From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mx0a-001b2d01.pphosted.com (mx0a-001b2d01.pphosted.com [148.163.156.1]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id B31BB37EFFB; Wed, 12 Aug 2026 20:02:57 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=148.163.156.1 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786564979; cv=none; b=u7H5lv8HTTppqbQvCxNaOEQNzwRIKkOyaGrwd1iJMDL+kZkKcq5J/vdHvwMikMlJBaElsD7kTJhVm9jFKizXOjlH+pz31Vt0cr8LWaQdURuqXglPt7rkri7AtHk0yB8B2LSivTEXT1ZQmHnbHligY5LToxFjqfHsG6AhedRCmeo= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786564979; c=relaxed/simple; bh=fW5pD8sDwhcCDXWf8ZIJJ55PI3tKhL6NSCRDBnsVJy8=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=Piv+Dnv5DSVkX9YSLVmtP5CsMWabPLfUDFzP8b3+REksWd3p3d3u2k34voQt9FexQWdEJEJvkGdwTNCKI0Nca0CpHsy+gxagoTQUlZ2lXqQqZLlGNgFm6ASHdkvicMwwO7BBci95YHm+VudNNP2PVdHNrMfOPjJu7OUef0fZeYI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.ibm.com; spf=pass smtp.mailfrom=linux.ibm.com; dkim=pass (2048-bit key) header.d=ibm.com header.i=@ibm.com header.b=Sr7j0rij; arc=none smtp.client-ip=148.163.156.1 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.ibm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.ibm.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=ibm.com header.i=@ibm.com header.b="Sr7j0rij" Received: from pps.filterd (m0360083.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.18.1.11/8.18.1.11) with ESMTP id 67CK2n4O242690; Wed, 12 Aug 2026 20:02:51 GMT DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=ibm.com; h=cc :content-transfer-encoding:date:from:in-reply-to:message-id :mime-version:references:subject:to; s=pp1; bh=9zSYwEpZLHwXh7QUa MzdW+WRNO+WXyysEw6YZbqHS/w=; b=Sr7j0rijk7sSCf2vX38ioD10BnTisGNgs C8UFiZO7ekWIXhREsWDvz1XBnKM43Nx5lGOY/bUJZlqOhf3avTvN3s9i9zYxexcD 5+3mJO12VR4ALTDHBhVxa545jyaaI579yOnT3jN6Odsos+h25MLS/+uQSt+pym8J kdzIRSORTPFM3ly7ebRQv+LeycCRp/JYbPW3+UZl7km7Sn25J+avXJVfg5sKEaFp tVeHE1Rz1UfEuFPvMw9UNd78Q8rjgbTj89O7H8OUDidCoA/Q3gCXWXlnxR4rFuas CRQlqkKvsHvPoqZL/VScSjOxDRKPn57SCwdXn/Uc8/w+6U7aCiiMw== Received: from ppma11.dal12v.mail.ibm.com (db.9e.1632.ip4.static.sl-reverse.com [50.22.158.219]) by mx0a-001b2d01.pphosted.com (PPS) with ESMTPS id 4fwvq9meh5-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Wed, 12 Aug 2026 20:02:50 +0000 (GMT) Received: from pps.filterd (ppma11.dal12v.mail.ibm.com [127.0.0.1]) by ppma11.dal12v.mail.ibm.com (8.18.1.7/8.18.1.7) with ESMTP id 67CJuXJX005189; Wed, 12 Aug 2026 20:02:49 GMT Received: from smtprelay03.wdc07v.mail.ibm.com ([172.16.1.70]) by ppma11.dal12v.mail.ibm.com (PPS) with ESMTPS id 4fxhfy7krk-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Wed, 12 Aug 2026 20:02:49 +0000 (GMT) Received: from smtpav04.wdc07v.mail.ibm.com (smtpav04.wdc07v.mail.ibm.com [10.39.53.231]) by smtprelay03.wdc07v.mail.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id 67CK2AhM11600638 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Wed, 12 Aug 2026 20:02:10 GMT Received: from smtpav04.wdc07v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 4F39658050; Wed, 12 Aug 2026 20:02:48 +0000 (GMT) Received: from smtpav04.wdc07v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id B4F0658045; Wed, 12 Aug 2026 20:02:46 +0000 (GMT) Received: from li-4c4c4544-004d-4810-8043-b7c04f423534.ibm.com.com (unknown [9.61.9.29]) by smtpav04.wdc07v.mail.ibm.com (Postfix) with ESMTP; Wed, 12 Aug 2026 20:02:46 +0000 (GMT) From: Anthony Krowiak To: linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org, kvm@vger.kernel.org Cc: jjherne@linux.ibm.com, borntraeger@de.ibm.com, mjrosato@linux.ibm.com, pasic@linux.ibm.com, alex@shazbot.org, kwankhede@nvidia.com, fiuczy@linux.ibm.com, pbonzini@redhat.com, frankja@linux.ibm.com, imbrenda@linux.ibm.com, agordeev@linux.ibm.com, hca@linux.ibm.com, gor@linux.ibm.com, stable@vger.kernel.org Subject: [PATCH v5 3/9] s390/vfio-ap: Fix missing lock required to access list of ap_matrix_mdev objects Date: Wed, 12 Aug 2026 16:02:34 -0400 Message-ID: <20260812200240.818004-4-akrowiak@linux.ibm.com> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260812200240.818004-1-akrowiak@linux.ibm.com> References: <20260812200240.818004-1-akrowiak@linux.ibm.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-TM-AS-GCONF: 00 X-Proofpoint-GUID: UviUfKZbtAMZzW0GtYftrv3vLP29CbH_ X-Authority-Analysis: v=2.4 cv=PbDPQChd c=1 sm=1 tr=0 ts=6a7cd16a cx=c_pps a=aDMHemPKRhS1OARIsFnwRA==:117 a=aDMHemPKRhS1OARIsFnwRA==:17 a=Sv0fKeRqtYgA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=iQ6ETzBq9ecOQQE5vZCe:22 a=VwQbUJbxAAAA:8 a=VnNF1IyMAAAA:8 a=9go2EFdEqeYIEFJGgSIA:9 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwODEyMDE2MSBTYWx0ZWRfX3+hClaubEFd3 osrMWWlaCa3HUiKoQoF1/+ccpKQx80ajmxs2CatukAMFaH+zvnxenUz0CctfiKyPs5UicDswUGJ 4h+ch7ArEtjGYKDDZraT7lX7KhJqEjenvCy9pUMBMTkFU/sPETgT2A0lBH6FFUu08plo8s8ROS+ +IqB/B15PCZZPRhDZOtynhnc5tveIGU1mmN4OqAkAE9MgOR/YtJ0ecVAWhdSeuDjFooyVRLUxHt 6Ovj0YD9usy/2WSnl4fPLW01z35IVtLYMFWC4gzHchhkAHSLw80rk+8HO4O4BtMn9iZE3LpHtga VJw8nQDYk3XYwUbaEwbdEUHqQlzpJWibvEpWuBq9amZE3cvII6D4xbnBY/klL9pTTvaXuTvZZEl T4ES4aI1LE0veK4n4NHxnF3IWbxgo3jAgNR1EcrusZK5D8JEwmQha0/FhFcfATgEbvRdq7m7KDX Y+JC7aS4mGA0uLL9grA== X-Proofpoint-ORIG-GUID: UviUfKZbtAMZzW0GtYftrv3vLP29CbH_ X-Proofpoint-Spam-Info: AW1haW4tMjYwODEyMDE2MSBTYWx0ZWRfXxxmndHviwsqw LE70bnNlG6PLwA+SzqfpFxZbTsbmutUxjz1++kuOl7cfZYrIYYqqxd7/GZLE/0CLEZlE0gqS6v7 f6nKqOZ+Hb9vMjt1AXpu6otBL1HshSM= X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1176,Hydra:6.1.134,FMLib:17.12.100.49 definitions=2026-08-12_06,2026-08-12_01,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 bulkscore=0 impostorscore=0 malwarescore=0 adultscore=0 clxscore=1015 priorityscore=1501 suspectscore=0 phishscore=0 lowpriorityscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2606150000 definitions=main-2608120161 In order to traverse or add/remove ap_matrix_mdev objects in the matrix_dev->mdev_list, the matrix_dev->guests_lock mutex must be held. There are two functions that access the list without holding the mutex: vfio_ap_mdev_probe function ~~~~~~~~~~~~~~~~~~~~~~~~~~~ The vfio_ap_mdev_probe function uses the matrix_dev->mdevs_lock mutex to guard the add of a newly created ap_matrix_mdev object to the matrix_dev->mdev_list. This mutex does not protect list access; its purpose is to guard against concurrent access to fields contained in an ap_matrix_mdev object. This could lead to kernel memory corruption or use-after-free if another mdev is created or removed concurrently. The adding of an ap_matrix_mdev object to matrix_dev->mdev_list is now guarded by the matrix_dev->guests_lock which is the correct way to protect against concurrent mdev_list access. Also removed the following two lines of code because the matrix_mdev is allocated via vfio_alloc_device macro which uses kzalloc, so req_trigger and cfg_chg_trigger are already zero-initialised when the struct is allocated before the call to vfio_register_emulated_iommu_dev. This prevents a window whereby these triggers are set to NULL after the device is exposed to userspace. matrix_mdev->req_trigger = NULL; matrix_mdev->cfg_chg_trigger = NULL; vfio_ap_mdev_for_queue function ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ The status_show function that supports display of the status attribute of the devices in /sys/bus/ap/devices calls the vfio_ap_mdev_for_queue function which iterates the matrix_dev->mdev_list to find the object representing the queue device whose status is to be displayed. In order to traverse this list, the matrix_dev->guests_lock mutex must be held. To fix this, the guests_lock mutex is taken prior to taking the matrix_dev->mdevs_lock mutex in the status_show function. It is taken there rather than the vfio_ap_mdev_for_queue function - where it is needed - because it must be taken prior to the mdevs_lock mutex in order to adhere to the proper locking order and prevent a lockdep splat; also because the mdevs_lock is needed there to access fields within the matrix_mdev object in that function. See the vfio-ap-locking.rst in the linux kernel tree. Fixes: 2c1ee8983aa3 ("s390/vfio-ap: prepare for dynamic update of guest's APCB on queue probe/remove") Cc: stable@vger.kernel.org Signed-off-by: Anthony Krowiak Reviewed-by: Matthew Rosato --- drivers/s390/crypto/vfio_ap_ops.c | 27 +++++++++++++++++++++++---- 1 file changed, 23 insertions(+), 4 deletions(-) diff --git a/drivers/s390/crypto/vfio_ap_ops.c b/drivers/s390/crypto/vfio_ap_ops.c index c6bee69cc22f..f2d662e388bd 100644 --- a/drivers/s390/crypto/vfio_ap_ops.c +++ b/drivers/s390/crypto/vfio_ap_ops.c @@ -800,12 +800,17 @@ static int vfio_ap_mdev_probe(struct mdev_device *mdev) ret = vfio_register_emulated_iommu_dev(&matrix_mdev->vdev); if (ret) goto err_put_vdev; - matrix_mdev->req_trigger = NULL; - matrix_mdev->cfg_chg_trigger = NULL; + + /* + * Take the matrix_dev->guests_lock mutex before adding the matrix_mdev + * to the mdev_list. All functions that traverse the list must also hold + * this lock to guard against additions to or removals from the list + * while it is being traversed. + */ + mutex_lock(&matrix_dev->guests_lock); dev_set_drvdata(&mdev->dev, matrix_mdev); - mutex_lock(&matrix_dev->mdevs_lock); list_add(&matrix_mdev->node, &matrix_dev->mdev_list); - mutex_unlock(&matrix_dev->mdevs_lock); + mutex_unlock(&matrix_dev->guests_lock); return 0; err_put_vdev: @@ -2297,6 +2302,8 @@ static struct ap_matrix_mdev *vfio_ap_mdev_for_queue(struct vfio_ap_queue *q) unsigned long apid = AP_QID_CARD(q->apqn); unsigned long apqi = AP_QID_QUEUE(q->apqn); + lockdep_assert_held(&matrix_dev->guests_lock); + list_for_each_entry(matrix_mdev, &matrix_dev->mdev_list, node) { if (test_bit_inv(apid, matrix_mdev->matrix.apm) && test_bit_inv(apqi, matrix_mdev->matrix.aqm)) @@ -2316,6 +2323,7 @@ static ssize_t status_show(struct device *dev, struct ap_matrix_mdev *matrix_mdev; struct ap_device *apdev = to_ap_dev(dev); + mutex_lock(&matrix_dev->guests_lock); mutex_lock(&matrix_dev->mdevs_lock); q = dev_get_drvdata(&apdev->device); matrix_mdev = vfio_ap_mdev_for_queue(q); @@ -2343,6 +2351,7 @@ static ssize_t status_show(struct device *dev, } mutex_unlock(&matrix_dev->mdevs_lock); + mutex_unlock(&matrix_dev->guests_lock); return nchars; } @@ -2761,6 +2770,12 @@ static void vfio_ap_mdev_cfg_add(unsigned long *apm_add, unsigned long *aqm_add, vfio_ap_filter_apid_by_qtype(apm_add, aqm_add); + /* + * It is safe to traverse this list here because the + * required guard - matrix_dev->guests_lock - is taken in the + * vfio_ap_on_cfg_changed function prior to this function getting + * called. + */ list_for_each_entry(matrix_mdev, &matrix_dev->mdev_list, node) { bitmap_and(matrix_mdev->apm_add, matrix_mdev->matrix.apm, apm_add, AP_DEVICES); @@ -2820,6 +2835,10 @@ void vfio_ap_on_cfg_changed(struct ap_config_info *cur_cfg_info, if (!cur_cfg_info || !prev_cfg_info) return; + /* + * Take the guests_lock mutex here to guard access to the + * matrix_dev->mdev_list in the two functions called below. + */ mutex_lock(&matrix_dev->guests_lock); vfio_ap_mdev_on_cfg_remove(cur_cfg_info, prev_cfg_info); -- 2.53.0