In the Linux kernel, the following vulnerability has been resolved: s390/vfio-ap: fix KVM GISC and page leak when queue removed from host c

 1AP_RESPONSE_Q_NOT_AVAIL not handled in vfio_ap_mdev_reset_queue()
 2 
 3When the AP bus removes a queue device whose adapter or domain has
 4been removed from the host's AP configuration,
 5vfio_ap_mdev_remove_queue() is called. If the queue is still in the
 6host's AP configuration at that point, it calls
 7vfio_ap_mdev_reset_queue(), which issues a PQAP(ZAPQ). Since the
 8adapter is already gone from the host configuration, ap_zapq() returns
 9AP_RESPONSE_Q_NOT_AVAIL (0x01). This response code is not handled in
10vfio_ap_mdev_reset_queue()'s switch statement and falls through to
11the default case, which issues a WARN but does not call
12vfio_ap_free_aqic_resources(). As a result, if IRQ handling was
13enabled for the queue by the guest, the KVM GISC registration and
14the pinned guest page holding the notification indicator byte (NIB)
15are both leaked.
16 
17This is fixed by adding AP_RESPONSE_Q_NOT_AVAIL to the same case as
18AP_RESPONSE_DECONFIGURED and AP_RESPONSE_CHECKSTOPPED in
19vfio_ap_mdev_reset_queue(). Like those response codes, Q_NOT_AVAIL
20indicates the queue is not operational and no further reset attempts
21are possible; the correct action is to free the IRQ resources
22immediately.
23 
24Problem 2:

 1vfio_ap_free_aqic_resources() leaks saved_isc when kvm is NULL
 2 
 3vfio_ap_free_aqic_resources() guards the call to
 4kvm_s390_gisc_unregister() with:
 5 
 6    if (q->saved_isc != VFIO_AP_ISC_INVALID &&
 7        !WARN_ON(!(q->matrix_mdev && q->matrix_mdev->kvm)))
 8 
 9If matrix_mdev->kvm is NULL -- which can happen when
10vfio_ap_mdev_unset_kvm() has already run and cleared kvm before a
11subsequent cleanup path reaches this function -- the WARN_ON fires
12and the entire block is skipped. This leaves q->saved_isc set to a
13non-invalid value, creating a potential double-free on any subsequent
14call to this function.
15 
16When kvm is NULL the KVM guest is already torn down, so
17kvm_s390_gisc_unregister() need not and cannot be called; however,
18q->saved_isc must always be cleared. Fix this by separating the
19kvm_s390_gisc_unregister() call from the q->saved_isc reset. The
20WARN_ON now guards only the genuinely impossible case of matrix_mdev
21being NULL. A NULL kvm is handled gracefully by skipping only the
22unregister call, and q->saved_isc = VFIO_AP_ISC_INVALID is set
23unconditionally whenever saved_isc was not already invalid.
24 
25Additionally, add an else clause to the host-config check in
26vfio_ap_mdev_remove_queue() to call vfio_ap_free_aqic_resources()
27directly when the queue is not in the host's AP configuration. This
28serves as a backstop: when the AP bus fires the driver .remove
29callback after an adapter is removed from the host config, the queue
30is by definition no longer addressable, so vfio_ap_mdev_reset_queue
31---truncated---