From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <SRS0=KIWy=C3=vger.kernel.org=io-uring-owner@kernel.org>
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
	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 18AB7C43464
	for <io-uring@archiver.kernel.org>; Fri, 18 Sep 2020 13:58:30 +0000 (UTC)
Received: from vger.kernel.org (vger.kernel.org [23.128.96.18])
	by mail.kernel.org (Postfix) with ESMTP id E897020878
	for <io-uring@archiver.kernel.org>; Fri, 18 Sep 2020 13:58:29 +0000 (UTC)
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
        id S1726406AbgIRN63 (ORCPT <rfc822;io-uring@archiver.kernel.org>);
        Fri, 18 Sep 2020 09:58:29 -0400
Received: from lindbergh.monkeyblade.net ([23.128.96.19]:51164 "EHLO
        lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
        with ESMTP id S1726392AbgIRN63 (ORCPT
        <rfc822;io-uring@vger.kernel.org>); Fri, 18 Sep 2020 09:58:29 -0400
Received: from ZenIV.linux.org.uk (zeniv.linux.org.uk [IPv6:2002:c35c:fd02::1])
        by lindbergh.monkeyblade.net (Postfix) with ESMTPS id DEB3AC0613CE;
        Fri, 18 Sep 2020 06:58:28 -0700 (PDT)
Received: from viro by ZenIV.linux.org.uk with local (Exim 4.92.3 #3 (Red Hat Linux))
        id 1kJGu6-0014uQ-9R; Fri, 18 Sep 2020 13:58:22 +0000
Date:   Fri, 18 Sep 2020 14:58:22 +0100
From:   Al Viro <viro@zeniv.linux.org.uk>
To:     Christoph Hellwig <hch@lst.de>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Jens Axboe <axboe@kernel.dk>, Arnd Bergmann <arnd@arndb.de>,
        David Howells <dhowells@redhat.com>,
        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: <20200918135822.GZ3421308@ZenIV.linux.org.uk>
References: <20200918124533.3487701-1-hch@lst.de>
 <20200918124533.3487701-2-hch@lst.de>
 <20200918134012.GY3421308@ZenIV.linux.org.uk>
 <20200918134406.GA17064@lst.de>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20200918134406.GA17064@lst.de>
Precedence: bulk
List-ID: <io-uring.vger.kernel.org>
X-Mailing-List: io-uring@vger.kernel.org

On Fri, Sep 18, 2020 at 03:44:06PM +0200, Christoph Hellwig wrote:
> On Fri, Sep 18, 2020 at 02:40:12PM +0100, Al Viro wrote:
> > >  	/* Vector 0x110 is LINUX_32BIT_SYSCALL_TRAP */
> > > -	return pt_regs_trap_type(current_pt_regs()) == 0x110;
> > > +	return pt_regs_trap_type(current_pt_regs()) == 0x110 ||
> > > +		(current->flags & PF_FORCE_COMPAT);
> > 
> > Can't say I like that approach ;-/  Reasoning about the behaviour is much
> > harder when it's controlled like that - witness set_fs() shite...
> 
> I don't particularly like it either.  But do you have a better idea
> how to deal with io_uring vs compat tasks?

<wry> git rm fs/io_uring.c would make a good starting point </wry>
Yes, I know it's not going to happen, but one can dream...

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...