Lightweight Hypervisor - Intel VT-x Implementation

Overview

Minimal Type-2 hypervisor implemented as a Linux kernel module using Intel VMX technology. Demonstrates hardware-assisted virtualization with VMCS management, guest state control, and VM lifecycle operations.

Architecture

Core Components

• VMX Operation Setup: Hardware detection, CR4/MSR configuration, VMXON region initialization
• VMCS Management: 4KB control structure allocation and configuration
• Execution Controls: Pin-based, processor-based, and secondary controls configuration
• I/O Virtualization: 2KB bitmap for port access control (0-65535)
• MSR Virtualization: 4KB bitmap for model-specific register access control
• Control Register Virtualization: CR0/CR4 mask and shadow register management
• Guest State Management: Complete processor state for host/guest contexts
• VM Entry/Exit Controls: 64-bit mode enforcement and MSR store/load areas

Memory Layout

VMXON Region:    4KB aligned, contains revision ID
VMCS Region:     4KB aligned, processor control structure
I/O Bitmap:      2KB, port access control (A: 0-7FFF, B: 8000-FFFF)
MSR Bitmap:      4KB, MSR access control for different ranges
MSR Store/Load:  Variable size arrays for VM entry/exit MSR handling

System Requirements

Hardware

• Intel processor with VMX support (CPUID.1:ECX.VMX[bit 5] = 1)
• VT-x enabled in BIOS/UEFI
• x86-64 architecture

Software

• Linux kernel with module support
• Kernel headers and build tools
• Root privileges

Build & Usage

# Build
make

# Load module
./init.sh 

# Unload
sudo rmmod hypervisor

Implementation Features

• VMX Support Detection: CPUID-based hardware capability verification
• MSR Configuration: IA32_FEATURE_CONTROL and VMX capability MSRs
• Fixed Bits Compliance: CR0/CR4 adjustment per VMX_FIXED0/FIXED1
• Exception Handling: Configurable exception bitmap for VM exits
• CR3 Target Values: Up to 4 target values for MOV CR3 optimization
• Guest Entry Point: Custom RIP/RSP setup with stack alignment

Error Handling

• Comprehensive VMWRITE/VMREAD validation macros
• Resource cleanup on failure paths
• Detailed kernel log messages for debugging
• Proper memory deallocation on module exit

Limitations

• Single-core operation only
• Basic guest execution environment
• No EPT (Extended Page Tables) support
• No device emulation
• Educational/research purposes only

Debug Output

VMX support present! continuing...
VMXON Region setup success
VMCS Region setup success
VMCS control fields set successfully
VM exit reason is [exit_code]
VMXOFF operation succeeded!

License

Dual BSD/GPL

Author

Chrinovic