Principled Microarchitectural Isolation on Cloud CPUs

We present Marghera, a system design that prevents cross-VM microarchitectural side-channel attacks in the cloud. Marghera is based on isolation contracts which, for a given CPU, describe partitions of physical threads and memory that prevent information leakage through shared microarchitectural resources. We develop isolation contracts for the AMD EPYC 7543P, a modern cloud CPU. To this end, we first identify how microarchitectural resources are shared between its physical threads, including caches, cache-coherence directories, and DRAM banks. We then develop coloring schemes-that comprehensively partition these resourcesusing previously unknown, reverse-engineered indexing functions. We implement Marghera in Microsoft Hyper-V and evaluate it using cloud benchmarks. Our results show that our approach effectively eliminates side-channels caused by shared microarchitectural resources with small performance overheads. CCS CONCEPTS • Security and privacy → Virtualization and security; Sidechannel analysis and countermeasures; Hardware reverse engineering.