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/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 const BugType BT{this, "Result of operation is garbage or undefined"}; 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 ElementCount = getDynamicElementCount( 54 state, ER->getSuperRegion(), C.getSValBuilder(), ER->getValueType()); 55 ProgramStateRef StInBound, StOutBound; 56 std::tie(StInBound, StOutBound) = state->assumeInBoundDual(Idx, ElementCount); 57 return StOutBound && !StInBound; 58 } 59 60 void UndefResultChecker::checkPostStmt(const BinaryOperator *B, 61 CheckerContext &C) const { 62 if (C.getSVal(B).isUndef()) { 63 64 // Do not report assignments of uninitialized values inside swap functions. 65 // This should allow to swap partially uninitialized structs 66 if (const FunctionDecl *EnclosingFunctionDecl = 67 dyn_cast<FunctionDecl>(C.getStackFrame()->getDecl())) 68 if (C.getCalleeName(EnclosingFunctionDecl) == "swap") 69 return; 70 71 // Generate an error node. 72 ExplodedNode *N = C.generateErrorNode(); 73 if (!N) 74 return; 75 76 SmallString<256> sbuf; 77 llvm::raw_svector_ostream OS(sbuf); 78 const Expr *Ex = nullptr; 79 bool isLeft = true; 80 81 if (C.getSVal(B->getLHS()).isUndef()) { 82 Ex = B->getLHS()->IgnoreParenCasts(); 83 isLeft = true; 84 } 85 else if (C.getSVal(B->getRHS()).isUndef()) { 86 Ex = B->getRHS()->IgnoreParenCasts(); 87 isLeft = false; 88 } 89 90 if (Ex) { 91 OS << "The " << (isLeft ? "left" : "right") << " operand of '" 92 << BinaryOperator::getOpcodeStr(B->getOpcode()) 93 << "' is a garbage value"; 94 if (isArrayIndexOutOfBounds(C, Ex)) 95 OS << " due to array index out of bounds"; 96 } else { 97 // Neither operand was undefined, but the result is undefined. 98 OS << "The result of the '" 99 << BinaryOperator::getOpcodeStr(B->getOpcode()) 100 << "' expression is undefined"; 101 } 102 auto report = std::make_unique<PathSensitiveBugReport>(BT, OS.str(), N); 103 if (Ex) { 104 report->addRange(Ex->getSourceRange()); 105 bugreporter::trackExpressionValue(N, Ex, *report); 106 } 107 else 108 bugreporter::trackExpressionValue(N, B, *report); 109 110 C.emitReport(std::move(report)); 111 } 112 } 113 114 void ento::registerUndefResultChecker(CheckerManager &mgr) { 115 mgr.registerChecker<UndefResultChecker>(); 116 } 117 118 bool ento::shouldRegisterUndefResultChecker(const CheckerManager &mgr) { 119 return true; 120 } 121