[PATCH v7 00/15] Restricted DMA

Claire Chang
2021-05-18T06:42:34Z

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

v7:
Fix debugfs, PageHighMem and comment style in rmem_swiotlb_device_init

v6:
Address the comments in v5
https://lore.kernel.org/patchwork/cover/1423201/

v5:
Rebase on latest linux-next
https://lore.kernel.org/patchwork/cover/1416899/

v4:
- Fix spinlock bad magic
- Use rmem->name for debugfs entry
- Address the comments in v3
https://lore.kernel.org/patchwork/cover/1378113/

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 (15):
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 | 27 ++
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 | 63 +++--
kernel/dma/direct.h | 9 +-
kernel/dma/swiotlb.c | 242 +++++++++++++-----
15 files changed, 356 insertions(+), 97 deletions(-)

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2.31.1.751.gd2f1c929bd-goog