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=-5.6 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,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 D7E9CC4346A for ; Sun, 20 Sep 2020 19:15:06 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id A0184207D3 for ; Sun, 20 Sep 2020 19:15:06 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1600629306; bh=01MigO53P6iyZydtBYB0dVEV2Jvv4nS2ce79nd2bE4Q=; h=References:In-Reply-To:From:Date:Subject:To:Cc:List-ID:From; b=rrkchG0WNzY7RNTWloHVxhrZKK3/oulqct0qE+kpxQ1wBfjeW6Ezy+otKk84nT466 R4leq01VOEPAOK/sQ3ohlMcalBiqiDvXnCj51M5+svoBVEy7F3BMahYYcTW5ZrLZek mC1AE71Zx5MEhnOTEQBQeG9JzjjbEYOcAvCjVcOU= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726178AbgITTPF (ORCPT ); Sun, 20 Sep 2020 15:15:05 -0400 Received: from mail.kernel.org ([198.145.29.99]:60152 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726221AbgITTPE (ORCPT ); Sun, 20 Sep 2020 15:15:04 -0400 Received: from mail-wm1-f43.google.com (mail-wm1-f43.google.com [209.85.128.43]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id C98602311D for ; Sun, 20 Sep 2020 19:15:02 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1600629303; bh=01MigO53P6iyZydtBYB0dVEV2Jvv4nS2ce79nd2bE4Q=; h=References:In-Reply-To:From:Date:Subject:To:Cc:From; b=Wk8q/6dLv8zgmnj6frKsNEMKKbkKgfK14ioTWVmkH7d8IpexStF61cruMi2XHvhA8 doLJhfcTQOHJbboIkLR9Ergg8mqu95ZgaifCJQWLC7i89TWc2osLpGGy7ezgQQQkzJ pDe1LbO4UQSuO8vfRtnIhj1TQBZOGhFNdwz0H6Iw= Received: by mail-wm1-f43.google.com with SMTP id y15so10414989wmi.0 for ; Sun, 20 Sep 2020 12:15:02 -0700 (PDT) X-Gm-Message-State: AOAM531B3ZxY6n1jYv6k/SCWtCW3H9kxRLIu8+t73Bzk6PYMxVNGQ3D6 Pd0pFuSROb8sjvQzLF/pSkj2Hb9OKFi1Qd0FIySbrA== X-Google-Smtp-Source: ABdhPJznW7DCp463LJOKwLIqH+/ZeaOskntfIIXR0IAAA+ZM4omIXer1gN2IBUUGrBDkxuviLF20WI9Nmbt3oWZvbk0= X-Received: by 2002:a05:600c:2183:: with SMTP id e3mr27891946wme.49.1600629301119; Sun, 20 Sep 2020 12:15:01 -0700 (PDT) MIME-Version: 1.0 References: <20200918124533.3487701-1-hch@lst.de> <20200918124533.3487701-2-hch@lst.de> <20200920151510.GS32101@casper.infradead.org> <20200920180742.GN3421308@ZenIV.linux.org.uk> In-Reply-To: <20200920180742.GN3421308@ZenIV.linux.org.uk> From: Andy Lutomirski Date: Sun, 20 Sep 2020 12:14:49 -0700 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH 1/9] kernel: add a PF_FORCE_COMPAT flag To: Al Viro Cc: Matthew Wilcox , Christoph Hellwig , Andrew Morton , Jens Axboe , Arnd Bergmann , David Howells , linux-arm-kernel , X86 ML , LKML , "open list:MIPS" , Parisc List , linuxppc-dev , linux-s390 , sparclinux , linux-block , Linux SCSI List , Linux FS Devel , linux-aio , io-uring@vger.kernel.org, linux-arch , Linux-MM , Network Development , keyrings@vger.kernel.org, LSM List Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: io-uring@vger.kernel.org On Sun, Sep 20, 2020 at 11:07 AM Al Viro wrote: > > On Sun, Sep 20, 2020 at 04:15:10PM +0100, Matthew Wilcox wrote: > > On Fri, Sep 18, 2020 at 02:45:25PM +0200, Christoph Hellwig wrote: > > > Add a flag to force processing a syscall as a compat syscall. This is > > > required so that in_compat_syscall() works for I/O submitted by io_uring > > > helper threads on behalf of compat syscalls. > > > > Al doesn't like this much, but my suggestion is to introduce two new > > opcodes -- IORING_OP_READV32 and IORING_OP_WRITEV32. The compat code > > can translate IORING_OP_READV to IORING_OP_READV32 and then the core > > code can know what that user pointer is pointing to. > > Let's separate two issues: > 1) compat syscalls want 32bit iovecs. Nothing to do with the > drivers, dealt with just fine. > 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. > I wonder if this is really quite cast in stone. We could also have FMODE_SHITTY_COMPAT and set that when a file like this is *opened* in compat mode. Then that particular struct file would be read and written using the compat data format. The change would be user-visible, but the user that would see it would be very strange indeed. I don't have a strong opinion as to whether that is better or worse than denying io_uring access to these things, but at least it moves the special case out of io_uring. --Andy