[RFC v2 0/5] Restricted DMA

From: Claire Chang
Date: Tue Jul 28 2020 - 01:01:56 EST

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 on one MTK platform 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. The
restricted DMA is implemented by per-device swiotlb and coherent memory
pools. 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

[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 (5):
swiotlb: Add io_tlb_mem struct
swiotlb: Add device swiotlb pool
swiotlb: Use device swiotlb pool if available
dt-bindings: of: Add plumbing for restricted DMA pool
of: Add plumbing for restricted DMA pool

.../reserved-memory/reserved-memory.txt | 35 ++
drivers/iommu/intel/iommu.c | 8 +-
drivers/of/address.c | 39 ++
drivers/of/device.c | 3 +
drivers/of/of_private.h | 6 +
drivers/xen/swiotlb-xen.c | 4 +-
include/linux/device.h | 4 +
include/linux/dma-direct.h | 8 +-
include/linux/swiotlb.h | 49 +-
kernel/dma/direct.c | 8 +-
kernel/dma/swiotlb.c | 418 +++++++++++-------
11 files changed, 393 insertions(+), 189 deletions(-)

v1: https://lore.kernel.org/patchwork/cover/1271660/
Changes in v2:
- build on top of swiotlb