From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 9075DC433E7 for ; Wed, 2 Sep 2020 14:46:26 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 718672078E for ; Wed, 2 Sep 2020 14:46:26 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728081AbgIBOqQ (ORCPT ); Wed, 2 Sep 2020 10:46:16 -0400 Received: from pegase1.c-s.fr ([93.17.236.30]:41323 "EHLO pegase1.c-s.fr" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727919AbgIBONH (ORCPT ); Wed, 2 Sep 2020 10:13:07 -0400 Received: from localhost (mailhub1-int [192.168.12.234]) by localhost (Postfix) with ESMTP id 4BhQrb14QDz9txSf; Wed, 2 Sep 2020 16:13:03 +0200 (CEST) X-Virus-Scanned: Debian amavisd-new at c-s.fr Received: from pegase1.c-s.fr ([192.168.12.234]) by localhost (pegase1.c-s.fr [192.168.12.234]) (amavisd-new, port 10024) with ESMTP id GuQVU6E922f3; Wed, 2 Sep 2020 16:13:03 +0200 (CEST) Received: from messagerie.si.c-s.fr (messagerie.si.c-s.fr [192.168.25.192]) by pegase1.c-s.fr (Postfix) with ESMTP id 4BhQrZ4lmSz9txS9; Wed, 2 Sep 2020 16:13:02 +0200 (CEST) Received: from localhost (localhost [127.0.0.1]) by messagerie.si.c-s.fr (Postfix) with ESMTP id EA6E38B7EE; Wed, 2 Sep 2020 16:13:03 +0200 (CEST) X-Virus-Scanned: amavisd-new at c-s.fr Received: from messagerie.si.c-s.fr ([127.0.0.1]) by localhost (messagerie.si.c-s.fr [127.0.0.1]) (amavisd-new, port 10023) with ESMTP id 6937B_9zfpgR; Wed, 2 Sep 2020 16:13:03 +0200 (CEST) Received: from [10.25.210.31] (po15451.idsi0.si.c-s.fr [10.25.210.31]) by messagerie.si.c-s.fr (Postfix) with ESMTP id 0F1C98B7E5; Wed, 2 Sep 2020 16:13:01 +0200 (CEST) Subject: Re: [PATCH 10/10] powerpc: remove address space overrides using set_fs() To: David Laight , 'Christoph Hellwig' Cc: Linus Torvalds , Al Viro , Michael Ellerman , "x86@kernel.org" , "linux-fsdevel@vger.kernel.org" , "linux-arch@vger.kernel.org" , "linuxppc-dev@lists.ozlabs.org" , Kees Cook , "linux-kernel@vger.kernel.org" References: <20200827150030.282762-1-hch@lst.de> <20200827150030.282762-11-hch@lst.de> <8974838a-a0b1-1806-4a3a-e983deda67ca@csgroup.eu> <20200902123646.GA31184@lst.de> <61b9a880a6424a34b841cf3dddb463ad@AcuMS.aculab.com> <8de54fe0-4be9-5624-dd1d-d95d792e933d@csgroup.eu> <0c298e0d972a48bd9ee178225e404b12@AcuMS.aculab.com> From: Christophe Leroy Message-ID: <6e88048a-8b30-400e-11c6-8d91ba77cbb0@csgroup.eu> Date: Wed, 2 Sep 2020 16:12:50 +0200 User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:68.0) Gecko/20100101 Thunderbird/68.12.0 MIME-Version: 1.0 In-Reply-To: <0c298e0d972a48bd9ee178225e404b12@AcuMS.aculab.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: fr Content-Transfer-Encoding: 8bit Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org Le 02/09/2020 à 15:51, David Laight a écrit : > From: Christophe Leroy >> Sent: 02 September 2020 14:25 >> Le 02/09/2020 à 15:13, David Laight a écrit : >>> From: Christoph Hellwig >>>> Sent: 02 September 2020 13:37 >>>> >>>> On Wed, Sep 02, 2020 at 08:15:12AM +0200, Christophe Leroy wrote: >>>>>> - return 0; >>>>>> - return (size == 0 || size - 1 <= seg.seg - addr); >>>>>> + if (addr >= TASK_SIZE_MAX) >>>>>> + return false; >>>>>> + if (size == 0) >>>>>> + return false; >>>>> >>>>> __access_ok() was returning true when size == 0 up to now. Any reason to >>>>> return false now ? >>>> >>>> No, this is accidental and broken. Can you re-run your benchmark with >>>> this fixed? >>> >>> Is TASK_SIZE_MASK defined such that you can do: >>> >>> return (addr | size) < TASK_SIZE_MAX) || !size; >> >> TASK_SIZE_MAX will usually be 0xc0000000 >> >> With: >> addr = 0x80000000; >> size = 0x80000000; >> >> I expect it to fail .... >> >> With the formula you propose it will succeed, won't it ? > > Hmmm... Was i getting confused about some comments for 64bit > about there being such a big hole between valid user and kernel > addresses that it was enough to check that 'size < TASK_SIZE_MAX'. > > That would be true for 64bit x86 (and probably ppc (& arm??)) > if TASK_SIZE_MAX were 0x4 << 60. > IIUC the highest user address is (much) less than 0x0 << 60 > and the lowest kernel address (much) greater than 0xf << 60 > on all these 64bit platforms. > > Actually if doing access_ok() inside get_user() you don't > need to check the size at all. You mean on 64 bit or on any platform ? What about a word write to 0xbffffffe, won't it overwrite 0xc0000000 ? > You don't even need to in copy_to/from_user() provided > it always does a forwards copy. Do you mean due to the gap ? Is it garantied to be a gap ? Even on a 32 bits having TASK_SIZE set to 0xc0000000 and PAGE_OFFSET set to the same ? Christophe