Jianming Huang

Jianming Huang, Yu Hua

Data integrity is important for non-volatile memory (NVM) systems that maintain data even without power. The data integrity in NVM is possibly compromised by integrity attacks, which can be defended against by integrity verification via integrity trees. After NVM system failures and reboots, the integrity tree root is responsible for providing a trusted execution environment. However, the root often becomes a performance bottleneck, since updating the root requires high latency on the write critical path to propagate the modifications from leaf nodes to the root. The root and leaf nodes have to ensure the crash consistency between each other to avoid any update failures that potentially result in misreporting the attacks after system reboots. In this paper, we propose an efficient and low-latency scheme, called SCUE, to directly update the root on the SGX integrity tree (SIT) by overlooking the updates upon the intermediate tree nodes. The idea behind SCUE explores and exploits the observation that only the persistent leaf nodes and root are useful to ensure the integrity after system failures and reboots, due to the loss of the cached intermediate tree nodes. To achieve the crash consistency between root and leaf nodes, we accurately predict the updates upon the root and pre-update the root before the leaf nodes are modified. Moreover, the SIT root is difficult to be reconstructed from the leaf nodes since updating one tree node needs its parent node as input. We use a counter-summing approach to reconstructing the SIT from leaf nodes. Our evaluation results show that compared with the state-of-the-art integrity tree update schemes, our SCUE scheme delivers high performance while ensuring the system integrity.

Jianming Huang, Yu Hua

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.