xen/blkfront: harden blkfront against event channel storms

commit 0fd08a34e8e3b67ec9bd8287ac0facf8374b844a upstream.

The Xen blkfront driver is still vulnerable for an attack via excessive
number of events sent by the backend. Fix that by using lateeoi event
channels.

This is part of XSA-391

Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
index 878eb9ba06b2799dd53a9409d610eeeaab9b3c65..4487530217246acd4467f4e10a06555b2694dcfa 100644 (file)
--- a/drivers/block/xen-blkfront.c
+++ b/drivers/block/xen-blkfront.c
@@ -1566,9 +1566,12 @@ static irqreturn_t blkif_interrupt(int irq, void *dev_id)
        unsigned long flags;
        struct blkfront_ring_info *rinfo = (struct blkfront_ring_info *)dev_id;
        struct blkfront_info *info = rinfo->dev_info;
+       unsigned int eoiflag = XEN_EOI_FLAG_SPURIOUS;
 
-       if (unlikely(info->connected != BLKIF_STATE_CONNECTED))
+       if (unlikely(info->connected != BLKIF_STATE_CONNECTED)) {
+               xen_irq_lateeoi(irq, XEN_EOI_FLAG_SPURIOUS);
                return IRQ_HANDLED;
+       }
 
        spin_lock_irqsave(&rinfo->ring_lock, flags);
  again:
@@ -1584,6 +1587,8 @@ static irqreturn_t blkif_interrupt(int irq, void *dev_id)
                unsigned long id;
                unsigned int op;
 
+               eoiflag = 0;
+
                RING_COPY_RESPONSE(&rinfo->ring, i, &bret);
                id = bret.id;
 
@@ -1699,6 +1704,8 @@ static irqreturn_t blkif_interrupt(int irq, void *dev_id)
 
        spin_unlock_irqrestore(&rinfo->ring_lock, flags);
 
+       xen_irq_lateeoi(irq, eoiflag);
+
        return IRQ_HANDLED;
 
  err:
@@ -1706,6 +1713,8 @@ static irqreturn_t blkif_interrupt(int irq, void *dev_id)
 
        spin_unlock_irqrestore(&rinfo->ring_lock, flags);
 
+       /* No EOI in order to avoid further interrupts. */
+
        pr_alert("%s disabled for further use\n", info->gd->disk_name);
        return IRQ_HANDLED;
 }
@@ -1745,8 +1754,8 @@ static int setup_blkring(struct xenbus_device *dev,
        if (err)
                goto fail;
 
-       err = bind_evtchn_to_irqhandler(rinfo->evtchn, blkif_interrupt, 0,
-                                       "blkif", rinfo);
+       err = bind_evtchn_to_irqhandler_lateeoi(rinfo->evtchn, blkif_interrupt,
+                                               0, "blkif", rinfo);
        if (err <= 0) {
                xenbus_dev_fatal(dev, err,
                                 "bind_evtchn_to_irqhandler failed");