[Xen-devel] [PATCH v2] xen: arm: process XENMEM_add_to_physmap_range forwards not backwards.

[Ian Campbell <ian.campbell@xxxxxxxxxx>]

Jan points out that processing the list backwards is rather counter intuitive
and that the effect of the hypercall can differ between forwards and backwards
processing (e.g. in the presence of duplicate idx or gpfn, which would be
unusualy but as Jan says, users are a creative bunch)

Signed-off-by: Ian Campbell <ian.campbell@xxxxxxxxxx>
Cc: Jan Beulich <JBeulich@xxxxxxxx>
Cc: Mukesh Rathor <mukesh.rathor@xxxxxxxxxx>
---
v2: Remember to crank the errs array too.

    Resending despite abuse of overwriting the IN paramters, since coming to
    rely on backwards processing is a harder hole to get out of than going
    from modifying the strict to not.

Release: subtle ABI change, should go in to 4.4 before people rely on it (they
are not relying on it today TTBOMK and it seems unlikely but lets not risk it)
---
 xen/arch/arm/mm.c |   13 ++++++-------
 1 file changed, 6 insertions(+), 7 deletions(-)

diff --git a/xen/arch/arm/mm.c b/xen/arch/arm/mm.c
index e235364..f1b7099 100644
--- a/xen/arch/arm/mm.c
+++ b/xen/arch/arm/mm.c
@@ -1062,21 +1062,18 @@ static int xenmem_add_to_physmap_range(struct domain *d,
 {
     int rc;
 
-    /* Process entries in reverse order to allow continuations */
     while ( xatpr->size > 0 )
     {
         xen_ulong_t idx;
         xen_pfn_t gpfn;
 
-        if ( unlikely(copy_from_guest_offset(&idx, xatpr->idxs,
-                                             xatpr->size-1, 1)) )
+        if ( unlikely(copy_from_guest_offset(&idx, xatpr->idxs, 0, 1)) )
         {
             rc = -EFAULT;
             goto out;
         }
 
-        if ( unlikely(copy_from_guest_offset(&gpfn, xatpr->gpfns,
-                                             xatpr->size-1, 1)) )
+        if ( unlikely(copy_from_guest_offset(&gpfn, xatpr->gpfns, 0, 1)) )
         {
             rc = -EFAULT;
             goto out;
@@ -1086,8 +1083,7 @@ static int xenmem_add_to_physmap_range(struct domain *d,
                                        xatpr->foreign_domid,
                                        idx, gpfn);
 
-        if ( unlikely(copy_to_guest_offset(xatpr->errs,
-                                           xatpr->size-1, &rc, 1)) )
+        if ( unlikely(copy_to_guest_offset(xatpr->errs, 0, &rc, 1)) )
         {
             rc = -EFAULT;
             goto out;
@@ -1096,6 +1092,9 @@ static int xenmem_add_to_physmap_range(struct domain *d,
         if ( rc < 0 )
             goto out;
 
+        guest_handle_add_offset(xatpr->idxs, 1);
+        guest_handle_add_offset(xatpr->gpfns, 1);
+        guest_handle_add_offset(xatpr->errs, 1);
         xatpr->size--;
 
         /* Check for continuation if it's not the last interation */
-- 
1.7.10.4


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