xen: avoid calling rcu_lock_*target_domain when an XSM hook exists

The rcu_lock_{,remote_}target_domain_by_id functions are wrappers
around an IS_PRIV_FOR check for the current domain. This is now
redundant with XSM hooks, so replace these calls with
rcu_lock_domain_by_any_id or rcu_lock_remote_domain_by_id to remove
the duplicate permission checks.

When XSM_ENABLE is not defined or when the dummy XSM module is used,
this patch should not change any functionality. Because the locations
of privilege checks have sometimes moved below argument validation,
error returns of some functions may change from EPERM to EINVAL when
called with invalid arguments and from a domain without permission to
perform the operation.

Signed-off-by: Daniel De Graaf <dgdegra@tycho.nsa.gov>
Acked-by: Jan Beulich <jbeulich@suse.com>
Committed-by: Keir Fraser <keir@xen.org>

1 files changed, 9 insertions, 13 deletions

diff --git a/xen/arch/x86/mm.c b/xen/arch/x86/mm.c
index af2eafa6f5..c8e39c0a87 100644
--- a/xen/arch/x86/mm.c
+++ b/xen/arch/x86/mm.c
@@ -4375,9 +4375,9 @@ long arch_memory_op(int op, XEN_GUEST_HANDLE_PARAM(void) arg)
         if ( copy_from_guest(&xatp, arg, 1) )
             return -EFAULT;
 
-        rc = rcu_lock_target_domain_by_id(xatp.domid, &d);
-        if ( rc != 0 )
-            return rc;
+        d = rcu_lock_domain_by_any_id(xatp.domid);
+        if ( d == NULL )
+            return -ESRCH;
 
         if ( xsm_add_to_physmap(current->domain, d) )
         {
@@ -4414,9 +4414,9 @@ long arch_memory_op(int op, XEN_GUEST_HANDLE_PARAM(void) arg)
         if ( fmap.map.nr_entries > E820MAX )
             return -EINVAL;
 
-        rc = rcu_lock_target_domain_by_id(fmap.domid, &d);
-        if ( rc != 0 )
-            return rc;
+        d = rcu_lock_domain_by_any_id(fmap.domid);
+        if ( d == NULL )
+            return -ESRCH;
 
         rc = xsm_domain_memory_map(d);
         if ( rc )
@@ -4569,16 +4569,12 @@ long arch_memory_op(int op, XEN_GUEST_HANDLE_PARAM(void) arg)
         struct domain *d;
         struct p2m_domain *p2m;
 
-        /* Support DOMID_SELF? */
-        if ( !IS_PRIV(current->domain) )
-            return -EPERM;
-
         if ( copy_from_guest(&target, arg, 1) )
             return -EFAULT;
 
-        rc = rcu_lock_target_domain_by_id(target.domid, &d);
-        if ( rc != 0 )
-            return rc;
+        d = rcu_lock_domain_by_any_id(target.domid);
+        if ( d == NULL )
+            return -ESRCH;
 
         if ( op == XENMEM_set_pod_target )
             rc = xsm_set_pod_target(d);