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

[Xen patchbot-unstable <patchbot@xxxxxxx>]

# HG changeset patch
# User Jan Beulich <jbeulich@xxxxxxxx>
# Date 1354646294 0
# Node ID b406e395995fcf174475e4ca3db21a2d55e627cd
# Parent  96fed5bcd0971c74e8751489278011407f9f91f3
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 96fed5bcd097 -r b406e395995f xen/common/compat/memory.c
--- a/xen/common/compat/memory.c        Tue Dec 04 18:38:05 2012 +0000
+++ b/xen/common/compat/memory.c        Tue Dec 04 18:38:14 2012 +0000
@@ -115,6 +115,12 @@ 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 96fed5bcd097 -r b406e395995f xen/common/memory.c
--- a/xen/common/memory.c       Tue Dec 04 18:38:05 2012 +0000
+++ b/xen/common/memory.c       Tue Dec 04 18:38:14 2012 +0000
@@ -308,6 +308,13 @@ 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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