Embedded devices in the Internet of Things (IoT) face a wide variety of security challenges. For example, software attackers perform code injection and code-reuse attacks on their remote interfaces, and physical access to IoT devices allows to tamper with code in memory, steal confidential Intellectual Property (IP), or mount fault attacks to manipulate a CPU's control flow. In this work, we present Sponge-based Control Flow Protection (SCFP). SCFP is a stateful, sponge-based scheme to ensure the confidentiality of software IP and its authentic execution on IoT devices. At compile time, SCFP encrypts and authenticates software with instruction-level granularity. During execution, an SCFP hardware extension between the CPU's fetch and decode stage continuously decrypts and authenticates instructions. Sponge-based authenticated encryption in SCFP yields fine-grained control-flow integrity and thus prevents code-reuse, code-injection, and fault attacks on the code and the control flow. In addition, SCFP withstands any modification of software in memory. For evaluation, we extended a RISC-V core with SCFP and fabricated a real System on Chip (SoC). The average overhead in code size and execution time of SCFP on this design is 19.8 and 9.1 , respectively, and thus meets the requirements of embedded IoT devices.
. tee typically also provide confidentiality and authenticity for code. However, tee operate on a completely different level of granularity than scfp . The authenticated encryption in Intel SGX @cite_19 , for example, only ensures that the code and data in memory is protected against tampering. Physical faults in caches or on processor internal buses, on the other hand, are still possible. Also, SGX does not prevent common software attack techniques like code-reuse attacks within enclaves. Therefore, additional cfi schemes are needed to reach similar properties as scfp for code.
@cite_19
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Shielded execution based on Intel SGX provides strong security guarantees for legacy applications running on untrusted platforms. However, memory safety attacks such as Heartbleed can render the confidentiality and integrity properties of shielded execution completely ineffective. To prevent these attacks, the state-of-the-art memory-safety approaches can be used in the context of shielded execution. In this work, we first showcase that two prominent software- and hardware-based defenses, AddressSanitizer and Intel MPX respectively, are impractical for shielded execution due to high performance and memory overheads. This motivated our design of SGXBounds---an efficient memory-safety approach for shielded execution exploiting the architectural features of Intel SGX. Our design is based on a simple combination of tagged pointers and compact memory layout. We implemented SGXBounds based on the LLVM compiler framework targeting unmodified multithreaded applications. Our evaluation using Phoenix, PARSEC, and RIPE benchmark suites shows that SGXBounds has performance and memory overheads of 17 and 0.1 respectively, while providing security guarantees similar to AddressSanitizer and Intel MPX. We have obtained similar results with SPEC CPU2006 and four real-world case studies: SQLite, Memcached, Apache, and Nginx.