[PATCH v4 0/4] s390/vfio-ap: Fix pre-existing bugs in vfio_ap device driver

[PATCH v4 0/4] s390/vfio-ap: Fix pre-existing bugs in vfio_ap device driver

[Anthony Krowiak]

The sashiko AI reported several pre-existing bugs in the vfio_ap device
driver code while reviewing unrelated patches. This series fixes four
such bugs.

Change log v3 => v4:
~~~~~~~~~~~~~~~~~~~
Patch 1/4: Fix leak of pinned NIB and registered NISC in
           vfio_ap_irq_enable/disable()
* Overrode the response status in vfio_irq_disable() for the
  AP_RESPONSE_NORMAL case when vfio_ap_wait_for_irqclear() returns false.
* Changed name of vfio_ap_wait_for_irqclear() to
  vfio_ap_wait_for_irq_state() and added a parameter to specify
  the value (0 = disabled, 1 = enabled) to which the status.irq_enabled
  (I-bit) is to be compared.
* Added a call to vfio_ap_wait_for_irq_state() to vfio_ap_irq_enable()
  to verify that the I-bit is set when AP_RESPONSE_NORMAL is returned
  from the AQIC call before proceeding.

Patch 3/4: Fix unbounded loop in apq_reset_check()
* Check return code from apq_status_check() called from apq_reset_check().
  If it returns 0 when the AP_RESET_MAX_WAIT timeout is detected, then
  clean up AQIC resources.

Anthony Krowiak (4):
  s390/vfio-ap: Fix leak of pinned NIB and registered NISC in
    vfio_ap_irq_enable/disable()
  s390/vfio-ap: Fix failure to release IRQ notification eventfd contexts
  s390/vfio-ap: Fix unbounded loop in apq_reset_check()
  s390/vfio-ap: Use AP_DOMAINS for adm_add bitmap size in
    vfio_ap_mdev_cfg_add()

 drivers/s390/crypto/vfio_ap_ops.c | 216 +++++++++++++++++++++++++-----
 1 file changed, 186 insertions(+), 30 deletions(-)

-- 
2.53.0

[PATCH v4 1/4] s390/vfio-ap: Fix leak of pinned NIB and registered NISC in vfio_ap_irq_enable/disable()

[Anthony Krowiak]

The vfio_ap_irq_enable() and vfio_ap_disable() functions execute the
PQAP(AQIC) instructions to enable/disable interrupts for an AP queue.
A switch statement is used to examine the status response code returned
from the instruction to determine whether it succeeded or failed and react
accordingly.

vfio_ap_irq_enable()
~~~~~~~~~~~~~~~~~~~~
For the default case, the vfio_ap_irq_disable function is invoked to
disable interrupts for the queue and clean up the AQIC resources (i.e.,
unpin the NIB and unregister the NISC) that are stored with the
vfio_ap_queue object. There are a number of problems with this:

1. Neither the q->saved_iova nor q->saved_isc has been set for the current
   AQIC call, so the AQIC resources - assuming those values have been
   previously set - will be the NIB and NISC resources from a prior call;
   the NIB and NISC from the current call are therefore leaked.

2. Interrupts may never have been enabled. Sending a disable instruction to
   a queue that the hardware just told you is in a bad state (CHECKSTOPPED,
   DECONFIGURED, Q_NOT_AVAIL) is at best wasted work and at worst generates
   a further WARN_ONCE from inside vfio_ap_irq_disable's own default.

3. The hardware just rejected the new ap_aqic() enable attempt with an
   unexpected status. Disabling a previously-working IRQ config - assuming
   that is even possible - as a reaction to a failed enable attempt does
   not make sense; it is actively destructive, tearing down something that
   was working for no valid reason.

The fix is to unregister the NISC and an unpin the NIB used in the AQIC
call in the default case of the switch statement and leave the AQIC
resources stored with the vfio_ap_queue object alone.

Another problem with vfio_ap_irq_enable() is that the old NIB stored in
q->saved_iova from a previous AQIC are immediately freed - assuming they
are stored - as soon as the AQIC response status returns
AP_RESPONSE_NORMAL. The problem with this is, AQIC is an asynchronous
operation; the only way to tell if it has completed is to check the
I-bit (7) in the status returned from AQIC. This bit indicates whether
interrupts are enabled (1) or disabled (0).

The fix for this is to wait a specified period of time until the I-bit is
set, similar to vfio_ap_wait_for_irqclear() - waits for I-bit==0 - which
is called from vfio_ap_irq_disable() to verify the operation has completed.
If verification of I-bit == 1 occurs within a specified period of time,
freeing the old NIB (q->saved_iova) because once the I-bit is set, the new
NIB is made available for queue interrupts and any old NIB will no longer
be used. If the verification times out, then the new NIB will
be freed and the old NIB will be allowed to leak which is preferable
because the queue might still have in-flight DMA writes directed to the
old NIB which would result in a use-after-free kernel crash.

vfio_ap_irq_disable()
~~~~~~~~~~~~~~~~~~~~~
There are two problems with the way this function handles the response
code returned from the PQAP(AQIC) instruction:

1. For response codes AP_RESPONSE_NORMAL or AP_RESPONSE_OTHERWISE_CHANGED,
   a call is made to vfio_ap_wait_for_irqclear() which waits for the
   I-bit (7) - indicates whether interrupts are enabled (1) or
   disabled (0) - to be cleared. That function does not return anything, so
   there is no way to determine whether it succeeded or not. The
   vfio_ap_irq_disable() function then frees the AQIC resources. This is a
   problem because the hardware may still write to the NIB resulting in a
   use-after-free kernel crash.

   The fix for this is to add a boolean return code from
   vfio_ap_wait_for_irqclear(). This will be checked in
   vfio_ap_irq_disable() and if clearing of the IR bit could not be
   verified, the AQIC resources will be allowed to leak. This is
   preferable to a kernel crash.

2. For response code AP_RESPONSE_INVALID_ADDRESS - indicates the NIB
   address passed to PQAP(AQIC) is not valid - as well as the default case,
   the vfio_ap_irq_disable() frees the AQIC resources. Since the AQIC
   disable was rejected, the IRQ is still enabled and the hardware still
   holds the NIB address, so freeing the NIB could result in a
   use-after-free kernel crash.

   The fix for this is to allow the AQIC resources to be leaked. This is
   preferable to a kernel crash.

Fixes: ec89b55e3bce7 ("s390: ap: implement PAPQ AQIC interception in kernel")
Cc: stable@vger.kernel.org
Signed-off-by: Anthony Krowiak <akrowiak@linux.ibm.com>
---
 drivers/s390/crypto/vfio_ap_ops.c | 152 +++++++++++++++++++++++++-----
 1 file changed, 129 insertions(+), 23 deletions(-)

diff --git a/drivers/s390/crypto/vfio_ap_ops.c b/drivers/s390/crypto/vfio_ap_ops.c
index 940c0ff668be..24e93fb7f81a 100644
--- a/drivers/s390/crypto/vfio_ap_ops.c
+++ b/drivers/s390/crypto/vfio_ap_ops.c
@@ -30,6 +30,9 @@
 #define AP_QUEUE_UNASSIGNED "unassigned"
 #define AP_QUEUE_IN_USE "in use"
 
+#define AP_IRQ_DISABLED	0
+#define AP_IRQ_ENABLED	1
+
 #define AP_RESET_INTERVAL		20	/* Reset sleep interval (20ms)		*/
 
 static int vfio_ap_mdev_reset_queues(struct ap_matrix_mdev *matrix_mdev);
@@ -226,16 +229,27 @@ static struct vfio_ap_queue *vfio_ap_mdev_get_queue(
 }
 
 /**
- * vfio_ap_wait_for_irqclear - clears the IR bit or gives up after 5 tries
- * @apqn: The AP Queue number
+ * vfio_ap_wait_for_irqstate - wait for the IR bit to reach the requested state
  *
- * Checks the IRQ bit for the status of this APQN using ap_tapq.
- * Returns if the ap_tapq function succeeded and the bit is clear.
- * Returns if ap_tapq function failed with invalid, deconfigured or
- * checkstopped AP.
- * Otherwise retries up to 5 times after waiting 20ms.
+ * @apqn: the APQN of the queue
+ * @ir: the expected state of the IR bit: AP_IRQ_DISABLED or AP_IRQ_ENABLED
+ *
+ * Repeatedly polls the AP queue status via PQAP(TAPQ) every 20ms until the IR
+ * bit matches @ir, the queue becomes non-operational, or 5 retries are
+ * exhausted.
+ *
+ * Because PQAP(AQIC) initiates an asynchronous process, a condition-code 0
+ * completion does not guarantee the IR bit has reached the requested state.
+ * The caller must use this function to confirm the state before proceeding.
+ *
+ * Return:
+ * - true if the IR bit matches @ir, or the AP is non-operational (in which
+ *   case no further interrupts can be generated)
+ *
+ * - false if the IR bit still does not match @ir after all retries are
+ *   exhausted
  */
-static void vfio_ap_wait_for_irqclear(int apqn)
+static bool vfio_ap_wait_for_irqstate(int apqn, int ir)
 {
 	struct ap_queue_status status;
 	int retry = 5;
@@ -245,8 +259,8 @@ static void vfio_ap_wait_for_irqclear(int apqn)
 		switch (status.response_code) {
 		case AP_RESPONSE_NORMAL:
 		case AP_RESPONSE_RESET_IN_PROGRESS:
-			if (!status.irq_enabled)
-				return;
+			if (status.irq_enabled == ir)
+				return true;
 			fallthrough;
 		case AP_RESPONSE_BUSY:
 			msleep(20);
@@ -257,12 +271,15 @@ static void vfio_ap_wait_for_irqclear(int apqn)
 		default:
 			WARN_ONCE(1, "%s: tapq rc %02x: %04x\n", __func__,
 				  status.response_code, apqn);
-			return;
+			return true;
 		}
 	} while (--retry);
 
-	WARN_ONCE(1, "%s: tapq rc %02x: %04x could not clear IR bit\n",
-		  __func__, status.response_code, apqn);
+	WARN_ONCE(1, "%s: tapq rc %02x: timed out waiting for interrupts %s for %02x.%04x\n",
+		  __func__, status.response_code,
+		  ir ? "enabled" : "disabled",
+		  AP_QID_CARD(apqn), AP_QID_QUEUE(apqn));
+	return false;
 }
 
 /**
@@ -317,8 +334,30 @@ static struct ap_queue_status vfio_ap_irq_disable(struct vfio_ap_queue *q)
 		switch (status.response_code) {
 		case AP_RESPONSE_OTHERWISE_CHANGED:
 		case AP_RESPONSE_NORMAL:
-			vfio_ap_wait_for_irqclear(q->apqn);
-			goto end_free;
+			/*
+			 * AQIC disable was accepted (NORMAL), or the queue was
+			 * already disabled or a prior async request is still
+			 * completing (OTHERWISE_CHANGED).  In both cases, we must
+			 * wait until interrupt processing has been disabled
+			 * before proceeding.
+			 */
+			if (vfio_ap_wait_for_irqstate(q->apqn, AP_IRQ_DISABLED))
+				goto end_free;
+			/*
+			 * Timed out waiting to confirm interrupts are disabled.
+			 * If ap_aqic returned NORMAL, the guest would incorrectly
+			 * interpret that as a successful disable and may free or
+			 * reuse the NIB while hardware can still write to it.
+			 * Zero the status word and set OTHERWISE_CHANGED to mimic
+			 * what the hardware does for that response code. This
+			 * signals to the guest that the reset operation did not
+			 * complete.
+			 */
+			if (status.response_code == AP_RESPONSE_NORMAL) {
+				memset(&status, 0, sizeof(status));
+				status.response_code = AP_RESPONSE_OTHERWISE_CHANGED;
+			}
+			goto end_fail;
 		case AP_RESPONSE_RESET_IN_PROGRESS:
 		case AP_RESPONSE_BUSY:
 			msleep(20);
@@ -326,18 +365,46 @@ static struct ap_queue_status vfio_ap_irq_disable(struct vfio_ap_queue *q)
 		case AP_RESPONSE_Q_NOT_AVAIL:
 		case AP_RESPONSE_DECONFIGURED:
 		case AP_RESPONSE_CHECKSTOPPED:
+			/* AP not operational; no further interrupts possible */
+			WARN_ONCE(1, "%s: ap_aqic status %d\n", __func__,
+				  status.response_code);
+			goto end_free;
 		case AP_RESPONSE_INVALID_ADDRESS:
 		default:
-			/* All cases in default means AP not operational */
+			/*
+			 * The AQIC disable was rejected; IRQ is still enabled
+			 * and the hardware still holds the NIB address. Do not
+			 * free resources.
+			 */
 			WARN_ONCE(1, "%s: ap_aqic status %d\n", __func__,
 				  status.response_code);
-			goto end_free;
+			goto end_fail;
 		}
 	} while (retries--);
 
 	WARN_ONCE(1, "%s: ap_aqic status %d\n", __func__,
 		  status.response_code);
+
+end_fail:
+	/*
+	 * We are here either because of a failure to verify that
+	 * interrupts have been disabled, or because the AQIC instruction
+	 * failed to disable them. The AQIC resources - the pinned NIB page
+	 * and the registered guest ISC - cannot be freed here. The hardware
+	 * may still write to the NIB; freeing the pinned page would result
+	 * in a use-after-free kernel crash. The resources will therefore be
+	 * leaked. This is preferable to a use-after-free.
+	 */
+	return status;
+
 end_free:
+	/*
+	 * This label is reached because the queue was successfully disabled,
+	 * or because the queue is not operational, in which case interrupts
+	 * can not be processed, so free the AQIC resources - the pinned NIB
+	 * page and the registered guest ISC - used to enable interrupts
+	 * so they will not be leaked.
+	 */
 	vfio_ap_free_aqic_resources(q);
 	return status;
 }
@@ -432,6 +499,7 @@ static struct ap_queue_status vfio_ap_irq_enable(struct vfio_ap_queue *q,
 	struct kvm *kvm;
 	phys_addr_t h_nib;
 	dma_addr_t nib;
+	char *msg;
 	int ret;
 
 	/* Verify that the notification indicator byte address is valid */
@@ -489,13 +557,49 @@ static struct ap_queue_status vfio_ap_irq_enable(struct vfio_ap_queue *q,
 	status = ap_aqic(q->apqn, aqic_gisa, h_nib);
 	switch (status.response_code) {
 	case AP_RESPONSE_NORMAL:
-		/* See if we did clear older IRQ configuration */
+		/*
+		 * AQIC initiates an asynchronous process; however, AP_RESPONSE_NORMAL
+		 * does not guarantee the IR bit is set yet.  Wait to confirm before
+		 * committing the new NIB and freeing the old resources.
+		 */
+		if (!vfio_ap_wait_for_irqstate(q->apqn, AP_IRQ_ENABLED)) {
+			/*
+			 * Timed out: the hardware may not have accepted the new
+			 * NIB.  Clean up the new resources and return
+			 * OTHERWISE_CHANGED to signal the guest to retry.
+			 */
+			ret = kvm_s390_gisc_unregister(kvm, isc);
+			if (ret) {
+				msg = "%s: kvm_s390_gisc_unregister: rc=%d isc=%d, apqn=%#04x\n";
+				VFIO_AP_DBF_WARN(msg, __func__, ret, isc, q->apqn);
+			}
+			vfio_unpin_pages(&q->matrix_mdev->vdev, nib, 1);
+			memset(&status, 0, sizeof(status));
+			status.response_code = AP_RESPONSE_OTHERWISE_CHANGED;
+			break;
+		}
+		/*
+		 * IR bit confirmed set. AQIC enable initiates an asynchronous
+		 * process; a CC=0 completion does not guarantee the process is
+		 * done. If the queue was already enabled for interrupts, the old
+		 * NIB (q->saved_iova) must not be freed until IR=1 is observed,
+		 * because until then the hardware has not completed its
+		 * transition to the new NIB. Now that IR=1 is confirmed, the
+		 * new NIB is in use for this queue, so no interrupts can be made
+		 * pending via any previously-registered NIB and the old
+		 * resources can be safely freed.
+		 */
 		vfio_ap_free_aqic_resources(q);
 		q->saved_iova = nib;
 		q->saved_isc = isc;
 		break;
 	case AP_RESPONSE_OTHERWISE_CHANGED:
-		/* We could not modify IRQ settings: clear new configuration */
+		/*
+		 * IRQ control is already set as requested or a prior async
+		 * request has not yet completed; in either case, this response
+		 * comes with CC=3 indicating the new NIB and ISC were not accepted by
+		 * the hardware, so clean them up.
+		 */
 		ret = kvm_s390_gisc_unregister(kvm, isc);
 		if (ret)
 			VFIO_AP_DBF_WARN("%s: kvm_s390_gisc_unregister: rc=%d isc=%d, apqn=%#04x\n",
@@ -503,9 +607,12 @@ static struct ap_queue_status vfio_ap_irq_enable(struct vfio_ap_queue *q,
 		vfio_unpin_pages(&q->matrix_mdev->vdev, nib, 1);
 		break;
 	default:
-		pr_warn("%s: apqn %04x: response: %02x\n", __func__, q->apqn,
-			status.response_code);
-		vfio_ap_irq_disable(q);
+		/* We could not modify IRQ settings: clear new configuration */
+		ret = kvm_s390_gisc_unregister(kvm, isc);
+		if (ret)
+			VFIO_AP_DBF_WARN("%s: kvm_s390_gisc_unregister: rc=%d isc=%d, apqn=%#04x\n",
+					 __func__, ret, isc, q->apqn);
+		vfio_unpin_pages(&q->matrix_mdev->vdev, nib, 1);
 		break;
 	}
 
@@ -635,7 +742,6 @@ static int handle_pqap(struct kvm_vcpu *vcpu)
 	}
 
 	status = vcpu->run->s.regs.gprs[1];
-
 	/* If IR bit(16) is set we enable the interrupt */
 	if ((status >> (63 - 16)) & 0x01)
 		qstatus = vfio_ap_irq_enable(q, status & 0x07, vcpu);
-- 
2.53.0

[PATCH v4 2/4] s390/vfio-ap: Fix failure to release IRQ notification eventfd contexts

[Anthony Krowiak]

When userspace registers IRQ notification eventfds via the
VFIO_DEVICE_SET_IRQS ioctl, vfio_ap_set_request_irq() and
vfio_ap_set_cfg_change_irq() each call eventfd_ctx_fdget(), which
takes a reference on the eventfd_ctx and stores it in
matrix_mdev->req_trigger and matrix_mdev->cfg_chg_trigger
respectively.

These references are dropped only when userspace explicitly replaces
or clears them via a subsequent SET_IRQS call.  If the device is
closed without that explicit teardown - because the guest exits,
the VM process crashes, or the device file is simply closed -
neither vfio_ap_mdev_close_device() nor the remove path releases
these references.  The eventfd_ctx backing objects and their
associated file references therefore leak for the lifetime of the
kernel.

Fix this by introducing vfio_ap_mdev_release_eventfds() and calling
it from vfio_ap_mdev_close_device() after vfio_ap_mdev_unset_kvm().
The VFIO core guarantees that close_device is called before
vfio_unregister_group_dev() returns in the remove path, so fixing
close_device is sufficient to cover both teardown paths.

Note:
~~~~
The matrix_dev->mdevs lock must be held during the call to
vfio_ap_mdev_release_eventfds(). There is a small window between the calls
to vfio_ap_mdev_unset_kvm() which gets and releases the update locks
and the acquisition of the matrix_dev->mdevs_lock mutex during which
it is possible - although highly unlikely during normal operation - whereby
a concurrent SET_IRQS call can get in.

Taking matrix_dev->mdevs_lock around vfio_ap_mdev_release_eventfds()
is sufficient to make this race-free. The SET_IRQS ioctl path writes
req_trigger and cfg_chg_trigger only from vfio_ap_mdev_ioctl(), which
holds mdevs_lock for its entire duration and always calls
eventfd_ctx_put() on the previous value before storing the new one.

Any number of concurrent SET_IRQS calls during the window between
vfio_ap_mdev_unset_kvm() and the acquisition of mdevs_lock are
therefore safe: each ioctl invocation puts the reference it found and
installs a new one, leaving exactly one live reference in the field
when it releases the lock. When release_eventfds subsequently acquires
mdevs_lock it finds that single surviving reference and puts it.
Conversely, a SET_IRQS call that loses the race and blocks on
mdevs_lock will find the field NULL after release_eventfds finishes,
take ownership of the reference it just created, and install it into a
field that will never be read again - a transient leak. To close that
final case, callers must ensure no new SET_IRQS ioctls can be issued
after close_device() is called, which the VFIO core guarantees by
releasing the device file before invoking close_device().

Fixes: bf48961f6f48e ("s390/vfio-ap: realize the VFIO_DEVICE_SET_IRQS ioctl")
Cc: stable@vger.kernel.org
Signed-off-by: Anthony Krowiak <akrowiak@linux.ibm.com>
Reviewed-by: Matthew Rosato <mjrosato@linux.ibm.com>
---
 drivers/s390/crypto/vfio_ap_ops.c | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/drivers/s390/crypto/vfio_ap_ops.c b/drivers/s390/crypto/vfio_ap_ops.c
index 24e93fb7f81a..363d9e53e249 100644
--- a/drivers/s390/crypto/vfio_ap_ops.c
+++ b/drivers/s390/crypto/vfio_ap_ops.c
@@ -2167,12 +2167,28 @@ static int vfio_ap_mdev_open_device(struct vfio_device *vdev)
 	return vfio_ap_mdev_set_kvm(matrix_mdev, vdev->kvm);
 }
 
+static void vfio_ap_mdev_release_eventfds(struct ap_matrix_mdev *matrix_mdev)
+{
+	if (matrix_mdev->req_trigger) {
+		eventfd_ctx_put(matrix_mdev->req_trigger);
+		matrix_mdev->req_trigger = NULL;
+	}
+	if (matrix_mdev->cfg_chg_trigger) {
+		eventfd_ctx_put(matrix_mdev->cfg_chg_trigger);
+		matrix_mdev->cfg_chg_trigger = NULL;
+	}
+}
+
 static void vfio_ap_mdev_close_device(struct vfio_device *vdev)
 {
 	struct ap_matrix_mdev *matrix_mdev =
 		container_of(vdev, struct ap_matrix_mdev, vdev);
 
 	vfio_ap_mdev_unset_kvm(matrix_mdev);
+
+	mutex_lock(&matrix_dev->mdevs_lock);
+	vfio_ap_mdev_release_eventfds(matrix_mdev);
+	mutex_unlock(&matrix_dev->mdevs_lock);
 }
 
 static void vfio_ap_mdev_request(struct vfio_device *vdev, unsigned int count)
-- 
2.53.0

[PATCH v4 3/4] s390/vfio-ap: Fix unbounded loop in apq_reset_check()

[Anthony Krowiak]

The apq_reset_check() worker polls ap_tapq() in a while(true) loop
waiting for a queue reset to complete. When ap_tapq() returns
AP_RESPONSE_BUSY or AP_RESPONSE_RESET_IN_PROGRESS,
apq_status_check() returns -EBUSY and the loop continues after
sleeping AP_RESET_MAX_WAIT (20ms). There is no upper bound on how
many times the loop iterates, so if the hardware continuously
returns a busy response the worker runs indefinitely.

This is particularly harmful because several callers of
vfio_ap_reset_queue() - such as vfio_ap_mdev_reset_queues(),
vfio_ap_mdev_reset_qlist() and vfio_ap_mdev_remove_queue - call
flush_work() on the queue's reset_work while holding one or more
of the global matrix_dev locks (guests_lock, mdevs_lock) or the
KVM lock. An indefinitely spinning worker permanently blocks access
to all ap_matrix_mdev objects which could hang other guests that are
using them.

Fix this by introducing AP_RESET_MAX_WAIT (2000ms) and breaking out
of the poll loop when elapsed time reaches that threshold. On
timeout, if the apq_reset_check() on that last loop has determined
that the reset has completed or that the queue is not operational,
the AQIC resources associated with this queue - the pinned page
containing the NIB and the registered guest ISC - will be cleared
because a successful reset disables interrupts nor can interrupts
be signaled from a non-operational queue.

If the apq_reset_check() did not verify completion of the reset,
the AQIC resources associated with this queue cannot be freed
because the NIB is the active DMA target for AP interrupt
delivery until the reset completes; freeing the pinned page while the
hardware may still write to it would result in a use-after-free
kernel crash. If the reset eventually completes, interrupts will be
terminated, but the pinned NIB page and ISC registration will be leaked.
This is preferable to either a use-after-free kernel crash or waiting
indefinitely and blocking access to all mdevs, hanging the guests to
which they are attached.

Note that on timeout, q->reset_status will hold the status from the most
recent reset operation so that callers inspecting
q->reset_status.response_code after flush_work() will see the value
and can return an appropriate return code.

Fixes: dd174833e44e ("s390/vfio-ap: remove upper limit on wait for queue reset to complete")
Cc: stable@vger.kernel.org
Signed-off-by: Anthony Krowiak <akrowiak@linux.ibm.com>
---
 drivers/s390/crypto/vfio_ap_ops.c | 40 ++++++++++++++++++++++++++++---
 1 file changed, 37 insertions(+), 3 deletions(-)

diff --git a/drivers/s390/crypto/vfio_ap_ops.c b/drivers/s390/crypto/vfio_ap_ops.c
index 363d9e53e249..3f5b012be450 100644
--- a/drivers/s390/crypto/vfio_ap_ops.c
+++ b/drivers/s390/crypto/vfio_ap_ops.c
@@ -34,6 +34,7 @@
 #define AP_IRQ_ENABLED	1
 
 #define AP_RESET_INTERVAL		20	/* Reset sleep interval (20ms)		*/
+#define AP_RESET_MAX_WAIT		2000	/* Maximum wait for reset (2000ms)	*/
 
 static int vfio_ap_mdev_reset_queues(struct ap_matrix_mdev *matrix_mdev);
 static int vfio_ap_mdev_reset_qlist(struct list_head *qlist);
@@ -2067,6 +2068,37 @@ static void apq_reset_check(struct work_struct *reset_work)
 		ret = apq_status_check(q->apqn, &status);
 		if (ret == -EIO)
 			return;
+		if (elapsed >= AP_RESET_MAX_WAIT) {
+			/*
+			 * If the status check determined that the reset completed
+			 * successfully or the queue is not operational, clean up
+			 * the AQIC resources because queue reset disables
+			 * interrupts, or because interrupts are not possible on a
+			 * non-operational queue.
+			 */
+			if (!ret)
+				goto done;
+			/*
+			 * Timed out without being able to verify reset completed.
+			 *
+			 * The AQIC resources associated with this queue - the pinned page
+			 * containing the NIB and the registered guest ISC - cannot be freed
+			 * here. The NIB is the active DMA target for AP interrupt delivery
+			 * until the reset completes; freeing the pinned page while the
+			 * hardware may still write to it would result in a use-after-free
+			 * kernel crash.
+			 *
+			 * If the reset eventually completes, interrupts will be terminated
+			 * and the pinned NIB page and ISC registration will be leaked. This
+			 * is preferable to either a use-after-free or waiting indefinitely:
+			 * the caller of apq_reset_check() holds mdevs_lock while flush_work()
+			 * blocks holds the matrix_dev->mdevs_lock mutex, which
+			 * serializes access to all mdev objects system-wide, so blocking
+			 * here would stall all other guests using AP queues.
+			 */
+
+			return;
+		}
 		if (ret == -EBUSY) {
 			pr_notice_ratelimited(WAIT_MSG, elapsed,
 					      AP_QID_CARD(q->apqn),
@@ -2083,11 +2115,13 @@ static void apq_reset_check(struct work_struct *reset_work)
 				memcpy(&q->reset_status, &status, sizeof(status));
 				continue;
 			}
-			if (q->saved_isc != VFIO_AP_ISC_INVALID)
-				vfio_ap_free_aqic_resources(q);
-			break;
+			goto done;
 		}
 	}
+
+done:
+	if (q->saved_isc != VFIO_AP_ISC_INVALID)
+		vfio_ap_free_aqic_resources(q);
 }
 
 static void vfio_ap_mdev_reset_queue(struct vfio_ap_queue *q)
-- 
2.53.0

[PATCH v4 4/4] s390/vfio-ap: Use AP_DOMAINS for adm_add bitmap size in vfio_ap_mdev_cfg_add()

[Anthony Krowiak]

Domain and control domain bitmaps are sized by the AP_DOMAINS constant, not
AP_DEVICES. The two constants are both 256 today so there is no functional
impact, but using the wrong constant is inconsistent with every operation
on aqm/adm bitmaps.

Use AP_DOMAINS to keep the code consistent and correct in case
the two constants ever diverge.

Note:
This patch was submitted in response to a sashiko review comment pointing
out there are other functions besides vfio_ap_mdev_cfg_add(), so there are
fixes included here for those also. The subject line was kept the same
since this is in v2 of this patch.

Signed-off-by: Anthony Krowiak <akrowiak@linux.ibm.com>
---
 drivers/s390/crypto/vfio_ap_ops.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/drivers/s390/crypto/vfio_ap_ops.c b/drivers/s390/crypto/vfio_ap_ops.c
index 3f5b012be450..d9a8844020bd 100644
--- a/drivers/s390/crypto/vfio_ap_ops.c
+++ b/drivers/s390/crypto/vfio_ap_ops.c
@@ -1517,7 +1517,7 @@ static void vfio_ap_mdev_hot_unplug_domain(struct ap_matrix_mdev *matrix_mdev,
 {
 	DECLARE_BITMAP(apqis, AP_DOMAINS);
 
-	bitmap_zero(apqis, AP_DEVICES);
+	bitmap_zero(apqis, AP_DOMAINS);
 	set_bit_inv(apqi, apqis);
 	vfio_ap_mdev_hot_unplug_domains(matrix_mdev, apqis);
 }
@@ -2853,11 +2853,11 @@ static void vfio_ap_mdev_on_cfg_remove(struct ap_config_info *cur_config_info,
 	do_remove |= bitmap_andnot(aqrem,
 				   (unsigned long *)prev_config_info->aqm,
 				   (unsigned long *)cur_config_info->aqm,
-				   AP_DEVICES);
+				   AP_DOMAINS);
 	do_remove |= bitmap_andnot(cdrem,
 				   (unsigned long *)prev_config_info->adm,
 				   (unsigned long *)cur_config_info->adm,
-				   AP_DEVICES);
+				   AP_DOMAINS);
 
 	if (do_remove)
 		vfio_ap_mdev_cfg_remove(aprem, aqrem, cdrem);
@@ -2968,7 +2968,7 @@ static void vfio_ap_mdev_cfg_add(unsigned long *apm_add, unsigned long *aqm_add,
 		bitmap_and(matrix_mdev->aqm_add,
 			   matrix_mdev->matrix.aqm, aqm_add, AP_DOMAINS);
 		bitmap_and(matrix_mdev->adm_add,
-			   matrix_mdev->matrix.adm, adm_add, AP_DEVICES);
+			   matrix_mdev->matrix.adm, adm_add, AP_DOMAINS);
 
 		mutex_unlock(&matrix_dev->mdevs_lock);
 	}
-- 
2.53.0