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/DynamicExtent.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 ElementCount = getDynamicElementCount( 55 state, ER->getSuperRegion(), C.getSValBuilder(), ER->getValueType()); 56 ProgramStateRef StInBound = state->assumeInBound(Idx, ElementCount, true); 57 ProgramStateRef StOutBound = state->assumeInBound(Idx, ElementCount, 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 assert(LHS && RHS && "Values unknown, inconsistent state"); 73 return (unsigned)RHS->getZExtValue() > LHS->countLeadingZeros(); 74 } 75 76 void UndefResultChecker::checkPostStmt(const BinaryOperator *B, 77 CheckerContext &C) const { 78 if (C.getSVal(B).isUndef()) { 79 80 // Do not report assignments of uninitialized values inside swap functions. 81 // This should allow to swap partially uninitialized structs 82 // (radar://14129997) 83 if (const FunctionDecl *EnclosingFunctionDecl = 84 dyn_cast<FunctionDecl>(C.getStackFrame()->getDecl())) 85 if (C.getCalleeName(EnclosingFunctionDecl) == "swap") 86 return; 87 88 // Generate an error node. 89 ExplodedNode *N = C.generateErrorNode(); 90 if (!N) 91 return; 92 93 if (!BT) 94 BT.reset( 95 new BuiltinBug(this, "Result of operation is garbage or undefined")); 96 97 SmallString<256> sbuf; 98 llvm::raw_svector_ostream OS(sbuf); 99 const Expr *Ex = nullptr; 100 bool isLeft = true; 101 102 if (C.getSVal(B->getLHS()).isUndef()) { 103 Ex = B->getLHS()->IgnoreParenCasts(); 104 isLeft = true; 105 } 106 else if (C.getSVal(B->getRHS()).isUndef()) { 107 Ex = B->getRHS()->IgnoreParenCasts(); 108 isLeft = false; 109 } 110 111 if (Ex) { 112 OS << "The " << (isLeft ? "left" : "right") << " operand of '" 113 << BinaryOperator::getOpcodeStr(B->getOpcode()) 114 << "' is a garbage value"; 115 if (isArrayIndexOutOfBounds(C, Ex)) 116 OS << " due to array index out of bounds"; 117 } else { 118 // Neither operand was undefined, but the result is undefined. 119 if ((B->getOpcode() == BinaryOperatorKind::BO_Shl || 120 B->getOpcode() == BinaryOperatorKind::BO_Shr) && 121 C.isNegative(B->getRHS())) { 122 OS << "The result of the " 123 << ((B->getOpcode() == BinaryOperatorKind::BO_Shl) ? "left" 124 : "right") 125 << " shift is undefined because the right operand is negative"; 126 Ex = B->getRHS(); 127 } else if ((B->getOpcode() == BinaryOperatorKind::BO_Shl || 128 B->getOpcode() == BinaryOperatorKind::BO_Shr) && 129 isShiftOverflow(B, C)) { 130 131 OS << "The result of the " 132 << ((B->getOpcode() == BinaryOperatorKind::BO_Shl) ? "left" 133 : "right") 134 << " shift is undefined due to shifting by "; 135 Ex = B->getRHS(); 136 137 SValBuilder &SB = C.getSValBuilder(); 138 const llvm::APSInt *I = 139 SB.getKnownValue(C.getState(), C.getSVal(B->getRHS())); 140 if (!I) 141 OS << "a value that is"; 142 else if (I->isUnsigned()) 143 OS << '\'' << I->getZExtValue() << "\', which is"; 144 else 145 OS << '\'' << I->getSExtValue() << "\', which is"; 146 147 OS << " greater or equal to the width of type '" 148 << B->getLHS()->getType().getAsString() << "'."; 149 } else if (B->getOpcode() == BinaryOperatorKind::BO_Shl && 150 C.isNegative(B->getLHS())) { 151 OS << "The result of the left shift is undefined because the left " 152 "operand is negative"; 153 Ex = B->getLHS(); 154 } else if (B->getOpcode() == BinaryOperatorKind::BO_Shl && 155 isLeftShiftResultUnrepresentable(B, C)) { 156 ProgramStateRef State = C.getState(); 157 SValBuilder &SB = C.getSValBuilder(); 158 const llvm::APSInt *LHS = 159 SB.getKnownValue(State, C.getSVal(B->getLHS())); 160 const llvm::APSInt *RHS = 161 SB.getKnownValue(State, C.getSVal(B->getRHS())); 162 OS << "The result of the left shift is undefined due to shifting \'" 163 << LHS->getSExtValue() << "\' by \'" << RHS->getZExtValue() 164 << "\', which is unrepresentable in the unsigned version of " 165 << "the return type \'" << B->getLHS()->getType().getAsString() 166 << "\'"; 167 Ex = B->getLHS(); 168 } else { 169 OS << "The result of the '" 170 << BinaryOperator::getOpcodeStr(B->getOpcode()) 171 << "' expression is undefined"; 172 } 173 } 174 auto report = std::make_unique<PathSensitiveBugReport>(*BT, OS.str(), N); 175 if (Ex) { 176 report->addRange(Ex->getSourceRange()); 177 bugreporter::trackExpressionValue(N, Ex, *report); 178 } 179 else 180 bugreporter::trackExpressionValue(N, B, *report); 181 182 C.emitReport(std::move(report)); 183 } 184 } 185 186 void ento::registerUndefResultChecker(CheckerManager &mgr) { 187 mgr.registerChecker<UndefResultChecker>(); 188 } 189 190 bool ento::shouldRegisterUndefResultChecker(const CheckerManager &mgr) { 191 return true; 192 } 193