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=-3.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,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 046A5C43463 for ; Sat, 19 Sep 2020 22:43:11 +0000 (UTC) Received: from lists.ozlabs.org (lists.ozlabs.org [203.11.71.2]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 0E05720E65 for ; Sat, 19 Sep 2020 22:43:09 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 0E05720E65 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=zeniv.linux.org.uk Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Received: from bilbo.ozlabs.org (lists.ozlabs.org [IPv6:2401:3900:2:1::3]) by lists.ozlabs.org (Postfix) with ESMTP id 4Bv5MH5SvlzDqxG for ; Sun, 20 Sep 2020 08:43:07 +1000 (AEST) Authentication-Results: lists.ozlabs.org; spf=none (no SPF record) smtp.mailfrom=ftp.linux.org.uk (client-ip=2002:c35c:fd02::1; helo=zeniv.linux.org.uk; envelope-from=viro@ftp.linux.org.uk; receiver=) Authentication-Results: lists.ozlabs.org; dmarc=none (p=none dis=none) header.from=zeniv.linux.org.uk Received: from ZenIV.linux.org.uk (zeniv.linux.org.uk [IPv6:2002:c35c:fd02::1]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 4Bv5KT3vxDzDqL9 for ; Sun, 20 Sep 2020 08:41:33 +1000 (AEST) Received: from viro by ZenIV.linux.org.uk with local (Exim 4.92.3 #3 (Red Hat Linux)) id 1kJlXm-001zb3-7c; Sat, 19 Sep 2020 22:41:22 +0000 Date: Sat, 19 Sep 2020 23:41:22 +0100 From: Al Viro To: Andy Lutomirski Subject: Re: [PATCH 1/9] kernel: add a PF_FORCE_COMPAT flag Message-ID: <20200919224122.GJ3421308@ZenIV.linux.org.uk> References: <20200919220920.GI3421308@ZenIV.linux.org.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linux-aio@kvack.org, linux-mips@vger.kernel.org, David Howells , linux-mm@kvack.org, keyrings@vger.kernel.org, sparclinux@vger.kernel.org, Christoph Hellwig , linux-arch@vger.kernel.org, linux-s390@vger.kernel.org, linux-scsi@vger.kernel.org, x86@kernel.org, Arnd Bergmann , linux-block@vger.kernel.org, io-uring@vger.kernel.org, linux-arm-kernel@lists.infradead.org, Jens Axboe , linux-parisc@vger.kernel.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, linux-security-module@vger.kernel.org, linux-fsdevel@vger.kernel.org, Andrew Morton , linuxppc-dev@lists.ozlabs.org Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" On Sat, Sep 19, 2020 at 03:23:54PM -0700, Andy Lutomirski wrote: > > > On Sep 19, 2020, at 3:09 PM, Al Viro wrote: > > > > On Fri, Sep 18, 2020 at 05:16:15PM +0200, Christoph Hellwig wrote: > >>> 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 that > >> I recently ran into is drivers/scsi/sg.c. > > > > So screw such read/write methods - don't use them with io_uring. > > That, BTW, is one of the reasons I'm sceptical about burying the > > decisions deep into the callchain - we don't _want_ different > > data layouts on read/write depending upon the 32bit vs. 64bit > > caller, let alone the pointer-chasing garbage that is /dev/sg. > > Well, we could remove in_compat_syscall(), etc and instead have an implicit parameter in DEFINE_SYSCALL. Then everything would have to be explicit. This would probably be a win, although it could be quite a bit of work. It would not be a win - most of the syscalls don't give a damn about 32bit vs. 64bit...