From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from lindbergh.monkeyblade.net ([23.128.96.19]:59802 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726109AbgITTCJ (ORCPT ); Sun, 20 Sep 2020 15:02:09 -0400 Date: Sun, 20 Sep 2020 20:01:59 +0100 From: Matthew Wilcox 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> List-ID: To: Al Viro 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 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)