Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752068AbdCMPaY (ORCPT ); Mon, 13 Mar 2017 11:30:24 -0400 Received: from mail-vk0-f50.google.com ([209.85.213.50]:36479 "EHLO mail-vk0-f50.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751089AbdCMPaP (ORCPT ); Mon, 13 Mar 2017 11:30:15 -0400 MIME-Version: 1.0 In-Reply-To: References: <20170306141721.9188-1-dsafonov@virtuozzo.com> <20170306141721.9188-5-dsafonov@virtuozzo.com> <35a16a2c-c799-fe0c-2689-bf105b508663@virtuozzo.com> From: Andy Lutomirski Date: Mon, 13 Mar 2017 08:29:53 -0700 Message-ID: Subject: Re: [PATCHv6 4/5] x86/mm: check in_compat_syscall() instead TIF_ADDR32 for mmap(MAP_32BIT) To: Thomas Gleixner Cc: Dmitry Safonov , "linux-kernel@vger.kernel.org" , Dmitry Safonov <0x7f454c46@gmail.com>, Ingo Molnar , "H. Peter Anvin" , Andy Lutomirski , Borislav Petkov , X86 ML , "linux-mm@kvack.org" , Cyrill Gorcunov , "Kirill A. Shutemov" 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: 2178 Lines: 51 On Mon, Mar 13, 2017 at 6:47 AM, Thomas Gleixner wrote: > On Mon, 13 Mar 2017, Dmitry Safonov wrote: >> On 03/13/2017 12:39 PM, Thomas Gleixner wrote: >> > On Mon, 6 Mar 2017, Dmitry Safonov wrote: >> > >> > > Result of mmap() calls with MAP_32BIT flag at this moment depends >> > > on thread flag TIF_ADDR32, which is set during exec() for 32-bit apps. >> > > It's broken as the behavior of mmap() shouldn't depend on exec-ed >> > > application's bitness. Instead, it should check the bitness of mmap() >> > > syscall. >> > > How it worked before: >> > > o for 32-bit compatible binaries it is completely ignored. Which was >> > > fine when there were one mmap_base, computed for 32-bit syscalls. >> > > After introducing mmap_compat_base 64-bit syscalls do use computed >> > > for 64-bit syscalls mmap_base, which means that we can allocate 64-bit >> > > address with 64-bit syscall in application launched from 32-bit >> > > compatible binary. And ignoring this flag is not expected behavior. >> > >> > Well, the real question here is, whether we should allow 32bit applications >> > to obtain 64bit mappings at all. We can very well force 32bit applications >> > into the 4GB address space as it was before your mmap base splitup and be >> > done with it. >> >> Hmm, yes, we could restrict 32bit applications to 32bit mappings only. >> But the approach which I tried to follow in the patches set, it was do >> not base the logic on the bitness of launched applications >> (native/compat) - only base on bitness of the performing syscall. >> The idea was suggested by Andy and I made mmap() logic here independent >> from original application's bitness. >> >> It also seems to me simpler: >> if 32-bit application wants to allocate 64-bit mapping, it should >> long-jump with 64-bit segment descriptor and do `syscall` instruction >> for 64-bit syscall entry path. So, in my point of view after this dance >> the application does not differ much from native 64-bit binary and can >> have 64-bit address mapping. I agree. > > Works for me, but it lacks documentation ..... > > Thanks, > > tglx -- Andy Lutomirski AMA Capital Management, LLC