UNIX for Advanced & Expert Users

Can kernel process access user address space ?

The kernel can indeed access user address space. However, the kernel is not usually considered to have "processes" and this makes your question confusing.

As one quick example, consider a simple system call:
iret=write(0, "hello\n", 6);

0 and "hello\n" and 6 all reside in the user's address space. The kernel must acquire these values to perform the write system call.

Its a generic question , but your explanation makes alot of sense Thanks!