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The memory system is vulnerable to a number of security breaches, e.g., an attacker can interfere with program execution by disrupting values stored in memory. Modern Intel® Software Guard Extension (SGX) systems already support integrity trees to detect such malicious behavior. However, in spite of recent innovations, the bandwidth overhead of integrity+replay protection is non-trivial; state-of-the-art solutions like Synergy introduce average slowdowns of $2.3 \times$ for memory-intensive benchmarks. Prior work also implements a tree that is shared by multiple applications, thus introducing a potential side channel. In this work, we build on the Synergy and SGX baselines, and introduce three new techniques. First, we isolate each application by implementing a separate integrity tree and metadata cache for each application; this improves metadata cache efficiency and improves performance by 39%, while eliminating the potential side channel. Second, we reduce the footprint of the metadata. Synergy uses a combination of integrity and error correction metadata to provide low-overhead support for both. We share error correction metadata across multiple blocks, thus lowering its footprint (by $16 \times$) while preventing error correction only in rare corner cases. However, we discover that shared error correction metadata, even with caching, does not improve performance. Third, we observe that thanks to its lower footprint, the error correction metadata can be embedded into the integrity tree. This reduces the metadata blocks that must be accessed to support both integrity verification and chipkill reliability. The proposed Isolated Tree with Embedded Shared Parity (ITESP) yields an overall performance improvement of 64%, relative to baseline Synergy. |
