From: Jan Beulich <jbeulich@suse.com>
Subject: x86/domain: locking for ioport_caps accesses

In order to be able to pull at least the XEN_DOMCTL_ioport_mapping
handling out of the domctl-locked region, the new separate (per-domain)
lock is used to synchronize in particular with
XEN_DOMCTL_ioport_permission.

Locking is added only as far as domctl-s are affected. Uses presently
outside of the domctl lock may want dealing with subsequently (perhaps
limited to non-__init code).

This is part of XSA-492.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Roger Pau Monné <roger.pau@citrix.com>

--- a/xen/arch/x86/domctl.c
+++ b/xen/arch/x86/domctl.c
@@ -225,6 +225,8 @@ long arch_do_domctl(
         unsigned int np = domctl->u.ioport_permission.nr_ports;
         int allow = domctl->u.ioport_permission.allow_access;
 
+        iocaps_double_lock(d, true);
+
         if ( (fp + np) <= fp || (fp + np) > MAX_IOPORTS )
             ret = -EINVAL;
         else if ( !ioports_access_permitted(currd, fp, fp + np - 1) ||
@@ -234,6 +236,8 @@ long arch_do_domctl(
             ret = ioports_permit_access(d, fp, fp + np - 1);
         else
             ret = ioports_deny_access(d, fp, fp + np - 1);
+
+        iocaps_double_unlock(d, true);
         break;
     }
 
@@ -608,16 +612,13 @@ long arch_do_domctl(
             break;
         }
 
-        ret = -EPERM;
-        if ( !ioports_access_permitted(currd, fmp, fmp + np - 1) )
-            break;
-
-        ret = xsm_ioport_mapping(XSM_HOOK, d, fmp, fmp + np - 1, add);
-        if ( ret )
-            break;
-
         hvm = &d->arch.hvm;
-        if ( add )
+        iocaps_double_lock(d, true);
+
+        if ( !ioports_access_permitted(currd, fmp, fmp + np - 1) ||
+             (ret = xsm_ioport_mapping(XSM_HOOK, d, fmp, fmp + np - 1, add)) )
+            ret = ret ?: -EPERM;
+        else if ( add )
         {
             printk(XENLOG_G_INFO
                    "ioport_map:add: dom%d gport=%x mport=%x nr=%x\n",
@@ -678,6 +680,8 @@ long arch_do_domctl(
                        "ioport_map: error %ld denying dom%d access to [%x,%x]\n",
                        ret, d->domain_id, fmp, fmp + np - 1);
         }
+
+        iocaps_double_unlock(d, true);
         break;
     }
 
--- a/xen/arch/x86/setup.c
+++ b/xen/arch/x86/setup.c
@@ -2173,9 +2173,12 @@ void __hwdom_init setup_io_bitmap(struct
         return;
 
     bitmap_fill(d->arch.hvm.io_bitmap, 0x10000);
+
+    read_lock(&d->caps_lock);
     if ( rangeset_report_ranges(d->arch.ioport_caps, 0, 0x10000,
                                 io_bitmap_cb, d) )
         BUG();
+    read_unlock(&d->caps_lock);
 
     /*
      * We need to trap 4-byte accesses to 0xcf8 (see admin_io_okay(),