[Xen-changelog] [xen-unstable] x86: fix hypercall continuation cancellation in XENMAPSPACE_gmfn_range compat wrapper

[Xen patchbot-unstable <patchbot@xxxxxxx>]

# HG changeset patch
# User Jan Beulich <jbeulich@xxxxxxxx>
# Date 1354093346 -3600
# Node ID 7670eabcbafc7251c336550cd7ce3ea4078a36b9
# Parent  0aa1c5136a548a9d2498febc0d3bcee71ebeeafe
x86: fix hypercall continuation cancellation in XENMAPSPACE_gmfn_range compat 
wrapper

When no continuation was established, there must also not be an attempt
to cancel it - hypercall_cancel_continuation(), in the non-HVM, non-
multicall case, adjusts the guest mode return address in a way assuming
that an earlier call hypercall_create_continuation() took place.

Once touching this code, also restructure it slightly to improve
readability and switch to using the more relaxed copy function (copying
from the same guest memory already validated the virtual address
range).

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
Acked-by: Keir Fraser <keir@xxxxxxx>
---


diff -r 0aa1c5136a54 -r 7670eabcbafc xen/arch/x86/x86_64/compat/mm.c
--- a/xen/arch/x86/x86_64/compat/mm.c   Wed Nov 28 10:01:33 2012 +0100
+++ b/xen/arch/x86/x86_64/compat/mm.c   Wed Nov 28 10:02:26 2012 +0100
@@ -66,21 +66,20 @@ int compat_arch_memory_op(int op, XEN_GU
         XLAT_add_to_physmap(nat, &cmp);
         rc = arch_memory_op(op, guest_handle_from_ptr(nat, void));
 
-        if ( cmp.space == XENMAPSPACE_gmfn_range )
+        if ( !rc || cmp.space != XENMAPSPACE_gmfn_range )
+            break;
+
+        XLAT_add_to_physmap(&cmp, nat);
+        if ( __copy_to_guest(arg, &cmp, 1) )
         {
-            if ( rc )
-            {
-                XLAT_add_to_physmap(&cmp, nat);
-                if ( copy_to_guest(arg, &cmp, 1) )
-                {
-                    hypercall_cancel_continuation();
-                    return -EFAULT;
-                }
-            }
             if ( rc == __HYPERVISOR_memory_op )
-                hypercall_xlat_continuation(NULL, 0x2, nat, arg);
+                hypercall_cancel_continuation();
+            return -EFAULT;
         }
 
+        if ( rc == __HYPERVISOR_memory_op )
+            hypercall_xlat_continuation(NULL, 0x2, nat, arg);
+
         break;
     }
 

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