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SubjectRe: Reading /proc/kcore causes a BUG()
On Fri, 4 Sep 2009 10:31:56 -0700
Andrew Morton <akpm@linux-foundation.org> wrote:

> On Fri, 4 Sep 2009 18:16:45 +0900 KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> wrote:
>
> > On Fri, 4 Sep 2009 10:00:39 +0100
> > Nick Craig-Wood <nick@craig-wood.com> wrote:
> >
> > > On Fri, Sep 04, 2009 at 09:06:42AM +0900, KAMEZAWA Hiroyuki wrote:
> > > > On Thu, 3 Sep 2009 15:14:55 +0300
> > > > Pekka Enberg <penberg@cs.helsinki.fi> wrote:
> > > > > On Thu, Sep 3, 2009 at 2:34 PM, Nick Craig-Wood<nick@craig-wood.com> wrote:
> > > > > > Is a fix for this going to make 2.6.31?
> > > > > >
> > > > > > To replicate
> > > > > >
> > > > > > __cat /proc/kcore >/dev/null
> > > > > >
> > > > > > See also
> > > > > >
> > > > > > __http://bugzilla.kernel.org/show_bug.cgi?id=13850
> > > [snip]
> > > > > > I tried this on the latest git checkout (as of 2009-09-03 11:00 GMT)
> > > > > > under Xen as a domU. __The bugzilla report states it happens on non xen
> > > > > > machines also.
>
> Is this a regression? I've lost track..
>
regression. (this comes from new per-cpu area implemantation, which uses
vmalloc area with memory holes.)


> > > > > > I know reading /proc/kcore isn't such a good idea, but badly written
> > > > > > backup scripts are triggering this on our customer's servers :-(
> > > > >
> > > > > AFAICT the bug was fixed but I can't seem to find the patches in
> > > > > Linus' git either. Lets CC Andrew and Hiroyuki-san.
> > > >
> > > > Ah, it's now tested under mmotm. please wait.
> > >
> > > I tried mmotm but I couldn't get it to boot under Xen :-(
> > >
> > > If you send me a patch against latest git I'm willing to test it (I
> > > tried to extract the relevant patch from mmotm but failed dismally)
> > >
> > > Thanks
> > >
> >
> > If you already downloaded mmotm, use these patches.
> >
> > vmalloc-unmap-vmalloc-area-after-hiding-it.patch
> > kcore-fix-vread-vwrite-to-be-aware-of-holes.patch
> > kcore-fix-vread-vwrite-to-be-aware-of-holes-update.patch
> > kcore-proc-kcore-should-use-vread.patch
> >
> > All I tested was x86-32/x86-64. then more tests are welcomed.
>
> That's a lot of stuff for 2.6.31. Is there some simple quickfix we can do?
>
I don't like this patch. But here, my 1st version which wasn't sent out.
-Kame
==
/proc/kcore may access in memory holes in vmalloc area. skip it
by using copy_from_user().

Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
---
fs/proc/kcore.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)
Index: linux-2.6.31-rc8/fs/proc/kcore.c
===================================================================
--- linux-2.6.31-rc8.orig/fs/proc/kcore.c
+++ linux-2.6.31-rc8/fs/proc/kcore.c
@@ -361,7 +361,9 @@ read_kcore(struct file *file, char __use
/* don't dump ioremap'd stuff! (TA) */
if (m->flags & VM_IOREMAP)
continue;
- memcpy(elf_buf + (vmstart - start),
+ /* we may access memory holes */
+ __copy_from_user_inatomic(
+ elf_buf + (vmstart - start),
(char *)vmstart, vmsize);
}
read_unlock(&vmlist_lock);







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