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=-5.6 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED 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 48D6AC4727C for ; Mon, 21 Sep 2020 23:51:16 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 0D44123A84 for ; Mon, 21 Sep 2020 23:51:16 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1600732276; bh=39KukzOe6AolOem+gjVISioBf02u3SpMpVZVGYy+mj0=; h=References:In-Reply-To:From:Date:Subject:To:Cc:List-ID:From; b=jTH8qgQE2WVxeAwKwfve0x5S0saeX+ik48h7zC40ErRMWG+gfARw8HuXcR7QnCc90 vFtqvDd2C8jUbU4gX0JupE3abQgHY90o29OyFSydgmisWe8LB3vep4/Xygmuod1wpe Y99jMBAg8ef4SIloGjSgWCyff4sPGiMV79hQI4+k= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728938AbgIUXvP (ORCPT ); Mon, 21 Sep 2020 19:51:15 -0400 Received: from mail.kernel.org ([198.145.29.99]:60602 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728058AbgIUXvP (ORCPT ); Mon, 21 Sep 2020 19:51:15 -0400 Received: from mail-wr1-f53.google.com (mail-wr1-f53.google.com [209.85.221.53]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 9B12423A79 for ; Mon, 21 Sep 2020 23:51:14 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1600732274; bh=39KukzOe6AolOem+gjVISioBf02u3SpMpVZVGYy+mj0=; h=References:In-Reply-To:From:Date:Subject:To:Cc:From; b=CQl/bTc6Te74pAw6+D+sJO31hgooXd1lkXVQyxDfGKz1Liczz1BI7NPcqJhTuNqcT fnFpNuCOXIfJl8K7eXwl9pCc8CXzuV86S9ibqoMrPRXETBdCXtl0g/rP48hc1vB+jG xW2h3Zo8OM2lyDPqAHm7IdDEhvR5Hy6ynKk6lJOA= Received: by mail-wr1-f53.google.com with SMTP id t10so15013817wrv.1 for ; Mon, 21 Sep 2020 16:51:14 -0700 (PDT) X-Gm-Message-State: AOAM531tDNhln7vFFWblr8M+6CBX/VOmB5b/fy3nn/zcp9RP5C+qaCQO tzmNj8KLnh7GA7TIw0Lft8yGdmWLcpN2au1SBIC/Mg== X-Google-Smtp-Source: ABdhPJzKuMXKYXqnIGS0yDLp4LGoqUZ+je+eZvXpafAIww15bS0o/seL9c9Y7bM14ZwES1psTTy6TgvO3gjUrDpJ/g4= X-Received: by 2002:adf:ce8e:: with SMTP id r14mr2144251wrn.257.1600732273206; Mon, 21 Sep 2020 16:51:13 -0700 (PDT) MIME-Version: 1.0 References: <563138b5-7073-74bc-f0c5-b2bad6277e87@gmail.com> <486c92d0-0f2e-bd61-1ab8-302524af5e08@gmail.com> In-Reply-To: <486c92d0-0f2e-bd61-1ab8-302524af5e08@gmail.com> From: Andy Lutomirski Date: Mon, 21 Sep 2020 16:51:01 -0700 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH 1/9] kernel: add a PF_FORCE_COMPAT flag To: Pavel Begunkov Cc: Arnd Bergmann , Andy Lutomirski , Christoph Hellwig , Al Viro , Andrew Morton , Jens Axboe , David Howells , linux-arm-kernel , X86 ML , LKML , "open list:MIPS" , Parisc List , linuxppc-dev , linux-s390 , sparclinux , linux-block , Linux SCSI List , Linux FS Devel , linux-aio , io-uring@vger.kernel.org, linux-arch , Linux-MM , Network Development , keyrings@vger.kernel.org, LSM List Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On Mon, Sep 21, 2020 at 9:15 AM Pavel Begunkov wro= te: > > On 21/09/2020 19:10, Pavel Begunkov wrote: > > On 20/09/2020 01:22, Andy Lutomirski wrote: > >> > >>> On Sep 19, 2020, at 2:16 PM, Arnd Bergmann wrote: > >>> > >>> =EF=BB=BFOn Sat, Sep 19, 2020 at 6:21 PM Andy Lutomirski wrote: > >>>>> On Fri, Sep 18, 2020 at 8:16 AM Christoph Hellwig wrot= e: > >>>>> On Fri, Sep 18, 2020 at 02:58:22PM +0100, Al Viro wrote: > >>>>>> Said that, why not provide a variant that would take an explicit > >>>>>> "is it compat" argument and use it there? And have the normal > >>>>>> one pass in_compat_syscall() to that... > >>>>> > >>>>> That would help to not introduce a regression with this series yes. > >>>>> But it wouldn't fix existing bugs when io_uring is used to access > >>>>> read or write methods that use in_compat_syscall(). One example th= at > >>>>> I recently ran into is drivers/scsi/sg.c. > >>> > >>> Ah, so reading /dev/input/event* would suffer from the same issue, > >>> and that one would in fact be broken by your patch in the hypothetica= l > >>> case that someone tried to use io_uring to read /dev/input/event on x= 32... > >>> > >>> For reference, I checked the socket timestamp handling that has a > >>> number of corner cases with time32/time64 formats in compat mode, > >>> but none of those appear to be affected by the problem. > >>> > >>>> Aside from the potentially nasty use of per-task variables, one thin= g > >>>> I don't like about PF_FORCE_COMPAT is that it's one-way. If we're > >>>> going to have a generic mechanism for this, shouldn't we allow a ful= l > >>>> override of the syscall arch instead of just allowing forcing compat > >>>> so that a compat syscall can do a non-compat operation? > >>> > >>> The only reason it's needed here is that the caller is in a kernel > >>> thread rather than a system call. Are there any possible scenarios > >>> where one would actually need the opposite? > >>> > >> > >> I can certainly imagine needing to force x32 mode from a kernel thread= . > >> > >> As for the other direction: what exactly are the desired bitness/arch = semantics of io_uring? Is the operation bitness chosen by the io_uring cre= ation or by the io_uring_enter() bitness? > > > > It's rather the second one. Even though AFAIR it wasn't discussed > > specifically, that how it works now (_partially_). > > Double checked -- I'm wrong, that's the former one. Most of it is based > on a flag that was set an creation. > Could we get away with making io_uring_enter() return -EINVAL (or maybe -ENOTTY?) if you try to do it with bitness that doesn't match the io_uring? And disable SQPOLL in compat mode? --Andy