Fix critical memory corruption bug caused by overwriting active page tables marked as free memory

boot/xtldr/arch/amd64/memory.cc

@@ -28,13 +28,12 @@ EFI_STATUS
 Memory::BuildPageMap(IN PXTBL_PAGE_MAPPING PageMap,
                      IN ULONG_PTR SelfMapAddress)
 {
-    PLIST_ENTRY ListEntry, ModulesList, ModulesListEntry;
-    PXTBL_MEMORY_MAPPING Mapping;
+    PLIST_ENTRY ModulesList, ModulesListEntry;
     PXTBL_MODULE_INFO ModuleInfo;
     EFI_PHYSICAL_ADDRESS Address;
-    PVOID LoaderBase;
     ULONGLONG LoaderSize;
     EFI_STATUS Status;
+    PVOID LoaderBase;
 
     /* Allocate pages for the Page Map */
     Status = AllocatePages(AllocateAnyPages, 1, &Address);
@@ -65,7 +64,7 @@ Memory::BuildPageMap(IN PXTBL_PAGE_MAPPING PageMap,
     }
 
     /* Map the trampoline code area */
-    Status = MapVirtualMemory(PageMap, MM_TRAMPOLINE_ADDRESS,MM_TRAMPOLINE_ADDRESS,
+    Status = MapVirtualMemory(PageMap, MM_TRAMPOLINE_ADDRESS, MM_TRAMPOLINE_ADDRESS,
                               1, LoaderFirmwareTemporary);
     if(Status != STATUS_EFI_SUCCESS)
     {
@@ -117,6 +116,28 @@ Memory::BuildPageMap(IN PXTBL_PAGE_MAPPING PageMap,
         return STATUS_EFI_PROTOCOL_ERROR;
     }
 
+    /* Return success */
+    return STATUS_EFI_SUCCESS;
+}
+
+/**
+ * Iterates through the memory map and physically maps all virtual addresses to page tables.
+ *
+ * @param PageMap
+ *        Supplies a pointer to the page mapping structure.
+ *
+ * @return This routine returns a status code.
+ *
+ * @since XT 1.0
+ */
+XTCDECL
+EFI_STATUS
+Memory::CommitPageMap(IN PXTBL_PAGE_MAPPING PageMap)
+{
+    PXTBL_MEMORY_MAPPING Mapping;
+    PLIST_ENTRY ListEntry;
+    EFI_STATUS Status;
+
     /* Iterate through and map all the mappings*/
     Debug::Print(L"Mapping and dumping EFI memory:\n");
     ListEntry = PageMap->MemoryMap.Flink;