Rkt-io: A direct I/O stack for shielded execution

The shielding of applications using trusted execution environments (TEEs) can provide strong security guarantees in untrusted cloud environments. When executing I/O operations, today's shielded execution frameworks, however, exhibit performance and security limitations: they assign resources to the I/O path inefficiently, perform redundant data copies, use untrusted host I/O stacks with security risks and performance overheads. This prevents TEEs from running modern I/O-intensive applications that require high-performance networking and storage. We describe rkt-io (pronounced "rocket I/O"), a direct user-space network and storage I/O stack specifically designed for TEEs that combines high-performance, POSIX compatibility and security. rkt-io achieves high I/O performance by employing direct userspace I/O libraries (DPDK and SPDK) inside the TEE for kernel-bypass I/O. For efficiency, rkt-io polls for I/O events directly, by interacting with the hardware instead of relying on interrupts, and it avoids data copies by mapping DMA regions in the untrusted host memory. To maintain full Linux ABI compatibility, the userspace I/O libraries are integrated with userspace versions of the Linux VFS and network stacks inside the TEE. Since it omits the host OS from the I/O path, does not suffer from host interface/Iago attacks. Our evaluation with Intel SGX TEEs shows that rkt-io is 9×faster for networking and 7× faster for storage compared to host- (Scone) and LibOS-based (SGX-LKL) I/O approaches.