1 files changed, 9 insertions, 6 deletions

diff --git a/virt/kvm/arm/vgic/vgic-its.c b/virt/kvm/arm/vgic/vgic-its.c
index 465095355666..a8f07243aa9f 100644
--- a/virt/kvm/arm/vgic/vgic-its.c
+++ b/virt/kvm/arm/vgic/vgic-its.c
@@ -316,21 +316,24 @@ static int vgic_copy_lpi_list(struct kvm_vcpu *vcpu, u32 **intid_ptr)
 	struct vgic_dist *dist = &vcpu->kvm->arch.vgic;
 	struct vgic_irq *irq;
 	u32 *intids;
-	int irq_count = dist->lpi_list_count, i = 0;
+	int irq_count, i = 0;
 
 	/*
-	 * We use the current value of the list length, which may change
-	 * after the kmalloc. We don't care, because the guest shouldn't
-	 * change anything while the command handling is still running,
-	 * and in the worst case we would miss a new IRQ, which one wouldn't
-	 * expect to be covered by this command anyway.
+	 * There is an obvious race between allocating the array and LPIs
+	 * being mapped/unmapped. If we ended up here as a result of a
+	 * command, we're safe (locks are held, preventing another
+	 * command). If coming from another path (such as enabling LPIs),
+	 * we must be careful not to overrun the array.
 	 */
+	irq_count = READ_ONCE(dist->lpi_list_count);
 	intids = kmalloc_array(irq_count, sizeof(intids[0]), GFP_KERNEL);
 	if (!intids)
 		return -ENOMEM;
 
 	spin_lock(&dist->lpi_list_lock);
 	list_for_each_entry(irq, &dist->lpi_list_head, lpi_list) {
+		if (i == irq_count)
+			break;
 		/* We don't need to "get" the IRQ, as we hold the list lock. */
 		if (irq->target_vcpu != vcpu)
 			continue;