linux kernel classify all kernel address that is "NOT PRESENT" as
general protection fault:
In arch/x86/mm/fault.c:do_page_fault():
tsk->thread.cr2 = address;
/* Kernel addresses are always protection faults */
tsk->thread.error_code = error_code | (address >= TASK_SIZE);
tsk->thread.trap_no = 14;
force_sig_info_fault(SIGSEGV, si_code, address, tsk);
Ie, so long as the ptr (which is pointing into the kernel range: ">=
TASK_SIZE") is not a valid memory address (__PAGE_PRESENT flag set to
0 for the page's PTE) - it is illegitimate and will fault.
--
On Mon, Nov 3, 2008 at 6:31 AM, taraniteja vishwanatha
<taraniteja@xxxxxxxxx> wrote:
> Hey,
>
> when do we get a general fault protection in the kernel? I am trying to
> lookup in for some data pointer and when its not present , I return 0.
> I am getting this error.
>
> Can anybody help??
>
> -Tarani
>
Regards,
Peter Teoh