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
