[PATCH v4 00/14] Restricted DMA

Claire Chang
2021-02-09T06:22:46Z

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