Trusted Execution Environments (TEEs) have been widely used in many security-critical applications. The popularity of TEEs derives from its high security and trustworthiness supported by secure hardware. Intel Software Guard Extensions (SGX) is one of the most representative TEEs that creates an isolated environment on an untrusted operating system, thus providing run-time protection for the execution of security-critical code and data. However, Intel SGX is far from the acme of perfection. It has become a target of various attacks due to its security vulnerabilities. Researchers and practitioners have paid attention to the security vulnerabilities of SGX and investigated optimization solutions in real applications. Unfortunately, existing literature lacks a thorough review of security vulnerabilities of SGX and their countermeasures. In this article, we fill this gap. Specifically, we propose two sets of criteria for estimating security risks of existing attacks and evaluating defense effects brought by attack countermeasures. Furthermore, we propose a taxonomy of SGX security vulnerabilities and shed light on corresponding attack vectors. After that, we review published attacks and existing countermeasures, as well as evaluate them by employing our proposed criteria. At last, on the strength of our survey, we propose some open challenges and future directions in the research of SGX security.
Security Vulnerabilities of SGX and Countermeasures