ReadPRO: Read Prioritization Scheduling in ORAM for Efficient Obfuscation in Main Memories

Abstract

Modern memory systems are susceptible to data confidentiality attacks that leverage memory access pattern information to obtain secret data. Oblivious RAM (ORAM) is a secure cryptographic construct that effectively thwarts access-pattern-based attacks. However, in Path ORAM (state-of-the-art efficient ORAM for main memories) and its variants, each memory request (read or write) is transformed to an ORAM access, which is a sequence of read and write operations, increasing the latency of the memory requests and degrading system performance. In practice, the ORAM access for a read request is on the critical path of program execution, blocked by ORAM accesses for older write requests. Although modern memory controllers (MCs) realize read prioritization through write buffering, the ORAM access translation of each memory request to multiple memory read and write operations results in frequent MC write buffer overflow, decreasing its efficiency. ReadPRO (Read Prioritization) scheduling in ORAM addresses this challenge by promoting read requests over write requests in the ORAM controller prior to their ORAM access translation, while preserving all data dependencies. ReadPRO complements read promotion with staggered writes, wherein ORAM accesses for write requests can be paused securely to serve ORAM accesses for read requests. Full-system evaluations on composite SPEC CPU2006 workloads show that ReadPRO decreases the average ORAM read latency by 75%, improving system performance by 40%.