Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757553AbdCUQaH (ORCPT ); Tue, 21 Mar 2017 12:30:07 -0400 Received: from mail-vk0-f43.google.com ([209.85.213.43]:34791 "EHLO mail-vk0-f43.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933170AbdCUQ3T (ORCPT ); Tue, 21 Mar 2017 12:29:19 -0400 MIME-Version: 1.0 In-Reply-To: References: <20170321064539.GB30094@gmail.com> <20170321075934.o4sccpawzn4rmtvh@angband.pl> <5b3938fb-ee84-c78d-be9b-e3ba6656065d@virtuozzo.com> From: Andy Lutomirski Date: Tue, 21 Mar 2017 09:28:56 -0700 Message-ID: Subject: Re: linux-next: x86: Unalbe to run x32 processes on the x86_64 kernel To: Dmitry Safonov Cc: Thomas Gleixner , Adam Borowski , Ingo Molnar , Andrei Vagin , Ingo Molnar , LKML , Cyrill Gorcunov , Andy Lutomirski , Thomas Garnier , "H. Peter Anvin" Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1665 Lines: 54 On Tue, Mar 21, 2017 at 8:59 AM, Dmitry Safonov wrote: > On 03/21/2017 03:50 PM, Dmitry Safonov wrote: >> >> 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 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. > > > Which is not set during exec() for x32. So in_compat_syscall() doesn't > work there. > I've tested this patch on x32-debian port: > https://lkml.org/lkml/2017/3/21/489 Seems generally reasonable to me. It aligns x32 with existing practice for i386, I think. > > Though I'm not very happy with the resulting patch :( > Maybe one could suggest a better idea.. IMO it would be nice if execve() didn't call into any function that checked in_compat_syscall(), etc, but maybe that's a pipe dream.