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=-2.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_SANE_2 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 B889FC432C3 for ; Thu, 14 Nov 2019 08:15:59 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 96A66206EF for ; Thu, 14 Nov 2019 08:15:59 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1573719359; bh=hMyqzpTf+//VUBiUaJT2l3Ku9IgCB9y0boQvKGMnJHY=; h=Date:From:To:Cc:Subject:In-Reply-To:References:List-ID:From; b=0W5DoW5WxBnTL1sobEzuFdjs8Zefl5wHpHtdeuh2RuRpCIO1BpA7ERjSxj2jGCKR7 py7ZsfE3FhRKp4LHKV9I7nvmfCgNqmTdXugVuMWc1WBQNuA1JuuSYiULXNzIk9eBTK 8+V3orEVbcLHZiQ4FM/axIEEoxYsC1jdeRbRo3eI= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726369AbfKNIP6 (ORCPT ); Thu, 14 Nov 2019 03:15:58 -0500 Received: from inca-roads.misterjones.org ([213.251.177.50]:36562 "EHLO inca-roads.misterjones.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725976AbfKNIP6 (ORCPT ); Thu, 14 Nov 2019 03:15:58 -0500 Received: from 78.163-31-62.static.virginmediabusiness.co.uk ([62.31.163.78] helo=why) by cheepnis.misterjones.org with esmtpsa (TLSv1.2:AES256-GCM-SHA384:256) (Exim 4.80) (envelope-from ) id 1iVAIC-0007GE-Cl; Thu, 14 Nov 2019 09:15:52 +0100 Date: Thu, 14 Nov 2019 08:15:50 +0000 From: Marc Zyngier To: Peter Maydell Cc: Christian Borntraeger , kvm-devel , Paolo Bonzini , Radim =?UTF-8?Q?Kr=C4=8Dm=C3=A1=C5=99?= , James Morse , Julien Thierry , Suzuki K Poulose , James Hogan , Paul Mackerras , Janosch Frank , David Hildenbrand , Cornelia Huck , Sean Christopherson , Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel Subject: Re: [PATCH] KVM: Forbid /dev/kvm being opened by a compat task when CONFIG_KVM_COMPAT=n Message-ID: <20191114081550.3c6a7a47@why> In-Reply-To: References: <20191113160523.16130-1-maz@kernel.org> <2b846839-ea81-e40c-5106-90776d964e33@de.ibm.com> Organization: Approximate X-Mailer: Claws Mail 3.17.4 (GTK+ 2.24.32; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-SA-Exim-Connect-IP: 62.31.163.78 X-SA-Exim-Rcpt-To: peter.maydell@linaro.org, borntraeger@de.ibm.com, kvm@vger.kernel.org, pbonzini@redhat.com, rkrcmar@redhat.com, james.morse@arm.com, julien.thierry.kdev@gmail.com, suzuki.poulose@arm.com, jhogan@kernel.org, paulus@ozlabs.org, frankja@linux.ibm.com, david@redhat.com, cohuck@redhat.com, sean.j.christopherson@intel.com, vkuznets@redhat.com, wanpengli@tencent.com, jmattson@google.com, joro@8bytes.org X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on cheepnis.misterjones.org); SAEximRunCond expanded to false Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On Wed, 13 Nov 2019 21:23:07 +0000 Peter Maydell wrote: > On Wed, 13 Nov 2019 at 18:44, Christian Borntraeger > wrote: > > On 13.11.19 17:05, Marc Zyngier wrote: > > > On a system without KVM_COMPAT, we prevent IOCTLs from being issued > > > by a compat task. Although this prevents most silly things from > > > happening, it can still confuse a 32bit userspace that is able > > > to open the kvm device (the qemu test suite seems to be pretty > > > mad with this behaviour). > > > > > > Take a more radical approach and return a -ENODEV to the compat > > > task. > > > Do we still need compat_ioctl if open never succeeds? > > I wondered about that, but presumably you could use > fd-passing, or just inheriting open fds across exec(), > to open the fd in a 64-bit process and then hand it off > to a 32-bit process to call the ioctl with. (That's > probably only something you'd do if you were > deliberately playing silly games, of course, but > preventing silly games is useful as it makes it > easier to reason about kernel behaviour.) This was exactly my train of thoughts, which I should have made clear in the commit log. Thanks Peter for reading my mind! ;-) M. -- Jazz is not dead. It just smells funny...