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Wed, 12 Aug 2026 11:51:48 +0000 (GMT) Received: from li-4c4c4544-004d-4810-8043-b7c04f423534.ibm.com.com (unknown [9.61.9.29]) by smtpav06.dal12v.mail.ibm.com (Postfix) with ESMTP; Wed, 12 Aug 2026 11:51:48 +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 v3 3/9] s390/vfio-ap: Fix missing lock required to access list of ap_matrix_mdev objects Date: Wed, 12 Aug 2026 07:51:33 -0400 Message-ID: <20260812115139.576303-4-akrowiak@linux.ibm.com> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260812115139.576303-1-akrowiak@linux.ibm.com> References: <20260812115139.576303-1-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-Authority-Analysis: v=2.4 cv=XqfK/1F9 c=1 sm=1 tr=0 ts=6a7c5e59 cx=c_pps a=aDMHemPKRhS1OARIsFnwRA==:117 a=aDMHemPKRhS1OARIsFnwRA==:17 a=Sv0fKeRqtYgA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=V8glGbnc2Ofi9Qvn3v5h:22 a=VwQbUJbxAAAA:8 a=VnNF1IyMAAAA:8 a=A59ciYRgiFgMSmRGxjkA:9 a=+jEqtf1s3R9VXZ0wqowq2kgwd+I=:19 a=0bXxn9q0MV6snEgNplNhOjQmxlI=:19 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwODEyMDA5MyBTYWx0ZWRfX7nCs8XA5mT0X 8I6f216k4JfxhMYCzeCkkK2z/FB7kSpa86VuV7rupvQ3emoaZVnXk9qi53KtIrV6TjyyZe1eYVC OQ6bt6Bbn85p8PH294SCzVqhdMamTPOUg19jpve73i2x/cwtVXiuiLE4ni9oV4rIvxYY8kBKzRw +nVOf+YabxTGrYYXu07rQEOqY+jWzsbJIz8Onpcv7czaT5IMLJoQreDyT/G+9w0UJCit5G1l+vX 0itHVZKJMTlCt6ZKZJ79DcGxHC89YlNNCuy9iW5FAWpeRIBAMS9Oo+75fFnyVxtCT0qAdNhtLdd vr2nwMvp/dRIAJ6A+/eEJOJ9q6z1kdnlUvcaqii8uRvTKRmxZUZWqcwiKnS9CAFN+h5KYYbxp1I jerz+lBInCGav1Q36haSucWvwQ0zcNA4WlLFPx54wakSX3dYuZuSSOP1IRSWJu32x8qcU29jHPF ED/kARWN2E1mQ6CbFhg== X-Proofpoint-ORIG-GUID: VMwSnsGx7ST3pqE32Jqw44tMwf4MRacq X-Proofpoint-GUID: VMwSnsGx7ST3pqE32Jqw44tMwf4MRacq X-Proofpoint-Spam-Info: AW1haW4tMjYwODEyMDA5MyBTYWx0ZWRfX98GaJUkij5Hi 0TSHG57+ds2A1mHcySLP6QjF5tVZKgnD6FdWeqO45v60dJxFPFL7CtoQlvdjbOYlm9Nu7jozcPA GkiEeJC+kWR0jPKlBvm/8/ENzsR/OAc= 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_03,2026-08-12_01,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 lowpriorityscore=0 spamscore=0 adultscore=0 malwarescore=0 clxscore=1015 suspectscore=0 priorityscore=1501 impostorscore=0 phishscore=0 bulkscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2606150000 definitions=main-2608120093 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. 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 --- drivers/s390/crypto/vfio_ap_ops.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-) diff --git a/drivers/s390/crypto/vfio_ap_ops.c b/drivers/s390/crypto/vfio_ap_ops.c index e382e5a1cb99..5c14ded4fd8e 100644 --- a/drivers/s390/crypto/vfio_ap_ops.c +++ b/drivers/s390/crypto/vfio_ap_ops.c @@ -803,9 +803,9 @@ static int vfio_ap_mdev_probe(struct mdev_device *mdev) matrix_mdev->req_trigger = NULL; matrix_mdev->cfg_chg_trigger = NULL; dev_set_drvdata(&mdev->dev, matrix_mdev); - mutex_lock(&matrix_dev->mdevs_lock); + mutex_lock(&matrix_dev->guests_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 +2297,8 @@ 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 +2318,7 @@ 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 +2346,7 @@ static ssize_t status_show(struct device *dev, } mutex_unlock(&matrix_dev->mdevs_lock); + mutex_unlock(&matrix_dev->guests_lock); return nchars; } -- 2.53.0