Cross-VM side channels and their use to extract private keys

TLDR

Virtualized symmetric multiprocessing systems are ubiquitous, from desktop sandboxing to cloud co‑location of mutually distrustful workloads. The paper constructs and demonstrates an access‑driven side‑channel attack that lets a malicious VM extract fine‑grained information, including an ElGamal decryption key, from a victim VM on the same host. The attack overcomes core migration, channel noise, and the need for frequent victim preemption to retrieve fine‑grained data from the victim VM. The authors show that the attack succeeds on a Xen‑virtualized SMP system, successfully extracting an ElGamal decryption key from libgcrypt.

Abstract

This paper details the construction of an access-driven side-channel attack by which a malicious virtual machine (VM) extracts fine-grained information from a victim VM running on the same physical computer. This attack is the first such attack demonstrated on a symmetric multiprocessing system virtualized using a modern VMM (Xen). Such systems are very common today, ranging from desktops that use virtualization to sandbox application or OS compromises, to clouds that co-locate the workloads of mutually distrustful customers. Constructing such a side-channel requires overcoming challenges including core migration, numerous sources of channel noise, and the difficulty of preempting the victim with sufficient frequency to extract fine-grained information from it. This paper addresses these challenges and demonstrates the attack in a lab setting by extracting an ElGamal decryption key from a victim using the most recent version of the libgcrypt cryptographic library.