Hi Claire,
On Wed, Jun 16, 2021 at 02:21:45PM +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... [1b] https://googleprojectzero.blogspot.com/2017/04/over-air-exploiting-broadcoms... [2] https://blade.tencent.com/en/advisories/qualpwn/ [3] https://www.bleepingcomputer.com/news/security/vulnerabilities-found-in-high... [4] https://github.com/ARM-software/arm-trusted-firmware/blob/master/plat/mediat...
v12: Split is_dev_swiotlb_force into is_swiotlb_force_bounce (patch 06/12) and is_swiotlb_for_alloc (patch 09/12)
I took this for a spin in an arm64 KVM guest with virtio devices using the DMA API and it works as expected on top of swiotlb devel/for-linus-5.14, so:
Tested-by: Will Deacon will@kernel.org
Thanks!
Will