Kernel Patch Protection

Kernel Patch Protection (KPP), informally known as PatchGuard, is a feature of 64-bit (x64) editions of Microsoft Windows that prevents patching the kernel. It was first introduced in 2005 with the x64 editions of Windows XP and Windows Server 2003 Service Pack 1.

"Patching the kernel" refers to unsupported modification of the central component or kernel of the Windows operating system. Such modification has never been supported by Microsoft because it can greatly reduce system security and reliability. However, though Microsoft does not recommend it, it is technically possible to patch the kernel on x86 editions of Windows. But with the x64 editions of Windows, Microsoft chose to implement technical barriers to kernel patching.

Since patching the kernel is technically permitted in 32-bit (x86) editions of Windows, several antivirus software developers use kernel patching to implement antivirus and other security services. This kind of antivirus software will not work on computers running x64 editions of Windows. Because of this, Kernel Patch Protection has been criticized for forcing antivirus makers to redesign their software without using kernel patching techniques.

Also, because of the design of the Windows kernel, Kernel Patch Protection cannot completely prevent kernel patching. This has led to additional criticism that since KPP is an imperfect defense, the problems caused to antivirus makers outweigh the benefits because authors of malicious software will simply find ways around its defenses. Nevertheless, Kernel Patching can still prevent system stability and reliability problems caused by legitimate software patching the kernel in unsupported ways.