Alejandro Mera

Alejandro Mera, Yi Hui Chen, Ruimin Sun et al.

Embedded and Internet-of-Things (IoT) devices have seen an increase in adoption in many domains. The security of these devices is of great importance as they are often used to control critical infrastructure, medical devices, and vehicles. Existing solutions to isolate microcontroller (MCU) resources in order to increase their security face significant challenges such as specific hardware unavailability, Memory Protection Unit (MPU) limitations and a significant lack of Direct Memory Access (DMA) support. Nevertheless, DMA is fundamental for the power and performance requirements of embedded applications. In this paper, we present D-Box, a systematic approach to enable secure DMA operations for compartmentalization solutions of embedded applications using real-time operating systems (RTOS). D-Box defines a reference architecture and a workflow to protect DMA operations holistically. It provides practical methods to harden the kernel and define capability-based security policies for easy definition of DMA operations with strong security properties. We implemented a D-Box prototype for the Cortex-M3/M4 on top of the popular FreeRTOS-MPU (F-MPU). The D-Box procedures and a stricter security model enabled DMA operations, yet it exposed 41 times less ROP (return-orienting-programming) gadgets when compared with the standard F-MPU. D-Box adds only a 2% processor overhead while reducing the power consumption of peripheral operation benchmarks by 18.2%. The security properties and performance of D-Box were tested and confirmed on a real-world case study of a Programmable Logic Controller (PLC) application.

Alejandro Mera, Bo Feng, Long Lu et al.

Microcontroller-based embedded devices are at the core of Internet-of-Things and Cyber-Physical Systems. The security of these devices is of paramount importance. Among the approaches to securing embedded devices, dynamic firmware analysis gained great attention lately, thanks to its offline nature and low false-positive rates. However, regardless of the analysis and emulation techniques used, existing dynamic firmware analyzers share a major limitation, namely the inability to handle firmware using DMA. It severely limits the types of devices supported and firmware code coverage. We present DICE, a drop-in solution for firmware analyzers to emulate DMA input channels and generate or manipulate DMA inputs. DICE is designed to be hardware-independent, and compatible with common MCU firmware and embedded architectures. DICE identifies DMA input channels as the firmware writes the source and destination DMA transfer pointers into the DMA controller. Then DICE manipulates the input transferred through DMA on behalf of the firmware analyzer. We integrated DICE to the firmware analyzer P2IM (Cortex-M architecture) and a PIC32 emulator (MIPS M4K/M-Class architecture). We evaluated it on 83 benchmarks and sample firmware, representing 9 different DMA controllers from 5 different vendors. DICE detected 33 out of 37 DMA input channels, with 0 false positives. It correctly supplied DMA inputs to 21 out of 22 DMA buffers, which previous firmware analyzers cannot achieve due to the lack of DMA emulation. DICE's overhead is fairly low, it adds 3.4% on average to P2IM execution time. We also fuzz-tested 7 real-world firmware using DICE and compared the results with the original P2IM. DICE uncovered tremendously more execution paths (as much as 79X) and found 5 unique previously-unknown bugs that are unreachable without DMA emulation. All our source code and dataset are publicly available.

Ruimin Sun, Alejandro Mera, Long Lu et al.

Programmable Logic Controllers (PLCs) play a critical role in the industrial control systems. Vulnerabilities in PLC programs might lead to attacks causing devastating consequences to the critical infrastructure, as shown in Stuxnet and similar attacks. In recent years, we have seen an exponential increase in vulnerabilities reported for PLC control logic. Looking back on past research, we found extensive studies explored control logic modification attacks, as well as formal verification-based security solutions. We performed systematization on these studies, and found attacks that can compromise a full chain of control and evade detection. However, the majority of the formal verification research investigated ad-hoc techniques targeting PLC programs. We discovered challenges in every aspect of formal verification, rising from (1) the ever-expanding attack surface from evolved system design, (2) the real-time constraint during the program execution, and (3) the barrier in security evaluation given proprietary and vendor-specific dependencies on different techniques. Based on the knowledge systematization, we provide a set of recommendations for future research directions, and we highlight the need of defending security issues besides safety issues.

Bo Feng, Alejandro Mera, Long Lu

Dynamic testing or fuzzing of embedded firmware is severely limited by hardware-dependence and poor scalability, partly contributing to the widespread vulnerable IoT devices. We propose a software framework that continuously executes a given firmware binary while channeling inputs from an off-the-shelf fuzzer, enabling hardware-independent and scalable firmware testing. Our framework, using a novel technique called P$^2$IM, abstracts diverse peripherals and handles firmware I/O on the fly based on automatically generated models. P$^2$IM is oblivious to peripheral designs and generic to firmware implementations, and therefore, applicable to a wide range of embedded devices. We evaluated our framework using 70 sample firmware and 10 firmware from real devices, including a drone, a robot, and a PLC. It successfully executed 79% of the sample firmware without any manual assistance. We also performed a limited fuzzing test on the real firmware, which unveiled 7 unique unknown bugs.