[PATCH 0/4] Bounced DMA support

[Claire Chang]

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 bounced DMA. The bounced
DMA ops provide an implementation of DMA ops that bounce streaming DMA
in and out of a specially allocated 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. in ATF on some ARM platforms).

Currently, 32-bit architectures are not supported because of the need to
handle HIGHMEM, which increases code complexity and adds more
performance penalty for such platforms. Also, bounced DMA can not be
enabled on devices behind an IOMMU, as those require an IOMMU-aware
implementation of DMA ops and do not require this kind of mitigation
anyway.

[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/


Claire Chang (4):
  dma-mapping: Add bounced DMA ops
  dma-mapping: Add bounced DMA pool
  dt-bindings: of: Add plumbing for bounced DMA pool
  of: Add plumbing for bounced DMA pool

 .../reserved-memory/reserved-memory.txt       |  36 +++
 drivers/of/address.c                          |  37 +++
 drivers/of/device.c                           |   3 +
 drivers/of/of_private.h                       |   6 +
 include/linux/device.h                        |   3 +
 include/linux/dma-mapping.h                   |   1 +
 kernel/dma/Kconfig                            |  17 +
 kernel/dma/Makefile                           |   1 +
 kernel/dma/bounced.c                          | 304 ++++++++++++++++++
 9 files changed, 408 insertions(+)
 create mode 100644 kernel/dma/bounced.c

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2.27.0.383.g050319c2ae-goog