GHSA-GFV9-X355-HV69
Vulnerability from github – Published: 2026-09-16 12:30 – Updated: 2026-09-16 15:31In 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.
{
"affected": [],
"aliases": [
"CVE-2026-89960"
],
"database_specific": {
"cwe_ids": [],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2026-09-16T11:17:06Z",
"severity": "HIGH"
},
"details": "In the Linux kernel, the following vulnerability has been resolved:\n\ns390/vfio-ap: fix stale pqap_hook pointer on error in vfio_ap_mdev_set_kvm()\n\nIn vfio_ap_mdev_set_kvm(), kvm-\u003earch.crypto.pqap_hook is set to\n\u0026matrix_mdev-\u003epqap_hook before the update locks are acquired and the\nmdev list is checked for a conflicting assignment. If another mdev is\nalready attached to the same KVM instance, the function returns -EPERM\nwithout restoring the hook pointer, leaving kvm-\u003earch.crypto.pqap_hook\npointing at the failing matrix_mdev instead of the mdev that legitimately\nowns the KVM.\n\nSince matrix_mdev-\u003ekvm is never set on this error path,\nvfio_ap_mdev_unset_kvm() will not clean up the hook when matrix_mdev\nis later closed. If matrix_mdev is subsequently freed, any PQAP\ninstruction executed by the guest will dereference the stale pointer\nthrough pqap_hook_rwsem, resulting in a use-after-free.\n\nSince kvm-\u003earch.crypto.pqap_hook is only set in the vfio_ap_mdev_set_kvm()\nfunction and is cleared in the vfio_ap_mdev_unset_kvm() function, a check\nfor \u0027kvm-\u003earch.crypto.pqap_hook != NULL\u0027 is all that is needed to determine\nwhether it belongs to another mdev. This will alleviate the need to iterate\nthe matrix_dev-\u003emdev_list list to see if the kvm object is assigned to\nanother mdev.This was introduced in v3 to alleviate the need to take the\nmdevs_lock while iterating the list; however, this did not prevent a\npotential race condition.\n\nThe pqap_hook_rwsem(write) is now performed inside\nget_update_locks_for_kvm(), which is updated to acquire\npqap_hook_rwsem(write) between kvm-\u003elock and mdevs_lock. This ordering\nis consistent with the PQAP intercept path, which acquires pqap_hook_rwsem\nin read mode while srcu is held under vcpu-\u003emutex, establishing the\ndependency: kvm-\u003elock -\u003e vcpu-\u003emutex -\u003e srcu -\u003e pqap_hook_rwsem(read).\n\nThe pqap_hook_rwsem is now released inside the\nrelease_update_locks_for_kvm(), which is updated to release\npqap_hook_rwsem(write) between mdevs_lock and kvm-\u003elock.\n\nAdditionally, kvm_put_kvm() in vfio_ap_mdev_unset_kvm() is moved\nafter release_update_locks_for_kvm(). Previously it was called while\nkvm-\u003elock was held; if it were ever the last reference, kvm_destroy_vm()\nwould run under kvm-\u003elock, which would deadlock.",
"id": "GHSA-gfv9-x355-hv69",
"modified": "2026-09-16T15:31:03Z",
"published": "2026-09-16T12:30:43Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-89960"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/13bfc94eef389bd664ffc67b00184919902c938a"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/4400270ec0348d05dc0439d8f0130853ce7f9e20"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/6a180adafc2a8a5fbe815985c71b2201e93ab5e1"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/eb6cc898501a004c0fa8aab951351d9c959b91cc"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/fc069d00a0dbef40042fd681554d48dcd5a1d524"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H",
"type": "CVSS_V3"
}
]
}
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