A Write-Friendly and Fast-Recovery Scheme for Security Metadata in NVM

Non-Volatile Memories (NVMs) have attracted the attentions of academia and industry, which is expected to become the next-generation memory. However, due to the nonvolatile property, NVMs become vulnerable to attacks and require security mechanisms, e.g., counter mode encryption and integrity tree, which introduce the security metadata. NVMs promise to recover these security metadata after a system crash, including the counter and integrity tree. However, unlike merkle tree reconstructed from user data, recovering SGX integrity tree (SIT) has to address the challenges from unique top-down hierarchical dependency. Moreover, writing overhead and recovery time are important metrics for evaluating persistent memory system due to the high costs of NVM writes and IT downtime. How to recover the security metadata, i.e., counter blocks and integrity tree nodes, with low write overhead and short recovery time, becomes much important. To provide a fast recovery scheme with low write overhead, we propose STAR, a cost-efficient scheme for recovering counter blocks and SGX integrity tree nodes after crashes. For fast recovery and verification, STAR synergizes the MAC and correct data, uses bitmap lines in ADR to indicate the location of stale node and constructs a cached merkle tree to verify the correctness of the recovery process. Moreover, STAR uses a multi-layer index to speed up the recovery process. STAR also allows different configurations to meet adaptive requirements for write overhead and recovery time. Our evaluation results show that the proposed STAR reduces the number of memory writes by up to 87\% compared with state-of-the-art work, Anubis, which needs extra 1x memory writes. For a 4MB security metadata cache, STAR needs 0.039s/0.023s/0.004s in three different configurations to recover the metadata cache while Anubis needs 0.020s.