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

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Date:   Tue, 21 Mar 2017 21:40:58 +0300
From:   Cyrill Gorcunov <gorcunov@...il.com>
To:     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>, "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 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!