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

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Message-ID: <dfdb16d4-aa6e-8635-1ea5-f6ac57b1dd05@virtuozzo.com>
Date:   Tue, 21 Mar 2017 22:19:01 +0300
From:   Dmitry Safonov <dsafonov@...tuozzo.com>
To:     Cyrill Gorcunov <gorcunov@...il.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>, "H. Peter Anvin" <hpa@...or.com>,
        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 03/21/2017 09:40 PM, Cyrill Gorcunov 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!

Also, even more simple-minded: for now we could just check binary magic
from /proc/.../exe, for now stopping on x32 binaries.

-- 
              Dmitry