Hi Simona,

On Wed, 18 Dec 2024 at 16:36, Simona Vetter simona.vetter@ffwll.ch wrote:

On Tue, Dec 17, 2024 at 11:07:36AM +0100, Jens Wiklander wrote:

...

Hi,

This patch set allocates the restricted DMA-bufs via the TEE subsystem.

The TEE subsystem handles the DMA-buf allocations since it is the TEE (OP-TEE, AMD-TEE, TS-TEE, or perhaps a future QCOMTEE) which sets up the restrictions for the memory used for the DMA-bufs.

I've added a new IOCTL, TEE_IOC_RSTMEM_ALLOC, to allocate the restricted DMA-bufs. This IOCTL reaches the backend TEE driver, allowing it to choose how to allocate the restricted physical memory.

TEE_IOC_RSTMEM_ALLOC takes in addition to a size and flags parameters also a use-case parameter. This is used by the backend TEE driver to decide on allocation policy and which devices should be able to access the memory.

Three use-cases (Secure Video Playback, Trusted UI, and Secure Video Recording) has been identified so far to serve as examples of what can be expected. More use-cases can be added in userspace ABI, but it's up to the backend TEE drivers to provide the implementation.

Each use-case has it's own restricted memory pool since different use-cases requires isolation from different parts of the system. A restricted memory pool can be based on a static carveout instantiated while probing the TEE backend driver, or dynamically allocated from CMA and made restricted as needed by the TEE.

This can be tested on QEMU with the following steps: repo init -u https://github.com/jenswi-linaro/manifest.git -m qemu_v8.xml \ -b prototype/sdp-v4 repo sync -j8 cd build make toolchains -j$(nproc) make SPMC_AT_EL=1 all -j$(nproc) make SPMC_AT_EL=1 run-only # login and at the prompt: xtest --sdp-basic

The SPMC_AT_EL=1 parameter configures the build with FF-A and an SPMC at S-EL1 inside OP-TEE. The parameter can be changed into SPMC_AT_EL=n to test without FF-A using the original SMC ABI instead. Please remember to do %rm -rf ../trusted-firmware-a/build/qemu for TF-A to be rebuilt properly using the new configuration.

https://optee.readthedocs.io/en/latest/building/prerequisites.html list dependencies needed to build the above.

The tests are pretty basic, mostly checking that a Trusted Application in the secure world can access and manipulate the memory. There are also some negative tests for out of bounds buffers etc.

I think I've dropped this on earlier encrypted dma-buf discussions for TEE, but can't find one right now ...

Thanks for raising this query.

Do we have some open source userspace for this? To my knowledge we have two implementations of encrypted/content protected dma-buf in upstream right now in the amd and intel gpu drivers, and unless I'm mistaken they both have some minimal userspace supporting EXT_protected_textures:

First of all to clarify the support Jens is adding here for allocating restricted shared memory allocation in TEE subsystem is meant to be generic and not specific to only secure media pipeline use-case. Then here we not only have open source test applications but rather open source firmware too (OP-TEE as a Trusted OS) [1] supporting this as a core feature where we maintain a stable and extensible ABI among the kernel and the OP-TEE core.

Restricted memory is a feature enforced by hardware specific firewalls where a particular TEE implementation governs which particular block of memory is accessible to a particular peripheral or a CPU running in a higher privileged mode than the Linux kernel. There can be numeric use-cases surrounding that as follows:

- Secure media pipeline where the contents gets decrypted and stored in a restricted buffer which are then accessible only to media display pipeline peripherals. - Trusted user interface where a peripheral takes input from the user and stores it in a restricted buffer which then is accessible to TEE implementation only. - Another possible use-case can be for the TEE implementation to store key material in a restricted buffer which is only accessible to the hardware crypto accelerator.

I am sure there will be more use-cases related to this feature but those will only be possible once we provide a stable and extensible restricted memory interface among the Linux user-space and the secure world user-space (normally referred to as Trusted Applications).

[1] https://github.com/OP-TEE/optee_os/pull/7159

https://github.com/KhronosGroup/OpenGL-Registry/blob/main/extensions/EXT/EXT...

It's not great, but it does just barely clear the bar in my opinion. I guess something in gstreamer or similar video pipeline framework would also do the job.

Especially with the context of the uapi discussion in the v1/RFC thread I think we need more than a bare-bones testcase to make sure this works in actual use.

Currently the TEE subsystem already supports a stable ABI for shared memory allocator among Linux user-space and secure world user-space here [2]. And the stable ABI for restricted memory is also along the same lines meant to be a vendor neutral abstraction for the user-space access. The current test cases not only test the interface but also perform regression tests too.

I am also in favour of end to end open source use-cases. But I fear without progressing in a step wise manner as with this proposal we would rather force developers to upstream all the software pieces in one go which will be kind of a chicken and egg situation. I am sure once this feature lands Mediatek folks will be interested to port their secure video playback patchset [3] on top of it. Similarly other silicon vendors like NXP, Qcom etc. will be motivated to do the same.

[2] https://docs.kernel.org/userspace-api/tee.html [3] https://lore.kernel.org/linux-arm-kernel/20240515112308.10171-1-yong.wu@medi...

-Sumit

Cheers, Sima

...

Thanks, Jens

Changes since V3:

• Make the use_case and flags field in struct tee_shm u32's instead of u16's
• Add more description for TEE_IOC_RSTMEM_ALLOC in the header file
• Import namespace DMA_BUF in module tee, reported by lkp@intel.com
• Added a note in the commit message for "optee: account for direction while converting parameters" why it's needed
• Factor out dynamic restricted memory allocation from "optee: support restricted memory allocation" into two new commits "optee: FF-A: dynamic restricted memory allocation" and "optee: smc abi: dynamic restricted memory allocation"
• Guard CMA usage with #ifdef CONFIG_CMA, effectively disabling dynamic restricted memory allocate if CMA isn't configured

Changes since the V2 RFC:

• Based on v6.12
• Replaced the flags for SVP and Trusted UID memory with a u32 field with unique id for each use case
• Added dynamic allocation of restricted memory pools
• Added OP-TEE ABI both with and without FF-A for dynamic restricted memory
• Added support for FF-A with FFA_LEND

Changes since the V1 RFC:

• Based on v6.11
• Complete rewrite, replacing the restricted heap with TEE_IOC_RSTMEM_ALLOC

Changes since Olivier's post [2]:

• Based on Yong Wu's post [1] where much of dma-buf handling is done in the generic restricted heap
• Simplifications and cleanup
• New commit message for "dma-buf: heaps: add Linaro restricted dmabuf heap support"
• Replaced the word "secure" with "restricted" where applicable

Jens Wiklander (6): tee: add restricted memory allocation optee: account for direction while converting parameters optee: sync secure world ABI headers optee: support restricted memory allocation optee: FF-A: dynamic restricted memory allocation optee: smc abi: dynamic restricted memory allocation

drivers/tee/Makefile | 1 + drivers/tee/optee/Makefile | 1 + drivers/tee/optee/call.c | 10 +- drivers/tee/optee/core.c | 1 + drivers/tee/optee/ffa_abi.c | 178 +++++++++++++- drivers/tee/optee/optee_ffa.h | 27 ++- drivers/tee/optee/optee_msg.h | 65 ++++- drivers/tee/optee/optee_private.h | 75 ++++-- drivers/tee/optee/optee_smc.h | 71 +++++- drivers/tee/optee/rpc.c | 31 ++- drivers/tee/optee/rstmem.c | 388 ++++++++++++++++++++++++++++++ drivers/tee/optee/smc_abi.c | 213 ++++++++++++++-- drivers/tee/tee_core.c | 38 ++- drivers/tee/tee_private.h | 2 + drivers/tee/tee_rstmem.c | 201 ++++++++++++++++ drivers/tee/tee_shm.c | 2 + drivers/tee/tee_shm_pool.c | 69 +++++- include/linux/tee_core.h | 15 ++ include/linux/tee_drv.h | 2 + include/uapi/linux/tee.h | 44 +++- 20 files changed, 1358 insertions(+), 76 deletions(-) create mode 100644 drivers/tee/optee/rstmem.c create mode 100644 drivers/tee/tee_rstmem.c

base-commit: fac04efc5c793dccbd07e2d59af9f90b7fc0dca4

2.43.0

-- Simona Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch