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=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 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 8FCF5C432C3 for ; Thu, 14 Nov 2019 08:20:36 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 6BCF520725 for ; Thu, 14 Nov 2019 08:20:36 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726115AbfKNIUf (ORCPT ); Thu, 14 Nov 2019 03:20:35 -0500 Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:6658 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1725920AbfKNIUf (ORCPT ); Thu, 14 Nov 2019 03:20:35 -0500 Received: from pps.filterd (m0098417.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.16.0.27/8.16.0.27) with SMTP id xAE8Gp4e052513 for ; Thu, 14 Nov 2019 03:20:33 -0500 Received: from e06smtp07.uk.ibm.com (e06smtp07.uk.ibm.com [195.75.94.103]) by mx0a-001b2d01.pphosted.com with ESMTP id 2w91npk8mk-1 (version=TLSv1.2 cipher=AES256-GCM-SHA384 bits=256 verify=NOT) for ; Thu, 14 Nov 2019 03:20:33 -0500 Received: from localhost by e06smtp07.uk.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! 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Violators will be prosecuted; (version=TLSv1/SSLv3 cipher=AES256-GCM-SHA384 bits=256/256) Thu, 14 Nov 2019 08:20:25 -0000 Received: from d06av26.portsmouth.uk.ibm.com (d06av26.portsmouth.uk.ibm.com [9.149.105.62]) by b06cxnps4076.portsmouth.uk.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id xAE8KOHR52756568 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Thu, 14 Nov 2019 08:20:24 GMT Received: from d06av26.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 3AE23AE04D; Thu, 14 Nov 2019 08:20:24 +0000 (GMT) Received: from d06av26.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id AFED3AE045; Thu, 14 Nov 2019 08:20:23 +0000 (GMT) Received: from oc7455500831.ibm.com (unknown [9.152.224.80]) by d06av26.portsmouth.uk.ibm.com (Postfix) with ESMTP; Thu, 14 Nov 2019 08:20:23 +0000 (GMT) Subject: Re: [PATCH] KVM: Forbid /dev/kvm being opened by a compat task when CONFIG_KVM_COMPAT=n To: Marc Zyngier , Peter Maydell Cc: kvm-devel , Paolo Bonzini , =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= , 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 References: <20191113160523.16130-1-maz@kernel.org> <2b846839-ea81-e40c-5106-90776d964e33@de.ibm.com> <20191114081550.3c6a7a47@why> From: Christian Borntraeger Autocrypt: addr=borntraeger@de.ibm.com; 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Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.2.0 MIME-Version: 1.0 In-Reply-To: <20191114081550.3c6a7a47@why> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 x-cbid: 19111408-0028-0000-0000-000003B6C512 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 19111408-0029-0000-0000-00002479D0CF Message-Id: <5576baca-458e-3206-bdc5-5fb8da00cf6d@de.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2019-11-14_01:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 suspectscore=0 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 mlxscore=0 impostorscore=0 mlxlogscore=841 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1910280000 definitions=main-1911140079 Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On 14.11.19 09:15, Marc Zyngier wrote: > 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! ;-) Makes sense. Looks like this is already in kvm/master so we cannot improve the commit message easily any more. Hopefully we will not forget :-)