Re: [PATCH v4 0/6] TEE subsystem for restricted dma-buf allocations

Simona Vetter
2025-01-08T16:57:50Z

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On Tue, Dec 24, 2024 at 12:05:19PM +0530, Sumit Garg wrote:
> 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_protected_textures.txt
> >
> > 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(a)mediatek.com/

We get entire opengl/vulkan driver stacks ready before we merge new drm
drivers, I really don't think this is too hard from a technical pov. And I
think the mediatek patches had the same issue of lacking userspace for it,
so that's not moving things forward.
-Sima

>
> -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(a)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

--
Simona Vetter
Software Engineer, Intel Corporation