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Date: Fri, 18 May 2018 00:19:13 +0300
From: Alexey Izbyshev <izbyshev@ispras.ru>
Subject: Re: [4.11 Regression] 64-bit process gets AT_BASE in the first 4 GB
 if exec'ed from 32-bit process
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To: Dmitry Safonov <0x7f454c46@gmail.com>
Cc: Andy Lutomirski <luto@kernel.org>, Dmitry Safonov <dsafonov@virtuozzo.com>, Thomas Gleixner <tglx@linutronix.de>, Cyrill Gorcunov <gorcunov@openvz.org>, Borislav Petkov <bp@suse.de>, "Kirill A.
 Shutemov" <kirill.shutemov@linux.intel.com>, Alexander Monakov <amonakov@ispras.ru>, Linux-MM <linux-mm@kvack.org>

On 2018-05-18 00:11, Dmitry Safonov wrote:
> 2018-05-17 22:07 GMT+01:00 Andy Lutomirski <luto@kernel.org>:
>> On Thu, May 17, 2018 at 1:51 PM Dmitry Safonov <0x7f454c46@gmail.com> 
>> wrote:
>> 
>>> 2018-05-17 21:46 GMT+01:00 Andy Lutomirski <luto@kernel.org>:
>>> > On Thu, May 17, 2018 at 1:25 PM Alexey Izbyshev <izbyshev@ispras.ru>
>> wrote:
>>> >
>>> >> Hello everyone,
>>> >
>>> >> I've discovered the following strange behavior of a 4.15.13-based
>> kernel
>>> >> (bisected to
>>> >
>>> >
>>> >
>> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=1b028f784e8c341e762c264f70dc0ca1418c8b7a
>>> >> between 4.11-rc2 and -rc3 thanks to Alexander Monakov).
>>> >
>>> >
>>> > It's definitely not intended.  Can you confirm that the problem still
>>> > exists in 4.16?  I have some vague recollection that this was a known
>> issue
>>> > that got fixed, and we could plausibly just be missing a backport.
>> 
>>> I'm looking into that ATM, the problem like that was fixed with
>> 
>> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=ada26481dfe6
>> 
>>> Will check what's happening there.
>> 
>> I haven't tried to figure out exactly what code calls which function, 
>> but
>> it seems like set_personality_64bit() really ought to clear TS_COMPAT.
> 
> Ugh, yeah, the same way __set_personality_x32().
> Will test it and prepare a patch for that Cc'ing stable.
> 
> Thanks, Alexey, Andy!
> 
Thanks, Dmitry, Andy for the quick investigation, and Alexander for the 
confirmation!

-Alexey