linux-kernel - Re: linux-next: x86: Unalbe to run x32 processes on the x86

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Date:   Tue, 21 Mar 2017 15:50:11 +0300
From:   Dmitry Safonov <dsafonov@...tuozzo.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Adam Borowski <kilobyte@...band.pl>
CC:     Ingo Molnar <mingo@...nel.org>, Andrei Vagin <avagin@...il.com>,
        Ingo Molnar <mingo@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Cyrill Gorcunov <gorcunov@...nvz.org>,
        Andy Lutomirski <luto@...nel.org>,
        Thomas Garnier <thgarnie@...gle.com>,
        "H. Peter Anvin" <hpa@...or.com>
Subject: Re: linux-next: x86: Unalbe to run x32 processes on the x86_64 kernel

On 03/21/2017 03:49 PM, Thomas Gleixner wrote:
> On Tue, 21 Mar 2017, Adam Borowski wrote:
>> On Tue, Mar 21, 2017 at 07:45:39AM +0100, Ingo Molnar wrote:
>>> * Andrei Vagin <avagin@...il.com> wrote:
>>>
>>>> # first bad commit: [45fc8757d1d2128e342b4e7ef39adedf7752faac] x86:
>>>> Make the GDT remapping read-only on 64-bit
>>>
>>> Just wondering, does the following commit fix it:
>>>
>>>   5b781c7e317f x86/tls: Forcibly set the accessed bit in TLS segments
>>
>> It does fix i386 but not x32.
>>
>> By "x32" I mean CONFIG_X86_X32, by "i386" CONFIG_IA32_EMULATION, contrary to
>> Andrei's first report.  The naming of the new ABI wasn't too fortunate...
>
> The X32 issue is unrelated to the GDT mapping.
>
> What happens is that the mmap rework from Dmitry switched X32 to use 64bit
> mappings, which is wrong. X32 has 64bit instructions and syscalls and 32bit
> address space.

Hmm, in_compat_syscall() checks x32 syscall bit.
I'll take a look, what happens there.

> Dmitry, can you please have a look and fix that up? For reproduction just
> compile helloworld.c with gcc -mx32.

Sure, thanks.

-- 
              Dmitry