IChannels: Exploiting Current Management Mechanisms to Create Covert Channels in Modern Processors

TL;DR

This paper uncovers how current management mechanisms in modern processors can be exploited to create covert channels, revealing new security vulnerabilities and proposing mitigations.

Contribution

It introduces IChannels, a novel set of covert channels exploiting current management side-effects in modern Intel processors, with significantly higher capacity than previous methods.

Findings

IChannels achieves over 24x the capacity of existing power management covert channels.

Current management mechanisms can leak information across different software contexts.

Effective mitigations can be implemented based on system characterization.

Abstract

To operate efficiently across a wide range of workloads with varying power requirements, a modern processor applies different current management mechanisms, which briefly throttle instruction execution while they adjust voltage and frequency to accommodate for power-hungry instructions (PHIs) in the instruction stream. Doing so 1) reduces the power consumption of non-PHI instructions in typical workloads and 2) optimizes system voltage regulators' cost and area for the common use case while limiting current consumption when executing PHIs. However, these mechanisms may compromise a system's confidentiality guarantees. In particular, we observe that multilevel side-effects of throttling mechanisms, due to PHI-related current management mechanisms, can be detected by two different software contexts (i.e., sender and receiver) running on 1) the same hardware thread, 2) co-located Simultaneous Multi-Threading (SMT) threads, and 3) different physical cores. Based on these new observations on current management mechanisms, we develop a new set of covert channels, IChannels, and demonstrate them in real modern Intel processors (which span more than 70% of the entire client and server processor market). Our analysis shows that IChannels provides more than 24x the channel capacity of state-of-the-art power management covert channels. We propose practical and effective mitigations to each covert channel in IChannels by leveraging the insights we gain through a rigorous characterization of real systems.