Re: [RFC PATCH 0/4] Linaro restricted heap

[Jens Wiklander <jens.wiklander@linaro.org>]

On Mon, Sep 23, 2024 at 09:33:29AM +0300, Dmitry Baryshkov wrote:
> Hi,
> 
> On Fri, Aug 30, 2024 at 09:03:47AM GMT, Jens Wiklander wrote:
> > Hi,
> > 
> > This patch set is based on top of Yong Wu's restricted heap patch set [1].
> > It's also a continuation on Olivier's Add dma-buf secure-heap patch set [2].
> > 
> > The Linaro restricted heap uses genalloc in the kernel to manage the heap
> > carvout. This is a difference from the Mediatek restricted heap which
> > relies on the secure world to manage the carveout.
> > 
> > I've tried to adress the comments on [2], but [1] introduces changes so I'm
> > afraid I've had to skip some comments.
> 
> I know I have raised the same question during LPC (in connection to
> Qualcomm's dma-heap implementation). Is there any reason why we are
> using generic heaps instead of allocating the dma-bufs on the device
> side?
> 
> In your case you already have TEE device, you can use it to allocate and
> export dma-bufs, which then get imported by the V4L and DRM drivers.
> 
> I have a feeling (I might be completely wrong here) that by using
> generic dma-buf heaps we can easily end up in a situation when the
> userspace depends heavily on the actual platform being used (to map the
> platform to heap names). I think we should instead depend on the
> existing devices (e.g. if there is a TEE device, use an IOCTL to
> allocate secured DMA BUF from it, otherwise check for QTEE device,
> otherwise check for some other vendor device).

That makes sense, it's similar to what we do with TEE_IOC_SHM_ALLOC
where we allocate from a carveout reserverd for shared memory with the
secure world. It was even based on dma-buf until commit dfd0743f1d9e
("tee: handle lookup of shm with reference count 0").

We should use a new TEE_IOC_*_ALLOC for these new dma-bufs to avoid
confusion and to have more freedom when designing the interface.

> 
> The mental experiment to check if the API is correct is really simple:
> Can you use exactly the same rootfs on several devices without
> any additional tuning (e.g. your QEMU, HiKey, a Mediatek board, Qualcomm
> laptop, etc)?

No, I don't think so.

> 
> > 
> > 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-v1
> > repo sync -j8
> > cd build
> > make toolchains -j4
> > make all -j$(nproc)
> > make run-only
> > # login and at the prompt:
> > xtest --sdp-basic
> > 
> > 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.
> 
> - Can we test that the system doesn't crash badly if user provides
>   non-secured memory to the users which expect a secure buffer?
> 
> - At the same time corresponding entities shouldn't decode data to the
>   buffers accessible to the rest of the sytem.

I'll a few tests along that.

Thanks,
Jens

> 
> > 
> > Cheers,
> > Jens
> > 
> > [1] https://lore.kernel.org/dri-devel/20240515112308.10171-1-yong.wu@mediatek.com/
> > [2] https://lore.kernel.org/lkml/20220805135330.970-1-olivier.masse@nxp.com/
> > 
> > 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
> > 
> > Etienne Carriere (1):
> >   tee: new ioctl to a register tee_shm from a dmabuf file descriptor
> > 
> > Jens Wiklander (2):
> >   dma-buf: heaps: restricted_heap: add no_map attribute
> >   dma-buf: heaps: add Linaro restricted dmabuf heap support
> > 
> > Olivier Masse (1):
> >   dt-bindings: reserved-memory: add linaro,restricted-heap
> > 
> >  .../linaro,restricted-heap.yaml               |  56 ++++++
> >  drivers/dma-buf/heaps/Kconfig                 |  10 ++
> >  drivers/dma-buf/heaps/Makefile                |   1 +
> >  drivers/dma-buf/heaps/restricted_heap.c       |  17 +-
> >  drivers/dma-buf/heaps/restricted_heap.h       |   2 +
> >  .../dma-buf/heaps/restricted_heap_linaro.c    | 165 ++++++++++++++++++
> >  drivers/tee/tee_core.c                        |  38 ++++
> >  drivers/tee/tee_shm.c                         | 104 ++++++++++-
> >  include/linux/tee_drv.h                       |  11 ++
> >  include/uapi/linux/tee.h                      |  29 +++
> >  10 files changed, 426 insertions(+), 7 deletions(-)
> >  create mode 100644 Documentation/devicetree/bindings/reserved-memory/linaro,restricted-heap.yaml
> >  create mode 100644 drivers/dma-buf/heaps/restricted_heap_linaro.c
> > 
> > -- 
> > 2.34.1
> > 
> 
> -- 
> With best wishes
> Dmitry