Re: what is the right behavior of copy_to_user(0x0, ..., ...)?

[Jun Sun <jsun@mvista.com>]

Ralf Baechle wrote:

> On Fri, May 03, 2002 at 02:46:19PM -0700, Jun Sun wrote:
>
>
> > When running LTP, I notice that recent kernel has a kernel access fault:
> >
> > <1>Unable to handle kernel paging request at virtual address 00000000, epc
> > == 80273860, ra == 80205aa4
> Well, decode the oops message.  The question is what is at 0x80273860?

0x80273860 is copy_bytes in arch/mips/lib/memcpy.S, which is reached through 
__copy_user.

The faulting instruction, not suprisingly, is writing a byte to the 
destination at 0x0.
Anybody can try to call copy_to_user(0x0, ...) inside kernel and see the 
scene.  The question here is whether we should reach do_page_fault() and 
terminate calling process or try to catch the fault and return some meaningful 
error.
It appears earlier version of kernel does not have this problem.  I have not 
fully figured out why.
Jun