Reach kernel session space from kernel driver

Question

I'm writing a kernel driver, which should read (and in some cases, also write) some memory addresses in kernel session space (win32k.sys). I've read in another topic that for example in Windbg I should change the context to a random user process to read the memory of kernel session space (with .process /p). How can I do that in a kernel driver? Should I create a user process which communicate with the driver (that's my idea now, but I hope that there is a better solution) or there is a more simple solution for this?

Answer 1

Session space are not mapped in system address space (that drivers share, if not attached to any process). Those why you getting BSOD while accessing win32k.

You need to be attached to EPROCESS via KeStackAttachProcess to perform this operation. You can get session id with ZwQueryInformationProcess(ProcessSessionInformation) function.

Answer 2

Kernel memory space is shared among all of the kernel objects ( just like a real/unprotected mode in DOS and early Windows versions). Kernel driver can access any address within the kernel space, whether it belongs to him or not.

Answer 3

You must find and attach to the csrss process! win32k.sys is not loaded in the system address space of all process only for csrss.

You should do stack attach to csrss process.