PMEMORY_AREA NTAPI
MmLocateMemoryAreaByRegion(
   PMMSUPPORT AddressSpace,
   PVOID Address,
   ULONG_PTR Length)
{
   PMEMORY_AREA Node;
   PVOID Extent = (PVOID)((ULONG_PTR)Address + Length);

   /* Special case for empty tree. */
   if (AddressSpace->WorkingSetExpansionLinks.Flink == NULL)
      return NULL;

   /* Traverse the tree from left to right. */
   for (Node = MmIterateFirstNode((PMEMORY_AREA)AddressSpace->WorkingSetExpansionLinks.Flink);
        Node != NULL;
        Node = MmIterateNextNode(Node))
   {
      if (Node->StartingAddress >= Address &&
          Node->StartingAddress < Extent)
      {
         DPRINT("MmLocateMemoryAreaByRegion(%p - %p): %p - %p\n",
                Address, (ULONG_PTR)Address + Length, Node->StartingAddress,
                Node->EndingAddress);
         return Node;
      }
      if (Node->EndingAddress > Address &&
          Node->EndingAddress < Extent)
      {
         DPRINT("MmLocateMemoryAreaByRegion(%p - %p): %p - %p\n",
                Address, (ULONG_PTR)Address + Length, Node->StartingAddress,
                Node->EndingAddress);
         return Node;
      }
      if (Node->StartingAddress <= Address &&
          Node->EndingAddress >= Extent)
      {
         DPRINT("MmLocateMemoryAreaByRegion(%p - %p): %p - %p\n",
                Address, (ULONG_PTR)Address + Length, Node->StartingAddress,
                Node->EndingAddress);
         return Node;
      }
      if (Node->StartingAddress >= Extent)
      {
         DPRINT("Finished MmLocateMemoryAreaByRegion() = NULL\n");
         return NULL;
      }
   }

   return NULL;
}