Plutus: Bandwidth-Efficient Memory Security for GPUs

Graphic-Processing Units (GPUs) are increasingly used in systems where security is a critical design requirement. Such systems include cloud computing, safety-critical systems, and edge devices, where sensitive data is processed or/and generated. Thus, the ability to reduce the attack surface while achieving high performance is of utmost importance. However, adding security features to GPUs comes at the expense of high-performance overheads due to the extra memory bandwidth required to handle security metadata. In particular, memory authentication metadata (e.g., authentication tags) along with encryption counters can lead to significant performance overheads due to the memory bandwidth used to fetch the metadata. Such metadata can lead to more than 200% extra bandwidth usage for irregular access patterns.In this work, we propose a novel design, Plutus, which enables low-overhead secure GPU memory. Plutus has three key ideas. The first is to leverage value locality to reduce authentication metadata. Our observation is that a large percentage of memory accesses could be verified without the need to bring the authentication tags. Specifically, through comparing decrypted blocks against known/verified values, we can with high confidence guarantee that no tampering occurred. Our analysis shows that the probability of the decryption of a tampered (and/or replayed) block leading to a known value is extremely low, in fact, lower than the collision probability in the most secure hash functions. Second, based on the observation that many GPU workloads have limited numbers of dirty block evictions, Plutus proposes a second layer of compact counters to reduce the memory traffic due to both the encryption counters and integrity tree. Third, by exploring the interesting tradeoff between the integrity tree organization vs. metadata fetch granularity, Plutus uses smaller block sizes for security metadata caches to optimize the number of security metadata memory requests. Based on our evaluation, Plutus can improve the GPU throughput by 16.86% (up to 58.38%) and reduce the memory bandwidth usage of secure memory by 48.14% (up to 80.30%).