[Xen-changelog] [xen-4.1-testing] xen: add missing guest address range checks to XENMEM_exchange handlers

[Xen patchbot-4.1-testing <patchbot@xxxxxxx>]

# HG changeset patch
# User Jan Beulich <jbeulich@xxxxxxxx>
# Date 1354646996 0
# Node ID f81286b3be32cc1292d279013ce61e8636dd8cdb
# Parent  e7c8ffa11596af038713773d984e3ee1759f4083
xen: add missing guest address range checks to XENMEM_exchange handlers

Ever since its existence (3.0.3 iirc) the handler for this has been
using non address range checking guest memory accessors (i.e.
the ones prefixed with two underscores) without first range
checking the accessed space (via guest_handle_okay()), allowing
a guest to access and overwrite hypervisor memory.

This is XSA-29 / CVE-2012-5513.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
Acked-by: Ian Campbell <ian.campbell@xxxxxxxxxx>
Acked-by: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
Committed-by: Ian Jackson <ian.jackson.citrix.com>
---


diff -r e7c8ffa11596 -r f81286b3be32 xen/common/compat/memory.c
--- a/xen/common/compat/memory.c        Tue Dec 04 18:49:53 2012 +0000
+++ b/xen/common/compat/memory.c        Tue Dec 04 18:49:56 2012 +0000
@@ -114,6 +114,12 @@ int compat_memory_op(unsigned int cmd, X
                   (cmp.xchg.out.nr_extents << cmp.xchg.out.extent_order)) )
                 return -EINVAL;
 
+            if ( !compat_handle_okay(cmp.xchg.in.extent_start,
+                                     cmp.xchg.in.nr_extents) ||
+                 !compat_handle_okay(cmp.xchg.out.extent_start,
+                                     cmp.xchg.out.nr_extents) )
+                return -EFAULT;
+
             start_extent = cmp.xchg.nr_exchanged;
             end_extent = (COMPAT_ARG_XLAT_SIZE - sizeof(*nat.xchg)) /
                          (((1U << ABS(order_delta)) + 1) *
diff -r e7c8ffa11596 -r f81286b3be32 xen/common/memory.c
--- a/xen/common/memory.c       Tue Dec 04 18:49:53 2012 +0000
+++ b/xen/common/memory.c       Tue Dec 04 18:49:56 2012 +0000
@@ -289,6 +289,13 @@ static long memory_exchange(XEN_GUEST_HA
         goto fail_early;
     }
 
+    if ( !guest_handle_okay(exch.in.extent_start, exch.in.nr_extents) ||
+         !guest_handle_okay(exch.out.extent_start, exch.out.nr_extents) )
+    {
+        rc = -EFAULT;
+        goto fail_early;
+    }
+
     /* Only privileged guests can allocate multi-page contiguous extents. */
     if ( !multipage_allocation_permitted(current->domain,
                                          exch.in.extent_order) ||

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