[analyzer] INT50-CPP. Do not cast to an out-of-range enumeration checker

This checker implements a solution to the "INT50-CPP. Do not cast to an
out-of-range enumeration value" rule [1].
It lands in alpha for now, and a number of followup patches are planned in order
to enable it by default.

[1] https://www.securecoding.cert.org/confluence/display/cplusplus/INT50-CPP.+Do+not+cast+to+an+out-of-range+enumeration+value

Patch by: Endre Fülöp and Alexander Zaitsev!

Differential Revision: https://reviews.llvm.org/D33672

llvm-svn: 347513

Author: Szelethus

clang/include/clang/StaticAnalyzer/Checkers/Checkers.td

@@ -290,6 +290,9 @@ def DeleteWithNonVirtualDtorChecker : Checker<"DeleteWithNonVirtualDtor">,
   HelpText<"Reports destructions of polymorphic objects with a non-virtual "
            "destructor in their base class">;
 
+def EnumCastOutOfRangeChecker : Checker<"EnumCastOutOfRange">,
+  HelpText<"Check integer to enumeration casts for out of range values">;
+
 def InvalidatedIteratorChecker : Checker<"InvalidatedIterator">,
   HelpText<"Check for use of invalidated iterators">;
 

clang/lib/StaticAnalyzer/Checkers/CMakeLists.txt

@@ -34,6 +34,7 @@ add_clang_library(clangStaticAnalyzerCheckers
   DivZeroChecker.cpp
   DynamicTypePropagation.cpp
   DynamicTypeChecker.cpp
+  EnumCastOutOfRangeChecker.cpp
   ExprInspectionChecker.cpp
   FixedAddressChecker.cpp
   GCDAntipatternChecker.cpp

clang/lib/StaticAnalyzer/Checkers/EnumCastOutOfRangeChecker.cpp

@@ -0,0 +1,128 @@
+//===- EnumCastOutOfRangeChecker.cpp ---------------------------*- C++ -*--===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// The EnumCastOutOfRangeChecker is responsible for checking integer to
+// enumeration casts that could result in undefined values. This could happen
+// if the value that we cast from is out of the value range of the enumeration.
+// Reference:
+// [ISO/IEC 14882-2014] ISO/IEC 14882-2014.
+//   Programming Languages — C++, Fourth Edition. 2014.
+// C++ Standard, [dcl.enum], in paragraph 8, which defines the range of an enum
+// C++ Standard, [expr.static.cast], paragraph 10, which defines the behaviour
+//   of casting an integer value that is out of range
+// SEI CERT C++ Coding Standard, INT50-CPP. Do not cast to an out-of-range
+//   enumeration value
+//===----------------------------------------------------------------------===//
+
+#include "ClangSACheckers.h"
+#include "clang/StaticAnalyzer/Core/BugReporter/BugType.h"
+#include "clang/StaticAnalyzer/Core/PathSensitive/CheckerContext.h"
+
+using namespace clang;
+using namespace ento;
+
+namespace {
+// This evaluator checks two SVals for equality. The first SVal is provided via
+// the constructor, the second is the parameter of the overloaded () operator.
+// It uses the in-built ConstraintManager to resolve the equlity to possible or
+// not possible ProgramStates.
+class ConstraintBasedEQEvaluator {
+  const DefinedOrUnknownSVal CompareValue;
+  const ProgramStateRef PS;
+  SValBuilder &SVB;
+
+public:
+  ConstraintBasedEQEvaluator(CheckerContext &C,
+                             const DefinedOrUnknownSVal CompareValue)
+      : CompareValue(CompareValue), PS(C.getState()), SVB(C.getSValBuilder()) {}
+
+  bool operator()(const llvm::APSInt &EnumDeclInitValue) {
+    DefinedOrUnknownSVal EnumDeclValue = SVB.makeIntVal(EnumDeclInitValue);
+    DefinedOrUnknownSVal ElemEqualsValueToCast =
+        SVB.evalEQ(PS, EnumDeclValue, CompareValue);
+
+    return static_cast<bool>(PS->assume(ElemEqualsValueToCast, true));
+  }
+};
+
+// This checker checks CastExpr statements.
+// If the value provided to the cast is one of the values the enumeration can
+// represent, the said value matches the enumeration. If the checker can
+// establish the impossibility of matching it gives a warning.
+// Being conservative, it does not warn if there is slight possibility the
+// value can be matching.
+class EnumCastOutOfRangeChecker : public Checker<check::PreStmt<CastExpr>> {
+  mutable std::unique_ptr<BuiltinBug> EnumValueCastOutOfRange;
+  void reportWarning(CheckerContext &C) const;
+
+public:
+  void checkPreStmt(const CastExpr *CE, CheckerContext &C) const;
+};
+
+using EnumValueVector = llvm::SmallVector<llvm::APSInt, 6>;
+
+// Collects all of the values an enum can represent (as SVals).
+EnumValueVector getDeclValuesForEnum(const EnumDecl *ED) {
+  EnumValueVector DeclValues(
+      std::distance(ED->enumerator_begin(), ED->enumerator_end()));
+  llvm::transform(ED->enumerators(), DeclValues.begin(),
+                 [](const EnumConstantDecl *D) { return D->getInitVal(); });
+  return DeclValues;
+}
+} // namespace
+
+void EnumCastOutOfRangeChecker::reportWarning(CheckerContext &C) const {
+  if (const ExplodedNode *N = C.generateNonFatalErrorNode()) {
+    if (!EnumValueCastOutOfRange)
+      EnumValueCastOutOfRange.reset(
+          new BuiltinBug(this, "Enum cast out of range",
+                         "The value provided to the cast expression is not in "
+                         "the valid range of values for the enum"));
+    C.emitReport(llvm::make_unique<BugReport>(
+        *EnumValueCastOutOfRange, EnumValueCastOutOfRange->getDescription(),
+        N));
+  }
+}
+
+void EnumCastOutOfRangeChecker::checkPreStmt(const CastExpr *CE,
+                                             CheckerContext &C) const {
+  // Get the value of the expression to cast.
+  const llvm::Optional<DefinedOrUnknownSVal> ValueToCast =
+      C.getSVal(CE->getSubExpr()).getAs<DefinedOrUnknownSVal>();
+
+  // If the value cannot be reasoned about (not even a DefinedOrUnknownSVal),
+  // don't analyze further.
+  if (!ValueToCast)
+    return;
+
+  const QualType T = CE->getType();
+  // Check whether the cast type is an enum.
+  if (!T->isEnumeralType())
+    return;
+
+  // If the cast is an enum, get its declaration.
+  // If the isEnumeralType() returned true, then the declaration must exist
+  // even if it is a stub declaration. It is up to the getDeclValuesForEnum()
+  // function to handle this.
+  const EnumDecl *ED = T->castAs<EnumType>()->getDecl();
+
+  EnumValueVector DeclValues = getDeclValuesForEnum(ED);
+  // Check if any of the enum values possibly match.
+  bool PossibleValueMatch = llvm::any_of(
+      DeclValues, ConstraintBasedEQEvaluator(C, *ValueToCast));
+
+  // If there is no value that can possibly match any of the enum values, then
+  // warn.
+  if (!PossibleValueMatch)
+    reportWarning(C);
+}
+
+void ento::registerEnumCastOutOfRangeChecker(CheckerManager &mgr) {
+  mgr.registerChecker<EnumCastOutOfRangeChecker>();
+}