CATalyst: Defeating last-level cache side channel attacks in cloud computing

TLDR

Cache side‑channel attacks threaten multi‑tenant cloud platforms, with recent work showing high‑bandwidth, low‑noise attacks on the last‑level cache that can be mounted even when VMs run on different cores, and the Intel Cache Allocation Technology (CAT) provides a hardware cache‑partitioning mechanism for quality‑of‑service. The paper proposes to defeat LLC side‑channel attacks by leveraging Intel’s Cache Allocation Technology (CAT) through a new pseudo‑locking mechanism called CATalyst. CATalyst partitions the LLC into a hybrid hardware‑software managed cache using CAT, implemented as a pseudo‑locking mechanism on Intel processors and deployed in a Xen/Linux environment. The proof‑of‑concept implementation demonstrates that CATalyst defeats LLC side‑channel attacks with only minimal performance overhead and negligible impact on legacy applications.

Abstract

Cache side channel attacks are serious threats to multi-tenant public cloud platforms. Past work showed how secret information in one virtual machine (VM) can be extracted by another co-resident VM using such attacks. Recent research demonstrated the feasibility of high-bandwidth, low-noise side channel attacks on the last-level cache (LLC), which is shared by all the cores in the processor package, enabling attacks even when VMs are scheduled on different cores. This paper shows how such LLC side channel attacks can be defeated using a performance optimization feature recently introduced in commodity processors. Since most cloud servers use Intel processors, we show how the Intel Cache Allocation Technology (CAT) can be used to provide a system-level protection mechanism to defend from side channel attacks on the shared LLC. CAT is a way-based hardware cache-partitioning mechanism for enforcing quality-of-service with respect to LLC occupancy. However, it cannot be directly used to defeat cache side channel attacks due to the very limited number of partitions it provides. We present CATalyst, a pseudo-locking mechanism which uses CAT to partition the LLC into a hybrid hardware-software managed cache. We implement a proof-of-concept system using Xen and Linux running on a server with Intel processors, and show that LLC side channel attacks can be defeated. Furthermore, CATalyst only causes very small performance overhead when used for security, and has negligible impact on legacy applications.