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Message-ID: <20201217212803.GE14556@grain>
Date: Fri, 18 Dec 2020 00:28:03 +0300
From: Cyrill Gorcunov <gorcunov@...il.com>
To: Keno Fischer <keno@...iacomputing.com>
Cc: Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
Andrew Morton <akpm@...ux-foundation.org>, mkoutny@...e.com,
ktkhai@...tuozzo.com, Andrey Vagin <avagin@...il.com>,
Dmitry Safonov <0x7f454c46@...il.com>, CriuML <criu@...nvz.org>
Subject: Re: brk checks in PR_SET_MM code
On Thu, Dec 17, 2020 at 10:42:02AM +0300, Cyrill Gorcunov wrote:
> On Wed, Dec 16, 2020 at 08:29:30PM -0500, Keno Fischer wrote:
> > Hi all,
> >
> > The code in prctl(PR_SET_MM, ...) performs a number of sanity checks,
> > among them
> >
> > ```
> > /*
> > * @brk should be after @end_data in traditional maps.
> > */
> > if (prctl_map->start_brk <= prctl_map->end_data ||
> > prctl_map->brk <= prctl_map->end_data)
> > goto out;
> > ```
> >
>
> Thanks for pointing, Keno! I don't remember the details right now,
> gimme some time and once I refresh my memory I'll reply with
> details.
Indeed, when loaded via ld directly we've got a different layout:
# /lib64/ld-linux-x86-64.so.2 ~/t
start_code 7fc25b0a4000
end_code 7fc25b0c4524
start_stack 7fffcc6b2400
start_data 7fc25b0ce4c0
end_data 7fc25b0cff98
start_brk 55555710c000
sbrk(0) 55555710c000
Note though that as far as I understand the layout is provided by
ld loader. I contrast the regular load
# ~/t
start_code 401000
end_code 401a15
start_stack 7ffce4577dd0
start_data 403e10
end_data 40408c
start_brk b5b000
sbrk(0) b5b000
I fear we've not been using ld's loaded programs in c/r procedure much
that's why it has not been noted earlier. Need to think how to fix it.
Using the whole memory map for verification procedure is a correct way
thus the commit you mention is doing exactly what it should but we need
to figure out how to deal with fdpic loaded files... I'll back once I
figure it out (hopefully more-less soon). Thanks a huge for report!
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