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>,
"H. Peter Anvin" <hpa@zytor.com>
Subject: Re: mm: NULL ptr deref handling mmaping of special mappings
Date: Fri, 16 May 2014 15:40:48 -0700 [thread overview]
Message-ID: <CALCETrU5-4sMyOW7t75PJ4RQ3WdUg=s2xhYG5uEstm_LEOV+mg@mail.gmail.com> (raw)
In-Reply-To: <CALCETrUTM7ZJrWvWa4bHi0RSFhzAZu7+z5XHbJuP+==Cd8GRqw@mail.gmail.com>
On Thu, May 15, 2014 at 3:15 PM, Andy Lutomirski <luto@amacapital.net> wrote:
> On Thu, May 15, 2014 at 2:57 PM, Cyrill Gorcunov <gorcunov@gmail.com> wrote:
>> On Thu, May 15, 2014 at 02:42:48PM -0700, Andy Lutomirski wrote:
>>> >
>>> > Looking forward the question appear -- will VDSO_PREV_PAGES and rest of variables
>>> > be kind of immutable constants? If yes, we could calculate where the additional
>>> > vma lives without requiring any kind of [vdso] mark in proc/pid/maps output.
>>>
>>> Please don't!
>>>
>>> These might, in principle, even vary between tasks on the same system.
>>> Certainly the relative positions of the vmas will be different
>>> between 3.15 and 3.16, since we need almost my entire cleanup series
>>> to reliably put them into their 3.16 location. And I intend to change
>>> the number of pages in 3.16 or 3.17.
>>
>> There are other ways how to find where additional pages are laying but it
>> would be great if there a straightforward interface for that (ie some mark
>> in /proc/pid/maps output).
>
> I'll try to write a patch in time for 3.15.
>
My current draft is here:
https://git.kernel.org/cgit/linux/kernel/git/luto/linux.git/log/?h=vdso/cleanups
On 64-bit userspace, it results in:
7fffa1dfd000-7fffa1dfe000 r-xp 00000000 00:00 0 [vdso]
7fffa1dfe000-7fffa1e00000 r--p 00000000 00:00 0 [vvar]
ffffffffff600000-ffffffffff601000 r-xp 00000000 00:00 0
[vsyscall]
On 32-bit userspace, it results in:
f7748000-f7749000 r-xp 00000000 00:00 0 [vdso]
f7749000-f774b000 r--p 00000000 00:00 0 [vvar]
ffd94000-ffdb5000 rw-p 00000000 00:00 0 [stack]
Is this good for CRIU? Another approach would be to name both of
these things "vdso", since they are sort of both the vdso, but that
might be a bit confusing -- [vvar] is not static text the way that
[vdso] is.
If I backport this for 3.15 (which might be nasty -- I would argue
that the code change is actually a cleanup, but it's fairly
intrusive), then [vvar] will be *before* [vdso], not after it. I'd be
very hesitant to name both of them "[vdso]" in that case, since there
is probably code that assumes that the beginning of "[vdso]" is a DSO.
Note that it is *not* safe to blindly read from "[vvar]". On some
configurations you *will* get SIGBUS if you try to read from some of
the vvar pages. (That's what started this whole thread.) Some pages
in "[vvar]" may have strange caching modes, so SIGBUS might not be the
only surprising thing about poking at it.
--Andy
next prev parent reply other threads:[~2014-05-16 22:41 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
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 [this message]
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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