analyzer: Add support of placement new and improved operator new [PR105948,PR94355]

Fixed spurious possibly-NULL warning always tagging along throwing
operator new despite it never returning NULL.
Now operator new is correctly recognized as possibly returning NULL
if and only if it is non-throwing or exceptions have been disabled.
Different standard signatures of operator new are now properly
recognized.

Added support of placement new, so that it is now properly recognized,
and a 'heap_allocated' region is no longer created for it.
Placement new size is also checked and a 'Wanalyzer-allocation-size'
is emitted when relevant, as well as always a 'Wanalyzer-out-of-bounds'.

'operator new' non-throwing variants are detected y checking the types
of the parameters.
Indeed, in a call to new (std::nothrow) () the chosen overload
has signature 'operator new (void*, std::nothrow_t&)', where the second
parameter is a reference. In a placement new, the second parameter will
always be a void pointer.

Prior to this patch, some buffers first allocated with 'new', then deleted
an thereafter used would result in a 'Wanalyzer-user-after-free'
warning. However the wording was "use after 'free'" instead of the
expected "use after 'delete'".
This patch fixes this by introducing a new kind of poisoned value,
namely POISON_KIND_DELETED.

Due to how the analyzer sees calls to non-throwing variants of
operator new, dereferencing a pointer freshly allocated in this fashion
caused both a 'Wanalyzer-use-of-uninitialized-value' and a
'Wanalyzer-null-dereference' to be emitted, while only the latter was
relevant. As a result, 'null-dereference' now supersedes
'use-of-uninitialized'.

Signed-off-by: benjamin priour <vultkayn@gcc.gnu.org>

gcc/analyzer/ChangeLog:

	PR analyzer/105948
	PR analyzer/94355
	* analyzer.h (is_placement_new_p): New declaration.
	* call-details.cc
	(call_details::deref_ptr_arg): New function.
	Dereference the argument at given index if possible.
	* call-details.h: Declaration of the above function.
	* kf-lang-cp.cc (is_placement_new_p): Returns true if the gcall
	is recognized as a placement new.
	(kf_operator_delete::impl_call_post): Unbinding a region and its
	descendents now poisons with POISON_KIND_DELETED.
	(register_known_functions_lang_cp): Known function "operator
	delete" is now registered only once independently of its number of
	arguments.
	* region-model.cc (region_model::eval_condition): Now
	recursively calls itself if any of the operand is wrapped in a
	cast.
	* sm-malloc.cc (malloc_state_machine::on_stmt):
	Add placement new recognition.
	* svalue.cc (poison_kind_to_str): Wording for the new PK.
	* svalue.h (enum poison_kind): Add value POISON_KIND_DELETED.

gcc/testsuite/ChangeLog:

	PR analyzer/105948
	PR analyzer/94355
	* g++.dg/analyzer/out-of-bounds-placement-new.C: Added a directive.
	* g++.dg/analyzer/placement-new.C: Added tests.
	* g++.dg/analyzer/new-2.C: New test.
	* g++.dg/analyzer/noexcept-new.C: New test.
	* g++.dg/analyzer/placement-new-size.C: New test.

8 files changed, 182 insertions, 25 deletions

diff --git a/gcc/analyzer/analyzer.h b/gcc/analyzer/analyzer.h
index 9b351b5..208b850 100644
--- a/gcc/analyzer/analyzer.h
+++ b/gcc/analyzer/analyzer.h
@@ -423,6 +423,7 @@ extern bool is_std_named_call_p (const_tree fndecl, const char *funcname,
 				 const gcall *call, unsigned int num_args);
 extern bool is_setjmp_call_p (const gcall *call);
 extern bool is_longjmp_call_p (const gcall *call);
+extern bool is_placement_new_p (const gcall *call);
 
 extern const char *get_user_facing_name (const gcall *call);
 
diff --git a/gcc/analyzer/call-details.cc b/gcc/analyzer/call-details.cc
index 66fb0fe..9480f03 100644
--- a/gcc/analyzer/call-details.cc
+++ b/gcc/analyzer/call-details.cc
@@ -295,6 +295,17 @@ call_details::get_arg_svalue (unsigned idx) const
   return m_model->get_rvalue (arg, m_ctxt);
 }
 
+/* If argument IDX's svalue at the callsite is of pointer type,
+   return the region it points to.
+   Otherwise return NULL.  */
+
+const region *
+call_details::deref_ptr_arg (unsigned idx) const
+{
+  const svalue *ptr_sval = get_arg_svalue (idx);
+  return m_model->deref_rvalue (ptr_sval, get_arg_tree (idx), m_ctxt);
+}
+
 /* Attempt to get the string literal for argument IDX, or return NULL
    otherwise.
    For use when implementing "__analyzer_*" functions that take
diff --git a/gcc/analyzer/call-details.h b/gcc/analyzer/call-details.h
index 57b9d6e..976517b 100644
--- a/gcc/analyzer/call-details.h
+++ b/gcc/analyzer/call-details.h
@@ -61,6 +61,7 @@ public:
   tree get_arg_tree (unsigned idx) const;
   tree get_arg_type (unsigned idx) const;
   const svalue *get_arg_svalue (unsigned idx) const;
+  const region *deref_ptr_arg (unsigned idx) const;
   const char *get_arg_string_literal (unsigned idx) const;
 
   tree get_fndecl_for_call () const;
diff --git a/gcc/analyzer/kf-lang-cp.cc b/gcc/analyzer/kf-lang-cp.cc
index 393b4f2..c7ee622 100644
--- a/gcc/analyzer/kf-lang-cp.cc
+++ b/gcc/analyzer/kf-lang-cp.cc
@@ -35,6 +35,38 @@ along with GCC; see the file COPYING3.  If not see
 
 #if ENABLE_ANALYZER
 
+/* Return true if CALL is a non-allocating operator new or operator new []
+   that contains no user-defined args, i.e. having any signature of:
+
+    - void* operator new (std::size_t count, void* ptr);
+    - void* operator new[] (std::size_t count, void* ptr);
+
+   See https://en.cppreference.com/w/cpp/memory/new/operator_new.  */
+
+bool is_placement_new_p (const gcall *call)
+{
+  gcc_assert (call);
+  tree fndecl = gimple_call_fndecl (call);
+
+  if (!fndecl || TREE_CODE (TREE_TYPE (fndecl)) == METHOD_TYPE)
+    /* Give up on overloaded operator new.  */
+    return false;
+
+  if (!is_named_call_p (fndecl, "operator new", call, 2)
+      && !is_named_call_p (fndecl, "operator new []", call, 2))
+    return false;
+
+  /* We must distinguish between an allocating non-throwing new
+    and a non-allocating new.
+
+    The former might have one of the following signatures :
+    void* operator new (std::size_t count, const std::nothrow_t& tag);
+    void* operator new[] (std::size_t count, const std::nothrow_t& tag);
+    Whereas a placement new would take a pointer.  */
+  tree arg1_type = TREE_CHAIN (TYPE_ARG_TYPES (TREE_TYPE (fndecl)));
+  return TREE_CODE (TREE_VALUE (arg1_type)) == POINTER_TYPE;
+}
+
 namespace ana {
 
 /* Implementations of specific functions.  */
@@ -46,7 +78,11 @@ class kf_operator_new : public known_function
 public:
   bool matches_call_types_p (const call_details &cd) const final override
   {
-    return cd.num_args () == 1;
+    return (cd.num_args () == 1
+      && cd.arg_is_size_p (0))
+      || (cd.num_args () == 2
+      && cd.arg_is_size_p (0)
+      && POINTER_TYPE_P (cd.get_arg_type (1)));
   }
 
   void impl_call_pre (const call_details &cd) const final override
@@ -54,28 +90,74 @@ public:
     region_model *model = cd.get_model ();
     region_model_manager *mgr = cd.get_manager ();
     const svalue *size_sval = cd.get_arg_svalue (0);
-    const region *new_reg
-      = model->get_or_create_region_for_heap_alloc (size_sval, cd.get_ctxt ());
-    if (cd.get_lhs_type ())
+    region_model_context *ctxt = cd.get_ctxt ();
+    const gcall *call = cd.get_call_stmt ();
+
+    /* If the call was actually a placement new, check that accessing
+       the buffer lhs is placed into does not result in out-of-bounds.  */
+    if (is_placement_new_p (call))
       {
-	const svalue *ptr_sval
-	  = mgr->get_ptr_svalue (cd.get_lhs_type (), new_reg);
-	cd.maybe_set_lhs (ptr_sval);
+	const region *ptr_reg = cd.deref_ptr_arg (1);
+	if (ptr_reg && cd.get_lhs_type ())
+	  {
+	    const svalue *num_bytes_sval = cd.get_arg_svalue (0);
+	    const region *sized_new_reg
+		= mgr->get_sized_region (ptr_reg,
+					 cd.get_lhs_type (),
+					 num_bytes_sval);
+	    model->check_region_for_write (sized_new_reg,
+					   nullptr,
+					   ctxt);
+	    const svalue *ptr_sval
+	      = mgr->get_ptr_svalue (cd.get_lhs_type (), sized_new_reg);
+	    cd.maybe_set_lhs (ptr_sval);
+	  }
+      }
+    /* If the call is an allocating new, then create a heap allocated
+       region.  */
+    else
+      {
+	const region *new_reg
+	  = model->get_or_create_region_for_heap_alloc (size_sval, ctxt);
+	if (cd.get_lhs_type ())
+	  {
+	    const svalue *ptr_sval
+	      = mgr->get_ptr_svalue (cd.get_lhs_type (), new_reg);
+	    cd.maybe_set_lhs (ptr_sval);
+	  }
+      }
+  }
+
+  void impl_call_post (const call_details &cd) const final override
+  {
+    region_model *model = cd.get_model ();
+    region_model_manager *mgr = cd.get_manager ();
+    tree callee_fndecl = cd.get_fndecl_for_call ();
+    region_model_context *ctxt = cd.get_ctxt ();
+
+    /* If the call is guaranteed to return nonnull
+       then add a nonnull constraint to the allocated region.  */
+    if (!TREE_NOTHROW (callee_fndecl) && flag_exceptions)
+      {
+	const svalue *null_sval
+	  = mgr->get_or_create_null_ptr (cd.get_lhs_type ());
+	const svalue *result
+	  = model->get_store_value (cd.get_lhs_region (), ctxt);
+	model->add_constraint (result, NE_EXPR, null_sval, ctxt);
       }
   }
 };
 
-/* Handler for "operator delete", both the sized and unsized variants
-   (2 arguments and 1 argument respectively), and for "operator delete []"  */
+/* Handler for "operator delete" and for "operator delete []",
+   both the sized and unsized variants
+   (2 arguments and 1 argument respectively).  */
 
 class kf_operator_delete : public known_function
 {
 public:
-  kf_operator_delete (unsigned num_args) : m_num_args (num_args) {}
-
   bool matches_call_types_p (const call_details &cd) const final override
   {
-    return cd.num_args () == m_num_args;
+    return cd.num_args () == 1 or cd.num_args () == 2;
   }
 
   void impl_call_post (const call_details &cd) const final override
@@ -86,12 +168,11 @@ public:
       {
 	/* If the ptr points to an underlying heap region, delete it,
 	   poisoning pointers.  */
-	model->unbind_region_and_descendents (freed_reg, POISON_KIND_FREED);
+	model->unbind_region_and_descendents (freed_reg,
+					      POISON_KIND_DELETED);
       }
   }
 
-private:
-  unsigned m_num_args;
 };
 
 /* Populate KFM with instances of known functions relating to C++.  */
@@ -101,9 +182,8 @@ register_known_functions_lang_cp (known_function_manager &kfm)
 {
   kfm.add ("operator new", make_unique<kf_operator_new> ());
   kfm.add ("operator new []", make_unique<kf_operator_new> ());
-  kfm.add ("operator delete", make_unique<kf_operator_delete> (1));
-  kfm.add ("operator delete", make_unique<kf_operator_delete> (2));
-  kfm.add ("operator delete []", make_unique<kf_operator_delete> (1));
+  kfm.add ("operator delete", make_unique<kf_operator_delete> ());
+  kfm.add ("operator delete []", make_unique<kf_operator_delete> ());
 }
 
 } // namespace ana
diff --git a/gcc/analyzer/region-model.cc b/gcc/analyzer/region-model.cc
index eb01175..82bc3b2 100644
--- a/gcc/analyzer/region-model.cc
+++ b/gcc/analyzer/region-model.cc
@@ -502,6 +502,7 @@ public:
       case POISON_KIND_UNINIT:
 	return OPT_Wanalyzer_use_of_uninitialized_value;
       case POISON_KIND_FREED:
+      case POISON_KIND_DELETED:
 	return OPT_Wanalyzer_use_after_free;
       case POISON_KIND_POPPED_STACK:
 	return OPT_Wanalyzer_use_of_pointer_in_stale_stack_frame;
@@ -534,6 +535,15 @@ public:
 			       m_expr);
 	}
 	break;
+      case POISON_KIND_DELETED:
+	{
+	  diagnostic_metadata m;
+	  m.add_cwe (416); /* "CWE-416: Use After Free".  */
+	  return warning_meta (rich_loc, m, get_controlling_option (),
+			       "use after %<delete%> of %qE",
+			       m_expr);
+	}
+	break;
       case POISON_KIND_POPPED_STACK:
 	{
 	  /* TODO: which CWE?  */
@@ -558,6 +568,9 @@ public:
       case POISON_KIND_FREED:
 	return ev.formatted_print ("use after %<free%> of %qE here",
 				   m_expr);
+      case POISON_KIND_DELETED:
+	return ev.formatted_print ("use after %<delete%> of %qE here",
+				   m_expr);
       case POISON_KIND_POPPED_STACK:
 	return ev.formatted_print
 	  ("dereferencing pointer %qE to within stale stack frame",
@@ -4194,6 +4207,29 @@ region_model::eval_condition (const svalue *lhs,
 	}
     }
 
+  /* Attempt to unwrap cast if there is one, and the types match.  */
+  tree lhs_type = lhs->get_type ();
+  tree rhs_type = rhs->get_type ();
+  if (lhs_type && rhs_type)
+  {
+    const unaryop_svalue *lhs_un_op = dyn_cast <const unaryop_svalue *> (lhs);
+    const unaryop_svalue *rhs_un_op = dyn_cast <const unaryop_svalue *> (rhs);
+    if (lhs_un_op && CONVERT_EXPR_CODE_P (lhs_un_op->get_op ())
+	&& rhs_un_op && CONVERT_EXPR_CODE_P (rhs_un_op->get_op ())
+	&& lhs_type == rhs_type)
+      return eval_condition (lhs_un_op->get_arg (),
+			     op,
+			     rhs_un_op->get_arg ());
+
+    else if (lhs_un_op && CONVERT_EXPR_CODE_P (lhs_un_op->get_op ())
+	     && lhs_type == rhs_type)
+      return eval_condition (lhs_un_op->get_arg (), op, rhs);
+
+    else if (rhs_un_op && CONVERT_EXPR_CODE_P (rhs_un_op->get_op ())
+	     && lhs_type == rhs_type)
+      return eval_condition (lhs, op, rhs_un_op->get_arg ());
+  }
+
   /* Otherwise, try constraints.
      Cast to const to ensure we don't change the constraint_manager as we
      do this (e.g. by creating equivalence classes).  */
diff --git a/gcc/analyzer/sm-malloc.cc b/gcc/analyzer/sm-malloc.cc
index 2ff777d..5af6544 100644
--- a/gcc/analyzer/sm-malloc.cc
+++ b/gcc/analyzer/sm-malloc.cc
@@ -759,7 +759,7 @@ public:
     override
   {
     if (change.m_old_state == m_sm.get_start_state ()
-	&& unchecked_p (change.m_new_state))
+	&& (unchecked_p (change.m_new_state) || nonnull_p (change.m_new_state)))
       // TODO: verify that it's the allocation stmt, not a copy
       return label_text::borrow ("allocated here");
     if (unchecked_p (change.m_old_state)
@@ -1179,6 +1179,21 @@ public:
   {
     return ev.formatted_print ("dereference of NULL %qE", ev.m_expr);
   }
+
+  /* Implementation of pending_diagnostic::supercedes_p for
+     null-deref.
+
+     We want null-deref to supercede use-of-unitialized-value,
+     so that if we have these at the same stmt, we don't emit
+     a use-of-uninitialized, just the null-deref.  */
+
+  bool supercedes_p (const pending_diagnostic &other) const final override
+  {
+    if (other.use_of_uninit_p ())
+      return true;
+
+    return false;
+  }
 };
 
 /* Concrete subclass for describing passing a NULL value to a
@@ -1915,12 +1930,20 @@ malloc_state_machine::on_stmt (sm_context *sm_ctxt,
 	    return true;
 	  }
 
-	if (is_named_call_p (callee_fndecl, "operator new", call, 1))
-	  on_allocator_call (sm_ctxt, call, &m_scalar_delete);
-	else if (is_named_call_p (callee_fndecl, "operator new []", call, 1))
-	  on_allocator_call (sm_ctxt, call, &m_vector_delete);
-	else if (is_named_call_p (callee_fndecl, "operator delete", call, 1)
-		 || is_named_call_p (callee_fndecl, "operator delete", call, 2))
+	if (!is_placement_new_p (call))
+	  {
+	    bool returns_nonnull = !TREE_NOTHROW (callee_fndecl)
+				   && flag_exceptions;
+	    if (is_named_call_p (callee_fndecl, "operator new"))
+	      on_allocator_call (sm_ctxt, call,
+				 &m_scalar_delete, returns_nonnull);
+	    else if (is_named_call_p (callee_fndecl, "operator new []"))
+	      on_allocator_call (sm_ctxt, call,
+				 &m_vector_delete, returns_nonnull);
+	  }
+
+	if (is_named_call_p (callee_fndecl, "operator delete", call, 1)
+	    || is_named_call_p (callee_fndecl, "operator delete", call, 2))
 	  {
 	    on_deallocator_call (sm_ctxt, node, call,
 				 &m_scalar_delete.m_deallocator, 0);
diff --git a/gcc/analyzer/svalue.cc b/gcc/analyzer/svalue.cc
index 064627f..35eb830 100644
--- a/gcc/analyzer/svalue.cc
+++ b/gcc/analyzer/svalue.cc
@@ -970,6 +970,8 @@ poison_kind_to_str (enum poison_kind kind)
       return "uninit";
     case POISON_KIND_FREED:
       return "freed";
+    case POISON_KIND_DELETED:
+      return "deleted";
     case POISON_KIND_POPPED_STACK:
       return "popped stack";
     }
diff --git a/gcc/analyzer/svalue.h b/gcc/analyzer/svalue.h
index 5492b1e..263a0d7 100644
--- a/gcc/analyzer/svalue.h
+++ b/gcc/analyzer/svalue.h
@@ -350,6 +350,9 @@ enum poison_kind
   /* For use to describe freed memory.  */
   POISON_KIND_FREED,
 
+  /* For use to describe deleted memory.  */
+  POISON_KIND_DELETED,
+
   /* For use on pointers to regions within popped stack frames.  */
   POISON_KIND_POPPED_STACK
 };