[PATCH] domain: Validate __copy_to_guest in VCPUOP_register_runstate_memory_area

[Michal Orzel <michal.orzel@xxxxxxx>]

For guests with paging mode external, guest_handle_okay() always returns
success, even if the guest handle is invalid (e.g. address not in P2M).
In VCPUOP_register_runstate_memory_area, we would then blindly set
runstate_guest() for a given vCPU to invalid handle. Moreover, we don't
check the return value from __copy_to_guest() and return success to the
guest, even in case of a failure during copy. Fix it, by checking the
return value from __copy_to_guest() and set runstate_guest() only on
success.

Signed-off-by: Michal Orzel <michal.orzel@xxxxxxx>
---
I'm not sure what would be the appropriate commit for a Fixes tag. Arm port
only moved this code to common in 8968bafa3170d46d21d8f6ee2d0856f270c864ad,
so if at all, it would be:
Fixes: 8968bafa3170 ("xen: move VCPUOP_register_runstate_memory_area to common 
code")
---
 xen/common/domain.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/xen/common/domain.c b/xen/common/domain.c
index 92263a4fbdc5..3f6fb0798fa3 100644
--- a/xen/common/domain.c
+++ b/xen/common/domain.c
@@ -2046,19 +2046,21 @@ long common_vcpu_op(int cmd, struct vcpu *v, 
XEN_GUEST_HANDLE_PARAM(void) arg)
         if ( !guest_handle_okay(area.addr.h, 1) )
             break;
 
-        rc = 0;
-        runstate_guest(v) = area.addr.h;
-
         if ( v == current )
         {
-            __copy_to_guest(runstate_guest(v), &v->runstate, 1);
+            if ( __copy_to_guest(area.addr.h, &v->runstate, 1) )
+                break;
         }
         else
         {
             vcpu_runstate_get(v, &runstate);
-            __copy_to_guest(runstate_guest(v), &runstate, 1);
+            if ( __copy_to_guest(area.addr.h, &runstate, 1) )
+                break;
         }
 
+        rc = 0;
+        runstate_guest(v) = area.addr.h;
+
         break;
     }
 
-- 
2.25.1