The paper “Rage Against the Machine Clear: A Systematic Analysis of Machine Clears and Their Implications for Transient Execution Attacks” has won the Distinguished Paper Award at the 30th USENIX Security Symposium, organized from August 11-13. Slides and the presentation video are already available.
As it’s described by authors, “since the discovery of the Spectre and Meltdown vulnerabilities, transient execution attacks have increasingly gained momentum. However, while the community has investigated several variants to trigger attacks during transient execution, much less attention has been devoted to the analysis of the root causes of transient execution itself. Most attack variants simply build on well-known root causes, such as branch misprediction and aborts of Intel TSX—which are no longer supported on many recent processors”.
In this paper, the authors tackle the problem from a new perspective, closely examining the different root causes of transient execution rather than focusing on new attacks based on known transient windows. Their analysis specifically focuses on the class of transient execution based on machine clears (MC), reverse engineering previously unexplored root causes such as Floating Point MC, Self-Modifying Code MC, Memory Ordering MC, and Memory Disambiguation MC. They show these events not only originate new transient execution windows that widen the horizon for known attacks, but also yield entirely new attack primitives to inject transient values (Floating Point Value Injection or FPVI) and executing stale code (Speculative Code Store Bypass or SCSB).
Congratulations to Hany Ragab, Enrico Barberis, Herbert Bos, and Cristiano Giuffrida, Vrije Universiteit Amsterdam!