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Reversing Windows Kernel Drivers

Reverse Engineering Advanced 📅 Published: 05/08/2025

Deep dive into reverse engineering Windows kernel drivers, analyzing driver structures, and understanding kernel-mode operations.

Reversing Windows Kernel Drivers

Deep dive into reverse engineering Windows kernel drivers, analyzing driver structures, and understanding kernel-mode operations.

Introduction to Windows Kernel Drivers

Windows kernel drivers operate in the most privileged execution mode (Ring 0) and have direct access to system hardware and memory. Understanding their internal workings is crucial for security researchers, malware analysts, and system administrators. This guide covers the fundamentals of reversing kernel drivers, from basic structures to advanced analysis techniques.

Driver Architecture Overview

Windows Driver Model (WDM)

Windows drivers follow a layered architecture with several key components:

  • Driver Object: Represents the driver instance in memory
  • Device Object: Represents a logical or physical device
  • I/O Request Packets (IRPs): Communication mechanism between user and kernel mode
  • Dispatch Routines: Functions that handle specific IRP types

Driver Entry Point

Every driver must implement a DriverEntry function, which serves as the main entry point:

NTSTATUS DriverEntry(
    PDRIVER_OBJECT  DriverObject,
    PUNICODE_STRING RegistryPath
);

This function is responsible for:

  • Initializing the driver object
  • Setting up dispatch routines
  • Creating device objects
  • Registering unload routines

Setting Up the Analysis Environment

Required Tools

  • IDA Pro: Primary disassembler with kernel debugging support
  • WinDbg: Microsoft's official kernel debugger
  • VMware/VirtualBox: Isolated environment for testing
  • OSR Driver Loader: For loading test drivers
  • DebugView: Monitor kernel debug output

Setting Up Kernel Debugging

Configure a two-machine debugging setup:

# Target machine (VM)
bcdedit /debug on
bcdedit /dbgsettings serial debugport:1 baudrate:115200

# Host machine
windbg -k com:port=\\.\pipe\com_1,baud=115200,pipe

Driver Analysis Methodology

Static Analysis Workflow

1. Initial Reconnaissance

Begin with basic file analysis:

# File information
file driver.sys
strings driver.sys | head -20

# PE structure analysis
pefile driver.sys

2. Import Analysis

Examine imported functions to understand driver capabilities:

  • IoCreateDevice: Device object creation
  • IoCreateSymbolicLink: User-mode interface creation
  • ExAllocatePool: Kernel memory allocation
  • KeWaitForSingleObject: Synchronization primitives

3. Entry Point Analysis

Load the driver in IDA Pro and locate the DriverEntry function:

; Typical DriverEntry pattern
push    ebp
mov     ebp, esp
sub     esp, 10h
mov     eax, [ebp+DriverObject]
mov     dword ptr [eax+38h], offset DriverUnload

Identifying Key Structures

DRIVER_OBJECT Structure

typedef struct _DRIVER_OBJECT {
    CSHORT Type;                    // +0x00
    CSHORT Size;                    // +0x02
    PDEVICE_OBJECT DeviceObject;    // +0x04
    ULONG Flags;                    // +0x08
    PVOID DriverStart;              // +0x0C
    ULONG DriverSize;               // +0x10
    PVOID DriverSection;            // +0x14
    PDRIVER_EXTENSION DriverExtension; // +0x18
    UNICODE_STRING DriverName;      // +0x1C
    PUNICODE_STRING HardwareDatabase; // +0x24
    PFAST_IO_DISPATCH FastIoDispatch; // +0x28
    PDRIVER_INITIALIZE DriverInit;  // +0x2C
    PDRIVER_STARTIO DriverStartIo;  // +0x30
    PDRIVER_UNLOAD DriverUnload;    // +0x34
    PDRIVER_DISPATCH MajorFunction[IRP_MJ_MAXIMUM_FUNCTION + 1]; // +0x38
} DRIVER_OBJECT, *PDRIVER_OBJECT;

IRP Analysis

I/O Request Packets are the primary communication mechanism. Key IRP major function codes:

  • IRP_MJ_CREATE (0x00): Handle file/device open
  • IRP_MJ_READ (0x03): Read operations
  • IRP_MJ_WRITE (0x04): Write operations
  • IRP_MJ_DEVICE_CONTROL (0x0E): IOCTL handling
  • IRP_MJ_CLOSE (0x02): Handle cleanup

IOCTL Analysis

Understanding IOCTL Codes

IOCTLs (Input/Output Control codes) provide the interface between user-mode applications and kernel drivers:

#define CTL_CODE(DeviceType, Function, Method, Access) \
    (((DeviceType) << 16) | ((Access) << 14) | ((Function) << 2) | (Method))

// Example IOCTL definition
#define IOCTL_CUSTOM_OPERATION \
    CTL_CODE(FILE_DEVICE_UNKNOWN, 0x800, METHOD_BUFFERED, FILE_ANY_ACCESS)

IOCTL Handler Analysis

Locate and analyze the device control dispatch routine:

NTSTATUS DeviceControlHandler(
    PDEVICE_OBJECT DeviceObject,
    PIRP Irp
)
{
    PIO_STACK_LOCATION ioStack = IoGetCurrentIrpStackLocation(Irp);
    ULONG ioControlCode = ioStack->Parameters.DeviceIoControl.IoControlCode;
    
    switch (ioControlCode) {
        case IOCTL_CUSTOM_OPERATION:
            // Handle custom operation
            break;
        default:
            return STATUS_INVALID_DEVICE_REQUEST;
    }
}

Dynamic Analysis Techniques

Kernel Debugging with WinDbg

Setting Breakpoints

# Break on DriverEntry
bp MyDriver!DriverEntry

# Break on specific function
bp MyDriver!DeviceControlHandler

# Break on IRP dispatch
bp nt!IopParseDevice

Examining Structures

# Display driver object
dt nt!_DRIVER_OBJECT @esi

# Display IRP
dt nt!_IRP @eax

# Display current IRP stack location
dt nt!_IO_STACK_LOCATION poi(@eax+0x60)

Memory Analysis

Pool Allocation Tracking

# Enable pool tagging
gflags +ptg

# Display pool allocations
!poolused

# Examine specific pool tag
!poolfind 'MyTag'

Rootkit Detection Techniques

SSDT Hooking Detection

System Service Descriptor Table (SSDT) hooks are common in rootkits:

# Display SSDT
dds nt!KiServiceTable

# Check for hooks
!chkimg -d nt

# Display modified service addresses
.foreach (entry {dd nt!KiServiceTable l poi(nt!KiServiceLimit)}) { 
    ln entry; 
}

Direct Kernel Object Manipulation (DKOM)

Detect process hiding through EPROCESS list manipulation:

# List processes via different methods
!process 0 0

# Compare with manual EPROCESS walking
dt nt!_EPROCESS @@(nt!PsActiveProcessHead)

Advanced Analysis Scenarios

Analyzing Filter Drivers

File system and network filter drivers require special analysis approaches:

# List filter drivers
!fltkd.filters

# Display filter callbacks
!fltkd.callbacks

# Show attached devices
!devstack

Boot Driver Analysis

For drivers that load early in the boot process:

  • Use kernel debugging from boot
  • Analyze boot logs with WPA (Windows Performance Analyzer)
  • Check registry entries under HKLM\System\CurrentControlSet\Services

Obfuscation and Anti-Analysis

Common Evasion Techniques

  • API Hashing: Dynamic resolution of function addresses
  • Control Flow Obfuscation: Complicating code analysis
  • String Encryption: Runtime decryption of sensitive strings
  • Code Injection: Loading code from external sources

Dealing with Packers

Kernel drivers may use custom packers:

# Find original entry point
!analyze -v

# Memory dump after unpacking
.dump /ma c:\temp\unpacked_driver.dmp

Security Implications

Privilege Escalation Vectors

  • IOCTL Vulnerabilities: Improper input validation
  • Buffer Overflows: Stack and heap corruption
  • Race Conditions: TOCTOU vulnerabilities
  • Double Fetch: Inconsistent data validation

Common Vulnerability Patterns

Improper IOCTL Validation

// VULNERABLE: No input validation
NTSTATUS BadHandler(PDEVICE_OBJECT DeviceObject, PIRP Irp) {
    PIO_STACK_LOCATION stack = IoGetCurrentIrpStackLocation(Irp);
    PVOID userBuffer = Irp->AssociatedIrp.SystemBuffer;
    ULONG inputLength = stack->Parameters.DeviceIoControl.InputBufferLength;
    
    // Direct use without validation - DANGEROUS!
    memcpy(kernelBuffer, userBuffer, inputLength);
}

Secure Implementation

// SECURE: Proper validation
NTSTATUS SecureHandler(PDEVICE_OBJECT DeviceObject, PIRP Irp) {
    PIO_STACK_LOCATION stack = IoGetCurrentIrpStackLocation(Irp);
    PVOID userBuffer = Irp->AssociatedIrp.SystemBuffer;
    ULONG inputLength = stack->Parameters.DeviceIoControl.InputBufferLength;
    
    // Validate input size
    if (inputLength != sizeof(EXPECTED_STRUCTURE)) {
        return STATUS_INVALID_PARAMETER;
    }
    
    // Use __try/__except for additional protection
    __try {
        ProbeForRead(userBuffer, inputLength, sizeof(ULONG));
        memcpy(kernelBuffer, userBuffer, inputLength);
    }
    __except (EXCEPTION_EXECUTE_HANDLER) {
        return STATUS_INVALID_USER_BUFFER;
    }
}

Tools and Resources

Essential Tools

  • IDA Pro: Professional disassembler with kernel support
  • Ghidra: Free alternative with good kernel analysis capabilities
  • WinDbg Preview: Modern version of Microsoft's debugger
  • VMware Workstation: Reliable virtualization for testing
  • ProcessMonitor: Monitor file/registry operations

Useful WinDbg Extensions

  • !analyze: Automated crash analysis
  • !poolused: Memory pool analysis
  • !irql: Check current IRQL
  • !drvobj: Display driver objects
  • !devobj: Display device objects

Practical Exercise

Sample Driver Analysis

Let's analyze a simple vulnerable driver:

1. Load the driver in IDA Pro
2. Identify the DriverEntry function
3. Map out the dispatch routines
4. Analyze IOCTL handlers for vulnerabilities
5. Set up kernel debugging
6. Test with crafted inputs
7. Document findings and IOCs

Conclusion

Reverse engineering Windows kernel drivers requires a deep understanding of the Windows kernel architecture, strong assembly language skills, and familiarity with specialized debugging tools. The techniques covered in this guide provide a foundation for analyzing both legitimate drivers and malicious kernel-mode software.

Key takeaways include:

  • Understanding the Windows Driver Model and key structures
  • Setting up proper analysis environments with kernel debugging
  • Recognizing common vulnerability patterns in kernel code
  • Using dynamic analysis to understand runtime behavior
  • Detecting rootkit-like behaviors and evasion techniques

As kernel-level threats continue to evolve, these analysis skills become increasingly important for security professionals defending against advanced persistent threats and sophisticated malware.