Fantastic Interrupts and Where to Find Them: Exploiting Non-Movable Interrupts on x86

While interrupts play a critical role in modern OSes, they have been exploited as a wide range of side channel attacks to break system confidentiality, such as keystroke interrupts, graphic interrupts and network interrupts. However, as previous attacks mainly focus on the exploitation of movable interrupts, they are required to determine which core is handling the target interrupts before their attack, which is non-trivial. The exploitability of non-movable interrupts, which cannot be reassigned by privileged softwares at will, remains unclear. In this paper, we conduct an empirical study on exploitable non-movable interrupts and their contribution to interrupt-based side-channel leakages in x86-based systems. We propose a dynamic analysis technique to investigate how various types of non-movable interrupts are influenced by different workloads. We then conduct a model fingerprinting attack as the benchmark to show that 7 types of non-movable interrupts are exploitable. To demonstrate the viability of these non-movable interrupts, we have created two concrete side channels, called ThermalScope and TimerScope. Specifically, ThermalScope exploits the thermal event interrupts that are triggered only when the CPU temperature exceeds a pre-determined threshold, and TimerScope exploits timer interrupts that are activated regularly to enable the process schedule. Both techniques are adaptable to different attack scenarios, functioning regardless of whether the attacker and victim share the same core or reside on separate cores. Last, we successfully apply them to mount realistic case studies, ranging from constructing cross-core covert channels to breaking kernel address space layout randomization. We also demonstrate successful DNN model fingerprinting attacks under browser scenarios when the frequency scaling is disabled and attacker core is isolated from movable interrupts, where previous HertzBleed, ThermalBleed, and movable interrupt-based attacks are ineffective.