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 7919BC43469 for ; Sat, 19 Sep 2020 22:41:35 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 046F7235FA for ; Sat, 19 Sep 2020 22:41:34 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 046F7235FA 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=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 12F756B0055; Sat, 19 Sep 2020 18:41:34 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 0B99F6B0037; Sat, 19 Sep 2020 18:41:34 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id E9C9B6B005C; Sat, 19 Sep 2020 18:41:33 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0162.hostedemail.com [216.40.44.162]) by kanga.kvack.org (Postfix) with ESMTP id CE01F6B0037 for ; Sat, 19 Sep 2020 18:41:33 -0400 (EDT) Received: from smtpin18.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay01.hostedemail.com (Postfix) with ESMTP id 9D3E0180AD802 for ; Sat, 19 Sep 2020 22:41:33 +0000 (UTC) X-FDA: 77281284066.18.point40_0f1669327137 Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin18.hostedemail.com (Postfix) with ESMTP id 71FED1005705F; Sat, 19 Sep 2020 22:41:33 +0000 (UTC) X-HE-Tag: point40_0f1669327137 X-Filterd-Recvd-Size: 3020 Received: from ZenIV.linux.org.uk (zeniv.linux.org.uk [195.92.253.2]) by imf33.hostedemail.com (Postfix) with ESMTP; Sat, 19 Sep 2020 22:41:32 +0000 (UTC) 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 Cc: Christoph Hellwig , Andrew Morton , Jens Axboe , Arnd Bergmann , David Howells , linux-arm-kernel@lists.infradead.org, x86@kernel.org, linux-kernel@vger.kernel.org, linux-mips@vger.kernel.org, linux-parisc@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-s390@vger.kernel.org, sparclinux@vger.kernel.org, linux-block@vger.kernel.org, linux-scsi@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-aio@kvack.org, io-uring@vger.kernel.org, linux-arch@vger.kernel.org, linux-mm@kvack.org, netdev@vger.kernel.org, keyrings@vger.kernel.org, linux-security-module@vger.kernel.org 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 In-Reply-To: Content-Transfer-Encoding: quoted-printable X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Sat, Sep 19, 2020 at 03:23:54PM -0700, Andy Lutomirski wrote: >=20 > > On Sep 19, 2020, at 3:09 PM, Al Viro wrote: > >=20 > > =EF=BB=BFOn 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... > >>=20 > >> 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 tha= t > >> I recently ran into is drivers/scsi/sg.c. > >=20 > > 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. >=20 > Well, we could remove in_compat_syscall(), etc and instead have an impl= icit parameter in DEFINE_SYSCALL. Then everything would have to be expli= cit. This would probably be a win, although it could be quite a bit of w= ork. It would not be a win - most of the syscalls don't give a damn about 32bit vs. 64bit...