Message-ID: <bktt4yanmfn4gjljy2wxmigj6mncpga237oxyf4g4h2vxu2a3q@asnsn7smi4u2>
Date: Wed, 25 Sep 2024 14:41:07 +0300
From: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To: Jens Wiklander <jens.wiklander@...aro.org>
Cc: linux-kernel@...r.kernel.org, devicetree@...r.kernel.org, 
	linux-media@...r.kernel.org, dri-devel@...ts.freedesktop.org, linaro-mm-sig@...ts.linaro.org, 
	op-tee@...ts.trustedfirmware.org, linux-arm-kernel@...ts.infradead.org, 
	linux-mediatek@...ts.infradead.org, Olivier Masse <olivier.masse@....com>, 
	Thierry Reding <thierry.reding@...il.com>, Yong Wu <yong.wu@...iatek.com>, 
	Sumit Semwal <sumit.semwal@...aro.org>, Benjamin Gaignard <benjamin.gaignard@...labora.com>, 
	Brian Starkey <Brian.Starkey@....com>, John Stultz <jstultz@...gle.com>, 
	"T . J . Mercier" <tjmercier@...gle.com>, Christian König <christian.koenig@....com>, 
	Sumit Garg <sumit.garg@...aro.org>, Matthias Brugger <matthias.bgg@...il.com>, 
	AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>, Rob Herring <robh@...nel.org>, 
	Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley <conor+dt@...nel.org>
Subject: Re: [RFC PATCH 0/4] Linaro restricted heap

On Wed, Sep 25, 2024 at 09:15:04AM GMT, Jens Wiklander wrote:
> 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.

Then the API needs to be modified.

Or the userspace needs to be modified in the way similar to Vulkan /
OpenCL / glvnd / VA / VDPU: platform-specific backends, coexisting on a
single rootfs.

It is more or less fine to have platform-specific rootfs when we are
talking about the embedded, resource-limited devices. But for the
end-user devices we must be able to install a generic distro with no
device-specific packages being selected.

> 
> > 
> > > 
> > > 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

-- 
With best wishes
Dmitry

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