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Wed, 22 Jul 2026 14:09:28 +0000 (GMT) Received: from li-4c4c4544-004d-4810-8043-b7c04f423534.ibm.com.com (unknown [9.61.82.206]) by smtpav01.wdc07v.mail.ibm.com (Postfix) with ESMTP; Wed, 22 Jul 2026 14:09:28 +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] s390/vfio-ap: fix stale pqap_hook pointer on error in vfio_ap_mdev_set_kvm() Date: Wed, 22 Jul 2026 10:09:23 -0400 Message-ID: <20260722140927.892342-1-akrowiak@linux.ibm.com> X-Mailer: git-send-email 2.53.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-TM-AS-GCONF: 00 X-Authority-Analysis: v=2.4 cv=HJXz0Itv c=1 sm=1 tr=0 ts=6a60cf1c cx=c_pps a=AfN7/Ok6k8XGzOShvHwTGQ==:117 a=AfN7/Ok6k8XGzOShvHwTGQ==:17 a=RAioF0-LDSMA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=Y2IxJ9c9Rs8Kov3niI8_:22 a=VwQbUJbxAAAA:8 a=VnNF1IyMAAAA:8 a=VZnb1T10RMzx8gLIHewA:9 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwNzIyMDEzNCBTYWx0ZWRfX6Al0SIgWnisR STNkIQprqoO/qseKxAapQZjOlx+3PbR5trlxNBp2XGuqNVWaPL/XhxXXxYjCrpY5gjNd6DqaZQA FNnR0nbeavZz2W8EWok/vFiLAx0DW7R9/dNfIR7Idar/2AZWBV4b4Po8HgadJwNZKL1PwFjheWo GE74cTB9w75l2+kfuABe/f3tP7OXLuJwDrKq1jGaQ+aRrlnp3cX4yXRbsQo2Wx2mQ6wDGAUpnQk OcYTJzNpli9rWFQ1L4tz2a9hYt0fP4uEHTHtdIvgkK42G0lZjJ9nUxgMZdBmH1H3LTQqghRN25e xKgC9fgo0RfJkJyul8hsJRgsSowWjU/5dDAzeASwLEc+Y2gFqZkJAndNyUGvYH8YUlj/nVK4oWo GajVbj7Yj39v3Gb34hDBfFbgCTOacgJF8dZh+HE8kDnH0YyOid6XB2xDO+Jas4458N8NBAQrdnk pN63a74ADUMtlTgntCw== X-Proofpoint-ORIG-GUID: SuH1A5062gk_zueftlgBBHAmF6XNIcT7 X-Proofpoint-Spam-Info: AW1haW4tMjYwNzIyMDEzNCBTYWx0ZWRfX2jkeqlExX4KP J1+WR3PSgZ8HuNKeKO5sXEsnEJNT+IiXDQcObPhnH2HCxMPjDYJe8zYxJvppl5T1wqM7tdy3cnr pO838DBKADwnsKKhaeMxZ7J9bjHGInE= X-Proofpoint-GUID: SuH1A5062gk_zueftlgBBHAmF6XNIcT7 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=2026-07-22_04,2026-07-22_01,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 bulkscore=0 priorityscore=1501 lowpriorityscore=0 suspectscore=0 malwarescore=0 impostorscore=0 clxscore=1011 phishscore=0 spamscore=0 adultscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2606150000 definitions=main-2607220134 Content-Type: text/plain; charset="utf-8" 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. Fix this by restoring kvm->arch.crypto.pqap_hook to &m->pqap_hook on the -EPERM path, where m is the already-attached mdev discovered during the conflict check. This is the value the hook held before it was overwritten, and it is the only safe value to restore since m remains live and its pqap_hook is the handler the guest must continue to use. The rwsem is re-taken under write before restoring the pointer, which is consistent with the existing locking pattern and ensures no VCPU thread can observe a torn value. Fixes: 86956e70761b3 ("s390/vfio-ap: replace open coded locks for VFIO_GROU= P_NOTIFY_SET_KVM notification") Cc: stable@vger.kernel.org Signed-off-by: Anthony Krowiak --- drivers/s390/crypto/vfio_ap_ops.c | 10 ++++++++++ 1 file changed, 10 insertions(+) diff --git a/drivers/s390/crypto/vfio_ap_ops.c b/drivers/s390/crypto/vfio_a= p_ops.c index 44b3a1dcc1b3..e18540fd6dc7 100644 --- a/drivers/s390/crypto/vfio_ap_ops.c +++ b/drivers/s390/crypto/vfio_ap_ops.c @@ -1824,6 +1824,12 @@ static int vfio_ap_mdev_set_kvm(struct ap_matrix_mde= v *matrix_mdev, struct ap_matrix_mdev *m; =20 if (kvm->arch.crypto.crycbd) { + /* + * Taking the kvm->arch.crypto.pqap_hook_rwsem lock while + * holding the update locks (below) could result in a + * deadlock condition, so let's hold the rwsem here while we + * update the pqap_hook. + */ down_write(&kvm->arch.crypto.pqap_hook_rwsem); kvm->arch.crypto.pqap_hook =3D &matrix_mdev->pqap_hook; up_write(&kvm->arch.crypto.pqap_hook_rwsem); @@ -1833,6 +1839,10 @@ static int vfio_ap_mdev_set_kvm(struct ap_matrix_mde= v *matrix_mdev, list_for_each_entry(m, &matrix_dev->mdev_list, node) { if (m !=3D matrix_mdev && m->kvm =3D=3D kvm) { release_update_locks_for_kvm(kvm); + /* Undo the hook installation since we're failing */ + down_write(&kvm->arch.crypto.pqap_hook_rwsem); + kvm->arch.crypto.pqap_hook =3D &m->pqap_hook; + up_write(&kvm->arch.crypto.pqap_hook_rwsem); return -EPERM; } } --=20 2.53.0