Pinghai Yuan

Jinhua Cui, Shweta Shinde, Satyaki Sen et al.

Enclaves, such as those enabled by Intel SGX, offer a hardware primitive for shielding user-level applications from the OS. While enclaves are a useful starting point, code running in the enclave requires additional checks whenever control or data is transferred to/from the untrusted OS. The enclave-OS interface on SGX, however, can be extremely large if we wish to run existing unmodified binaries inside enclaves. This paper presents Ratel, a dynamic binary translation engine running inside SGX enclaves on Linux. Ratel offers complete interposition, the ability to interpose on all executed instructions in the enclave and monitor all interactions with the OS. Instruction-level interposition offers a general foundation for implementing a large variety of inline security monitors in the future. We take a principled approach in explaining why complete interposition on SGX is challenging. We draw attention to 5 design decisions in SGX that create fundamental trade-offs between performance and ensuring complete interposition, and we explain how to resolve them in the favor of complete interposition. To illustrate the utility of the Ratel framework, we present the first attempt to offer binary compatibility with existing software on SGX. We report that Ratel offers binary compatibility with over 200 programs we tested, including micro-benchmarks and real applications such as Linux shell utilities. Runtimes for two programming languages, namely Python and R, tested with standard benchmarks work out-of-the-box on Ratel without any specialized handling.

Shweta Shinde, Jinhua Cui, Satyaki Sen et al.

Enclaves, such as those enabled by Intel SGX, offer a powerful hardware isolation primitive for application partitioning. To become universally usable on future commodity OSes, enclave designs should offer compatibility with existing software. In this paper, we draw attention to 5 design decisions in SGX that create incompatibility with existing software. These represent concrete starting points, we hope, for improvements in future TEEs. Further, while many prior works have offered partial forms of compatibility, we present the first attempt to offer binary compatibility with existing software on SGX. We present Ratel, a system that enables a dynamic binary translation engine inside SGX enclaves on Linux. Through the lens of Ratel, we expose the fundamental trade-offs between performance and complete mediation on the OS-enclave interface, which are rooted in the aforementioned 5 SGX design restrictions. We report on an extensive evaluation of Ratel on over 200 programs, including micro-benchmarks and real applications such as Linux utilities.

Shweta Shinde, Shengyi Wang, Pinghai Yuan et al.

New trusted computing primitives such as Intel SGX have shown the feasibility of running user-level applications in enclaves on a commodity trusted processor without trusting a large OS. However, the OS can still compromise the integrity of an enclave by tampering with the system call return values. In fact, it has been shown that a subclass of these attacks, called Iago attacks, enables arbitrary logic execution in enclave programs. Existing enclave systems have very large TCB and they implement ad-hoc checks at the system call interface which are hard to verify for completeness. To this end, we present BesFS--the first filesystem interface which provably protects the enclave integrity against a completely malicious OS. We prove 167 lemmas and 2 key theorems in 4625 lines of Coq proof scripts, which directly proves the safety properties of the BesFS specification. BesFS comprises of 15 APIs with compositional safety and is expressive enough to support 31 real applications we test. BesFS integrates into existing SGX-enabled applications with minimal impact to TCB. BesFS can serve as a reference implementation for hand-coded API checks.