1 //== BoolAssignmentChecker.cpp - Boolean assignment checker -----*- C++ -*--==// 2 // 3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. 4 // See https://llvm.org/LICENSE.txt for license information. 5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception 6 // 7 //===----------------------------------------------------------------------===// 8 // 9 // This defines BoolAssignmentChecker, a builtin check in ExprEngine that 10 // performs checks for assignment of non-Boolean values to Boolean variables. 11 // 12 //===----------------------------------------------------------------------===// 13 14 #include "clang/StaticAnalyzer/Checkers/BuiltinCheckerRegistration.h" 15 #include "clang/StaticAnalyzer/Core/BugReporter/BugType.h" 16 #include "clang/StaticAnalyzer/Core/Checker.h" 17 #include "clang/StaticAnalyzer/Core/CheckerManager.h" 18 #include "clang/StaticAnalyzer/Core/PathSensitive/CheckerContext.h" 19 20 using namespace clang; 21 using namespace ento; 22 23 namespace { 24 class BoolAssignmentChecker : public Checker< check::Bind > { 25 mutable std::unique_ptr<BuiltinBug> BT; 26 void emitReport(ProgramStateRef state, CheckerContext &C) const; 27 public: 28 void checkBind(SVal loc, SVal val, const Stmt *S, CheckerContext &C) const; 29 }; 30 } // end anonymous namespace 31 32 void BoolAssignmentChecker::emitReport(ProgramStateRef state, 33 CheckerContext &C) const { 34 if (ExplodedNode *N = C.generateNonFatalErrorNode(state)) { 35 if (!BT) 36 BT.reset(new BuiltinBug(this, "Assignment of a non-Boolean value")); 37 38 C.emitReport( 39 std::make_unique<PathSensitiveBugReport>(*BT, BT->getDescription(), N)); 40 } 41 } 42 43 static bool isBooleanType(QualType Ty) { 44 if (Ty->isBooleanType()) // C++ or C99 45 return true; 46 47 if (const TypedefType *TT = Ty->getAs<TypedefType>()) 48 return TT->getDecl()->getName() == "BOOL" || // Objective-C 49 TT->getDecl()->getName() == "_Bool" || // stdbool.h < C99 50 TT->getDecl()->getName() == "Boolean"; // MacTypes.h 51 52 return false; 53 } 54 55 void BoolAssignmentChecker::checkBind(SVal loc, SVal val, const Stmt *S, 56 CheckerContext &C) const { 57 58 // We are only interested in stores into Booleans. 59 const TypedValueRegion *TR = 60 dyn_cast_or_null<TypedValueRegion>(loc.getAsRegion()); 61 62 if (!TR) 63 return; 64 65 QualType valTy = TR->getValueType(); 66 67 if (!isBooleanType(valTy)) 68 return; 69 70 // Get the value of the right-hand side. We only care about values 71 // that are defined (UnknownVals and UndefinedVals are handled by other 72 // checkers). 73 Optional<DefinedSVal> DV = val.getAs<DefinedSVal>(); 74 if (!DV) 75 return; 76 77 // Check if the assigned value meets our criteria for correctness. It must 78 // be a value that is either 0 or 1. One way to check this is to see if 79 // the value is possibly < 0 (for a negative value) or greater than 1. 80 ProgramStateRef state = C.getState(); 81 SValBuilder &svalBuilder = C.getSValBuilder(); 82 ConstraintManager &CM = C.getConstraintManager(); 83 84 // First, ensure that the value is >= 0. 85 DefinedSVal zeroVal = svalBuilder.makeIntVal(0, valTy); 86 SVal greaterThanOrEqualToZeroVal = 87 svalBuilder.evalBinOp(state, BO_GE, *DV, zeroVal, 88 svalBuilder.getConditionType()); 89 90 Optional<DefinedSVal> greaterThanEqualToZero = 91 greaterThanOrEqualToZeroVal.getAs<DefinedSVal>(); 92 93 if (!greaterThanEqualToZero) { 94 // The SValBuilder cannot construct a valid SVal for this condition. 95 // This means we cannot properly reason about it. 96 return; 97 } 98 99 ProgramStateRef stateLT, stateGE; 100 std::tie(stateGE, stateLT) = CM.assumeDual(state, *greaterThanEqualToZero); 101 102 // Is it possible for the value to be less than zero? 103 if (stateLT) { 104 // It is possible for the value to be less than zero. We only 105 // want to emit a warning, however, if that value is fully constrained. 106 // If it it possible for the value to be >= 0, then essentially the 107 // value is underconstrained and there is nothing left to be done. 108 if (!stateGE) 109 emitReport(stateLT, C); 110 111 // In either case, we are done. 112 return; 113 } 114 115 // If we reach here, it must be the case that the value is constrained 116 // to only be >= 0. 117 assert(stateGE == state); 118 119 // At this point we know that the value is >= 0. 120 // Now check to ensure that the value is <= 1. 121 DefinedSVal OneVal = svalBuilder.makeIntVal(1, valTy); 122 SVal lessThanEqToOneVal = 123 svalBuilder.evalBinOp(state, BO_LE, *DV, OneVal, 124 svalBuilder.getConditionType()); 125 126 Optional<DefinedSVal> lessThanEqToOne = 127 lessThanEqToOneVal.getAs<DefinedSVal>(); 128 129 if (!lessThanEqToOne) { 130 // The SValBuilder cannot construct a valid SVal for this condition. 131 // This means we cannot properly reason about it. 132 return; 133 } 134 135 ProgramStateRef stateGT, stateLE; 136 std::tie(stateLE, stateGT) = CM.assumeDual(state, *lessThanEqToOne); 137 138 // Is it possible for the value to be greater than one? 139 if (stateGT) { 140 // It is possible for the value to be greater than one. We only 141 // want to emit a warning, however, if that value is fully constrained. 142 // If it is possible for the value to be <= 1, then essentially the 143 // value is underconstrained and there is nothing left to be done. 144 if (!stateLE) 145 emitReport(stateGT, C); 146 147 // In either case, we are done. 148 return; 149 } 150 151 // If we reach here, it must be the case that the value is constrained 152 // to only be <= 1. 153 assert(stateLE == state); 154 } 155 156 void ento::registerBoolAssignmentChecker(CheckerManager &mgr) { 157 mgr.registerChecker<BoolAssignmentChecker>(); 158 } 159 160 bool ento::shouldRegisterBoolAssignmentChecker(const LangOptions &LO) { 161 return true; 162 } 163