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From:   Claire Chang <tientzu@chromium.org>
Date:   Wed, 16 Jun 2021 11:55:47 +0800
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Subject: Re: [PATCH v10 00/12] Restricted DMA
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v11 https://lore.kernel.org/patchwork/cover/1447216/

On Tue, Jun 15, 2021 at 9:27 PM Claire Chang <tientzu@chromium.org> wrote:
>
> This series implements mitigations for lack of DMA access control on
> systems without an IOMMU, which could result in the DMA accessing the
> system memory at unexpected times and/or unexpected addresses, possibly
> leading to data leakage or corruption.
>
> For example, we plan to use the PCI-e bus for Wi-Fi and that PCI-e bus is
> not behind an IOMMU. As PCI-e, by design, gives the device full access to
> system memory, a vulnerability in the Wi-Fi firmware could easily escalate
> to a full system exploit (remote wifi exploits: [1a], [1b] that shows a
> full chain of exploits; [2], [3]).
>
> To mitigate the security concerns, we introduce restricted DMA. Restricted
> DMA utilizes the existing swiotlb to bounce streaming DMA in and out of a
> specially allocated region and does memory allocation from the same region.
> The feature on its own provides a basic level of protection against the DMA
> overwriting buffer contents at unexpected times. However, to protect
> against general data leakage and system memory corruption, the system needs
> to provide a way to restrict the DMA to a predefined memory region (this is
> usually done at firmware level, e.g. MPU in ATF on some ARM platforms [4]).
>
> [1a] https://googleprojectzero.blogspot.com/2017/04/over-air-exploiting-broadcoms-wi-fi_4.html
> [1b] https://googleprojectzero.blogspot.com/2017/04/over-air-exploiting-broadcoms-wi-fi_11.html
> [2] https://blade.tencent.com/en/advisories/qualpwn/
> [3] https://www.bleepingcomputer.com/news/security/vulnerabilities-found-in-highly-popular-firmware-for-wifi-chips/
> [4] https://github.com/ARM-software/arm-trusted-firmware/blob/master/plat/mediatek/mt8183/drivers/emi_mpu/emi_mpu.c#L132
>
> v10:
> Address the comments in v9 to
>   - fix the dev->dma_io_tlb_mem assignment
>   - propagate swiotlb_force setting into io_tlb_default_mem->force
>   - move set_memory_decrypted out of swiotlb_init_io_tlb_mem
>   - move debugfs_dir declaration into the main CONFIG_DEBUG_FS block
>   - add swiotlb_ prefix to find_slots and release_slots
>   - merge the 3 alloc/free related patches
>   - move the CONFIG_DMA_RESTRICTED_POOL later
>
> v9:
> Address the comments in v7 to
>   - set swiotlb active pool to dev->dma_io_tlb_mem
>   - get rid of get_io_tlb_mem
>   - dig out the device struct for is_swiotlb_active
>   - move debugfs_create_dir out of swiotlb_create_debugfs
>   - do set_memory_decrypted conditionally in swiotlb_init_io_tlb_mem
>   - use IS_ENABLED in kernel/dma/direct.c
>   - fix redefinition of 'of_dma_set_restricted_buffer'
> https://lore.kernel.org/patchwork/cover/1445081/
>
> v8:
> - Fix reserved-memory.txt and add the reg property in example.
> - Fix sizeof for of_property_count_elems_of_size in
>   drivers/of/address.c#of_dma_set_restricted_buffer.
> - Apply Will's suggestion to try the OF node having DMA configuration in
>   drivers/of/address.c#of_dma_set_restricted_buffer.
> - Fix typo in the comment of drivers/of/address.c#of_dma_set_restricted_buffer.
> - Add error message for PageHighMem in
>   kernel/dma/swiotlb.c#rmem_swiotlb_device_init and move it to
>   rmem_swiotlb_setup.
> - Fix the message string in rmem_swiotlb_setup.
> https://lore.kernel.org/patchwork/cover/1437112/
>
> v7:
> Fix debugfs, PageHighMem and comment style in rmem_swiotlb_device_init
> https://lore.kernel.org/patchwork/cover/1431031/
>
> v6:
> Address the comments in v5
> https://lore.kernel.org/patchwork/cover/1423201/
>
> v5:
> Rebase on latest linux-next
> https://lore.kernel.org/patchwork/cover/1416899/
>
> v4:
> - Fix spinlock bad magic
> - Use rmem->name for debugfs entry
> - Address the comments in v3
> https://lore.kernel.org/patchwork/cover/1378113/
>
> v3:
> Using only one reserved memory region for both streaming DMA and memory
> allocation.
> https://lore.kernel.org/patchwork/cover/1360992/
>
> v2:
> Building on top of swiotlb.
> https://lore.kernel.org/patchwork/cover/1280705/
>
> v1:
> Using dma_map_ops.
> https://lore.kernel.org/patchwork/cover/1271660/
>
>
> Claire Chang (12):
>   swiotlb: Refactor swiotlb init functions
>   swiotlb: Refactor swiotlb_create_debugfs
>   swiotlb: Set dev->dma_io_tlb_mem to the swiotlb pool used
>   swiotlb: Update is_swiotlb_buffer to add a struct device argument
>   swiotlb: Update is_swiotlb_active to add a struct device argument
>   swiotlb: Use is_dev_swiotlb_force for swiotlb data bouncing
>   swiotlb: Move alloc_size to swiotlb_find_slots
>   swiotlb: Refactor swiotlb_tbl_unmap_single
>   swiotlb: Add restricted DMA pool initialization
>   swiotlb: Add restricted DMA alloc/free support
>   dt-bindings: of: Add restricted DMA pool
>   of: Add plumbing for restricted DMA pool
>
>  .../reserved-memory/reserved-memory.txt       |  36 ++-
>  drivers/base/core.c                           |   4 +
>  drivers/gpu/drm/i915/gem/i915_gem_internal.c  |   2 +-
>  drivers/gpu/drm/nouveau/nouveau_ttm.c         |   2 +-
>  drivers/iommu/dma-iommu.c                     |  12 +-
>  drivers/of/address.c                          |  33 +++
>  drivers/of/device.c                           |   3 +
>  drivers/of/of_private.h                       |   6 +
>  drivers/pci/xen-pcifront.c                    |   2 +-
>  drivers/xen/swiotlb-xen.c                     |   2 +-
>  include/linux/device.h                        |   4 +
>  include/linux/swiotlb.h                       |  40 ++-
>  kernel/dma/Kconfig                            |  14 +
>  kernel/dma/direct.c                           |  60 +++--
>  kernel/dma/direct.h                           |   8 +-
>  kernel/dma/swiotlb.c                          | 255 +++++++++++++-----
>  16 files changed, 380 insertions(+), 103 deletions(-)
>
> --
> 2.32.0.272.g935e593368-goog
>