Cooperative Path-ORAM for Effective Memory Bandwidth Sharing in Server Settings

Abstract

Path ORAM (Oblivious RAM) is a recently proposed ORAM protocol for preventing information leakage from memory access sequences. It receives wide adoption due to its simplicity, practical efficiency and asymptotic efficiency. However, Path ORAM has extremely large memory bandwidth demand, leading to severe memory competition in server settings, e.g., a server may service one application that uses Path ORAM and one or multiple applications that do not. While Path ORAM synchronously and intensively uses all memory channels, the non-secure applications often exhibit low access intensity and large channel level imbalance. Traditional memory scheduling schemes lead to wasted memory bandwidth to the system and large performance degradation to both types of applications. In this paper, we propose CP-ORAM, a Cooperative Path ORAM design, to effectively schedule the memory requests from both types of applications. CP-ORAM consists of three schemes: P-Path, R-Path, and W-Path. P-Path assigns and enforces scheduling priority for effective memory bandwidth sharing. R-Path maximizes bandwidth utilization by proactively scheduling read operations from the next Path ORAM access. W-Path mitigates contention on busy memory channels with write redirection. We evaluate CP-ORAM and compare it to the state-of-the-art. Our results show that CP-ORAM helps to achieve 20% performance improvement on average over the baseline Path ORAM for the secure application in a four-channel server setting.