[Xen-changelog] [xen master] xen/physmap: Do not permit a guest to populate PoD pages for itself

[patchbot@xxxxxxx]

commit 2a99aa99fc84a45f505f84802af56b006d14c52e
Author:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
AuthorDate: Fri Aug 19 15:08:10 2016 +0100
Commit:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
CommitDate: Fri Aug 19 18:40:11 2016 +0100

    xen/physmap: Do not permit a guest to populate PoD pages for itself
    
    PoD is supposed to be entirely transparent to guest, but this interface has
    been left exposed for a long time.
    
    The use of PoD requires careful co-ordination by the toolstack with the
    XENMEM_{get,set}_pod_target hypercalls, and xenstore ballooning target.  The
    best a guest can do without toolstack cooperation crash.
    
    Furthermore, there are combinations of features (e.g. c/s c63868ff "libxl:
    disallow PCI device assignment for HVM guest when PoD is enabled") which a
    toolstack might wish to explicitly prohibit (in this case, because the two
    simply don't function in combination).  In such cases, the guest mustn't be
    able to subvert the configuration chosen by the toolstack.
    
    Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    Acked-by: Jan Beulich <jbeulich@xxxxxxxx>
---
 xen/common/memory.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/xen/common/memory.c b/xen/common/memory.c
index 1ead35c..f34dd56 100644
--- a/xen/common/memory.c
+++ b/xen/common/memory.c
@@ -140,14 +140,14 @@ static void populate_physmap(struct memop_args *a)
     struct page_info *page;
     unsigned int i, j;
     xen_pfn_t gpfn, mfn;
-    struct domain *d = a->domain;
+    struct domain *d = a->domain, *curr_d = current->domain;
 
     if ( !guest_handle_subrange_okay(a->extent_list, a->nr_done,
                                      a->nr_extents-1) )
         return;
 
     if ( a->extent_order > (a->memflags & MEMF_populate_on_demand ? MAX_ORDER :
-                            max_order(current->domain)) )
+                            max_order(curr_d)) )
         return;
 
     for ( i = a->nr_done; i < a->nr_extents; i++ )
@@ -163,6 +163,10 @@ static void populate_physmap(struct memop_args *a)
 
         if ( a->memflags & MEMF_populate_on_demand )
         {
+            /* Disallow populating PoD pages on oneself. */
+            if ( d == curr_d )
+                goto out;
+
             if ( guest_physmap_mark_populate_on_demand(d, gpfn,
                                                        a->extent_order) < 0 )
                 goto out;
--
generated by git-patchbot for /home/xen/git/xen.git#master

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