Hardened MINIX 3 with Zig-Enhanced musl libc

Overview

This project refactors the MINIX 3 operating system with a hardened version of musl libc that includes security-enhanced functions implemented in Zig. By leveraging Zig’s safety features and modern syntax, this project aims to improve memory safety, error handling, and performance resilience in MINIX’s libc, creating a secure foundation for critical and embedded systems.

Project Goals

Enhanced Security: Improve the robustness of MINIX 3 by replacing high-risk functions (such as string and memory manipulation functions) in libc with safer implementations in Zig. Hybrid C-Zig Library: Maintain compatibility with standard C code in musl, while integrating Zig-based functions to provide added bounds checking, memory protection, and safer error handling. Real-World Demonstration: Showcase the security improvements in a bootable MINIX 3 system, with demonstrations of vulnerability mitigations and performance benchmarks.

Key Features

1. Refactored musl libc: Critical libc functions have been reimplemented or wrapped in Zig, such as strcpy, memcpy, malloc, and free, to incorporate safety features:

   • Bounds Checking: Functions like strcpy are replaced with safeStrcpy, a bounds-checked version that prevents buffer overflows.
   • Memory Management: Functions like malloc and free include security checks for buffer overflows and guard canaries to detect memory corruption.
   • Improved Error Handling: Enhanced error reporting for functions prone to misuse, ensuring safer operation in the OS.

2. Security Focus:

   • Protection against buffer overflows and use-after-free vulnerabilities.
   • Custom memory allocation strategies using Zig’s allocator capabilities.
   • Fuzz-tested functions to ensure resilience against malformed or malicious inputs.

3. Seamless MINIX Integration: The hardened libc is fully integrated into MINIX 3’s build system, replacing the standard libc. The result is a MINIX 3 image that runs with the security-enhanced library by default.

Testing and Validation

Basic Functionality Tests

Run basic commands and system calls in MINIX 3 to ensure compatibility with the new libc.

Security Demonstrations

• Buffer Overflow Mitigation: Run tests with oversized inputs on string functions to confirm bounds-checking behaviour.
• Memory Management Resilience: Test memory allocation and deallocation functions to prevent double-free and detect use-after-free vulnerabilities.
• Error Handling Examples: Demonstrate safe error handling in I/O functions, such as safeScanf and safeFgets, showing how they handle malformed input securely.

Performance Benchmarks

Benchmark enhanced functions against standard musl implementations to evaluate any performance impact from the additional safety checks.

Documentation

• Function Reference: Detailed overview of each refactored function, including security enhancements.
• Security Analysis: In-depth analysis of how Zig’s safety features contribute to the overall security of MINIX.
• Design Decisions: Rationale for using Zig in specific libc functions and explanation of trade-offs made during refactoring.

Future Enhancements

• Expanded Zig Refactoring: Additional libc functions in musl could be further enhanced with Zig’s safety features.
• Community Feedback and Iteration: Collect feedback on the hardened libc’s functionality and performance for further improvements.
• Embedded System Applications: Adapt the hardened MINIX 3 for embedded systems where security and resilience are critical.

License

This project is licensed under the MIT License. See LICENSE for details.