From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pg0-f72.google.com (mail-pg0-f72.google.com [74.125.83.72]) by kanga.kvack.org (Postfix) with ESMTP id 9EF256B038F for ; Mon, 13 Mar 2017 06:00:07 -0400 (EDT) Received: by mail-pg0-f72.google.com with SMTP id y17so291059961pgh.2 for ; Mon, 13 Mar 2017 03:00:07 -0700 (PDT) Received: from EUR02-HE1-obe.outbound.protection.outlook.com (mail-eopbgr10102.outbound.protection.outlook.com. [40.107.1.102]) by mx.google.com with ESMTPS id f17si10966205pgg.290.2017.03.13.03.00.06 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-SHA bits=128/128); Mon, 13 Mar 2017 03:00:06 -0700 (PDT) Subject: Re: [PATCHv6 4/5] x86/mm: check in_compat_syscall() instead TIF_ADDR32 for mmap(MAP_32BIT) References: <20170306141721.9188-1-dsafonov@virtuozzo.com> <20170306141721.9188-5-dsafonov@virtuozzo.com> From: Dmitry Safonov Message-ID: <35a16a2c-c799-fe0c-2689-bf105b508663@virtuozzo.com> Date: Mon, 13 Mar 2017 12:56:18 +0300 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset="windows-1252"; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Thomas Gleixner 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" 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. > > Thanks, > > tglx > > -- 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