From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-f71.google.com (mail-wm0-f71.google.com [74.125.82.71]) by kanga.kvack.org (Postfix) with ESMTP id 88A766B0389 for ; Mon, 13 Mar 2017 10:03:41 -0400 (EDT) Received: by mail-wm0-f71.google.com with SMTP id g8so14036920wmg.7 for ; Mon, 13 Mar 2017 07:03:41 -0700 (PDT) Received: from Galois.linutronix.de (Galois.linutronix.de. [2a01:7a0:2:106d:700::1]) by mx.google.com with ESMTPS id l81si10981717wma.110.2017.03.13.07.03.40 for (version=TLS1_2 cipher=AES128-SHA bits=128/128); Mon, 13 Mar 2017 07:03:40 -0700 (PDT) Date: Mon, 13 Mar 2017 15:03:25 +0100 (CET) From: Thomas Gleixner Subject: Re: [PATCHv6 4/5] x86/mm: check in_compat_syscall() instead TIF_ADDR32 for mmap(MAP_32BIT) In-Reply-To: <4f802f8b-07a6-f8cd-71fc-943e40714d1b@virtuozzo.com> Message-ID: References: <20170306141721.9188-1-dsafonov@virtuozzo.com> <20170306141721.9188-5-dsafonov@virtuozzo.com> <35a16a2c-c799-fe0c-2689-bf105b508663@virtuozzo.com> <4f802f8b-07a6-f8cd-71fc-943e40714d1b@virtuozzo.com> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Sender: owner-linux-mm@kvack.org List-ID: To: Dmitry Safonov Cc: linux-kernel@vger.kernel.org, 0x7f454c46@gmail.com, Ingo Molnar , "H. Peter Anvin" , Andy Lutomirski , Borislav Petkov , x86@kernel.org, linux-mm@kvack.org, Cyrill Gorcunov , "Kirill A. Shutemov" , Michael Kerrisk On Mon, 13 Mar 2017, Dmitry Safonov wrote: > On 03/13/2017 04:47 PM, 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. > > > > Works for me, but it lacks documentation ..... > > Sure, could you recommend a better place for it? > Should it be in-code comment in x86 mmap() code or Documentation/* > change or a patch to man-pages? I added a comment in the code and fixed up the changelogs. man-page needs some care as well. Thanks, tglx -- 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