[PATCH v5 00/16] Restricted DMA

Claire Chang tientzu at chromium.org
Thu Apr 22 08:14:52 UTC 2021


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

v5:
  Rebase on latest linux-next

v4:
  - Fix spinlock bad magic
  - Use rmem->name for debugfs entry
  - Address the comments in v3

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 (16):
  swiotlb: Fix the type of index
  swiotlb: Refactor swiotlb init functions
  swiotlb: Refactor swiotlb_create_debugfs
  swiotlb: Add DMA_RESTRICTED_POOL
  swiotlb: Add restricted DMA pool initialization
  swiotlb: Add a new get_io_tlb_mem getter
  swiotlb: Update is_swiotlb_buffer to add a struct device argument
  swiotlb: Update is_swiotlb_active to add a struct device argument
  swiotlb: Bounce data from/to restricted DMA pool if available
  swiotlb: Move alloc_size to find_slots
  swiotlb: Refactor swiotlb_tbl_unmap_single
  dma-direct: Add a new wrapper __dma_direct_free_pages()
  swiotlb: Add restricted DMA alloc/free support.
  dma-direct: Allocate memory from restricted DMA pool if available
  dt-bindings: of: Add restricted DMA pool
  of: Add plumbing for restricted DMA pool

 .../reserved-memory/reserved-memory.txt       |  24 ++
 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                          |  25 ++
 drivers/of/device.c                           |   3 +
 drivers/of/of_private.h                       |   5 +
 drivers/pci/xen-pcifront.c                    |   2 +-
 drivers/xen/swiotlb-xen.c                     |   2 +-
 include/linux/device.h                        |   4 +
 include/linux/swiotlb.h                       |  41 ++-
 kernel/dma/Kconfig                            |  14 +
 kernel/dma/direct.c                           |  57 +++--
 kernel/dma/direct.h                           |   9 +-
 kernel/dma/swiotlb.c                          | 242 +++++++++++++-----
 15 files changed, 347 insertions(+), 97 deletions(-)

-- 
2.31.1.368.gbe11c130af-goog



More information about the dri-devel mailing list