iommu/vt-d: Do access checks before calling handle_mm_fault()

Not doing so is a bug and might trigger a BUG_ON in
handle_mm_fault(). So add the proper permission checks
before calling into mm code.
Reviewed-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Acked-By: David Woodhouse <David.Woodhouse@intel.com>
Signed-off-by: Joerg Roedel <jroedel@suse.de>

drivers/iommu/intel-svm.c

@@ -484,6 +484,23 @@ struct page_req_dsc {
 };
 
 #define PRQ_RING_MASK ((0x1000 << PRQ_ORDER) - 0x10)
+
+static bool access_error(struct vm_area_struct *vma, struct page_req_dsc *req)
+{
+	unsigned long requested = 0;
+
+	if (req->exe_req)
+		requested |= VM_EXEC;
+
+	if (req->rd_req)
+		requested |= VM_READ;
+
+	if (req->wr_req)
+		requested |= VM_WRITE;
+
+	return (requested & ~vma->vm_flags) != 0;
+}
+
 static irqreturn_t prq_event_thread(int irq, void *d)
 {
 	struct intel_iommu *iommu = d;
@@ -539,6 +556,9 @@ static irqreturn_t prq_event_thread(int irq, void *d)
 		if (!vma || address < vma->vm_start)
 			goto invalid;
 
+		if (access_error(vma, req))
+			goto invalid;
+
 		ret = handle_mm_fault(svm->mm, vma, address,
 				      req->wr_req ? FAULT_FLAG_WRITE : 0);
 		if (ret & VM_FAULT_ERROR)