From: Andy Lutomirski <luto@amacapital.net>
To: Cyrill Gorcunov <gorcunov@gmail.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Sasha Levin <sasha.levin@oracle.com>,
"linux-mm@kvack.org" <linux-mm@kvack.org>,
Dave Jones <davej@redhat.com>,
LKML <linux-kernel@vger.kernel.org>,
Pavel Emelyanov <xemul@parallels.com>
Subject: Re: mm: NULL ptr deref handling mmaping of special mappings
Date: Thu, 15 May 2014 12:46:34 -0700 [thread overview]
Message-ID: <CALCETrWwWXEoNparvhx4yJB8YmiUBZCuR6yQxJOTjYKuA8AdqQ@mail.gmail.com> (raw)
In-Reply-To: <20140515084558.GI28328@moon>
On Thu, May 15, 2014 at 1:45 AM, Cyrill Gorcunov <gorcunov@gmail.com> wrote:
> On Wed, May 14, 2014 at 03:23:27PM -0700, Andy Lutomirski wrote:
>> I can summarize:
>>
>> On 3.14 and before, the vdso is just a bunch of ELF headers and
>> executable data. When executed by 64-bit binaries, it reads from the
>> fixmap to do its thing. That is, it reads from kernel addresses that
>> don't have vmas. When executed by 32-bit binaries, it doesn't read
>> anything, since there was no 32-bit timing code.
>>
>> On 3.15, the x86_64 vdso is unchanged. The 32-bit vdso is preceded by
>> a separate vma containing two pages worth of time-varying read-only
>> data. The vdso reads those pages using PIC references.
>
> Andy, could you please point me where is the code which creates a second vma?
> latest 3.15 master branch
Search for _install_special_mapping in arch/x86/vdso. It's in a
different place in 3.15-rc and -next.
>
> [root@fc ~]# cat /proc/self/maps
> ...
> 7fff57b6e000-7fff57b8f000 rw-p 00000000 00:00 0 [stack]
> 7fff57bff000-7fff57c00000 r-xp 00000000 00:00 0 [vdso]
> ffffffffff600000-ffffffffff601000 r-xp 00000000 00:00 0 [vsyscall]
> [root@fc ~]#
>
What version and bitness is this?
> Or you mean vsyscall area? If yes, then in criu we don't dump vsyscall zone.
> On restore we don't touch vsyscall either but for vdso there are two cases
vsyscalls are almost gone now :)
>
> - if there were no kernel change on vdso contents we simply use vdso provided
> by the kernel at the moment of criu startup
>
> - if vdso has been changed and looks different from one saved in image during
> checkpoint, we map it from image but then patch (push jmp instruction) so
> when application calls for some of vdso function it jumps into vdso code
> saved in image and then jumps into vdso mapped by the kernel (ie kind of
> proxy calls) This force us to do own Elf parsing inside criu to calculate
> proper offsets.
Yuck :)
--Andy
next prev parent reply other threads:[~2014-05-15 19:46 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-05-14 15:55 mm: NULL ptr deref handling mmaping of special mappings Sasha Levin
2014-05-14 20:23 ` Andrew Morton
2014-05-14 20:41 ` Sasha Levin
2014-05-14 21:03 ` Andrew Morton
2014-05-14 21:11 ` Sasha Levin
2014-05-14 21:31 ` Andrew Morton
2014-05-14 21:33 ` Andy Lutomirski
2014-05-14 22:11 ` Cyrill Gorcunov
2014-05-14 22:23 ` Andy Lutomirski
2014-05-15 2:36 ` Pavel Emelyanov
2014-05-15 19:42 ` Andy Lutomirski
2014-05-19 8:27 ` Pavel Emelyanov
2014-05-19 8:40 ` Cyrill Gorcunov
2014-05-15 8:45 ` Cyrill Gorcunov
2014-05-15 19:46 ` Andy Lutomirski [this message]
2014-05-15 19:53 ` Cyrill Gorcunov
2014-05-15 19:59 ` Andy Lutomirski
2014-05-15 20:19 ` Cyrill Gorcunov
2014-05-15 21:31 ` Cyrill Gorcunov
2014-05-15 21:42 ` Andy Lutomirski
2014-05-15 21:57 ` Cyrill Gorcunov
2014-05-15 22:15 ` Andy Lutomirski
2014-05-16 22:40 ` Andy Lutomirski
2014-05-16 22:56 ` H. Peter Anvin
2014-05-17 6:15 ` Cyrill Gorcunov
2014-05-14 22:51 ` Andy Lutomirski
2014-05-14 21:26 ` Andy Lutomirski
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