x86: properly check XEN_DOMCTL_ioport_mapping arguments for invalid range

In particular, the case of "np" being a very large value wasn't handled
correctly. The range start checks also were off by one (except that in
practice, when "np" is properly range checked, this would still have
been caught by the range end checks).

Also, is a GFN wrap in XEN_DOMCTL_memory_mapping really okay?

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Keir Fraser <keir@xen.org>

xen/arch/x86/domctl.c

@@ -884,7 +884,7 @@ long arch_do_domctl(
         int found = 0;
 
         ret = -EINVAL;
-        if ( (np == 0) || (fgp > MAX_IOPORTS) || (fmp > MAX_IOPORTS) ||
+        if ( ((fgp | fmp | (np - 1)) >= MAX_IOPORTS) ||
             ((fgp + np) > MAX_IOPORTS) || ((fmp + np) > MAX_IOPORTS) )
         {
             printk(XENLOG_G_ERR