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Wed, 12 Aug 2026 20:02:55 +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 20:02:55 +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 8/9] s390/vfio-ap: Fix NULL deref in status_show() during queue probe Date: Wed, 12 Aug 2026 16:02:39 -0400 Message-ID: <20260812200240.818004-9-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-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-TM-AS-GCONF: 00 X-Authority-Analysis: v=2.4 cv=RsP16imK c=1 sm=1 tr=0 ts=6a7cd173 cx=c_pps a=AfN7/Ok6k8XGzOShvHwTGQ==:117 a=AfN7/Ok6k8XGzOShvHwTGQ==:17 a=IkcTkHD0fZMA:10 a=Sv0fKeRqtYgA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=RzCfie-kr_QcCd8fBx8p:22 a=VwQbUJbxAAAA:8 a=VnNF1IyMAAAA:8 a=apN4ZTo8cY6xQFFfCyEA:9 a=3ZKOabzyN94A:10 a=QEXdDO2ut3YA:10 X-Proofpoint-GUID: ilKaj3sBk0HyDnN13kVmTbKMDsZtbK5q X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwODEyMDE2MSBTYWx0ZWRfX/tok9fgkjMjn rPRgev8ak8wlcia70UCGz45bbwUWp0rSK1RmNOtvd4h29J6LniqnlUmtzCa0ZAjjA3FYPXFmK+V 4RdOOrts4M6u9TEDlErkSVNc3R2ZygFmQA+0yj04RpThUT+vXbQUERHBNlK688ryeMlGQYXCI5J kyYp/6nyl66uCPypVXL7WblL4z9WcOZf+iv+QgP/FNn6dqblgZkuOVCU7ZWCk0eR85h3GdN396G nEJalQvMKJjnR+dui9aufd6JmFkReoAR6S4KGOdNi8nXv7NLBFjxvLh64x0Mt+rBoh1C5WBB233 dghjZd8EsUMXgMy8EkTsT/v4Mkcj91Qyw6jhH94GK28wwjsnelmFcD9aNcvFhh8rkUehcetjeAC uZY+QPoqzC+8h/JdHenPPhGQ39z2N4gC3W66Up/eLkQ0eKkVClIM1EpXIF3ED91q67p+KdrqZan U6c2dW7AYFdGXarKzAA== X-Proofpoint-ORIG-GUID: ilKaj3sBk0HyDnN13kVmTbKMDsZtbK5q X-Proofpoint-Spam-Info: AW1haW4tMjYwODEyMDE2MSBTYWx0ZWRfX2q8WNvZRrC3b URMWTponMTBqebt9YacSps7wSlRzN+6eHPZjeRa+i8XHlSHvgMOb6XROexsp7KO4kj/SKEN9bAw 0SK+VMm1ZM9ggJQE5mR2yCRv1oAJay4= 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 impostorscore=0 suspectscore=0 clxscore=1015 malwarescore=0 phishscore=0 adultscore=0 lowpriorityscore=0 priorityscore=1501 bulkscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2606150000 definitions=main-2608120161 When vfio_ap_mdev_probe_queue() creates the sysfs attribute group, the queue's driver data has not yet been set. A concurrent read of the 'status' attribute can therefore call dev_get_drvdata() and get NULL, which is then passed directly to vfio_ap_mdev_for_queue() where q->apqn is unconditionally dereferenced, causing a NULL pointer dereference. Fix this by acquiring the update locks before calling sysfs_create_group(). The status_show() function acquires guests_lock before reading the driver data, so any concurrent read will block until after dev_set_drvdata() has been called and the update locks are released. As a bonus, the APQN no longer needs to be read from the queue struct after allocation — it can be read directly from apdev before allocation and stored in a local variable, which is then assigned to q->apqn once the allocation succeeds. Fixes: 260f3ea141382 ("s390/vfio-ap: move probe and remove callbacks to vfio_ap_ops.c") Cc: stable@vger.kernel.org Signed-off-by: Anthony Krowiak --- drivers/s390/crypto/vfio_ap_ops.c | 33 +++++++++++++++++++++++++++---- 1 file changed, 29 insertions(+), 4 deletions(-) diff --git a/drivers/s390/crypto/vfio_ap_ops.c b/drivers/s390/crypto/vfio_ap_ops.c index 16779cfc64e8..1edd0b7a3cce 100644 --- a/drivers/s390/crypto/vfio_ap_ops.c +++ b/drivers/s390/crypto/vfio_ap_ops.c @@ -2326,6 +2326,23 @@ static ssize_t status_show(struct device *dev, mutex_lock(&matrix_dev->guests_lock); mutex_lock(&matrix_dev->mdevs_lock); q = dev_get_drvdata(&apdev->device); + + /* + * Make sure the drvdata has been set before proceeding. There is a + * possibility that the drvdata was not set if the vfio_ap_queue object + * could not be allocated when the queue device was probed. In that case, + * the locks used in vfio_ap_mdev_probe_queue() are released prior to + * removing the sysfs status attribute to avoid a lockdep + * splat. That opens a very small window where the status attribute is + * still available without the vfio_ap_queue object having been + * stored in the device drvdata. In that case, indicate the queue is not + * assigned. + */ + if (!q) { + nchars = sysfs_emit(buf, "%s\n", AP_QUEUE_UNASSIGNED); + goto done; + } + matrix_mdev = vfio_ap_mdev_for_queue(q); /* If the queue is assigned to the matrix mediated device, then @@ -2350,6 +2367,7 @@ static ssize_t status_show(struct device *dev, nchars = sysfs_emit(buf, "%s\n", AP_QUEUE_UNASSIGNED); } +done: mutex_unlock(&matrix_dev->mdevs_lock); mutex_unlock(&matrix_dev->guests_lock); @@ -2424,14 +2442,17 @@ void vfio_ap_mdev_unregister(void) int vfio_ap_mdev_probe_queue(struct ap_device *apdev) { - int ret; + int ret, apqn; struct vfio_ap_queue *q; DECLARE_BITMAP(apm_filtered, AP_DEVICES); struct ap_matrix_mdev *matrix_mdev; + apqn = to_ap_queue(&apdev->device)->qid; + matrix_mdev = get_update_locks_by_apqn(apqn); + ret = sysfs_create_group(&apdev->device.kobj, &vfio_queue_attr_group); if (ret) - return ret; + goto err_release_locks; q = kzalloc_obj(*q); if (!q) { @@ -2439,11 +2460,10 @@ int vfio_ap_mdev_probe_queue(struct ap_device *apdev) goto err_remove_group; } - q->apqn = to_ap_queue(&apdev->device)->qid; + q->apqn = apqn; q->saved_isc = VFIO_AP_ISC_INVALID; memset(&q->reset_status, 0, sizeof(q->reset_status)); INIT_WORK(&q->reset_work, apq_reset_check); - matrix_mdev = get_update_locks_by_apqn(q->apqn); if (matrix_mdev) { vfio_ap_mdev_link_queue(matrix_mdev, q); @@ -2472,8 +2492,13 @@ int vfio_ap_mdev_probe_queue(struct ap_device *apdev) return ret; err_remove_group: + release_update_locks_for_mdev(matrix_mdev); sysfs_remove_group(&apdev->device.kobj, &vfio_queue_attr_group); return ret; + +err_release_locks: + release_update_locks_for_mdev(matrix_mdev); + return ret; } void vfio_ap_mdev_remove_queue(struct ap_device *apdev) -- 2.53.0