In case anyone doesn't get it, this isn't an exploit in itself. It's a function you can use to gain system (root) privileges once you've found a bug in the Windows kernel that that gives you remote code execution.
> Windows x64 kernel-mode handcrafted shellcode to replace primary access token of executing process with SYSTEM process token for Elevation of Privilege(EoP).
So yes, privilege escalation.
Shellcode can be hard to write since it might be a small amount of code you can execute, you might not be able to jump precisely to your code, it might have to use a limited range of values (such as correctly parsing as something else) or other challenges.