Re: mm: NULL ptr deref handling mmaping of special mappings

Andy Lutomirski
2014-05-14T22:52:21Z

On Wed, May 14, 2014 at 2:31 PM, Andrew Morton
<akpm@linux-foundation.org> wrote:
> On Wed, 14 May 2014 17:11:00 -0400 Sasha Levin <sasha.levin@oracle.com> wrote:
>
>> > In my linux-next all that code got deleted by Andy's "x86, vdso:
>> > Reimplement vdso.so preparation in build-time C" anyway. What kernel
>> > were you looking at?
>>
>> Deleted? It appears in today's -next. arch/x86/vdso/vma.c:124 .
>>
>> I don't see Andy's patch removing that code either.
>
> ah, OK, it got moved from arch/x86/vdso/vdso32-setup.c into
> arch/x86/vdso/vma.c.
>
> Maybe you managed to take a fault against the symbol area between the
> _install_special_mapping() and the remap_pfn_range() call, but mmap_sem
> should prevent that.
>
> Or the remap_pfn_range() call never happened. Should map_vdso() be
> running _install_special_mapping() at all if
> image->sym_vvar_page==NULL?

You're almost right, but that was enough to point me in the right direction :)

The mapping is still needed, since there are two pages. qemu -no-hpet
will trigger this, but the nohpet kernel option will not. The latter
is arguably a bug in the nohpet option.

Fix coming.

--
Andy Lutomirski
AMA Capital Management, LLC