How to find ntdll base address in kernel mode?

You can link to it in your code and use the linked addresses. This is the same for any DLL in user or kernel space.

Another way is the standard GetProcAddress/LoadLibrary APIs.

No! I want to get the ntdll base with the PEB structure in kernel land. How to access PEB structure in kernel land with the GS register?

I wait with impatience for your answer.

Why don't you use search on the Internet? There's plenty of information there. Here, could be a starting point for you https://sites.google.com/site/x64lab/home/notes-on-x64-windows-gui-programming/exploring-peb-process-environment-block

I already search on google but I can't found how access PEB from kernel mode. The article above is to access PEB from user mode not ftom kernel mode. How to access EPROCESS to access PEB in EPROCESS with the GS register?

Ask on osronline.com

Apolo, no reason to get so mad at people. Most of us haven't done kernel or that kind of low level programming, so we don't know. I think this section is for userspace to begin with