Consider the following question on Stack Overflow on system call hooking by modifying the sys_call_table.
https://stackoverflow.com/questions/2103315/linux-kernel-system-call-hooking-example
Since CR0 "Write Protect" (bit 16) controls whether it's possible for the kernel to write to read-only pages, why does some code then calls set_memory_rw to set the permissions for the target pages to RW?
No.
The CR0.WP method disables write protect support globally, whereas the set_memory_rw method merely adds the write bit to specific pages. If you have already disabled write protection through the control register, then there is no need to do anything else. All kernel memory will be globally writable from within the kernel until you re-enable write protection through the same register.
Make sure you disable interrupts before writing to CR0, then re-enable them afterwards.
