Transient Execution and Side Channel Analysis: a Vulnerability or a Science Experiment?

In the world of computer security, attackers are constantly looking for new exploits to gain data from or control over a computer system. One category of exploit that can prove quite effective at accessing privileged data is side channel exploits. These exploits attempt to take advantage of vulnerabilities that are inherent in the design of a system rather than vulnerabilities in the code that has been written for and is running on said system. In other words, they exploit side effects of computation. Examples of this include measuring the power consumption of a system’s processor over time and analysing that power usage to leak system secrets or reading secrets from a system by analysing the electromagnetic radiation the system leaks as it processes data. Another type of side channel attack is a cache-based side channel attack, which exploits the timings of cache and memory accesses to determine data from the target system. We discuss some of the more common types of side channel attacks used to interpret data values from the microarchitectural changes created by transient executions. In particular, we will focus on attacks that are capable of recovering data that is processed through transient execution in some way and then wrongly accessed using a side channel, such as the Spectre and Meltdown classes of attack. We also discuss other attacks of a similar type and survey some popular mitigations for these attacks. We provide a survey of all available Spectre proof-of-concept repositories on GitHub, evaluating whether they work on different platforms. Finally, we review our experiences with these types of attacks on modern systems and comment on the attacks’ practicality, reliability, and portability. We conclude that these types of attacks are interesting, but there are some practicality and reliability concerns that make other attacks easier much of the time.