lkml.org 
[lkml]   [2003]   [Oct]   [17]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
SubjectRe: [RFC] prevent "dd if=/dev/mem" crash
Date
On Friday 17 October 2003 4:50 pm, Andrew Morton wrote:
> Bjorn Helgaas <bjorn.helgaas@hp.com> wrote:
> >
> > Old behavior:
> >
> > # dd if=/dev/mem of=/dev/null
> > <unrecoverable machine check>
>
> I recently fixed this for ia32 by changing copy_to_user() to not oops if
> the source address generated a fault. Similarly copy_from_user() returns
> an error if the destination generates a fault.
>
> In other words: drivers/char/mem.c requires that the architecture's
> copy_*_user() functions correctly handle faults on either the source or
> dest of the copy.

If we really believe copy_*_user() must correctly handle *all* faults,
isn't the "p >= __pa(high_memory)" test superfluous?

I don't know how ia32 handles a read to non-existent physical memory.
Are you saying that copy_*_user() can deal with that just like it does
a garden-variety TLB fault?

On ia64, a read to non-existent physical memory causes the processor
to time out and take a machine check. I'm not sure it's even possible
to recover from that.

Bjorn

-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2005-03-22 13:58    [W:0.057 / U:0.120 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site