Oblivious Demand Paging with Ring ORAM in RISC-V Trusted Execution Environments

Trusted execution environments based on RISC-V architecture like Keystone remain susceptible to leaking page access patterns of applications via simple demand paging, in which a malicious Operating System (OS) deduces sensitive information from it. To address this issue, Keystone requires protecting sensitive access patterns from being revealed to the malicious OS by implementing oblivious demand paging. In this paper, we use Oblivious RAM (ORAM) techniques that obfuscate access patterns while simultaneously making demand paging oblivious for Keystone. Furthermore, we present customized optimizations to Ring ORAM, aimed at minimizing the performance overhead incurred by applications during both secure and unsecure demand paging in Keystone. These optimizations encompass strategies such as encoding the position map within the page table, utilizing a resizable tree structure and selective eviction of only the root bucket. These improvements collectively contribute to minimizing performance slowdown. We implement and evaluate our optimized Ring ORAM for oblivious demand paging, which shows the average performance slowdown of 7.1x in comparison to the simple Ring ORAM slowdown of 26.2x.