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Thu, 30 Jul 2026 15:26:28 +0000 (GMT) Received: from li-4c4c4544-004d-4810-8043-b7c04f423534.ibm.com.com (unknown [9.61.176.239]) by smtpav03.wdc07v.mail.ibm.com (Postfix) with ESMTP; Thu, 30 Jul 2026 15:26:28 +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, hca@linux.ibm.com, gor@linux.ibm.com, agordeev@linux.ibm.com, stable@vger.kernel.org Subject: [PATCH v3] s390/vfio-ap: fix stale pqap_hook pointer on error in vfio_ap_mdev_set_kvm() Date: Thu, 30 Jul 2026 11:26:28 -0400 Message-ID: <20260730152628.3158573-1-akrowiak@linux.ibm.com> X-Mailer: git-send-email 2.53.0 Precedence: bulk X-Mailing-List: linux-s390@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-TM-AS-GCONF: 00 X-Proofpoint-ORIG-GUID: smjaB6l32E-0QoEII6AhYkI2a3OvqEBE X-Proofpoint-Spam-Info: AW1haW4tMjYwNzMwMDExNiBTYWx0ZWRfX/7zuDcMy1gbw i2jDeiESk7mA6Q7Vm5Q/Eu1iYiV0azT05QFhbIslKLAWo4Oy4NvwJzxJ0+cGjhuUIBq8peM/YjU 2K6YOPq/ZR3ZZEyX60VoZFNU+HjhLuU= X-Authority-Analysis: v=2.4 cv=E/z9Y6dl c=1 sm=1 tr=0 ts=6a6b6d29 cx=c_pps a=3Bg1Hr4SwmMryq2xdFQyZA==:117 a=3Bg1Hr4SwmMryq2xdFQyZA==:17 a=RAioF0-LDSMA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=RzCfie-kr_QcCd8fBx8p:22 a=VwQbUJbxAAAA:8 a=VnNF1IyMAAAA:8 a=-Zx3bMm5DJhKnsoAqjMA:9 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwNzMwMDExNiBTYWx0ZWRfX0sr67tKRTHyt CLQRDWlDRQhhUHf75LmVvgIL+EzF4/YSOrX6Bm73VtNaHoKgYZDx9jB27bGt1BbtbB53jb2Awz4 UvnELk1rGrPQSzW2ehJWz6/46HWKSVstxtwtojwQ2oIEs7P14qtks5mXEcojcj5aTi1RzFpuDuo dBQiNQgQhRfNLZV8OHDBaJeJxu9dqiOwg32ne93wAyc8annh6jZHIWyXeV1Y7QNPX5J9ybTbOjy LLrg4vvjiT5tLsDuGwl+ne8y8ZAd+xoJEvN6pljuMt+fhUvCZsVQcH+IFXiVECQuJDXfGQynwk2 pACfl378S+PzChMsUxNyOnYFjgL+2DvqkQEcQXM4MJnfedg9Ds/wNh4MXVdTZtFwvYZ3S1rIdMu NXJbh+LSXB7rCxc9XyUh8MEsTnHYYYp/6OhIeR5ZL4/9vkADlK5Zt7TH5+37qElv+MdSOD77/BX GgU6wxtR0CJ1b3D/ZCA== X-Proofpoint-GUID: smjaB6l32E-0QoEII6AhYkI2a3OvqEBE X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1143,Hydra:6.1.134,FMLib:17.12.100.49 definitions=2026-07-30_04,2026-07-29_01,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 adultscore=0 priorityscore=1501 spamscore=0 clxscore=1015 phishscore=0 lowpriorityscore=0 bulkscore=0 malwarescore=0 impostorscore=0 suspectscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2606150000 definitions=main-2607300116 In vfio_ap_mdev_set_kvm(), kvm->arch.crypto.pqap_hook is set to &matrix_mdev->pqap_hook before the update locks are acquired and the mdev list is checked for a conflicting assignment. If another mdev is already attached to the same KVM instance, the function returns -EPERM without restoring the hook pointer, leaving kvm->arch.crypto.pqap_hook pointing at the failing matrix_mdev instead of the mdev that legitimately owns the KVM. Since matrix_mdev->kvm is never set on this error path, vfio_ap_mdev_unset_kvm() will not clean up the hook when matrix_mdev is later closed. If matrix_mdev is subsequently freed, any PQAP instruction executed by the guest will dereference the stale pointer through pqap_hook_rwsem, resulting in a use-after-free. Since kvm->arch.crypto.pqap_hook is only set in the vfio_ap_mdev_set_kvm() function and is cleared in the vfio_ap_mdev_unset_kvm() function, a check for 'kvm->arch.crypto.pqap_hook != NULL' is all that is needed to determine whether it belongs to another mdev. This will alleviate the need to iterate the matrix_dev->mdev_list list to see if the kvm object is assigned to another mdev. Note that the 'matrix_mdev' pointer retrieved via the 'container_of' macro in the 'vfio_ap_mdev_open_device()' callback will be available for the duration of that function because 'matrix_mdev' cannot be freed while 'open_device' (which calls the 'vfio_ap_mdev_open_device()' function) is running. Fixes: 86956e70761b3 ("s390/vfio-ap: replace open coded locks for VFIO_GROUP_NOTIFY_SET_KVM notification") Cc: stable@vger.kernel.org Signed-off-by: Anthony Krowiak --- drivers/s390/crypto/vfio_ap_ops.c | 19 ++++++------------- 1 file changed, 6 insertions(+), 13 deletions(-) diff --git a/drivers/s390/crypto/vfio_ap_ops.c b/drivers/s390/crypto/vfio_ap_ops.c index 44b3a1dcc1b3..f9460310d47b 100644 --- a/drivers/s390/crypto/vfio_ap_ops.c +++ b/drivers/s390/crypto/vfio_ap_ops.c @@ -1821,27 +1821,20 @@ static const struct attribute_group *vfio_ap_mdev_attr_groups[] = { static int vfio_ap_mdev_set_kvm(struct ap_matrix_mdev *matrix_mdev, struct kvm *kvm) { - struct ap_matrix_mdev *m; - if (kvm->arch.crypto.crycbd) { down_write(&kvm->arch.crypto.pqap_hook_rwsem); + if (kvm->arch.crypto.pqap_hook) { + up_write(&kvm->arch.crypto.pqap_hook_rwsem); + return -EPERM; + } kvm->arch.crypto.pqap_hook = &matrix_mdev->pqap_hook; - up_write(&kvm->arch.crypto.pqap_hook_rwsem); get_update_locks_for_kvm(kvm); - - list_for_each_entry(m, &matrix_dev->mdev_list, node) { - if (m != matrix_mdev && m->kvm == kvm) { - release_update_locks_for_kvm(kvm); - return -EPERM; - } - } - kvm_get_kvm(kvm); matrix_mdev->kvm = kvm; vfio_ap_mdev_update_guest_apcb(matrix_mdev); - release_update_locks_for_kvm(kvm); + up_write(&kvm->arch.crypto.pqap_hook_rwsem); } return 0; @@ -1885,7 +1878,6 @@ static void vfio_ap_mdev_unset_kvm(struct ap_matrix_mdev *matrix_mdev) if (kvm && kvm->arch.crypto.crycbd) { down_write(&kvm->arch.crypto.pqap_hook_rwsem); kvm->arch.crypto.pqap_hook = NULL; - up_write(&kvm->arch.crypto.pqap_hook_rwsem); get_update_locks_for_kvm(kvm); @@ -1895,6 +1887,7 @@ static void vfio_ap_mdev_unset_kvm(struct ap_matrix_mdev *matrix_mdev) matrix_mdev->kvm = NULL; release_update_locks_for_kvm(kvm); + up_write(&kvm->arch.crypto.pqap_hook_rwsem); } } -- 2.53.0