Windows Kernel Security

Windows Kernel Security

Overview

This skill covers Windows kernel internals that matter for game security research: object callbacks, process and image notifications, APC behavior, driver loading, trust enforcement, memory manager structures, and the bookkeeping anti-cheats inspect to detect hostile drivers or hidden executable code.

README Coverage

• Cheat > PatchGuard-related
• Cheat > Driver Signature enforcement
• Cheat > Windows Kernel Explorer
• Anti Cheat > Detection:Attach
• Anti Cheat > Detection:Hide
• Anti Cheat > Detection:Vulnerable Driver
• Anti Cheat > Windows Ring0 Callback
• Windows Security Features

Core Kernel Concepts

Important Structures

• EPROCESS / ETHREAD
• KTHREAD / KAPC / KAPC_STATE
• MMVAD / VAD tree nodes
• PEB / TEB
• DRIVER_OBJECT
• DEVICE_OBJECT
• IRP (I/O Request Packet)

Key Tables

• SSDT (System Service Descriptor Table)
• IDT (Interrupt Descriptor Table)
• GDT (Global Descriptor Table)
• PspCidTable (Process/Thread handle table)
• PiDDBCacheTable / MmUnloadedDrivers / PoolBigPageTable

Security Features

PatchGuard (Kernel Patch Protection)

- Protects critical kernel structures
- Periodic verification checks
- BSOD on tampering detection
- Multiple trigger mechanisms

Driver Signature Enforcement (DSE)

- Requires signed drivers
- CI.dll verification
- Test signing mode
- WHQL certification

Virtualization-Based Security (VBS)

Architecture:
- Uses the Windows hypervisor to create an isolated execution environment
- Splits the system into Virtual Trust Levels (VTLs)
  - VTL0: Normal world — standard Windows kernel and user-mode processes
  - VTL1: Secure world — Secure Kernel, security policy enforcement
- Even if VTL0 kernel is fully compromised, VTL1 remains isolated
- Three main buckets:
  - Memory-protection features (HVCI)
  - Virtual Trust Levels (VTL0/VTL1 separation)
  - VBS enclaves (isolated execution for selected workloads)

Hypervisor-Enforced Code Integrity (HVCI)

- Also known as Memory Integrity
- Ensures only trusted, validated code executes in kernel mode
- Combines Windows hypervisor + Secure Kernel (VTL1) for enforcement
- Key mechanism: W→X transition restriction
  - Executable kernel pages cannot become writable
  - Writable pages cannot become executable without re-validation
- Enforcement pipeline:
  - Code integrity policy defines what is trusted
  - Hypervisor memory enforcement via second-stage address translation (EPT/SLAT)
  - Once a kernel page is validated, strict execution rules are enforced
- Driver compatibility requirements: drivers must be HVCI-compatible

Secure Boot

- UEFI-based boot verification
- Boot loader chain validation
- Kernel signature checks
- DBX (forbidden signatures)
- Foundation for attestation and DMA-hardening assumptions

Kernel Callbacks

Process Callbacks

PsSetCreateProcessNotifyRoutine
PsSetCreateProcessNotifyRoutineEx
PsSetCreateProcessNotifyRoutineEx2

Thread Callbacks

PsSetCreateThreadNotifyRoutine
PsSetCreateThreadNotifyRoutineEx

Image Load Callbacks

PsSetLoadImageNotifyRoutine
PsSetLoadImageNotifyRoutineEx

Object Callbacks

ObRegisterCallbacks
// OB_OPERATION_HANDLE_CREATE
// OB_OPERATION_HANDLE_DUPLICATE

APC / Execution Context

KeInitializeApc
KeInsertQueueApc
KeStackAttachProcess
RtlWalkFrameChain

Registry Callbacks

CmRegisterCallback
CmRegisterCallbackEx

Minifilter Callbacks

FltRegisterFilter
// IRP_MJ_CREATE, IRP_MJ_READ, etc.

Driver Development

Basic Structure

NTSTATUS DriverEntry(
    PDRIVER_OBJECT DriverObject,
    PUNICODE_STRING RegistryPath
) {
    DriverObject->DriverUnload = DriverUnload;
    DriverObject->MajorFunction[IRP_MJ_CREATE] = DispatchCreate;
    DriverObject->MajorFunction[IRP_MJ_DEVICE_CONTROL] = DispatchIoctl;
    // Create device, symbolic link...
    return STATUS_SUCCESS;
}

Communication Methods

• IOCTL (DeviceIoControl)
• Direct I/O
• Buffered I/O
• Shared memory

Vulnerable Driver Exploitation

Common Vulnerability Types

• Arbitrary read/write primitives
• IOCTL handler vulnerabilities
• Pool overflow
• Use-after-free

Notable Vulnerable Drivers

- gdrv.sys (Gigabyte)
- iqvw64e.sys (Intel)
- MsIo64.sys
- Mhyprot2.sys (Genshin Impact)
- dbutil_2_3.sys (Dell)
- RTCore64.sys (MSI)
- Capcom.sys

Exploitation Steps

1. Load vulnerable signed driver
2. Trigger vulnerability
3. Achieve kernel read/write
4. Disable DSE or load unsigned driver
5. Execute arbitrary kernel code

PatchGuard Bypass Techniques

Timing-Based

• Predict PG timer
• Modify between checks

Context Manipulation

• Exception handling
• DPC manipulation
• Thread context tampering

Hypervisor-Based

• EPT manipulation
• Memory virtualization
• Intercept PG checks

Kernel Hooking

ETW (Event Tracing for Windows)

- InfinityHook technique
- HalPrivateDispatchTable
- System call tracing

SSDT Hooking (Legacy)

- Modify service table entries
- Requires PG bypass
- High detection risk

IRP Hooking

- Hook driver dispatch routines
- Less monitored than SSDT
- Per-driver targeting

Memory Manipulation

Physical Memory Access

MmMapIoSpace
MmCopyMemory
\\Device\\PhysicalMemory

Virtual Memory

ZwReadVirtualMemory
ZwWriteVirtualMemory
KeStackAttachProcess
MmCopyVirtualMemory

MDL Operations

IoAllocateMdl
MmProbeAndLockPages
MmMapLockedPagesSpecifyCache

Research Tools

Analysis

• WinDbg / WinDbg Preview
• Process Hacker / System Informer
• OpenArk
• WinArk

Utilities

• KDU (Kernel Driver Utility)
• OSR Driver Loader
• DriverView

Monitoring

• Process Monitor
• API Monitor
• ETW consumers

EFI/UEFI Integration

Boot-Time Access

- EFI runtime services
- Boot driver loading
- Pre-OS execution

Memory Access

- GetVariable/SetVariable
- Runtime memory mapping
- Physical memory access

Hypervisor Development

Hypervisor Types

Type 1 (bare-metal):
- Runs directly on hardware
- Examples: VMware ESXi, Microsoft Hyper-V, Xen
- Used for VBS, production security enforcement

Type 2 (hosted):
- Runs on top of a host operating system
- Examples: Oracle VirtualBox, VMware Workstation
- Common for research, development, and testing

Hardware Virtualization Platforms

Intel VT-x:
- Introduced 2005, widely supported on modern Intel CPUs
- Foundation for VMCS, EPT, VM exits

AMD-V (SVM):
- AMD's counterpart to VT-x, also introduced 2005
- VMCB structure, NPT (Nested Page Tables)

ARM Virtualization Extensions:
- EL2 (hypervisor mode) and stage-2 memory translation
- Used on ARM platforms for mobile and embedded security

Intel VT-x Core Concepts

VMCS (Virtual Machine Control Structure)

Central data structure for Intel VT-x:
- Describes guest state, host state, and virtualization controls
- Tells the processor:
  - What state to restore on VM entry
  - What state to save on VM exit
  - Which events transfer control back to the hypervisor

Guest/Host State Areas:
- Control registers (CR0, CR3, CR4)
- Segment registers (CS, SS, DS, ES, FS, GS)
- Debug registers (DR7 — hardware breakpoints)
- Descriptor-table registers (GDTR, IDTR)
- Key fields:
  - CR3: root of guest page tables, central to virtual memory
  - GDTR/IDTR: Global/Interrupt Descriptor Tables
  - CS/SS: code and stack segments
  - DR7: hardware breakpoint control

Control Fields:
- Pin-based controls
- Primary processor-based controls
- Secondary processor-based controls
- Events that cause VM exits:
  - CPUID interception
  - INVLPG interception
  - Control-register access
  - EPT violations
  - MSR access

EPT (Extended Page Tables)

Intel's implementation of SLAT (Second-Level Address Translation):
- Gives the hypervisor independent control over guest memory
- Two-stage address translation pipeline:
  1. GVA → GPA: Guest Virtual → Guest Physical (via guest page tables, rooted at CR3)
  2. GPA → HPA: Guest Physical → Host Physical (via EPT, rooted at EPTP in VMCS)
- Guest believes it owns its own memory mappings
- Hypervisor has a second, independent layer controlling:
  - What physical memory is reachable
  - What permissions apply (read/write/execute)

EPT Hierarchy:
- PML4 → PDPT → PD → PT (4-level page table)
- Each entry carries read/write/execute permissions
- EPT violations trigger VM exits when access permissions are violated

Page Table Entries (PTE):
- Maps GVA to GPA
- Carries: read/write, supervisor-only, caching, software-defined bits
- Guest PTEs and EPT serve different roles:
  - Guest PTE: controls guest's view of memory
  - EPT: controls hypervisor's view of the guest

VM Exits & VMCALL

VM Exits:
- Occur when configured events happen in the guest
- Triggers: CPUID, CR access, I/O instructions, EPT violations, MSR access
- On exit: processor saves guest state (per VMCS), restores host state,
  records exit reason for hypervisor handler

VMCALL:
- Guest intentionally transfers control to hypervisor
- Similar in concept to a system call (guest → hypervisor)
- Used for guest-hypervisor communication interfaces

Nested Virtualization

- Running a hypervisor inside a VM managed by another hypervisor
- Useful for research, testing, and development
- Adds complexity: multiple layers participate in the same virtualization flow
- Relevant for testing hypervisor-based defense under VMware/Hyper-V

AMD-V (SVM)

• VMCB (Virtual Machine Control Block) structure
• NPT (Nested Page Tables) — AMD's SLAT equivalent
• SVM operations (VMRUN, VMSAVE, VMLOAD)

Use Cases

• Memory hiding
• Syscall interception
• Security monitoring
• Anti-cheat evasion
• EPT-based memory protection and introspection

Hypervisor-Based Defense

Concept

- Security approach using virtualization primitives to enforce protections
  from a higher privilege level than the guest kernel
- Moves security decisions into an isolated execution environment
  that a compromised kernel cannot easily tamper with
- Present across major OS platforms:
  - Windows: Virtualization-Based Security (VBS)
  - Android: Android Virtualization Framework (AVF)
  - Apple: Secure execution environments, hardware-backed isolation

EPT Hooks as Defensive Primitives

Mechanism:
- Instead of patching the guest kernel, modify EPT permissions
- Specific memory accesses trigger EPT violations → VM exit
- Hypervisor inspects the access and decides: allow, deny, or log

Example: Watching writes to a sensitive region
1. Remove write permission from the EPT entry for target region
2. Guest runs normally until it attempts a write to that region
3. EPT violation → VM exit → hypervisor receives control
4. Hypervisor evaluates context:
   - Which module performed the access
   - What memory was touched
   - Whether the access is authorized
5. Decision: allow write, deny and return, or log and continue

Advantages over traditional kernel hooks:
- Operate outside the guest OS
- Remain effective even if guest kernel is compromised
- Transparent to guest-level detection
- Cannot be removed by kernel-level rootkits

Protectable Assets via EPT

- Executable pages of EPP (Endpoint Protection Platform) drivers
  → Prevents silent patching of security software
- ETW-related structures
  → Unauthorized writes fault into hypervisor
- Callback/callout/routine lists (PsSetCreateProcessNotifyRoutine, etc.)
  → Write authorization moved outside the guest kernel
- Critical kernel data structures
  → PatchGuard-protected regions, SSDT, IDT

Threat Model for Hypervisor Defense

Assumes kernel compromise has already happened:
- Attacker has kernel code execution
- Attacker can load vulnerable drivers (BYOVD)
- Attacker can modify kernel memory
- Traditional kernel-resident protections are untrustworthy

Hypervisor advantage:
- Sits above the guest kernel in privilege hierarchy
- Enforces policies from a higher privilege layer
- Kernel-level rootkits cannot disable hypervisor-level enforcement

Attack Scenario: BYOVD vs EPT Protection

Without hypervisor defense:
1. Attacker loads vulnerable signed driver
2. Gains kernel R/W primitives
3. Patches callback list to remove EPP callbacks
4. EPP is blinded — attacker operates undetected

With EPT-based defense:
1. Attacker loads vulnerable signed driver
2. Gains kernel R/W primitives
3. Attempts to patch callback list
4. EPT violation triggers VM exit
5. Hypervisor catches the write, evaluates context
6. Write is denied — callback list remains intact

Resource Organization

The README contains categorized links for:

• PatchGuard research and bypasses
• DSE bypass techniques
• Vulnerable driver exploits
• Kernel callback enumeration
• ETW/PMI/NMI handlers
• Intel PT integration

Data Source

Important: This skill provides conceptual guidance and overview information. For detailed information use the following sources:

1. Project Overview & Resource Index

Fetch the main README for the full curated list of repositories, tools, and descriptions:

https://raw.githubusercontent.com/gmh5225/awesome-game-security/refs/heads/main/README.md

The main README contains thousands of curated links organized by category. When users ask for specific tools, projects, or implementations, retrieve and reference the appropriate sections from this source.

2. Repository Code Details (Archive)

For detailed repository information (file structure, source code, implementation details), the project maintains a local archive. If a repository has been archived, always prefer fetching from the archive over cloning or browsing GitHub directly.

Archive URL format:

https://raw.githubusercontent.com/gmh5225/awesome-game-security/refs/heads/main/archive/{owner}/{repo}.txt

Examples:

https://raw.githubusercontent.com/gmh5225/awesome-game-security/refs/heads/main/archive/ufrisk/pcileech.txt
https://raw.githubusercontent.com/gmh5225/awesome-game-security/refs/heads/main/archive/000-aki-000/GameDebugMenu.txt

How to use:

1. Identify the GitHub repository the user is asking about (owner and repo name from the URL).
2. Construct the archive URL: replace {owner} with the GitHub username/org and {repo} with the repository name (no .git suffix).
3. Fetch the archive file — it contains a full code snapshot with file trees and source code generated by code2prompt.
4. If the fetch returns a 404, the repository has not been archived yet; fall back to the README or direct GitHub browsing.

3. Repository Descriptions

For a concise English summary of what a repository does, the project maintains auto-generated description files.

Description URL format:

https://raw.githubusercontent.com/gmh5225/awesome-game-security/refs/heads/main/description/{owner}/{repo}/description_en.txt

Examples:

https://raw.githubusercontent.com/gmh5225/awesome-game-security/refs/heads/main/description/00christian00/UnityDecompiled/description_en.txt
https://raw.githubusercontent.com/gmh5225/awesome-game-security/refs/heads/main/description/ufrisk/pcileech/description_en.txt

How to use:

1. Identify the GitHub repository the user is asking about (owner and repo name from the URL).
2. Construct the description URL: replace {owner} with the GitHub username/org and {repo} with the repository name.
3. Fetch the description file — it contains a short, human-readable summary of the repository's purpose and contents.
4. If the fetch returns a 404, the description has not been generated yet; fall back to the README entry or the archive.

Priority order when answering questions about a specific repository:

1. Description (quick summary) — fetch first for concise context
2. Archive (full code snapshot) — fetch when deeper implementation details are needed
3. README entry — fallback when neither description nor archive is available

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