From mboxrd@z Thu Jan  1 00:00:00 1970
From: Andy Lutomirski <luto@kernel.org>
Date: Sat, 19 Sep 2020 16:21:44 +0000
Subject: Re: [PATCH 1/9] kernel: add a PF_FORCE_COMPAT flag
Message-Id: <CALCETrW=BzodXeTAjSvpCoUQoL+MKaKPEeSTRWnB=-C9jMotbQ@mail.gmail.com>
MIME-Version: 1.0
Content-Type: text/plain; charset="us-ascii"
Content-Transfer-Encoding: 7bit
List-Id: <keyrings.vger.kernel.org>
References: <20200918124533.3487701-1-hch@lst.de> <20200918124533.3487701-2-hch@lst.de>
 <20200918134012.GY3421308@ZenIV.linux.org.uk> <20200918134406.GA17064@lst.de>
 <20200918135822.GZ3421308@ZenIV.linux.org.uk> <20200918151615.GA23432@lst.de>
In-Reply-To: <20200918151615.GA23432@lst.de>
To: Christoph Hellwig <hch@lst.de>
Cc: Al Viro <viro@zeniv.linux.org.uk>, Andrew Morton <akpm@linux-foundation.org>, Jens Axboe <axboe@kernel.dk>, Arnd Bergmann <arnd@arndb.de>, David Howells <dhowells@redhat.com>, linux-arm-kernel <linux-arm-kernel@lists.infradead.org>, X86 ML <x86@kernel.org>, LKML <linux-kernel@vger.kernel.org>, "open list:MIPS" <linux-mips@vger.kernel.org>, Parisc List <linux-parisc@vger.kernel.org>, linuxppc-dev <linuxppc-dev@lists.ozlabs.org>, linux-s390 <linux-s390@vger.kernel.org>, sparclinux <sparclinux@vger.kernel.org>, linux-block <linux-block@vger.kernel.org>, Linux SCSI List <linux-scsi@vger.kernel.org>, Linux FS Devel <linux-fsdevel@vger.kernel.org>, linux-aio@kvack.org, io-uring@vger.kernel.org, linux-arch <linux-arch@vger.kernel.org>, Linux-MM <linux-mm@kvack.org>, Network Development <netdev@vger.kernel.org>, keyrings@vger.kernel.org, LSM List <linux-security-module@vger.kernel.org>

On Fri, Sep 18, 2020 at 8:16 AM Christoph Hellwig <hch@lst.de> 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.

Aside from the potentially nasty use of per-task variables, one thing
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 full
override of the syscall arch instead of just allowing forcing compat
so that a compat syscall can do a non-compat operation?