Hi, On Tue, Sep 24, 2024 at 01:13:18PM -0500, Andrew Davis wrote: > On 9/23/24 1:33 AM, 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. > > > > This goes to the heart of why we have dma-heaps in the first place. > We don't want to burden userspace with having to figure out the right > place to get a dma-buf for a given use-case on a given hardware. > That would be very non-portable, and fail at the core purpose of > a kernel: to abstract hardware specifics away. > > Worse, the actual interface for dma-buf exporting changes from > framework to framework (getting a dma-buf from DRM is different > than V4L, and there would be yet another API for TEE, etc..) > > Most subsystem don't need an allocator, they work just fine > simply being only dma-bufs importers. Recent example being the > IIO subsystem[0], for which some early posting included an > allocator, but in the end, all that was needed was to consume > buffers. > > For devices that don't actually contain memory there is no > reason to be an exporter. What most want is just to consume > normal system memory. Or system memory with some constraints > (e.g. contiguous, coherent, restricted, etc..). > > > 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). > > > > 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)? > > > > This is a great north star to follow. And exactly the reason we should > *not* be exposing device specific constraints to userspace. The constrains > change based on the platform. So a userspace would have to also pick > a different set of constraints based on each platform. > > Userspace knows which subsystems it will attach a buffer, and the > kernel knows what constraints those devices have on a given platform. > Ideal case is then allocate from the one exporter, attach to various > devices, and have the constraints solved at map time by the exporter > based on the set of attached devices. > > For example, on one platform the display needs contiguous buffers, > but on a different platform the display can scatter-gather. So > what heap should our generic application allocate from when it > wants a buffer consumable by the display, CMA or System? > Answer *should* be always use the generic exporter, and that > exporter then picks the right backing type based on the platform. > > Userspace shouldn't be dealing with any of these constraints > (looking back, adding the CMA heap was probably incorrect, > and the System heap should have been the only one. Idea back > then was a userspace helper would show up to do the constraint > solving and pick the right heap. That has yet to materialize and > folks are still just hardcoding which heap to use..). > > Same for this restricted heap, I'd like to explore if we can > enhance the System heap such that when attached to the TEE framework, > the backing memory is either made restricted by fire-walling, > or allocating from a TEE carveout (based on platform). So the exporter (you mentioned System heap) will somehow know how to interact with the TEE subsystem to allocate suitable memory? I suppose the memory could be from a static carveout, dynamic restricted memory allocation, or how to turn normal memory into restricted memory (fire-walling), depending on the platform. > > This will mean more inter-subsystem coordination, but we can > iterate on these in kernel interfaces. We cannot iterate on > userspace interfaces, those have to be correct the first time. Good point, this approach should make it easier for userspace. Thanks, Jens > > Andrew > > [0] https://www.kernel.org/doc/html/next/iio/iio_dmabuf_api.html > > > > > > > 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. > > > > > > > > Cheers, > > > Jens > > > > > > [1] https://lore.kernel.org/dri-devel/20240515112308.10171-1-yong.wu@xxxxxxxxxxxx/ > > > [2] https://lore.kernel.org/lkml/20220805135330.970-1-olivier.masse@xxxxxxx/ > > > > > > 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 > > > > >
