A Write-Friendly and Fast-Recovery Scheme for Security Metadata in Non-Volatile Memories

Non-Volatile Memories (NVMs) require security mechanisms, e.g., counter mode encryption and integrity tree verification, which are important to protect systems in terms of encryption and data integrity. These security mechanisms heavily rely on extra security metadata that need to be efficiently and accurately recovered after system crashes or power off. Established SGX integrity tree (SIT) becomes efficient to protect system integrity and however fails to be restored from leaves, since the computations of SIT nodes need their parent nodes as inputs. To recover the security metadata with low write overhead and short recovery time, we propose an efficient and instantaneous persistence scheme, called STAR, which instantly persists the modifications of security metadata without extra memory writes. STAR is motivated by our observation that the parent nodes in cache are modified due to persisting their child nodes. STAR stores the modifications of parent nodes in their child nodes and persists them just using one atomic memory write. To eliminate the overhead of persisting the modifications, STAR coalesces the modifications and MACs in the evicted metadata. For fast recovery and verification of the metadata, STAR uses bitmap lines in asynchronous DRAM refresh (ADR) to indicate the locations of stale metadata, and constructs a cached merkle tree to verify the correctness of the recovery process. Our evaluation results show that compared with state-of-the-art work, our proposed STAR delivers high performance, low write traffic, low energy consumption and short recovery time.