From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-io0-f197.google.com (mail-io0-f197.google.com [209.85.223.197]) by kanga.kvack.org (Postfix) with ESMTP id 860376B0394 for ; Tue, 21 Mar 2017 14:13:24 -0400 (EDT) Received: by mail-io0-f197.google.com with SMTP id y136so69024774iof.3 for ; Tue, 21 Mar 2017 11:13:24 -0700 (PDT) Received: from EUR03-VE1-obe.outbound.protection.outlook.com (mail-eopbgr50133.outbound.protection.outlook.com. [40.107.5.133]) by mx.google.com with ESMTPS id w10si14864921itf.37.2017.03.21.11.13.23 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-SHA bits=128/128); Tue, 21 Mar 2017 11:13:23 -0700 (PDT) Subject: Re: [PATCHv2] x86/mm: set x32 syscall bit in SET_PERSONALITY() References: <20170321163712.20334-1-dsafonov@virtuozzo.com> <20170321171723.GB21564@uranus.lan> From: Dmitry Safonov Message-ID: <6648805c-e0d8-5e27-9e19-602ab47937a7@virtuozzo.com> Date: Tue, 21 Mar 2017 21:09:40 +0300 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset="utf-8"; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Andy Lutomirski , Cyrill Gorcunov Cc: "linux-kernel@vger.kernel.org" , Dmitry Safonov <0x7f454c46@gmail.com>, Adam Borowski , "linux-mm@kvack.org" , Andrei Vagin , Borislav Petkov , "Kirill A. Shutemov" , X86 ML , "H. Peter Anvin" , Andy Lutomirski , Ingo Molnar , Thomas Gleixner On 03/21/2017 08:45 PM, Andy Lutomirski wrote: > On Tue, Mar 21, 2017 at 10:17 AM, Cyrill Gorcunov wrote: >> On Tue, Mar 21, 2017 at 07:37:12PM +0300, Dmitry Safonov wrote: >> ... >>> diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c >>> index d6b784a5520d..d3d4d9abcaf8 100644 >>> --- a/arch/x86/kernel/process_64.c >>> +++ b/arch/x86/kernel/process_64.c >>> @@ -519,8 +519,14 @@ void set_personality_ia32(bool x32) >>> if (current->mm) >>> current->mm->context.ia32_compat = TIF_X32; >>> current->personality &= ~READ_IMPLIES_EXEC; >>> - /* in_compat_syscall() uses the presence of the x32 >>> - syscall bit flag to determine compat status */ >>> + /* >>> + * in_compat_syscall() uses the presence of the x32 >>> + * syscall bit flag to determine compat status. >>> + * On the bitness of syscall relies x86 mmap() code, >>> + * so set x32 syscall bit right here to make >>> + * in_compat_syscall() work during exec(). >>> + */ >>> + task_pt_regs(current)->orig_ax |= __X32_SYSCALL_BIT; >>> current->thread.status &= ~TS_COMPAT; >> >> Hi! I must admit I didn't follow close the overall series (so can't >> comment much here :) but I have a slightly unrelated question -- is >> there a way to figure out if task is running in x32 mode say with >> some ptrace or procfs sign? > > You should be able to figure out of a *syscall* is x32 by simply > looking at bit 30 in the syscall number. (This is unlike i386, which > is currently not reflected in ptrace.) The process could be stopped with PTRACE_SEIZE and I think, it'll not have x32 syscall bit at that moment. 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. 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. > > Do we actually have an x32 per-task mode at all? If so, maybe we can > just remove it on top of Dmitry's series. -- Dmitry -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org