I am a big fan of Software Restriction Policies for Microsoft Windows and was recently updating our settings for this. I became curious as to where Microsoft implemented this technology in the stack. I can imagine a very naive implementation being in Windows Explorer where when you double click on an exe or other blocked file type, that Explorer would check against the policy. I call this naive because obviously this wouldn't protect against someone typing something in a CMD window. Or worse, Adobe Reader running an external application. On the other hand, I can imagine that software restriction policies could be implemented deep in the stack almost at the metal. In this case, the low level loader would load into memory the questionable file, but mark the memory in the memory manager as non-executable data.
I'm pretty sure that Microsoft did not do the most naive implementation, because if I block Java using a path block, Internet Explorer will crash if it attempts to load Java. Which is what I want. But I'm not sure how deep in the stack it's implemented and any insight would be appreciated.