s390/vfio-ap: fix stale pqap_hook pointer on error in vfio_ap_mdev_set_kvm()

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-89960
StatePUBLISHED
AssignerLinux
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-09-16 11:17:06 UTC
Updated2026-10-19 09:18:42 UTC
DescriptionIn the Linux kernel, the following vulnerability has been resolved: s390/vfio-ap: fix stale pqap_hook pointer on error in vfio_ap_mdev_set_kvm() 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.

Risk And Classification

Primary CVSS: v3.1 8.8 HIGH from 416baaa9-dc9f-4396-8d5f-8c081fb06d67

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H

VersionSourceTypeScoreSeverityVector
3.1416baaa9-dc9f-4396-8d5f-8c081fb06d67Secondary8.8HIGHCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H
3.1CNADECLARED8.8HIGHCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H

CVSS v3.1 Breakdown

Attack Vector
Local
Attack Complexity
Low
Privileges Required
Low
User Interaction
None
Scope
Changed
Confidentiality
High
Integrity
High
Availability
High

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Linux Linux affected 86956e70761b3292156d668e87126844334dd71b eb6cc898501a004c0fa8aab951351d9c959b91cc git Not specified
CNA Linux Linux affected 86956e70761b3292156d668e87126844334dd71b 6a180adafc2a8a5fbe815985c71b2201e93ab5e1 git Not specified
CNA Linux Linux affected 86956e70761b3292156d668e87126844334dd71b fc069d00a0dbef40042fd681554d48dcd5a1d524 git Not specified
CNA Linux Linux affected 86956e70761b3292156d668e87126844334dd71b 13bfc94eef389bd664ffc67b00184919902c938a git Not specified
CNA Linux Linux affected 86956e70761b3292156d668e87126844334dd71b 4400270ec0348d05dc0439d8f0130853ce7f9e20 git Not specified
CNA Linux Linux affected 5.15 Not specified
CNA Linux Linux unaffected 5.15 semver Not specified
CNA Linux Linux unaffected 6.6.157 6.6.* semver Not specified
CNA Linux Linux unaffected 6.12.110 6.12.* semver Not specified
CNA Linux Linux unaffected 6.18.51 6.18.* semver Not specified
CNA Linux Linux unaffected 7.2.5 7.2.* semver Not specified
CNA Linux Linux unaffected 7.3 * original_commit_for_fix Not specified

References

ReferenceSourceLinkTags
git.kernel.org/stable/c/4400270ec0348d05dc0439d8f0130853ce7f9e20 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/fc069d00a0dbef40042fd681554d48dcd5a1d524 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/6a180adafc2a8a5fbe815985c71b2201e93ab5e1 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/eb6cc898501a004c0fa8aab951351d9c959b91cc 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/13bfc94eef389bd664ffc67b00184919902c938a 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
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