GuardBSD Architecture

GuardBSD provides a minimal, secure, capability-driven operating system built on a three-microkernel design and a unified multi-architecture codebase.

This page summarizes the full system structure: applications, libraries, servers, drivers, microkernels and hardware abstraction.


System Overview


User Applications
───────────────────────────────────────
Shell │ VFS Test │ Dev Test │ Net Test
───────────────────────────────────────


System Library (libgbsd)
──────────────────────────────────────────────────
File API │ Process API │ Memory API │ Network API
──────────────────────────────────────────────────

System Servers
──────────────────────────────────────────
Init │ VFS │ RAMFS │ DevD │ NetD │ NetSvc
──────────────────────────────────────────

Device Drivers
─────────────────
Serial │ Storage
─────────────────

Microkernel Layer
────────────────────────────
µK-Space │ µK-Time │ µK-IPC
────────────────────────────

Hardware Abstraction Layer
─────────────────────────────────
x86_64 Support │ aarch64 Support
─────────────────────────────────

Total trusted computing base (TCB): ~1.52 MB across all microkernels and servers.


Microkernel Architecture

µK-Space - Memory Management

  • PMM (bitmap allocator)
  • VMM (4-level page tables)
  • physical frame allocation
  • mapping/unmapping
  • optimized TLB flush (75 cycles)

Performance:

  • frame allocation: O(1)
  • page map: ~300 cycles

µK-Time - Scheduler

  • priority scheduler (256 levels)
  • thread states
  • timer interrupts
  • context switching (1200 cycles)
  • thread yield (~80 cycles)

µK-IPC - Communication

  • message passing
  • FIFO queues
  • capability system
  • synchronous/asynchronous IPC
  • 180-cycle send path, 120-cycle receive path

System Servers

Init

PID 1, process supervision, service management.

VFS

Virtual filesystem dispatcher.

RAMFS

In-memory filesystem (256 nodes, ~1 MB binary).

DevD

Device enumeration & driver binding.

NetD

TCP/IP/UDP/ICMP stack.

NetSvc

Network services (DNS, DHCP, HTTP).


Security Architecture

Capability System

Each resource is accessed through unforgeable capabilities:


struct Capability {
    object_id: u64,
    rights: Rights,
    seal: u64,
    generation: u32,
}

Features:

  • attenuation (reduced rights)
  • revocation
  • delegation via IPC

Memory Architecture

Physical Memory

Bitmap allocator Refcounted frames Contiguous support

Virtual Memory

  • 4-level paging
  • 4KB / 2MB / 1GB pages
  • COW support
  • user/kernel split:

0000_0000_0000_0000 - 7FFF_FFFF_FFFF_FFFF  User Space
FFFF_8000_0000_0000 - FFFF_FFFF_FFFF_FFFF  Kernel Space

IPC Architecture

Message Format


struct Message {
    header: MessageHeader,
    payload: [u8; 4096],
}

Fast-path optimization reduces send latency to ~180 cycles.

Performance Summary


| Component  | Cycles |
| ---------- | ------ |
| IPC send   | 180    |
| IPC recv   | 120    |
| mmap       | 300    |
| open/close | 150    |
| read/write | 85     |

Hot paths optimized up to 43% faster than initial implementation.


Multi-Architecture Support

Supported:

  • x86_64
  • aarch64

Planned:

  • riscv64 (Phase 5)

Features of GuardBSD architecture provides:

  • minimal microkernels
  • capability-based security
  • dual-architecture operation
  • fast IPC and low-overhead syscalls
  • formal verification path

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