CosmOS

CosmOS (Custom Open-Source Modular Operating System) is a fully custom kernel and bootloader written in Rust and Assembly. It is designed with memory safety and exploit resistance as core principles.

Architecture

• Target: x86_64 bare-metal (x86_64-unknown-none)
• Language: Rust (10-20-2025 nightly toolchain, Rust edition 2021)
• Boot: Custom two-stage bootloader with BIOS/UEFI support
• Environment: Strict #![no_std] with selective alloc usage
• Security & memory safety:
  • Hardware-enforced privilege separation (Ring 0 / Ring 3)
  • Rust ownership model to reduce buffer overflows and use-after-free
• Minimal runtime dependencies to keep the attack surface small

Prerequisites

• Rust (nightly)
• NASM assembler
• QEMU or VirtualBox (for testing)
• On Windows, just uses winget (PowerShell) for setup and execution.

Quick start

Run the included just tasks to set up, build and run:

# one-line setup, build, and run (PowerShell may be required for setup on Windows)
just
# or run steps individually:
just setup
just build
just run-qemu   # QEMU
just run-uefi-qemu # QEMU UEFI Mode
# or
just run-vbox   # VirtualBox

Boot process

1. Stage 1: 512-byte MBR bootloader (sector 0)
2. Stage 2: Extended bootloader (sectors 1–64, ~32 KB)
3. Kernel: Flat binary loaded at sector 66+

The BIOS bootloader creates a 64 MB disk image with the kernel embedded, avoiding a separate filesystem for initial boot. UEFI creates a .EFI image.

Development

Dependencies are compiled with default-features = false for no_std compatibility:

• x86_64 — hardware abstractions
• spin — synchronization primitives
• linked_list_allocator — heap management

License

This project is licensed under the GNU GPL v3.