Fabian Rauscher (Graz University of Technology), Andreas Kogler (Graz University of Technology), Jonas Juffinger (Graz University of Technology), Daniel Gruss (Graz University of Technology)

Modern processors are equipped with numerous features to regulate energy consumption according to the workload. For this purpose, software brings processor cores into idle states via dedicated instructions such as hlt. Recently, Intel introduced the C0.1 and C0.2 idle states. While idle states previously could only be reached via privileged operations, these new idle states can also be reached by an unprivileged attacker. However, the attack surface these idle states open is still unclear.

In this paper, we present IdleLeak, a novel side-channel attack exploiting the new C0.1 and C0.2 idle states in two distinct ways. Specifically, we exploit the processor idle state C0.2 to monitor system activity and for novel means of data exfiltration, and the idle state C0.1 to monitor system activity on logical sibling cores. IdleLeak still works regardless of where the victim workload is scheduled, i.e., cross-core, due to the low-level x86 design. We demonstrate that IdleLeak leaks significant information in a native keystroke-timing attack, achieving an F1 score of 90.5% and a standard error on the timing prediction of only 12 μs. We also demonstrate website- and video-fingerprinting attacks using IdleLeak traces, pre-processed with short-time Fourier transforms, and classified with convolutional neural networks. These attacks are highly practical with F1 scores of 85.2% (open-world website fingerprinting) and 81.5% (open-world video fingerprinting). We evaluate the throughput of IdleLeak side channels in both directions in covert channel scenarios, i.e., using interrupts and performance-increasing effects. With the performance-increasing effect, IdleLeak achieves a true capacity of 7.1 Mbit/s in a native and 46.3 kbit/s in a cross-VM scenario. With interrupts, IdleLeak achieves 656.37 kbit/s in a native scenario. We conclude that mitigations against IdleLeak are necessary in both personal and cloud environments when running untrusted code.

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