EVEE FS : Securing Access to Untrusted Filesystems in Enclaved Execution

Enclaved execution techniques like Intel SGX guarantee secure execution of applications in presence of a compromised operating system. However, these techniques still rely on the underlying OS for services such as filesystem management. In this paper, we present attacks called syscall-abuse attacks on applications such as OpenSSL and ClamAV in presence of a compromised filesystem management service. To mitigate such attacks, we design and implement LEVEEFS — a filesystem abstraction to ensure secure access to untrusted storage in enclaved execution environment. LEVEEFS simultaneously provides security, efficiency and expressiveness guarantees. Unlike existing solutions, the trusted computing base (TCB) is small and comprises of approximately 3836 LOC i.e, 7.62 % of the total filesystem size. To evaluate the expressiveness, we execute various file benchmarks like Bonnie++, Iozone and FileBench along with application benchmarks like CoreUtils, OpenSSL and ClamAV. LEVEEFS system incurs an average overhead of 8.03 % on these benchmarks which is acceptable for practical use.