1 //=== UndefResultChecker.cpp ------------------------------------*- 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 UndefResultChecker, a builtin check in ExprEngine that 10 // performs checks for undefined results of non-assignment binary operators. 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 #include "clang/StaticAnalyzer/Core/PathSensitive/ExprEngine.h" 20 #include "llvm/ADT/SmallString.h" 21 #include "llvm/Support/raw_ostream.h" 22 23 using namespace clang; 24 using namespace ento; 25 26 namespace { 27 class UndefResultChecker 28 : public Checker< check::PostStmt<BinaryOperator> > { 29 30 mutable std::unique_ptr<BugType> BT; 31 32 public: 33 void checkPostStmt(const BinaryOperator *B, CheckerContext &C) const; 34 }; 35 } // end anonymous namespace 36 37 static bool isArrayIndexOutOfBounds(CheckerContext &C, const Expr *Ex) { 38 ProgramStateRef state = C.getState(); 39 40 if (!isa<ArraySubscriptExpr>(Ex)) 41 return false; 42 43 SVal Loc = C.getSVal(Ex); 44 if (!Loc.isValid()) 45 return false; 46 47 const MemRegion *MR = Loc.castAs<loc::MemRegionVal>().getRegion(); 48 const ElementRegion *ER = dyn_cast<ElementRegion>(MR); 49 if (!ER) 50 return false; 51 52 DefinedOrUnknownSVal Idx = ER->getIndex().castAs<DefinedOrUnknownSVal>(); 53 DefinedOrUnknownSVal NumElements = C.getStoreManager().getSizeInElements( 54 state, ER->getSuperRegion(), ER->getValueType()); 55 ProgramStateRef StInBound = state->assumeInBound(Idx, NumElements, true); 56 ProgramStateRef StOutBound = state->assumeInBound(Idx, NumElements, false); 57 return StOutBound && !StInBound; 58 } 59 60 static bool isShiftOverflow(const BinaryOperator *B, CheckerContext &C) { 61 return C.isGreaterOrEqual( 62 B->getRHS(), C.getASTContext().getIntWidth(B->getLHS()->getType())); 63 } 64 65 static bool isLeftShiftResultUnrepresentable(const BinaryOperator *B, 66 CheckerContext &C) { 67 SValBuilder &SB = C.getSValBuilder(); 68 ProgramStateRef State = C.getState(); 69 const llvm::APSInt *LHS = SB.getKnownValue(State, C.getSVal(B->getLHS())); 70 const llvm::APSInt *RHS = SB.getKnownValue(State, C.getSVal(B->getRHS())); 71 assert(LHS && RHS && "Values unknown, inconsistent state"); 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 Ex = B->getRHS(); 126 } else if ((B->getOpcode() == BinaryOperatorKind::BO_Shl || 127 B->getOpcode() == BinaryOperatorKind::BO_Shr) && 128 isShiftOverflow(B, C)) { 129 130 OS << "The result of the " 131 << ((B->getOpcode() == BinaryOperatorKind::BO_Shl) ? "left" 132 : "right") 133 << " shift is undefined due to shifting by "; 134 Ex = B->getRHS(); 135 136 SValBuilder &SB = C.getSValBuilder(); 137 const llvm::APSInt *I = 138 SB.getKnownValue(C.getState(), C.getSVal(B->getRHS())); 139 if (!I) 140 OS << "a value that is"; 141 else if (I->isUnsigned()) 142 OS << '\'' << I->getZExtValue() << "\', which is"; 143 else 144 OS << '\'' << I->getSExtValue() << "\', which is"; 145 146 OS << " greater or equal to the width of type '" 147 << B->getLHS()->getType().getAsString() << "'."; 148 } else if (B->getOpcode() == BinaryOperatorKind::BO_Shl && 149 C.isNegative(B->getLHS())) { 150 OS << "The result of the left shift is undefined because the left " 151 "operand is negative"; 152 Ex = B->getLHS(); 153 } else if (B->getOpcode() == BinaryOperatorKind::BO_Shl && 154 isLeftShiftResultUnrepresentable(B, C)) { 155 ProgramStateRef State = C.getState(); 156 SValBuilder &SB = C.getSValBuilder(); 157 const llvm::APSInt *LHS = 158 SB.getKnownValue(State, C.getSVal(B->getLHS())); 159 const llvm::APSInt *RHS = 160 SB.getKnownValue(State, C.getSVal(B->getRHS())); 161 OS << "The result of the left shift is undefined due to shifting \'" 162 << LHS->getSExtValue() << "\' by \'" << RHS->getZExtValue() 163 << "\', which is unrepresentable in the unsigned version of " 164 << "the return type \'" << B->getLHS()->getType().getAsString() 165 << "\'"; 166 Ex = B->getLHS(); 167 } else { 168 OS << "The result of the '" 169 << BinaryOperator::getOpcodeStr(B->getOpcode()) 170 << "' expression is undefined"; 171 } 172 } 173 auto report = llvm::make_unique<BugReport>(*BT, OS.str(), N); 174 if (Ex) { 175 report->addRange(Ex->getSourceRange()); 176 bugreporter::trackExpressionValue(N, Ex, *report); 177 } 178 else 179 bugreporter::trackExpressionValue(N, B, *report); 180 181 C.emitReport(std::move(report)); 182 } 183 } 184 185 void ento::registerUndefResultChecker(CheckerManager &mgr) { 186 mgr.registerChecker<UndefResultChecker>(); 187 } 188 189 bool ento::shouldRegisterUndefResultChecker(const LangOptions &LO) { 190 return true; 191 } 192