KVM: arm64: vgic-its: Avoid potential UAF in LPI translation cache

There is a potential UAF scenario in the case of an LPI translation
cache hit racing with an operation that invalidates the cache, such
as a DISCARD ITS command. The root of the problem is that
vgic_its_check_cache() does not elevate the refcount on the vgic_irq
before dropping the lock that serializes refcount changes.

Have vgic_its_check_cache() raise the refcount on the returned vgic_irq
and add the corresponding decrement after queueing the interrupt.

Cc: [email protected]
Signed-off-by: Oliver Upton <[email protected]>
Signed-off-by: Marc Zyngier <[email protected]>
Link: https://lore.kernel.org/r/[email protected]

Author: oupton

arch/arm64/kvm/vgic/vgic-its.c

@@ -590,7 +590,11 @@ static struct vgic_irq *vgic_its_check_cache(struct kvm *kvm, phys_addr_t db,
 	unsigned long flags;
 
 	raw_spin_lock_irqsave(&dist->lpi_list_lock, flags);
+
 	irq = __vgic_its_check_cache(dist, db, devid, eventid);
+	if (irq)
+		vgic_get_irq_kref(irq);
+
 	raw_spin_unlock_irqrestore(&dist->lpi_list_lock, flags);
 
 	return irq;
@@ -769,6 +773,7 @@ int vgic_its_inject_cached_translation(struct kvm *kvm, struct kvm_msi *msi)
 	raw_spin_lock_irqsave(&irq->irq_lock, flags);
 	irq->pending_latch = true;
 	vgic_queue_irq_unlock(kvm, irq, flags);
+	vgic_put_irq(kvm, irq);
 
 	return 0;
 }