Collide+Power: The Evolution of Software-based Power Side-Channels Attacks

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Presented at BlackHat Europe 2023 by

Andreas Kogler

Power side channels exploit leakage that is fundamentally a result of how we build processors. Over the recent years, these attacks evolved to target general-purpose desktop and server CPUs purely from software.In this talk, we explore this evolution to its most recent addition: Collide+Power, a novel technique to exploit the fundamental way we share components in modern general-purpose CPUs. In contrast to previous work, Collide+Power does not target specific programs or algorithms but the underlying CPU hardware. This advance in software-based power side channels echoes the discovery of Meltdown and Spectre — where similarly, the underlying hardware provided unforeseen attack possibilities.We present the root of the problem: shared CPU components, like the internal memory system. These components allow attacker-controlled data to collide with data from any other application, resulting in a combined leakage signal in the power consumption. Thus, the attacker can infer the values used in other applications by choosing its own data. We present two attacks belonging to the Collide+Power attack family: The first attack breaks the isolation between hyperthreads, leaking arbitrary data across programs. The second attack breaks the isolation between user programs and the operating system, leaking arbitrary data from the operating system and any other program from the same computer.Finally, we explore mitigations and discuss why Collide+Power has characteristics of a persistent threat: It is practically impossible to prevent data collisions due to the sheer amount of shared components. Therefore, the current advisories suggest preventing the observation of power-related signals. However, Collide+Power can use any power-related signal and is agnostic to discovered leakage sources like the direct power readings of the PLATYPUS attack or the indirect power readings of the Hertzbleed attack. Albeit the leakage rates of Collide+Power with the unmitigated Hertzbleed signal are low, it affects a broad spectrum of CPUs.