A keystone extension to defend against cache timing attacks

Trusted Execution Environment (TEE) find extensive applications in various scenarios such as secure cloud services, databases, big data computing, and blockchain. They establish a secure operational zone, often referred to as an Enclave, for applications. The Keystone Trusted Execution Environment offers a range of security primitives, including memory isolation, secure boot, and remote authentication. It stands out as the first open-source framework under the RISC-V architecture designed for constructing customized TEEs and is currently the mainstream TEE in the RISC-V architecture. However, Keystone itself does not provide protection for Enclaves or security monitors against Cache timing attacks. Recent research has demonstrated that malicious actors, leveraging Spectre attacks, can use Cache timing attack techniques to detect Enclave data through shared caches. This paper proposes a Keystone extension design, calling the extended framework Keyson-LLCI (Last Leavel Cache Isolation). Through security analysis, we prove that it can isolate enclaves and operating systems into different cache paths at the LLC level, thus eliminating the influence of cache side channels and increasing the isolation and security of enclaves. We implemented this hardware extension on an FPGA development board and conducted performance testing and IOZone testing. The test results indicate that Keystone-LLCI can effectively defend against Cache timing attacks, with a performance loss of approximately 14%. The latency of read and write operations increased by 12.4% and 14.1%, respectively. It represents an extension design with relatively low performance loss.