1 //=== UndefResultChecker.cpp ------------------------------------*- C++ -*-===// 2 // 3 // The LLVM Compiler Infrastructure 4 // 5 // This file is distributed under the University of Illinois Open Source 6 // License. See LICENSE.TXT for details. 7 // 8 //===----------------------------------------------------------------------===// 9 // 10 // This defines UndefResultChecker, a builtin check in ExprEngine that 11 // performs checks for undefined results of non-assignment binary operators. 12 // 13 //===----------------------------------------------------------------------===// 14 15 #include "ClangSACheckers.h" 16 #include "clang/StaticAnalyzer/Core/BugReporter/BugType.h" 17 #include "clang/StaticAnalyzer/Core/Checker.h" 18 #include "clang/StaticAnalyzer/Core/CheckerManager.h" 19 #include "clang/StaticAnalyzer/Core/PathSensitive/CheckerContext.h" 20 #include "clang/StaticAnalyzer/Core/PathSensitive/ExprEngine.h" 21 #include "llvm/ADT/SmallString.h" 22 #include "llvm/Support/raw_ostream.h" 23 24 using namespace clang; 25 using namespace ento; 26 27 namespace { 28 class UndefResultChecker 29 : public Checker< check::PostStmt<BinaryOperator> > { 30 31 mutable std::unique_ptr<BugType> BT; 32 33 public: 34 void checkPostStmt(const BinaryOperator *B, CheckerContext &C) const; 35 }; 36 } // end anonymous namespace 37 38 static bool isArrayIndexOutOfBounds(CheckerContext &C, const Expr *Ex) { 39 ProgramStateRef state = C.getState(); 40 41 if (!isa<ArraySubscriptExpr>(Ex)) 42 return false; 43 44 SVal Loc = C.getSVal(Ex); 45 if (!Loc.isValid()) 46 return false; 47 48 const MemRegion *MR = Loc.castAs<loc::MemRegionVal>().getRegion(); 49 const ElementRegion *ER = dyn_cast<ElementRegion>(MR); 50 if (!ER) 51 return false; 52 53 DefinedOrUnknownSVal Idx = ER->getIndex().castAs<DefinedOrUnknownSVal>(); 54 DefinedOrUnknownSVal NumElements = C.getStoreManager().getSizeInElements( 55 state, ER->getSuperRegion(), ER->getValueType()); 56 ProgramStateRef StInBound = state->assumeInBound(Idx, NumElements, true); 57 ProgramStateRef StOutBound = state->assumeInBound(Idx, NumElements, false); 58 return StOutBound && !StInBound; 59 } 60 61 static bool isShiftOverflow(const BinaryOperator *B, CheckerContext &C) { 62 return C.isGreaterOrEqual( 63 B->getRHS(), C.getASTContext().getIntWidth(B->getLHS()->getType())); 64 } 65 66 static bool isLeftShiftResultUnrepresentable(const BinaryOperator *B, 67 CheckerContext &C) { 68 SValBuilder &SB = C.getSValBuilder(); 69 ProgramStateRef State = C.getState(); 70 const llvm::APSInt *LHS = SB.getKnownValue(State, C.getSVal(B->getLHS())); 71 const llvm::APSInt *RHS = SB.getKnownValue(State, C.getSVal(B->getRHS())); 72 return (unsigned)RHS->getZExtValue() > LHS->countLeadingZeros(); 73 } 74 75 void UndefResultChecker::checkPostStmt(const BinaryOperator *B, 76 CheckerContext &C) const { 77 if (C.getSVal(B).isUndef()) { 78 79 // Do not report assignments of uninitialized values inside swap functions. 80 // This should allow to swap partially uninitialized structs 81 // (radar://14129997) 82 if (const FunctionDecl *EnclosingFunctionDecl = 83 dyn_cast<FunctionDecl>(C.getStackFrame()->getDecl())) 84 if (C.getCalleeName(EnclosingFunctionDecl) == "swap") 85 return; 86 87 // Generate an error node. 88 ExplodedNode *N = C.generateErrorNode(); 89 if (!N) 90 return; 91 92 if (!BT) 93 BT.reset( 94 new BuiltinBug(this, "Result of operation is garbage or undefined")); 95 96 SmallString<256> sbuf; 97 llvm::raw_svector_ostream OS(sbuf); 98 const Expr *Ex = nullptr; 99 bool isLeft = true; 100 101 if (C.getSVal(B->getLHS()).isUndef()) { 102 Ex = B->getLHS()->IgnoreParenCasts(); 103 isLeft = true; 104 } 105 else if (C.getSVal(B->getRHS()).isUndef()) { 106 Ex = B->getRHS()->IgnoreParenCasts(); 107 isLeft = false; 108 } 109 110 if (Ex) { 111 OS << "The " << (isLeft ? "left" : "right") << " operand of '" 112 << BinaryOperator::getOpcodeStr(B->getOpcode()) 113 << "' is a garbage value"; 114 if (isArrayIndexOutOfBounds(C, Ex)) 115 OS << " due to array index out of bounds"; 116 } else { 117 // Neither operand was undefined, but the result is undefined. 118 if ((B->getOpcode() == BinaryOperatorKind::BO_Shl || 119 B->getOpcode() == BinaryOperatorKind::BO_Shr) && 120 C.isNegative(B->getRHS())) { 121 OS << "The result of the " 122 << ((B->getOpcode() == BinaryOperatorKind::BO_Shl) ? "left" 123 : "right") 124 << " shift is undefined because the right operand is negative"; 125 } else if ((B->getOpcode() == BinaryOperatorKind::BO_Shl || 126 B->getOpcode() == BinaryOperatorKind::BO_Shr) && 127 isShiftOverflow(B, C)) { 128 129 OS << "The result of the " 130 << ((B->getOpcode() == BinaryOperatorKind::BO_Shl) ? "left" 131 : "right") 132 << " shift is undefined due to shifting by "; 133 134 SValBuilder &SB = C.getSValBuilder(); 135 const llvm::APSInt *I = 136 SB.getKnownValue(C.getState(), C.getSVal(B->getRHS())); 137 if (!I) 138 OS << "a value that is"; 139 else if (I->isUnsigned()) 140 OS << '\'' << I->getZExtValue() << "\', which is"; 141 else 142 OS << '\'' << I->getSExtValue() << "\', which is"; 143 144 OS << " greater or equal to the width of type '" 145 << B->getLHS()->getType().getAsString() << "'."; 146 } else if (B->getOpcode() == BinaryOperatorKind::BO_Shl && 147 C.isNegative(B->getLHS())) { 148 OS << "The result of the left shift is undefined because the left " 149 "operand is negative"; 150 } else if (B->getOpcode() == BinaryOperatorKind::BO_Shl && 151 isLeftShiftResultUnrepresentable(B, C)) { 152 ProgramStateRef State = C.getState(); 153 SValBuilder &SB = C.getSValBuilder(); 154 const llvm::APSInt *LHS = 155 SB.getKnownValue(State, C.getSVal(B->getLHS())); 156 const llvm::APSInt *RHS = 157 SB.getKnownValue(State, C.getSVal(B->getRHS())); 158 OS << "The result of the left shift is undefined due to shifting \'" 159 << LHS->getSExtValue() << "\' by \'" << RHS->getZExtValue() 160 << "\', which is unrepresentable in the unsigned version of " 161 << "the return type \'" << B->getLHS()->getType().getAsString() 162 << "\'"; 163 } else { 164 OS << "The result of the '" 165 << BinaryOperator::getOpcodeStr(B->getOpcode()) 166 << "' expression is undefined"; 167 } 168 } 169 auto report = llvm::make_unique<BugReport>(*BT, OS.str(), N); 170 if (Ex) { 171 report->addRange(Ex->getSourceRange()); 172 bugreporter::trackNullOrUndefValue(N, Ex, *report); 173 } 174 else 175 bugreporter::trackNullOrUndefValue(N, B, *report); 176 177 C.emitReport(std::move(report)); 178 } 179 } 180 181 void ento::registerUndefResultChecker(CheckerManager &mgr) { 182 mgr.registerChecker<UndefResultChecker>(); 183 } 184