From: Michal Hocko <mhocko@kernel.org>
To: Jann Horn <jannh@google.com>
Cc: Minchan Kim <minchan@kernel.org>, Linux-MM <linux-mm@kvack.org>,
kernel list <linux-kernel@vger.kernel.org>,
Daniel Colascione <dancol@google.com>,
Dave Hansen <dave.hansen@intel.com>,
"Joel Fernandes (Google)" <joel@joelfernandes.org>
Subject: Re: interaction of MADV_PAGEOUT with CoW anonymous mappings?
Date: Tue, 10 Mar 2020 19:48:14 +0100 [thread overview]
Message-ID: <20200310184814.GA8447@dhcp22.suse.cz> (raw)
In-Reply-To: <CAG48ez0G3JkMq61gUmyQAaCq=_TwHbi1XKzWRooxZkv08PQKuw@mail.gmail.com>
On Tue 10-03-20 19:08:28, Jann Horn wrote:
> Hi!
>
> >From looking at the source code, it looks to me as if using
> MADV_PAGEOUT on a CoW anonymous mapping will page out the page if
> possible, even if other processes still have the same page mapped. Is
> that correct?
>
> If so, that's probably bad in environments where many processes (with
> different privileges) are forked from a single zygote process (like
> Android and Chrome), I think? If you accidentally call it on a CoW
> anonymous mapping with shared pages, you'll degrade the performance of
> other processes. And if an attacker does it intentionally, they could
> use that to aid with exploiting race conditions or weird
> microarchitectural stuff (e.g. the new https://lviattack.eu/lvi.pdf
> talks about "the assumption that attackers can provoke page faults or
> microcode assists for (arbitrary) load operations in the victim
> domain").
>
> Should madvise_cold_or_pageout_pte_range() maybe refuse to operate on
> pages with mapcount>1, or something like that? Or does it already do
> that, and I just missed the check?
I have brought up side channel attacks earlier [1] but only in the
context of shared page cache pages. I didn't really consider shared
anonymous pages to be a real problem. I was under impression that CoW
pages shouldn't be a real problem because any security sensible
applications shouldn't allow untrusted code to be forked and CoW
anything really important. I believe we have made this assumption
in other places - IIRC on gup with FOLL_FORCE but I admit I have
very happily forgot most details.
[1] http://lkml.kernel.org/r/20190619132450.GQ2968@dhcp22.suse.cz
--
Michal Hocko
SUSE Labs
next prev parent reply other threads:[~2020-03-10 18:48 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-03-10 18:08 interaction of MADV_PAGEOUT with CoW anonymous mappings? Jann Horn
2020-03-10 18:48 ` Michal Hocko [this message]
2020-03-10 19:11 ` Jann Horn
2020-03-10 21:09 ` Michal Hocko
2020-03-10 22:48 ` Dave Hansen
2020-03-11 8:45 ` Michal Hocko
2020-03-11 22:02 ` Minchan Kim
2020-03-11 23:53 ` Shakeel Butt
2020-03-12 0:18 ` Minchan Kim
2020-03-12 2:03 ` Daniel Colascione
2020-03-12 15:15 ` Shakeel Butt
2020-03-10 20:19 ` Daniel Colascione
2020-03-10 21:40 ` Jann Horn
2020-03-10 21:52 ` Daniel Colascione
2020-03-10 22:14 ` Minchan Kim
2020-03-12 8:22 ` Michal Hocko
2020-03-12 15:40 ` Vlastimil Babka
2020-03-12 20:16 ` Minchan Kim
2020-03-12 20:26 ` Dave Hansen
2020-03-12 20:41 ` Michal Hocko
2020-03-13 2:08 ` Minchan Kim
2020-03-13 8:05 ` Michal Hocko
2020-03-13 20:59 ` Minchan Kim
2020-03-16 9:20 ` Michal Hocko
2020-03-17 1:43 ` Minchan Kim
2020-03-17 7:12 ` Michal Hocko
2020-03-17 15:00 ` Minchan Kim
2020-03-17 15:58 ` Michal Hocko
2020-03-17 17:20 ` Minchan Kim
2020-03-12 21:41 ` Dave Hansen
2020-03-13 2:00 ` Minchan Kim
2020-03-13 16:59 ` Dave Hansen
2020-03-13 21:13 ` Minchan Kim
2020-03-12 23:29 ` Jann Horn
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