SEC-472 Java instanceof: avoid dereferencing null pointer

jbmc/src/janalyzer/janalyzer_parse_options.cpp

@@ -670,9 +670,9 @@ bool janalyzer_parse_optionst::process_goto_program(const optionst &options)
     remove_virtual_functions(goto_model);
     // remove Java throw and catch
     // This introduces instanceof, so order is important:
-    remove_exceptions(goto_model);
+    remove_exceptions(goto_model, get_message_handler());
     // remove rtti
-    remove_instanceof(goto_model);
+    remove_instanceof(goto_model, get_message_handler());
 
     // do partial inlining
     status() << "Partial Inlining" << eom;

jbmc/src/java_bytecode/remove_exceptions.cpp

@@ -88,10 +88,12 @@ class remove_exceptionst
   explicit remove_exceptionst(
     symbol_table_baset &_symbol_table,
     function_may_throwt _function_may_throw,
-    bool remove_added_instanceof)
+    bool remove_added_instanceof,
+    message_handlert &message_handler)
     : symbol_table(_symbol_table),
       function_may_throw(_function_may_throw),
-      remove_added_instanceof(remove_added_instanceof)
+      remove_added_instanceof(remove_added_instanceof),
+      message_handler(message_handler)
   {
   }
 
@@ -102,6 +104,7 @@ class remove_exceptionst
   symbol_table_baset &symbol_table;
   function_may_throwt function_may_throw;
   bool remove_added_instanceof;
+  message_handlert &message_handler;
 
   symbol_exprt get_inflight_exception_global();
 
@@ -342,7 +345,7 @@ void remove_exceptionst::add_exception_dispatch_sequence(
         t_exc->guard=check;
 
         if(remove_added_instanceof)
-          remove_instanceof(t_exc, goto_program, symbol_table);
+          remove_instanceof(t_exc, goto_program, symbol_table, message_handler);
       }
     }
   }
@@ -574,6 +577,7 @@ void remove_exceptionst::operator()(goto_programt &goto_program)
 void remove_exceptions(
   symbol_table_baset &symbol_table,
   goto_functionst &goto_functions,
+  message_handlert &message_handler,
   remove_exceptions_typest type)
 {
   const namespacet ns(symbol_table);
@@ -586,7 +590,8 @@ void remove_exceptions(
   remove_exceptionst remove_exceptions(
     symbol_table,
     function_may_throw,
-    type == remove_exceptions_typest::REMOVE_ADDED_INSTANCEOF);
+    type == remove_exceptions_typest::REMOVE_ADDED_INSTANCEOF,
+    message_handler);
   remove_exceptions(goto_functions);
 }
 
@@ -600,12 +605,14 @@ void remove_exceptions(
 /// \param symbol_table: global symbol table. The `@inflight_exception` global
 ///   may be added if not already present. It will not be initialised; that is
 ///   the caller's responsibility.
+/// \param message_handler: logging output
 /// \param type: specifies whether instanceof operations generated by this pass
 ///   should be lowered to class-identifier comparisons (using
 ///   remove_instanceof).
 void remove_exceptions(
   goto_programt &goto_program,
   symbol_table_baset &symbol_table,
+  message_handlert &message_handler,
   remove_exceptions_typest type)
 {
   remove_exceptionst::function_may_throwt any_function_may_throw =
@@ -614,12 +621,17 @@ void remove_exceptions(
   remove_exceptionst remove_exceptions(
     symbol_table,
     any_function_may_throw,
-    type == remove_exceptions_typest::REMOVE_ADDED_INSTANCEOF);
+    type == remove_exceptions_typest::REMOVE_ADDED_INSTANCEOF,
+    message_handler);
   remove_exceptions(goto_program);
 }
 
 /// removes throws/CATCH-POP/CATCH-PUSH
-void remove_exceptions(goto_modelt &goto_model, remove_exceptions_typest type)
+void remove_exceptions(
+  goto_modelt &goto_model,
+  message_handlert &message_handler,
+  remove_exceptions_typest type)
 {
-  remove_exceptions(goto_model.symbol_table, goto_model.goto_functions, type);
+  remove_exceptions(
+    goto_model.symbol_table, goto_model.goto_functions, message_handler, type);
 }

jbmc/src/java_bytecode/remove_exceptions.h

@@ -16,6 +16,8 @@ Date:   December 2016
 
 #include <goto-programs/goto_model.h>
 
+#include <util/message.h>
+
 #define INFLIGHT_EXCEPTION_VARIABLE_BASENAME "@inflight_exception"
 #define INFLIGHT_EXCEPTION_VARIABLE_NAME \
   "java::" INFLIGHT_EXCEPTION_VARIABLE_BASENAME
@@ -32,11 +34,13 @@ enum class remove_exceptions_typest
 void remove_exceptions(
   goto_programt &goto_program,
   symbol_table_baset &symbol_table,
+  message_handlert &message_handler,
   remove_exceptions_typest type =
     remove_exceptions_typest::DONT_REMOVE_INSTANCEOF);
 
 void remove_exceptions(
   goto_modelt &goto_model,
+  message_handlert &message_handler,
   remove_exceptions_typest type =
     remove_exceptions_typest::DONT_REMOVE_INSTANCEOF);
 

jbmc/src/java_bytecode/remove_instanceof.cpp

@@ -13,6 +13,7 @@ Author: Chris Smowton, [email protected]
 
 #include <goto-programs/class_hierarchy.h>
 #include <goto-programs/class_identifier.h>
+#include <goto-programs/goto_convert.h>
 
 #include <util/fresh_symbol.h>
 #include <java_bytecode/java_types.h>
@@ -22,8 +23,11 @@ Author: Chris Smowton, [email protected]
 class remove_instanceoft
 {
 public:
-  explicit remove_instanceoft(symbol_table_baset &symbol_table)
-  : symbol_table(symbol_table), ns(symbol_table)
+  remove_instanceoft(
+    symbol_table_baset &symbol_table, message_handlert &message_handler)
+    : symbol_table(symbol_table)
+    , ns(symbol_table)
+    , message_handler(message_handler)
   {
     class_hierarchy(symbol_table);
   }
@@ -38,8 +42,9 @@ class remove_instanceoft
   symbol_table_baset &symbol_table;
   namespacet ns;
   class_hierarchyt class_hierarchy;
+  message_handlert &message_handler;
 
-  std::size_t lower_instanceof(
+  bool lower_instanceof(
     exprt &, goto_programt &, goto_programt::targett);
 };
 
@@ -49,18 +54,18 @@ class remove_instanceoft
 /// \param expr: Expression to lower (the code or the guard of an instruction)
 /// \param goto_program: program the expression belongs to
 /// \param this_inst: instruction the expression is found at
-/// \return number of instanceof expressions that have been replaced
-std::size_t remove_instanceoft::lower_instanceof(
+/// \return true if any instanceof instructionw was replaced
+bool remove_instanceoft::lower_instanceof(
   exprt &expr,
   goto_programt &goto_program,
   goto_programt::targett this_inst)
 {
   if(expr.id()!=ID_java_instanceof)
   {
-    std::size_t replacements=0;
+    bool changed = false;
     Forall_operands(it, expr)
-      replacements+=lower_instanceof(*it, goto_program, this_inst);
-    return replacements;
+      changed |= lower_instanceof(*it, goto_program, this_inst);
+    return changed;
   }
 
   INVARIANT(
@@ -94,46 +99,91 @@ std::size_t remove_instanceoft::lower_instanceof(
       return a.compare(b) < 0;
     });
 
-  // Insert an instruction before the new check that assigns the clsid we're
-  // checking for to a temporary, as GOTO program if-expressions should
-  // not contain derefs.
-  // We actually insert the assignment instruction after the existing one.
-  // This will briefly be ill-formed (use before def of instanceof_tmp) but the
-  // two will subsequently switch places. This makes sure that the inserted
-  // assignement doesn't end up before any labels pointing at this instruction.
+  // Make temporaries to store the class identifier (avoids repeated derefs) and
+  // the instanceof result:
+
   symbol_typet jlo=to_symbol_type(java_lang_object_type().subtype());
-  exprt object_clsid=get_class_identifier_field(check_ptr, jlo, ns);
+  exprt object_clsid = get_class_identifier_field(check_ptr, jlo, ns);
 
-  symbolt &newsym = get_fresh_aux_symbol(
+  symbolt &clsid_tmp_sym = get_fresh_aux_symbol(
     object_clsid.type(),
     id2string(this_inst->function),
-    "instanceof_tmp",
+    "class_identifier_tmp",
+    source_locationt(),
+    ID_java,
+    symbol_table);
+
+  symbolt &instanceof_result_sym = get_fresh_aux_symbol(
+    bool_typet(),
+    id2string(this_inst->function),
+    "instanceof_result_tmp",
     source_locationt(),
     ID_java,
     symbol_table);
 
-  auto newinst=goto_program.insert_after(this_inst);
-  newinst->make_assignment();
-  newinst->code=code_assignt(newsym.symbol_expr(), object_clsid);
-  newinst->source_location=this_inst->source_location;
-  newinst->function=this_inst->function;
+  // Create
+  // if(expr == null)
+  //   instanceof_result = false;
+  // else
+  //   string clsid = expr->@class_identifier
+  //   instanceof_result = clsid == "A" || clsid == "B" || ...
 
-  // Replace the instanceof construct with a conjunction of non-null and the
-  // disjunction of all possible object types. According to the Java
-  // specification, null instanceof T is false for all possible values of T.
+  // According to the Java specification, null instanceof T is false for all
+  // possible values of T.
   // (http://docs.oracle.com/javase/specs/jls/se7/html/jls-15.html#jls-15.20.2)
-  notequal_exprt non_null_expr(
-    check_ptr, null_pointer_exprt(to_pointer_type(check_ptr.type())));
+
+  code_ifthenelset is_null_branch;
+  is_null_branch.cond() =
+    equal_exprt(
+      check_ptr, null_pointer_exprt(to_pointer_type(check_ptr.type())));
+  is_null_branch.then_case() =
+    code_assignt(instanceof_result_sym.symbol_expr(), false_exprt());
+
+  code_blockt else_block;
+  else_block.add(code_declt(clsid_tmp_sym.symbol_expr()));
+  else_block.add(code_assignt(clsid_tmp_sym.symbol_expr(), object_clsid));
+
   exprt::operandst or_ops;
   for(const auto &clsname : children)
   {
     constant_exprt clsexpr(clsname, string_typet());
-    equal_exprt test(newsym.symbol_expr(), clsexpr);
+    equal_exprt test(clsid_tmp_sym.symbol_expr(), clsexpr);
     or_ops.push_back(test);
   }
-  expr = and_exprt(non_null_expr, disjunction(or_ops));
+  else_block.add(
+    code_assignt(instanceof_result_sym.symbol_expr(), disjunction(or_ops)));
+
+  is_null_branch.else_case() = std::move(else_block);
+
+  // Replace the instanceof construct with instanceof_result:
+  expr = instanceof_result_sym.symbol_expr();
 
-  return 1;
+  // Insert the new test block before it:
+  goto_programt new_check_program;
+  goto_convert(
+    is_null_branch,
+    symbol_table,
+    new_check_program,
+    message_handler,
+    ID_java);
+
+  goto_program.destructive_insert(this_inst, new_check_program);
+
+  return true;
+}
+
+static bool contains_instanceof(const exprt &e)
+{
+  if(e.id() == ID_java_instanceof)
+    return true;
+
+  for(const exprt &subexpr : e.operands())
+  {
+    if(contains_instanceof(subexpr))
+      return true;
+  }
+
+  return false;
 }
 
 /// Replaces expressions like e instanceof A with e.\@class_identifier == "A"
@@ -146,15 +196,20 @@ bool remove_instanceoft::lower_instanceof(
   goto_programt &goto_program,
   goto_programt::targett target)
 {
-  std::size_t replacements=
-    lower_instanceof(target->code, goto_program, target)+
-    lower_instanceof(target->guard, goto_program, target);
+  if(target->is_target() &&
+     (contains_instanceof(target->code) || contains_instanceof(target->guard)))
+  {
+    // If this is a branch target, add a skip beforehand so we can splice new
+    // GOTO programs before the target instruction without inserting into the
+    // wrong basic block.
+    goto_program.insert_before_swap(target);
+    target->make_skip();
+    // Actually alter the now-moved instruction:
+    ++target;
+  }
 
-  if(replacements==0)
-    return false;
-  // Swap the original instruction with the last assignment added after it
-  target->swap(*std::next(target, replacements));
-  return true;
+  return lower_instanceof(target->code, goto_program, target) |
+    lower_instanceof(target->guard, goto_program, target);
 }
 
 /// Replace every instanceof in the passed function body with an explicit
@@ -185,12 +240,14 @@ bool remove_instanceoft::lower_instanceof(goto_programt &goto_program)
 /// \param target: The instruction to work on.
 /// \param goto_program: The function body containing the instruction.
 /// \param symbol_table: The symbol table to add symbols to.
+/// \param message_handler: logging output
 void remove_instanceof(
   goto_programt::targett target,
   goto_programt &goto_program,
-  symbol_table_baset &symbol_table)
+  symbol_table_baset &symbol_table,
+  message_handlert &message_handler)
 {
-  remove_instanceoft rem(symbol_table);
+  remove_instanceoft rem(symbol_table, message_handler);
   rem.lower_instanceof(goto_program, target);
 }
 
@@ -199,11 +256,13 @@ void remove_instanceof(
 /// \remarks Extra auxiliary variables may be introduced into symbol_table.
 /// \param function: The function to work on.
 /// \param symbol_table: The symbol table to add symbols to.
+/// \param message_handler: logging output
 void remove_instanceof(
   goto_functionst::goto_functiont &function,
-  symbol_table_baset &symbol_table)
+  symbol_table_baset &symbol_table,
+  message_handlert &message_handler)
 {
-  remove_instanceoft rem(symbol_table);
+  remove_instanceoft rem(symbol_table, message_handler);
   rem.lower_instanceof(function.body);
 }
 
@@ -212,11 +271,13 @@ void remove_instanceof(
 /// \remarks Extra auxiliary variables may be introduced into symbol_table.
 /// \param goto_functions: The functions to work on.
 /// \param symbol_table: The symbol table to add symbols to.
+/// \param message_handler: logging output
 void remove_instanceof(
   goto_functionst &goto_functions,
-  symbol_table_baset &symbol_table)
+  symbol_table_baset &symbol_table,
+  message_handlert &message_handler)
 {
-  remove_instanceoft rem(symbol_table);
+  remove_instanceoft rem(symbol_table, message_handler);
   bool changed=false;
   for(auto &f : goto_functions.function_map)
     changed=rem.lower_instanceof(f.second.body) || changed;
@@ -228,8 +289,12 @@ void remove_instanceof(
 /// class-identifier test.
 /// \remarks Extra auxiliary variables may be introduced into symbol_table.
 /// \param goto_model: The functions to work on and the symbol table to add
+/// \param message_handler: logging output
 /// symbols to.
-void remove_instanceof(goto_modelt &goto_model)
+void remove_instanceof(
+  goto_modelt &goto_model,
+  message_handlert &message_handler)
 {
-  remove_instanceof(goto_model.goto_functions, goto_model.symbol_table);
+  remove_instanceof(
+    goto_model.goto_functions, goto_model.symbol_table, message_handler);
 }