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Subject[PATCH v4 00/14] Restricted DMA
Date
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

Claire Chang (14):
swiotlb: Remove external access to io_tlb_start
swiotlb: Move is_swiotlb_buffer() to swiotlb.c
swiotlb: Add struct swiotlb
swiotlb: Refactor swiotlb_late_init_with_tbl
swiotlb: Add DMA_RESTRICTED_POOL
swiotlb: Add restricted DMA pool
swiotlb: Update swiotlb API to gain a struct device argument
swiotlb: Use restricted DMA pool if available
swiotlb: Refactor swiotlb_tbl_{map,unmap}_single
dma-direct: Add a new wrapper __dma_direct_free_pages()
swiotlb: Add is_dev_swiotlb_force()
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 | 24 +
arch/powerpc/platforms/pseries/svm.c | 4 +-
drivers/iommu/dma-iommu.c | 12 +-
drivers/of/address.c | 25 +
drivers/of/device.c | 3 +
drivers/of/of_private.h | 5 +
drivers/xen/swiotlb-xen.c | 4 +-
include/linux/device.h | 4 +
include/linux/swiotlb.h | 32 +-
kernel/dma/Kconfig | 14 +
kernel/dma/direct.c | 51 +-
kernel/dma/direct.h | 8 +-
kernel/dma/swiotlb.c | 636 ++++++++++++------
13 files changed, 582 insertions(+), 240 deletions(-)

--

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/

2.30.0.478.g8a0d178c01-goog

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