From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mx0b-001b2d01.pphosted.com (mx0b-001b2d01.pphosted.com [148.163.158.5]) (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 AE61437AA78; Thu, 6 Aug 2026 17:34:43 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=148.163.158.5 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786037685; cv=none; b=KycIKJkMEfK+h7KnEYOPsH+Wmtel9u7kPOxizL+HFTpXeMDWgz3g7NMEfvHFBCakPkG+BnhbZUHWJ3VNXNIk+u9kx350YsxaeJR3CBf9DmHh5B+B+oVT4xpFld6pF5okoklkY9uKJqX8cFb027SxU81fJTt86zjr5N8QGOrH3uw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786037685; c=relaxed/simple; bh=7GorEvF/jVOLDZIzs1L7CU4lZAyoLfkklW8N2M3cMcc=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=pylvtFyomps7/dOTu0HIrIj/WkSAH1HM6A1m48HRF88A+bvUlQTpKAHqPaOX8fH8pR0nQ410TwYxDDRBw4id2oYIDytrxGi0aZZrebtOs8IW8JNV8rJognB6NXwaEBvEegLZUvM6I464uJehIosPYjbobaI+9GkcwfJjZbWlY1w= 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=LPyRZCUe; arc=none smtp.client-ip=148.163.158.5 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="LPyRZCUe" Received: from pps.filterd (m0356516.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.18.1.11/8.18.1.11) with ESMTP id 676HIBQ13199575; Thu, 6 Aug 2026 17:34:39 GMT DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=ibm.com; h=cc :content-transfer-encoding:date:from:message-id:mime-version :subject:to; s=pp1; bh=MmZEs0KHbXR7hApoZg4ASB60bne8zhEhk5RCSoNhD Dw=; b=LPyRZCUeUg/t/OCh2+K9jeyh9fyp4VJDkdmJGnb7yXMVVz59cejKHWlO3 DvqaTnBA5zo4EnRuxLX25/CibbTNeeBgZzZl97chu5O8uLGbad2rD9lTNGLM5eYZ kL6BxTvWSNX9cJvUfJqShpPD0dpP0n/G4kcwwZKJwqRQ4NZjwaRdCy33CaBprott 8DYoZkbcE6Q0AsYHWZI1zAnwYAun5KPebc5UxbukkYenyHrQp+Wq1dtBxwrDYv3z sYiJUKVE3mdYyVXYJIIOATVdswlzMVkkApwmNgMXFw0LzixR0l/aNlmQqQlFly9F PaOsU7D0T7x9NdsLjolQ9chs6rrRA== Received: from ppma22.wdc07v.mail.ibm.com (5c.69.3da9.ip4.static.sl-reverse.com [169.61.105.92]) by mx0a-001b2d01.pphosted.com (PPS) with ESMTPS id 4fs67j17y5-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Thu, 06 Aug 2026 17:34:39 +0000 (GMT) Received: from pps.filterd (ppma22.wdc07v.mail.ibm.com [127.0.0.1]) by ppma22.wdc07v.mail.ibm.com (8.18.1.7/8.18.1.7) with ESMTP id 676HQcbD013762; Thu, 6 Aug 2026 17:34:39 GMT Received: from smtprelay07.wdc07v.mail.ibm.com ([172.16.1.74]) by ppma22.wdc07v.mail.ibm.com (PPS) with ESMTPS id 4fsugwcatv-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Thu, 06 Aug 2026 17:34:39 +0000 (GMT) Received: from smtpav04.wdc07v.mail.ibm.com (smtpav04.wdc07v.mail.ibm.com [10.39.53.231]) by smtprelay07.wdc07v.mail.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id 676HYbKa13173494 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Thu, 6 Aug 2026 17:34:37 GMT Received: from smtpav04.wdc07v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 9A13658054; Thu, 6 Aug 2026 17:34:37 +0000 (GMT) Received: from smtpav04.wdc07v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 1E1C158050; Thu, 6 Aug 2026 17:34:36 +0000 (GMT) Received: from li-4c4c4544-004d-4810-8043-b7c04f423534.ibm.com.com (unknown [9.61.80.66]) by smtpav04.wdc07v.mail.ibm.com (Postfix) with ESMTP; Thu, 6 Aug 2026 17:34:35 +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, Christian Borntraeger Subject: [PATCH v5] s390/vfio-ap: fix stale pqap_hook pointer on error in vfio_ap_mdev_set_kvm() Date: Thu, 6 Aug 2026 13:34:35 -0400 Message-ID: <20260806173435.105044-1-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-Spam-Info: AW1haW4tMjYwODA2MDEzNSBTYWx0ZWRfX6Zben0ZGlMpc GtAylaAmcmEvIyNjUjv0mHrLjEuhz/OpZC2bb/IQn2fnnWC8f8uk+SYwjtFRHF3WKF756G8CF+c jCwdKKBi8b8W9Lx4zpzyZFLUfs/SAa8= X-Authority-Analysis: v=2.4 cv=I7VVgtgg c=1 sm=1 tr=0 ts=6a74c5af cx=c_pps a=5BHTudwdYE3Te8bg5FgnPg==:117 a=5BHTudwdYE3Te8bg5FgnPg==:17 a=Sv0fKeRqtYgA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=Y2IxJ9c9Rs8Kov3niI8_:22 a=VwQbUJbxAAAA:8 a=VnNF1IyMAAAA:8 a=RxNNRKBWKq487C2d6-kA:9 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwODA2MDEzNSBTYWx0ZWRfX0fEIr9NWwrgh /dneuq1MoVg57M72AvIxHA7ie7dtGudgOgbDtVn5rZeriFjmUnJAZa467fKJJejVQcvuon78dlH NykapbfKrCz7C8kZf84LbpXkrgVXpnbWnR38Tof/Cu8prH2FfSDuMy/z3qhiVmrdcM0eBHoXsaB 6rutp0eSCPSZg8+3zUgjdcUA0kpQzPpTuWeTwGzSP58L7YZBdtuVleVYcsxiXkNPe0l3anvDkPL pmWOvbrU1CJsdn7+1QA/9NQWeeg1WTN3XJDO/5QzIQeohnB+GkK89Jqmd7iMoEsDrb43q02sEO/ MfErmCIW8qxjs1NIXGqzqofV+dbC9WvoE6A4iOI5EgxQkA0zK3R+3Ba1oacagtaFfAtryobe2/K XzNx9/Gi+HnmPj+EMn77en+yMMg6P0MspCzGmqVRdZFw3FOFePT6YmgfdQZaO7zAzYKuKyFCJ04 VStDu+D/cfhk2ikqWjA== X-Proofpoint-ORIG-GUID: mdBoVvT0mfTv-m9EF0_2FKKRv7fTrDaM X-Proofpoint-GUID: mdBoVvT0mfTv-m9EF0_2FKKRv7fTrDaM 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=2026-08-06_01,2026-08-06_01,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 bulkscore=0 impostorscore=0 clxscore=1015 priorityscore=1501 suspectscore=0 malwarescore=0 adultscore=0 lowpriorityscore=0 phishscore=0 spamscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2606150000 definitions=main-2608060135 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.This was introduced in v3 to alleviate the need to take the mdevs_lock while iterating the list; however, this did not prevent a potential race condition. The pqap_hook_rwsem(write) is now performed inside get_update_locks_for_kvm(), which is updated to acquire pqap_hook_rwsem(write) between kvm->lock and mdevs_lock. This ordering is consistent with the PQAP intercept path, which acquires pqap_hook_rwsem in read mode while srcu is held under vcpu->mutex, establishing the dependency: kvm->lock -> vcpu->mutex -> srcu -> pqap_hook_rwsem(read). The pqap_hook_rwsem is now released inside the release_update_locks_for_kvm(), which is updated to release pqap_hook_rwsem(write) between mdevs_lock and kvm->lock. Additionally, kvm_put_kvm() in vfio_ap_mdev_unset_kvm() is moved after release_update_locks_for_kvm(). Previously it was called while kvm->lock was held; if it were ever the last reference, kvm_destroy_vm() would run under kvm->lock, which would deadlock. Fixes: 86956e70761b3 ("s390/vfio-ap: replace open coded locks for VFIO_GROUP_NOTIFY_SET_KVM notification") Cc: stable@vger.kernel.org Co-developed-by: Matthew Rosato Signed-off-by: Matthew Rosato Signed-off-by: Anthony Krowiak Acked-by: Christian Borntraeger --- drivers/s390/crypto/vfio_ap_ops.c | 45 ++++++++++++++----------------- 1 file changed, 20 insertions(+), 25 deletions(-) diff --git a/drivers/s390/crypto/vfio_ap_ops.c b/drivers/s390/crypto/vfio_ap_ops.c index 44b3a1dcc1b3..99a0efd999ef 100644 --- a/drivers/s390/crypto/vfio_ap_ops.c +++ b/drivers/s390/crypto/vfio_ap_ops.c @@ -48,15 +48,19 @@ static void vfio_ap_mdev_reset_queue(struct vfio_ap_queue *q); * 1. matrix_dev->guests_lock: required to use the KVM pointer to update a KVM * guest's APCB. * 2. kvm->lock: required to update a guest's APCB - * 3. matrix_dev->mdevs_lock: required to access data stored in a matrix_mdev + * 3. kvm->arch.crypto.pqap_hook_rwsem: required to update pqap_hook and + * serialize against PQAP intercepts + * 4. matrix_dev->mdevs_lock: required to access data stored in a matrix_mdev * - * Note: If @kvm is NULL, the KVM lock will not be taken. + * Note: If @kvm is NULL, the KVM lock and pqap_hook_rwsem will not be taken. */ static inline void get_update_locks_for_kvm(struct kvm *kvm) { mutex_lock(&matrix_dev->guests_lock); - if (kvm) + if (kvm) { mutex_lock(&kvm->lock); + down_write(&kvm->arch.crypto.pqap_hook_rwsem); + } mutex_lock(&matrix_dev->mdevs_lock); } @@ -68,16 +72,19 @@ static inline void get_update_locks_for_kvm(struct kvm *kvm) * * The proper unlocking order is: * 1. matrix_dev->mdevs_lock - * 2. kvm->lock - * 3. matrix_dev->guests_lock + * 2. kvm->arch.crypto.pqap_hook_rwsem + * 3. kvm->lock + * 4. matrix_dev->guests_lock * - * Note: If @kvm is NULL, the KVM lock will not be released. + * Note: If @kvm is NULL, the KVM lock and pqap_hook_rwsem will not be released. */ static inline void release_update_locks_for_kvm(struct kvm *kvm) { mutex_unlock(&matrix_dev->mdevs_lock); - if (kvm) + if (kvm) { + up_write(&kvm->arch.crypto.pqap_hook_rwsem); mutex_unlock(&kvm->lock); + } mutex_unlock(&matrix_dev->guests_lock); } @@ -1821,26 +1828,17 @@ 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); - 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; - } + if (kvm->arch.crypto.pqap_hook) { + release_update_locks_for_kvm(kvm); + return -EPERM; } + kvm->arch.crypto.pqap_hook = &matrix_mdev->pqap_hook; kvm_get_kvm(kvm); matrix_mdev->kvm = kvm; vfio_ap_mdev_update_guest_apcb(matrix_mdev); - release_update_locks_for_kvm(kvm); } @@ -1883,18 +1881,15 @@ static void vfio_ap_mdev_unset_kvm(struct ap_matrix_mdev *matrix_mdev) struct kvm *kvm = matrix_mdev->kvm; 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); + kvm->arch.crypto.pqap_hook = NULL; kvm_arch_crypto_clear_masks(kvm); vfio_ap_mdev_reset_queues(matrix_mdev); - kvm_put_kvm(kvm); matrix_mdev->kvm = NULL; release_update_locks_for_kvm(kvm); + kvm_put_kvm(kvm); } } -- 2.53.0