linux-kernel - Re: [PATCHv2] x86/mm: set x32 syscall bit in SET

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Date:   Tue, 21 Mar 2017 11:51:09 -0700
From:   hpa@...or.com
To:     Cyrill Gorcunov <gorcunov@...il.com>,
        Dmitry Safonov <dsafonov@...tuozzo.com>
CC:     Andy Lutomirski <luto@...capital.net>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Dmitry Safonov <0x7f454c46@...il.com>,
        Adam Borowski <kilobyte@...band.pl>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        Andrei Vagin <avagin@...il.com>, Borislav Petkov <bp@...e.de>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        X86 ML <x86@...nel.org>, Andy Lutomirski <luto@...nel.org>,
        Ingo Molnar <mingo@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCHv2] x86/mm: set x32 syscall bit in SET_PERSONALITY()

On March 21, 2017 11:40:58 AM PDT, Cyrill Gorcunov <gorcunov@...il.com> wrote:
>On Tue, Mar 21, 2017 at 09:09:40PM +0300, Dmitry Safonov wrote:
>> 
>> I guess the question comes from that we're releasing CRIU 3.0 with
>> 32-bit C/R and some other cool stuff, but we don't support x32 yet.
>> As we don't want release a thing that we aren't properly testing.
>> So for a while we should error on dumping x32 applications.
>
>yes
>
>> I think, the best way for now is to check physicall address of vdso
>> from /proc/.../pagemap. If it's CONFIG_VDSO=n kernel, I guess we
>could
>> also add check for %ds from ptrace's register set. For x32 it's set
>to
>> __USER_DS, while for native it's 0 (looking at start_thread() and
>> compat_start_thread()). The application can simply change it without
>> any consequence - so it's not very reliable, we could only warn at
>> catching it, not rely on this.
>
>indeed, thanks!

I proposed to the ptrace people a virtual register for this and a few other things, but it got bikeshed to death.
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