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 66538C43468 for ; Sun, 20 Sep 2020 19:15:06 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id E894720795 for ; Sun, 20 Sep 2020 19:15:05 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="Wk8q/6dL" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org E894720795 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 5A7D690000D; Sun, 20 Sep 2020 15:15:05 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 55865900009; Sun, 20 Sep 2020 15:15:05 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 3D20B90000F; Sun, 20 Sep 2020 15:15:05 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0192.hostedemail.com [216.40.44.192]) by kanga.kvack.org (Postfix) with ESMTP id 1A516900009 for ; Sun, 20 Sep 2020 15:15:05 -0400 (EDT) Received: from smtpin30.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay04.hostedemail.com (Postfix) with ESMTP id D3B0C1EE6 for ; Sun, 20 Sep 2020 19:15:04 +0000 (UTC) X-FDA: 77284392528.30.uncle89_1a160502713e Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin30.hostedemail.com (Postfix) with ESMTP id B7460180B3C83 for ; Sun, 20 Sep 2020 19:15:04 +0000 (UTC) X-HE-Tag: uncle89_1a160502713e X-Filterd-Recvd-Size: 5067 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by imf28.hostedemail.com (Postfix) with ESMTP for ; Sun, 20 Sep 2020 19:15:04 +0000 (UTC) Received: from mail-wm1-f46.google.com (mail-wm1-f46.google.com [209.85.128.46]) (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 2532920809 for ; Sun, 20 Sep 2020 19:15:03 +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-f46.google.com with SMTP id s13so10049060wmh.4 for ; Sun, 20 Sep 2020 12:15:03 -0700 (PDT) X-Gm-Message-State: AOAM533rewzX8bACsu7Ru2UBiKR/7lRrpHmtaiX5KrCcfJC1PZtJ9YBi DtPfUc10mMtB3vPYoKxQ7ie5YzoHnXJ/FW/R3PsQDA== 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" X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: 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