Triad-NVM: Persistency for Integrity-Protected and Encrypted Non-Volatile Memories

Non-Volatile Memory is here and provides an attractive fabric for main memory. Unlike DRAM, non-volatile main memory (NVMM) retains data after power loss. This allows memory to host data persistently across crashes and reboots, but opens up opportunities for attackers to snoop and/or tamper with data between boot episodes. While memory encryption and integrity verification have been well studied for DRAM systems, new challenges surface for NVMM if we want to simultaneously preserve security guarantees, data recovery across crashes/reboots, good persistence performance, and fast recovery. In this paper, we explore persistency of data with all security metadata (counters, MACs, and Merkle Tree) to achieve secure persistency. We show that to ensure security guarantees, message authentication code (MAC) and Bonsai Merkle Tree (BMT) need to be maintained, in addition to counters, and they provide the majority of persistency overheads. We analyze the requirements for achieving secure persistency for both persistent and non-persistent memory regions. We found that the non-volatility nature of memory may trigger integrity verification failure at reboot, hence we propose a separate mechanism to support non-persistent memory region. Fourth, we propose designs to make recovery fast. Our evaluation shows that the proposed design, Triad-Nvm, can improve the throughput by an average of 2× relative to strict persistence. Moreover, Triad-NVM can achieve orders of magnitude faster recovery time compared to systems without security metadata persistence.