improve XENMEM_add_to_physmap_batch address checking

As a follow-up to XSA-212 we should have addressed a similar issue here:
The handles being advanced at the top of xenmem_add_to_physmap_batch()
means we allow hypervisor space accesses (in particular, for "errs",
writes) with suitably crafted input arguments. This isn't a security
issue in this case because of the limited width of struct
xen_add_to_physmap_batch's size field: It being 16-bits wide, only the
r/o M2P area can be accessed. Still we can and should do better.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>
master commit: 7f080956e9eed821fd42013bef11c1a2873fbeba
master date: 2017-11-28 13:15:12 +0100

diff --git a/xen/common/memory.c b/xen/common/memory.c
index 2dedb8c9e459cf236d37f620192a3434387b0bf8..c0c691a98a83b0204e75cf842ba0c08d726888b3 100644 (file)
--- a/xen/common/memory.c
+++ b/xen/common/memory.c
@@ -774,6 +774,11 @@ static int xenmem_add_to_physmap_batch(struct domain *d,
     guest_handle_add_offset(xatpb->errs, start);
     xatpb->size -= start;
 
+    if ( !guest_handle_okay(xatpb->idxs, xatpb->size) ||
+         !guest_handle_okay(xatpb->gpfns, xatpb->size) ||
+         !guest_handle_okay(xatpb->errs, xatpb->size) )
+        return -EFAULT;
+
     while ( xatpb->size > done )
     {
         xen_ulong_t idx;
@@ -1092,10 +1097,7 @@ long do_memory_op(unsigned long cmd, XEN_GUEST_HANDLE_PARAM(void) arg)
         if ( start_extent != (typeof(xatpb.size))start_extent )
             return -EDOM;
 
-        if ( copy_from_guest(&xatpb, arg, 1) ||
-             !guest_handle_okay(xatpb.idxs, xatpb.size) ||
-             !guest_handle_okay(xatpb.gpfns, xatpb.size) ||
-             !guest_handle_okay(xatpb.errs, xatpb.size) )
+        if ( copy_from_guest(&xatpb, arg, 1) )
             return -EFAULT;
 
         /* This mapspace is unsupported for this hypercall. */