id);
>>>>>>>>  return ret;
>>>>>>>> @@ -573,7 +584,7 @@ static int mtk_vcodec_dec_ctrls_setup(struct
>>>>>>
>>>>>> mtk_vcodec_dec_ctx *ctx)
>>>>>>>>  unsigned int i;
>>>>>>>>  struct v4l2_ctrl *ctrl;
>>>>>>>>
>>>>>>>> -v4l2_ctrl_handler_init(&ctx->ctrl_hdl, NUM_CTRLS + 1);
>>>>>>>> +v4l2_ctrl_handler_init(&ctx->ctrl_hdl, NUM_CTRLS + 2);
>>>>>>>>  if (ctx->ctrl_hdl.error) {
>>>>>>>>  mtk_v4l2_vdec_err(ctx, "v4l2_ctrl_handler_init failed\n");
>>>>>>>>  return ctx->ctrl_hdl.error;
>>>>>>>> @@ -592,6 +603,8 @@ static int mtk_vcodec_dec_ctrls_setup(struct
>>>>>>
>>>>>> mtk_vcodec_dec_ctx *ctx)
>>>>>>>>
>>>>>>>>  ctrl = v4l2_ctrl_new_std(&ctx->ctrl_hdl,
>>>>>>
>>>>>> &mtk_vcodec_dec_ctrl_ops,
>>>>>>>>   V4L2_CID_MPEG_MTK_GET_SECURE_HANDLE, 0, 65535, 1, 0);
>>>>>>>> +ctrl = v4l2_ctrl_new_std(&ctx->ctrl_hdl,
>>>>>>
>>>>>> &mtk_vcodec_dec_ctrl_ops,
>>>>>>>> + V4L2_CID_MPEG_MTK_SET_SECURE_MODE, 0, 65535, 1, 0);
>>>>>>>>
>>>>>>>>  v4l2_ctrl_handler_setup(&ctx->ctrl_hdl);
>>>>>>>>
>>>>>>>> diff --git a/drivers/media/v4l2-core/v4l2-ctrls-defs.c
>>>>>>
>>>>>> b/drivers/media/v4l2-core/v4l2-ctrls-defs.c
>>>>>>>> index d8cf01f76aab..a507045a3f30 100644
>>>>>>>> --- a/drivers/media/v4l2-core/v4l2-ctrls-defs.c
>>>>>>>> +++ b/drivers/media/v4l2-core/v4l2-ctrls-defs.c
>>>>>>>> @@ -1042,6 +1042,7 @@ const char *v4l2_ctrl_get_name(u32 id)
>>>>>>>>  case V4L2_CID_MPEG_VIDEO_REF_NUMBER_FOR_PFRAMES:return
>>>>>>>> "Reference
>>>>>>
>>>>>> Frames for a P-Frame";
>>>>>>>>  case V4L2_CID_MPEG_VIDEO_PREPEND_SPSPPS_TO_IDR:return "Prepend
>>>>>>
>>>>>> SPS and PPS to IDR";
>>>>>>>>  case V4L2_CID_MPEG_MTK_GET_SECURE_HANDLE:return "MediaTek
>>>>>>>> Decoder
>>>>>>
>>>>>> get secure handle";
>>>>>>>> +case V4L2_CID_MPEG_MTK_SET_SECURE_MODE:return "MediaTek Decoder
>>>>>>
>>>>>> set secure mode";
>>>>>>>>
>>>>>>>>  /* AV1 controls */
>>>>>>>>  case V4L2_CID_MPEG_VIDEO_AV1_PROFILE:return "AV1 Profile";
>>>>>>>> @@ -1442,6 +1443,10 @@ void v4l2_ctrl_fill(u32 id, const char
>>>>>>
>>>>>> **name, enum v4l2_ctrl_type *type,
>>>>>>>>  *type = V4L2_CTRL_TYPE_INTEGER;
>>>>>>>>  *flags |= V4L2_CTRL_FLAG_WRITE_ONLY;
>>>>>>>>  break;
>>>>>>>> +case V4L2_CID_MPEG_MTK_SET_SECURE_MODE:
>>>>>>>> +*type = V4L2_CTRL_TYPE_INTEGER;
>>>>>>>> +*flags |= V4L2_CTRL_FLAG_WRITE_ONLY;
>>>>>>>> +break;
>>>>>>>>  case V4L2_CID_USER_CLASS:
>>>>>>>>  case V4L2_CID_CAMERA_CLASS:
>>>>>>>>  case V4L2_CID_CODEC_CLASS:
>>>>>>>> diff --git a/include/uapi/linux/v4l2-controls.h
>>>>>>
>>>>>> b/include/uapi/linux/v4l2-controls.h
>>>>>>>> index 7b3694985366..88e90d943e38 100644
>>>>>>>> --- a/include/uapi/linux/v4l2-controls.h
>>>>>>>> +++ b/include/uapi/linux/v4l2-controls.h
>>>>>>>> @@ -957,6 +957,7 @@ enum v4l2_mpeg_mfc51_video_force_frame_type {
>>>>>>>>  /*  MPEG-class control IDs specific to the MediaTek Decoder
>>>>>>
>>>>>> driver as defined by V4L2 */
>>>>>>>>  #define V4L2_CID_MPEG_MTK_BASE(V4L2_CTRL_CLASS_CODEC | 0x2000)
>>>>>>>>  #define
>>>>>>
>>>>>> V4L2_CID_MPEG_MTK_GET_SECURE_HANDLE(V4L2_CID_MPEG_MTK_BASE+8)
>>>>>>>> +#define
>>>>>>
>>>>>> V4L2_CID_MPEG_MTK_SET_SECURE_MODE(V4L2_CID_MPEG_MTK_BASE+9)
>>>>>>>>
>>>>>>>>  /*  Camera class control IDs */
>>>>>>>>
>>>>
>>>>
>>>> _______________________________________________
>>>> linux-arm-kernel mailing list
>>>> linux-arm-kernel@...ts.infradead.org
>>>> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
>>
> 

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