Re: [PATCH 12/14] media: medkatek: vcodec: set secure mode to decoder driver

quoted

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 [off-list ref] 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@mediatek.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 (local)

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?

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 ?

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.

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 */

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