On Tue, Sep 19, 2023 at 10:26 PM CK Hu (胡俊光) ck.hu@mediatek.com wrote:

Hi, Jason:

On Tue, 2023-09-19 at 11:03 +0800, Jason-JH.Lin wrote:

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The patch series provides drm driver support for enabling secure video path (SVP) playback on MediaiTek hardware in the Linux kernel.

Memory Definitions: secure memory - Memory allocated in the TEE (Trusted Execution Environment) which is inaccessible in the REE (Rich Execution Environment, i.e. linux kernel/userspace). secure handle - Integer value which acts as reference to 'secure memory'. Used in communication between TEE and REE to reference 'secure memory'. secure buffer - 'secure memory' that is used to store decrypted, compressed video or for other general purposes in the TEE. secure surface - 'secure memory' that is used to store graphic buffers.

Memory Usage in SVP: The overall flow of SVP starts with encrypted video coming in from an outside source into the REE. The REE will then allocate a 'secure buffer' and send the corresponding 'secure handle' along with the encrypted, compressed video data to the TEE. The TEE will then decrypt the video and store the result in the 'secure buffer'. The REE will then allocate a 'secure surface'. The REE will pass the 'secure handles' for both the 'secure buffer' and 'secure surface' into the TEE for video decoding. The video decoder HW will then decode the contents of the 'secure buffer' and place the result in the 'secure surface'. The REE will then attach the 'secure surface' to the overlay plane for rendering of the video.

Everything relating to ensuring security of the actual contents of the 'secure buffer' and 'secure surface' is out of scope for the REE and is the responsibility of the TEE.

DRM driver handles allocation of gem objects that are backed by a 'secure surface' and for displaying a 'secure surface' on the overlay plane. This introduces a new flag for object creation called DRM_MTK_GEM_CREATE_ENCRYPTED which indicates it should be a 'secure surface'. All changes here are in MediaTek specific code.

How do you define SVP? Is there standard requirement we could refer to? If the secure video buffer is read by display hardware and output to HDMI without any protection and user could capture HDMI signal, is this secure?

SVP (Secure Video Path) is essentially the video being completed isolated from the kernel/userspace. The specific requirements for it vary between implementations.

Regarding HDMI/HDCP output; it's the responsibility of the TEE to enforce that. Nothing on the kernel/userspace side needs to be concerned about enforcing HDCP. The only thing userspace is involved in there is actually turning on HDCP via the kernel drivers; and then the TEE ensures that it is active if the policy for the encrypted content requires it.

Regards, CK

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Based on 2 series: [1] Add CMDQ secure driver for SVP

https://urldefense.com/v3/__https://patchwork.kernel.org/project/linux-media...

[2] dma-buf: heaps: Add MediaTek secure heap

https://urldefense.com/v3/__https://patchwork.kernel.org/project/linux-media...

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CK Hu (1): drm/mediatek: Add interface to allocate MediaTek GEM buffer.

Jason-JH.Lin (9): drm/mediatek/uapi: Add DRM_MTK_GEM_CREATED_ENCRYPTTED flag drm/mediatek: Add secure buffer control flow to mtk_drm_gem drm/mediatek: Add secure identify flag and funcution to mtk_drm_plane drm/mediatek: Add mtk_ddp_sec_write to config secure buffer info drm/mediatek: Add get_sec_port interface to mtk_ddp_comp drm/mediatek: Add secure layer config support for ovl drm/mediatek: Add secure layer config support for ovl_adaptor drm/mediatek: Add secure flow support to mediatek-drm arm64: dts: mt8195-cherry: Add secure mbox settings for vdosys

.../boot/dts/mediatek/mt8195-cherry.dtsi | 10 + drivers/gpu/drm/mediatek/mtk_disp_drv.h | 3 + drivers/gpu/drm/mediatek/mtk_disp_ovl.c | 31 +- .../gpu/drm/mediatek/mtk_disp_ovl_adaptor.c | 15 + drivers/gpu/drm/mediatek/mtk_drm_crtc.c | 271 +++++++++++++++++- drivers/gpu/drm/mediatek/mtk_drm_crtc.h | 1 + drivers/gpu/drm/mediatek/mtk_drm_ddp_comp.c | 14 + drivers/gpu/drm/mediatek/mtk_drm_ddp_comp.h | 13 + drivers/gpu/drm/mediatek/mtk_drm_drv.c | 16 +- drivers/gpu/drm/mediatek/mtk_drm_gem.c | 121 ++++++++ drivers/gpu/drm/mediatek/mtk_drm_gem.h | 16 ++ drivers/gpu/drm/mediatek/mtk_drm_plane.c | 7 + drivers/gpu/drm/mediatek/mtk_drm_plane.h | 2 + drivers/gpu/drm/mediatek/mtk_mdp_rdma.c | 11 +- drivers/gpu/drm/mediatek/mtk_mdp_rdma.h | 2 + include/uapi/drm/mediatek_drm.h | 59 ++++ 16 files changed, 575 insertions(+), 17 deletions(-) create mode 100644 include/uapi/drm/mediatek_drm.h