Hi Claire, On Thu, May 27, 2021 at 08:58:30PM +0800, Claire Chang wrote: > 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 > > v8: > - Fix reserved-memory.txt and add the reg property in example. > - Fix sizeof for of_property_count_elems_of_size in > drivers/of/address.c#of_dma_set_restricted_buffer. > - Apply Will's suggestion to try the OF node having DMA configuration in > drivers/of/address.c#of_dma_set_restricted_buffer. > - Fix typo in the comment of drivers/of/address.c#of_dma_set_restricted_buffer. > - Add error message for PageHighMem in > kernel/dma/swiotlb.c#rmem_swiotlb_device_init and move it to > rmem_swiotlb_setup. > - Fix the message string in rmem_swiotlb_setup. Thanks for the v8. It works for me out of the box on arm64 under KVM, so: Tested-by: Will Deacon <will@xxxxxxxxxx> Note that something seems to have gone wrong with the mail threading, so the last 5 patches ended up as a separate thread for me. Probably worth posting again with all the patches in one place, if you can. Cheers, Will
