CVE-2026-89960 (GCVE-0-2026-89960)
Vulnerability from cvelistv5
Published
2026-09-16 10:32
Modified
2026-10-19 08:55
Severity ?
8.8 (High) - CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H
Summary
In 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.
References
Impacted products
Vendor Product Version
Linux Linux Version: 86956e70761b3292156d668e87126844334dd71b
Version: 86956e70761b3292156d668e87126844334dd71b
Version: 86956e70761b3292156d668e87126844334dd71b
Version: 86956e70761b3292156d668e87126844334dd71b
Version: 86956e70761b3292156d668e87126844334dd71b
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{
  "containers": {
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "drivers/s390/crypto/vfio_ap_ops.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "lessThan": "eb6cc898501a004c0fa8aab951351d9c959b91cc",
              "status": "affected",
              "version": "86956e70761b3292156d668e87126844334dd71b",
              "versionType": "git"
            },
            {
              "lessThan": "6a180adafc2a8a5fbe815985c71b2201e93ab5e1",
              "status": "affected",
              "version": "86956e70761b3292156d668e87126844334dd71b",
              "versionType": "git"
            },
            {
              "lessThan": "fc069d00a0dbef40042fd681554d48dcd5a1d524",
              "status": "affected",
              "version": "86956e70761b3292156d668e87126844334dd71b",
              "versionType": "git"
            },
            {
              "lessThan": "13bfc94eef389bd664ffc67b00184919902c938a",
              "status": "affected",
              "version": "86956e70761b3292156d668e87126844334dd71b",
              "versionType": "git"
            },
            {
              "lessThan": "4400270ec0348d05dc0439d8f0130853ce7f9e20",
              "status": "affected",
              "version": "86956e70761b3292156d668e87126844334dd71b",
              "versionType": "git"
            }
          ]
        },
        {
          "defaultStatus": "affected",
          "product": "Linux",
          "programFiles": [
            "drivers/s390/crypto/vfio_ap_ops.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "status": "affected",
              "version": "5.15"
            },
            {
              "lessThan": "5.15",
              "status": "unaffected",
              "version": "0",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.6.*",
              "status": "unaffected",
              "version": "6.6.157",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.12.*",
              "status": "unaffected",
              "version": "6.12.110",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.18.*",
              "status": "unaffected",
              "version": "6.18.51",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "7.2.*",
              "status": "unaffected",
              "version": "7.2.5",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "*",
              "status": "unaffected",
              "version": "7.3",
              "versionType": "original_commit_for_fix"
            }
          ]
        }
      ],
      "cpeApplicability": [
        {
          "nodes": [
            {
              "cpeMatch": [
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "6.6.157",
                  "versionStartIncluding": "5.15",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "6.12.110",
                  "versionStartIncluding": "5.15",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "6.18.51",
                  "versionStartIncluding": "5.15",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "7.2.5",
                  "versionStartIncluding": "5.15",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "7.3",
                  "versionStartIncluding": "5.15",
                  "vulnerable": true
                }
              ],
              "negate": false,
              "operator": "OR"
            }
          ]
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "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."
        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "baseScore": 8.8,
            "baseSeverity": "HIGH",
            "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H",
            "version": "3.1"
          },
          "scenarios": [
            {
              "lang": "en",
              "value": "AV:L - The bug is reached by opening vfio-ap mdev fds and linking them to a KVM instance (KVM_DEV_VFIO_FILE_ADD/BIND_IOMMUFD) so vfio_ap_mdev_open_device() calls vfio_ap_mdev_set_kvm(), then by a guest PQAP(AQIC) intercept in handle_pqap(); that is a local VFIO/KVM path with no network or USB exposure.\nAC:L - An attacker who can open two vfio-ap mdevs against the same KVM deterministically hits the -EPERM conflict path that overwrites kvm-\u003earch.crypto.pqap_hook without restoring it, then frees the failing mdev and issues PQAP from the still-running guest; the attacker controls every step, with no victim race or uncontrolled layout.\nPR:L - vfio_ap_mdev_set_kvm() and the PQAP intercept have no capable() gate; /dev/kvm and /dev/vfio nodes are routinely granted to an unprivileged qemu/kvm-group tenant with assigned vfio-ap mdevs, so host root is not required, and user namespaces cannot substitute for this path.\nUI:N - The attacker performs the conflicting VFIO attach, tears down the failing mdev, and executes PQAP in their own guest; prior administrator creation of vfio-ap mdevs is deployment configuration, not victim interaction during exploitation.\nS:C - A guest PQAP intercept on the host calls through kvm-\u003earch.crypto.pqap_hook into a freed ap_matrix_mdev in the host vfio-ap driver, hijacking a host kernel function pointer and crossing the KVM/VFIO guest-to-host isolation boundary (VM escape).\nC:H - After the failing mdev is kvfree\u0027d, handle_pqap() does pqap_hook = *vcpu-\u003ekvm-\u003earch.crypto.pqap_hook, reading a function pointer from the freed ap_matrix_mdev; reclaiming that object yields an arbitrary kernel-read primitive, which kernel UAF guidance scores High.\nI:H - The intercept then invokes that recovered pointer as pqap_hook(vcpu); spraying the freed ap_matrix_mdev replaces the hook with an attacker-controlled address, enabling host kernel control-flow hijack and arbitrary write.\nA:H - The same stale-pointer dereference and call on the freed object causes a host kernel oops or panic when the guest issues PQAP, even if the function pointer is not fully hijacked."
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-10-19T08:55:34.035Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/eb6cc898501a004c0fa8aab951351d9c959b91cc"
        },
        {
          "url": "https://git.kernel.org/stable/c/6a180adafc2a8a5fbe815985c71b2201e93ab5e1"
        },
        {
          "url": "https://git.kernel.org/stable/c/fc069d00a0dbef40042fd681554d48dcd5a1d524"
        },
        {
          "url": "https://git.kernel.org/stable/c/13bfc94eef389bd664ffc67b00184919902c938a"
        },
        {
          "url": "https://git.kernel.org/stable/c/4400270ec0348d05dc0439d8f0130853ce7f9e20"
        }
      ],
      "title": "s390/vfio-ap: fix stale pqap_hook pointer on error in vfio_ap_mdev_set_kvm()",
      "x_generator": {
        "engine": "bippy-1.2.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-89960",
    "datePublished": "2026-09-16T10:32:42.618Z",
    "dateReserved": "2026-09-11T19:38:34.778Z",
    "dateUpdated": "2026-10-19T08:55:34.035Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}


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