Squid : A RISC-V Emulator For Vulnerability Research

Squid is a powerful RISC-V emulator designed specifically for vulnerability research and fuzzing. It leverages Ahead-of-Time (AOT) compilation instead of Just-In-Time (JIT), allowing users to rewrite binary code before emulation.

This feature provides full control over system calls and events during runtime, making it ideal for creating custom sanitizers and test programs to detect various vulnerabilities beyond just memory corruptions.

Key Features Of Squid

• Fast Snapshots: Squid supports quick snapshots, which are useful for saving and restoring the state of the emulator during testing.
• Byte-Level Permissions on Memory: This feature allows for precise control over memory access, enhancing the ability to detect and analyze memory-related vulnerabilities.
• Rewriting Binaries Before Emulation: Users can modify the binary code before running it in the emulator, enabling the creation of custom test scenarios.
• Integration with LibAFL: Squid integrates with the LibAFL fuzzing framework, enhancing its capabilities for vulnerability detection.

Squid is designed to run single-threaded Linux user-space applications written in C. It requires the target binary to be compiled with specific flags:

bash-fPIE -pie -O0 -g -fno-jump-tables -mno-relax -D__thread=

This makes Squid unsuitable for blackbox fuzzing but highly effective for greybox fuzzing when combined with native fuzzers.

One of Squid’s notable capabilities is overcoming the limitations of LLVM’s sanitizers. For instance, LLVM does not allow combining multiple sanitizers like address and memory sanitizers in a single build.

Squid resolves this by allowing binary rewriting, enabling users to recreate ASAN and MSAN instrumentation manually.

This is achieved by compiling the target with the required flags and then instrumenting it using Squid’s custom IR and passes.

To utilize Squid for enhanced vulnerability detection, users can follow these steps:

1. Load and Lift the Target Binary: Load the RISC-V binary into Squid’s custom Intermediate Representation (IR).
2. Run ASAN Pass: Insert redzones around global variables and register interceptors similar to LLVM’s ASAN.
3. Compile to Native Code: Translate the IR to C code and compile it with Clang.
4. Run the Binary: Handle system calls and interceptors during runtime to detect vulnerabilities.

Squid is a versatile tool for vulnerability research, offering advanced features like binary rewriting and integration with fuzzing frameworks.

While it has limitations, such as requiring specific compilation flags and supporting only single-threaded applications, Squid is a valuable asset for enhancing the detection of vulnerabilities in RISC-V systems.