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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id EE727C77B61 for ; Thu, 27 Apr 2023 11:47:08 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S243729AbjD0LrF (ORCPT ); Thu, 27 Apr 2023 07:47:05 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:45576 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S243201AbjD0LrE (ORCPT ); Thu, 27 Apr 2023 07:47:04 -0400 Received: from mx0a-001b2d01.pphosted.com (mx0a-001b2d01.pphosted.com [148.163.156.1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id E03454C01; Thu, 27 Apr 2023 04:47:02 -0700 (PDT) Received: from pps.filterd (m0353726.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.17.1.19/8.17.1.19) with ESMTP id 33RBawxf005329; 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Thu, 27 Apr 2023 11:46:58 GMT Received: from smtprelay07.fra02v.mail.ibm.com ([9.218.2.229]) by ppma03fra.de.ibm.com (PPS) with ESMTPS id 3q47772e1v-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Thu, 27 Apr 2023 11:46:58 +0000 Received: from smtpav02.fra02v.mail.ibm.com (smtpav02.fra02v.mail.ibm.com [10.20.54.101]) by smtprelay07.fra02v.mail.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id 33RBkpqM42533216 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Thu, 27 Apr 2023 11:46:51 GMT Received: from smtpav02.fra02v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 8F06A20063; Thu, 27 Apr 2023 11:46:51 +0000 (GMT) Received: from smtpav02.fra02v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 4380E2004F; Thu, 27 Apr 2023 11:46:51 +0000 (GMT) Received: from p-imbrenda (unknown [9.152.224.56]) by smtpav02.fra02v.mail.ibm.com (Postfix) with ESMTP; Thu, 27 Apr 2023 11:46:51 +0000 (GMT) Date: Thu, 27 Apr 2023 13:46:49 +0200 From: Claudio Imbrenda To: Heiko Carstens Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org, linux-s390@vger.kernel.org, frankja@linux.ibm.com, borntraeger@de.ibm.com, nrb@linux.ibm.com, nsg@linux.ibm.com, seiden@linux.ibm.com, jgg@nvidia.com Subject: Re: [PATCH v2 1/1] KVM: s390: fix race in gmap_make_secure Message-ID: <20230427134649.1e482d91@p-imbrenda> In-Reply-To: References: <20230426134834.35199-1-imbrenda@linux.ibm.com> <20230426134834.35199-2-imbrenda@linux.ibm.com> Organization: IBM X-Mailer: Claws Mail 4.1.1 (GTK 3.24.35; x86_64-redhat-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-GUID: 2dfRSZKvCdx--75g5gZXU2l6elzZK5lg X-Proofpoint-ORIG-GUID: 2dfRSZKvCdx--75g5gZXU2l6elzZK5lg X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.254,Aquarius:18.0.942,Hydra:6.0.573,FMLib:17.11.170.22 definitions=2023-04-27_07,2023-04-27_01,2023-02-09_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 bulkscore=0 impostorscore=0 mlxlogscore=613 lowpriorityscore=0 suspectscore=0 priorityscore=1501 clxscore=1015 spamscore=0 adultscore=0 phishscore=0 mlxscore=0 malwarescore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2303200000 definitions=main-2304270102 Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On Thu, 27 Apr 2023 12:53:04 +0200 Heiko Carstens wrote: > On Wed, Apr 26, 2023 at 03:48:34PM +0200, Claudio Imbrenda wrote: > > This patch fixes a potential race in gmap_make_secure and removes the > > last user of follow_page without FOLL_GET. > > > > Signed-off-by: Claudio Imbrenda > > Suggested-by: Jason Gunthorpe > > Fixes: 214d9bbcd3a6 ("s390/mm: provide memory management functions for protected KVM guests") > > --- > > arch/s390/kernel/uv.c | 32 +++++++++++--------------------- > > 1 file changed, 11 insertions(+), 21 deletions(-) > > It would be helpful if this would be a bit more descriptive. "Fix > race" is not very helpful :) > > What race does this fix? > When can this happen? > What are the consequences if the race window is being hit? We are locking something we don't have a reference to, and as explained by Jason and David in this thread it can lead to all kind of bad things, including the page getting unmapped (MADV_DONTNEED), freed, reallocated as a larger folio and the unlock_page() would target the wrong bit. Also there is another race with the FOLL_WRITE, which could race between the follow_page and the get_locked_pte. The main point of the patch is to remove the last follow_page without FOLL_GET or FOLL_PIN, removing the races can be considered a nice bonus.