A. Theodore Markettos (University of Cambridge), Colin Rothwell (University of Cambridge), Brett F. Gutstein (Rice University), Allison Pearce (University of Cambridge), Peter G. Neumann (SRI International), Simon W. Moore (University of Cambridge), Robert N. M. Watson (University of Cambridge)

Direct Memory Access (DMA) attacks have been known for many years: DMA-enabled I/O peripherals have complete access to the state of a computer and can fully compromise it including reading and writing all of system memory.

With the popularity of Thunderbolt 3 over USB Type-C and smart internal devices, opportunities for these attacks to be performed casually with only seconds of physical access to a computer have greatly broadened. In response, commodity hardware and operating-system (OS) vendors have incorporated support for Input-Output Memory Management Units (IOMMUs), which impose memory protection on DMA, and are widely believed to protect against DMA attacks.

We investigate the state-of-the-art in IOMMU protection across OSes using a novel *I/O security research platform*, and find that current protections fall short when faced with a functional network peripheral that uses its complex interactions with the OS for ill intent, and demonstrate compromises against macOS, FreeBSD, and Linux, which notionally utilize IOMMUs to protect against DMA attackers. Windows only uses the IOMMU in limited cases and remains vulnerable.

Using Thunderclap, an open-source FPGA research platform we built, we explore a number of novel exploit techniques to expose new classes of OS vulnerability. The complex vulnerability space for IOMMU-exposed shared memory available to DMA-enabled peripherals allows attackers to extract private data (sniffing cleartext VPN traffic) and hijack kernel control flow (launching a root shell) in seconds using devices such as USB-C projectors or power adapters.

We have worked closely with OS vendors to remedy these vulnerability classes, and they have now shipped substantial feature improvements and mitigations as a result of our work.

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