AdrOS

Overview

AdrOS is a multi-architecture operating system developed for research and academic purposes. The goal is to build a secure, monolithic kernel from scratch, eventually serving as a platform for security testing and exploit development.

Architectures Targeted

• x86 (32-bit & 64-bit)
• ARM (32-bit & 64-bit)
• MIPS
• RISC-V (32-bit & 64-bit)

Technical Stack

• Language: C/C++ and Assembly
• Bootloader: GRUB2 (Multiboot2 compliant)
• Build System: Make + Cross-Compilers

Features

• Multi-arch build system
  • make ARCH=x86|arm|riscv|mips
  • x86 is the primary, working target
• x86 (i386) boot & memory layout
  • Multiboot2 (via GRUB)
  • Higher-half kernel mapping (3GB+)
  • Early paging + VMM initialization
  • W^X-oriented userspace layout (separate RX/R and RW segments)
  • Non-executable stack markers in assembly (.note.GNU-stack)
• Memory management
  • Physical Memory Manager (PMM)
  • Virtual Memory Manager (x86)
  • Kernel heap allocator (kmalloc/kfree)
• Basic drivers & console
  • UART serial console logging
  • VGA text console (x86)
  • Keyboard driver + input callback
  • PIT timer + periodic tick
• Kernel services
  • Simple scheduler / multitasking (kernel threads)
  • Minimal process lifecycle: parent/child tracking, zombies, waitpid
  • Basic shell with built-in commands (fallback when userspace fails)
• InitRD + VFS + mounts
  • InitRD image in TAR/USTAR format (with directory support)
  • InitRD-backed filesystem node tree (fs_node_t + finddir)
  • Absolute path lookup (vfs_lookup("/bin/init.elf"))
  • Mount table support (vfs_mount) + tmpfs and overlayfs
• File descriptors + syscalls (x86)
  • int 0x80 syscall gate
  • SYSCALL_WRITE, SYSCALL_EXIT, SYSCALL_GETPID, SYSCALL_GETPPID, SYSCALL_OPEN, SYSCALL_READ, SYSCALL_CLOSE
  • SYSCALL_LSEEK, SYSCALL_STAT, SYSCALL_FSTAT
  • SYSCALL_DUP, SYSCALL_DUP2, SYSCALL_PIPE
  • SYSCALL_FORK, SYSCALL_EXECVE (with minimal argv/envp stack setup)
  • SYSCALL_SELECT, SYSCALL_POLL
  • SYSCALL_SIGACTION, SYSCALL_SIGPROCMASK, SYSCALL_KILL
  • SYSCALL_SETSID, SYSCALL_SETPGID, SYSCALL_GETPGRP
  • Per-process fd table (starting at fd=3)
  • Centralized user-pointer access API (user_range_ok, copy_from_user, copy_to_user)
  • Ring3 init program (/bin/init.elf) exercising IO + process + exec smoke tests
  • Error returns use negative errno codes (Linux-style)
• TTY (canonical line discipline)
  • Keyboard -> TTY input path
  • Canonical mode input (line-buffered until \n)
  • Echo + backspace handling
  • Blocking reads with a simple wait queue (multiple waiters)
  • fd=0 wired to tty_read, fd=1/2 wired to tty_write
  • Minimal termios/ioctl support (TCGETS, TCSETS, TIOCGPGRP, TIOCSPGRP)
  • Basic job control enforcement (SIGTTIN/SIGTTOU when background pgrp touches the controlling TTY)
• Devices (devfs)
  • /dev mount
  • /dev/null
  • /dev/tty
• Persistent storage (x86 / QEMU)
  • ATA PIO driver (primary master IDE)
  • Minimal on-disk persistence filesystem mounted at /persist (single counter file used by smoke tests)
• W^X (Option 1) for user ELFs (x86)
  • User segments are mapped RW during load, then write permissions are dropped for non-writable segments
  • This provides "text is read-only" hardening without requiring NX/PAE

Running (x86)

• make ARCH=x86 iso
• make ARCH=x86 run
• Logs:
  • serial.log: kernel UART output
  • qemu.log: QEMU debug output when enabled

QEMU debug helpers:

• make ARCH=x86 run QEMU_DEBUG=1
• make ARCH=x86 run QEMU_DEBUG=1 QEMU_INT=1

TODO

• Multi-architecture kernel bring-up
  • Implement VMM/interrupts/scheduler for ARM/RISC-V/MIPS
  • Standardize arch entrypoint behavior (arch_early_setup) across architectures
• Userspace / POSIX process model
  • brk/sbrk
  • Signal return ABI (sigreturn) and default actions for more signals (current support is minimal)
• Syscalls / ABI
  • getcwd, chdir
  • Userspace errno variable + libc-style wrappers (-1 return + errno set)
• Virtual memory hardening
  • Option 2: PAE + NX enforcement (execute disable for data/stack)
  • Guard pages, and tighter user/kernel separation checks
• Filesystem
  • Expand persisted storage beyond the current minimal /persist filesystem
  • Permissions/ownership (uid/gid, mode bits) and umask
  • Special files: block devices, /proc
  • Real on-disk fs (ext2/fat)
• TTY / PTY
  • Termios-like mode flags (canonical/raw, echo, erase, intr)
  • Sessions / process groups / controlling terminal
  • PTYs for userland shells
• Observability & tooling
  • Better memory stats (mem shell command)
  • Debug facilities (panic backtraces, symbolization, structured logs)
  • CI-ish targets: cppcheck, scan-build, mkinitrd-asan

Directory Structure

• src/kernel/ - Architecture-independent kernel code
• src/arch/ - Architecture-specific code (boot, context switch, interrupts)
• src/drivers/ - Device drivers
• include/ - Header files