HardScope: Thwarting DOP with Hardware-assisted Run-time Scope Enforcement

The widespread use of memory unsafe programming languages (e.g., C and C++), especially in embedded systems and the Internet of Things (IoT), leaves many systems vulnerable to memory corruption attacks. A variety of defenses have been proposed to mitigate attacks that exploit memory errors to hijack the control flow of the code at run-time, e.g., (fine-grained) ASLR or Control Flow Integrity (CFI). However, recent work on data-oriented programming (DOP) demonstrated the possibility to construct highly-expressive (Turing-complete) attacks, even in the presence of these stateof-the-art defenses. Although multiple real-world DOP attacks have been demonstrated, no suitable defenses are yet available. We present run-time scope enforcement (RSE), a novel approach designed to mitigate all currently known DOP attacks by enforcing compile-time memory safety constraints (e.g., variable visibility rules) at run-time. We also present HardScope, a proof-of-concept implementation of hardwareassisted RSE for the new RISC-V open instruction set architecture. We demonstrate that HardScope mitigates all currently known DOP attacks at multiple points in each attack. We have implemented HardScope in hardware on the open-source RISC-V Pulpino microcontroller. Our cycleaccurate simulation shows a real-world performance overhead of 7.1% when providing complete mediation of all memory accesses.