Shining Light On Shadow Stacks

Control-Flow Hijacking attacks are the dominant attack vector against C/C++ programs. Control-Flow Integrity (CFI) solutions mitigate these attacks on the forward edge,i.e., indirect calls through function pointers and virtual calls. Protecting the backward edge is left to stack canaries, which are easily bypassed through information leaks. Shadow Stacks are a fully precise mechanism for protecting backwards edges, and should be deployed with CFI mitigations. We present a comprehensive analysis of all possible shadow stack mechanisms along three axes: performance, compatibility, and security. For performance comparisons we use SPEC CPU2006, while security and compatibility are qualitatively analyzed. Based on our study, we renew calls for a shadow stack design that leverages a dedicated register, resulting in low performance overhead, and minimal memory overhead, but sacrifices compatibility. We present case studies of our implementation of such a design, Shadesmar, on Phoronix and Apache to demonstrate the feasibility of dedicating a general purpose register to a security monitor on modern architectures, and the deployability of Shadesmar. Our comprehensive analysis, including detailed case studies for our novel design, allows compiler designers and practitioners to select the correct shadow stack design for different usage scenarios.Comment: To Appear in IEEE Security and Privacy 201

Intertwining ROP Gadgets and Opaque Predicates for Robust Obfuscation

Software obfuscation plays a crucial role in protecting intellectual property in software from reverse engineering attempts. While some obfuscation techniques originate from the obfuscation-reverse engineering arms race, others stem from different research areas, such as binary software exploitation. Return-oriented programming (ROP) gained popularity as one of the most effective exploitation techniques for memory error vulnerabilities. ROP interferes with our natural perception of a process control flow, which naturally inspires us to repurpose ROP as a robust and effective form of software obfuscation. Although previous work already explores ROP's effectiveness as an obfuscation technique, evolving reverse engineering research raises the need for principled reasoning to understand the strengths and limitations of ROP-based mechanisms against man-at-the-end (MATE) attacks. To this end, we propose ROPFuscator, a fine-grained obfuscation framework for C/C++ programs using ROP. We incorporate opaque predicates and constants and a novel instruction hiding technique to withstand sophisticated MATE attacks. More importantly, we introduce a realistic and unified threat model to thoroughly evaluate ROPFuscator and provide principled reasoning on ROP-based obfuscation techniques that answer to code coverage, incurred overhead, correctness, robustness, and practicality challenges

Exploiting More Binaries by Using Planning to Assemble ROP Attacks

Return oriented programming (ROP) attacks have been studied for many years, but they are usually still constructed manually. The existing tools to synthesize ROP exploits automatically, such as ROPGadget and angrop, are very limited by their ad-hoc design: they rely on matching fixed patterns and assembling gadgets in fixed ways. We propose a new method, PEACE, that uses symbolic execution and partial-order planning to assemble gadgets more flexibly. Our method incrementally selects gadgets to address a need in the partially-constructed exploit, and infers ordering constraints over those gadgets based on their effects. This approach enables PEACE to create exploits for many more binaries than existing tools. By creating a more flexible and powerful ROP attack generation tool, we hope to raise awareness of how much code is vulnerabl

Binary Program Integrity Models for Defeating Code-Reuse Attacks

During a cyber-attack, an adversary executes offensive maneuvers to target computer systems. Particularly, an attacker often exploits a vulnerability within a program, hijacks control-flow, and executes malicious code. Data Execution Prevention (DEP), a hardware-enforced security feature, prevents an attacker from directly executing the injected malicious code. Therefore, attackers have resorted to code-reuse attacks, wherein carefully chosen fragments of code within existing code sections of a program are sequentially executed to accomplish malicious logic. Code-reuse attacks are ubiquitous and account for majority of the attacks in the wild. On one hand, due to the wide use of closed-source software, binary-level solutions are essential. On the other hand, without access to source-code and debug-information, defending raw binaries is hard. A majority of defenses against code-reuse attacks enforce control-flow integrity , a program property that requires the runtime execution of a program to adhere to a statically determined control-flow graph (CFG) -- a graph that captures the intended flow of control within the program. While defenses against code-reuse attacks have focused on reducing the attack space, due to the lack of high-level semantics in the binary, they lack in precision, which in turn results in smaller yet significant attack space. This dissertation presents program integrity models aimed at narrowing the attack space available to execute code-reuse attacks. First, we take a semantic-recovery approach to restrict the targets of indirect branches in a binary. Then, we further improve the precision by recovering C++-level semantics, and enforce a strict integrity model that improves precision for virtual function calls in the binary. Finally, in order to further reduce the attack space, we take a different perspective on defense against code-reuse attacks, and introduce Stack-Pointer Integrity -- a novel integrity model targeted at ensuring the integrity of stack pointer as opposed to the instruction pointer. Our results show that the semantic-recovery-based approaches can help in significantly reducing the attack space by improving the precision of the underlying CFG. Function-level semantic recovery can eliminate 99.47% of inaccurate targets, whereas recovering virtual callsites and VTables at a C++ level can eliminate 99.99% of inaccurate targets

Preventing Code Reuse Attacks On Modern Operating Systems

Modern operating systems are often the target of attacks that exploit vulnerabilities to escalate their privilege level. Recently introduced hardening features prevent attackers from using traditional kernel exploitation methodologies and force them to employ techniques that were originally designed for user space exploitation —such as code reuse— to execute arbitrary code with elevated privileges. In this dissertation, we present novel protection mechanisms that render such methodologies ineffective and improve the security of today’s operating systems. Specifically, we present solutions that prevent the leakage and corruption of kernel code pointers without employing entities that execute on super-privileged mode (e.g., hypervisors). The leakage of code pointers is an essential step for the construction of reliable code reuse exploits and their corruption is typically necessary for mounting the attack. More concretely, we present the design and implementation of two systems: kR^X and kSplitStack. kR^X is a system that diversifies the code layout to thwart attackers from constructing code reuse exploits statically. It also prevents the leakage of return addresses through XOR- based encryption or by hiding them among decoys (fake pointers to instructions that trap the kernel when executed). Finally, it couples the above with a self-protection mechanism that prevents attackers from leaking the diversified code layout, either by instrumenting every memory read instruction with range checks on x86-64 systems or by imposing limits through the segmentation unit on x86 systems. Evaluation results show that it imposes small runtime overhead on real-world applications when measured on legacy x86-64 systems (~3.63%) and significantly lower on x86 systems (~1.32%) and newer x86-64 CPUs that provide hardware assistance (~2.32%). kSplitStack, on the other hand, provides stronger protection against leaks of return addresses and guarantees both their secrecy and their integrity by augmenting the isolation mechanism of kR^X on x86-64 systems. This is achieved through a split stack scheme: functions use an unprotected stack for their local variables but switch to a protected one when pushing or poping return addresses. Moreover, kSplitStack protects the secrecy and integrity of control data (e.g., the value of the instruction pointer) in interrupt contexts by redirecting them to protected stacks, thus thwarting attackers from leaking or corrupting code pointers by inducing interrupts or other hardware events. Finally, the evaluation of kSplitStack shows that it imposes a small runtime overhead, comparable to the one of kR^X, both on legacy x86-64 systems (~3.66%) and on newer CPUs with hardware assistance (~2.50%)