SGXLock: Towards Efficiently Establishing Mutual Distrust Between Host Application and Enclave for SGX

Since its debut, SGX has been used to secure various types of applications. However, existing systems usually assume a trusted enclave and ignore the security issues caused by an untrusted enclave. For instance, a vulnerable (or even malicious) third-party enclave can be exploited to attack the host application and the rest of the system. In this paper, we propose an efficient mechanism to confine an untrusted enclave's behaviors. In particular, the threats of an untrusted enclave come from the enclave-host asymmetries, which can be abused to access arbitrary memory regions of its host application, jump to any code location after leaving the enclave and forge the stack register to manipulate the saved context. Our solution breaks such asymmetries and establishes mutual distrust between the host application and the enclave. Specifically, it leverages Intel MPK for efficient memory isolation and the x86 single-step debugging mechanism to capture the exiting event of the enclave. Then it performs the integrity check of the jump target and the stack pointer. We have implemented a prototype system and solved two practical challenges. The evaluation with multiple micro-benchmarks and representative real-world applications demonstrated the effectiveness and the efficiency of our system, with less than 4% performance overhead.