Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Date:   Sun, 20 Sep 2020 20:01:59 +0100
From:   Matthew Wilcox <willy@infradead.org>
To:     Al Viro <viro@zeniv.linux.org.uk>
Cc:     Christoph Hellwig <hch@lst.de>,
        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: <20200920190159.GT32101@casper.infradead.org>
References: <20200918124533.3487701-1-hch@lst.de>
 <20200918124533.3487701-2-hch@lst.de>
 <20200920151510.GS32101@casper.infradead.org>
 <20200920180742.GN3421308@ZenIV.linux.org.uk>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20200920180742.GN3421308@ZenIV.linux.org.uk>
Precedence: bulk

On Sun, Sep 20, 2020 at 07:07:42PM +0100, Al Viro wrote:
> 	2) a few drivers are really fucked in head.  They use different
> *DATA* layouts for reads/writes, depending upon the calling process.
> IOW, if you fork/exec a 32bit binary and your stdin is one of those,
> reads from stdin in parent and child will yield different data layouts.
> On the same struct file.
> 	That's what Christoph worries about (/dev/sg he'd mentioned is
> one of those).
> 
> 	IMO we should simply have that dozen or so of pathological files
> marked with FMODE_SHITTY_ABI; it's not about how they'd been opened -
> it describes the userland ABI provided by those.  And it's cast in stone.
> 
> 	Any in_compat_syscall() in ->read()/->write() instances is an ABI
> bug, plain and simple.  Some are unfixable for compatibility reasons, but
> any new caller like that should be a big red flag.

So an IOCB_COMPAT flag would let us know whether the caller is expecting
a 32-bit or 64-bit layout?  And io_uring could set it based on the
ctx->compat flag.

> 	Current list of those turds:
> /dev/sg (pointer-chasing, generally insane)
> /sys/firmware/efi/vars/*/raw_var (fucked binary structure)
> /sys/firmware/efi/vars/new_var (fucked binary structure)
> /sys/firmware/efi/vars/del_var (fucked binary structure)
> /dev/uhid	(pointer-chasing for one obsolete command)
> /dev/input/event* (timestamps)
> /dev/uinput (timestamps)
> /proc/bus/input/devices (fucked bitmap-to-text representation)
> /sys/class/input/*/capabilities/* (fucked bitmap-to-text representation)