Uninformed: Informative Information for the Uninformed

Vol 3» 2006.Jan


Abstract: The Windows kernel that runs on the x64 platform has introduced a new feature, nicknamed PatchGuard, that is intended to prevent both malicious software and third-party vendors from modifying certain critical operating system structures. These structures include things like specific system images, the SSDT, the IDT, the GDT, and certain critical processor MSRs. This feature is intended to ensure kernel stability by preventing uncondoned behavior, such as hooking. However, it also has the side effect of preventing legitimate products from working properly. For that reason, this paper will serve as an in-depth analysis of PatchGuard's inner workings with an eye toward techniques that can be used to bypass it. Possible solutions will also be proposed for the bypass techniques that are suggested.

Thanks: The authors would like to thank westcose, bugcheck, Alex Ionescu, Filip Navara, uninformed, and everyone who is motivated to learn by their own self interest.

Disclaimer: The subject matter discussed in this document is presented in the interest of education. The authors cannot be held responsible for how the information is used. While the authors have tried to be as thorough as possible in their analysis, it is possible that they have made one or more mistakes. If a mistake is observed, please contact one or both of the authors so that it can be corrected.