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 const BugType BT{this, "Result of operation is garbage or undefined"}; 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, StOutBound; 57 std::tie(StInBound, StOutBound) = state->assumeInBoundDual(Idx, ElementCount); 58 return StOutBound && !StInBound; 59 } 60 61 void UndefResultChecker::checkPostStmt(const BinaryOperator *B, 62 CheckerContext &C) const { 63 if (C.getSVal(B).isUndef()) { 64 65 // Do not report assignments of uninitialized values inside swap functions. 66 // This should allow to swap partially uninitialized structs 67 if (const FunctionDecl *EnclosingFunctionDecl = 68 dyn_cast<FunctionDecl>(C.getStackFrame()->getDecl())) 69 if (C.getCalleeName(EnclosingFunctionDecl) == "swap") 70 return; 71 72 // Generate an error node. 73 ExplodedNode *N = C.generateErrorNode(); 74 if (!N) 75 return; 76 77 SmallString<256> sbuf; 78 llvm::raw_svector_ostream OS(sbuf); 79 const Expr *Ex = nullptr; 80 bool isLeft = true; 81 82 if (C.getSVal(B->getLHS()).isUndef()) { 83 Ex = B->getLHS()->IgnoreParenCasts(); 84 isLeft = true; 85 } 86 else if (C.getSVal(B->getRHS()).isUndef()) { 87 Ex = B->getRHS()->IgnoreParenCasts(); 88 isLeft = false; 89 } 90 91 if (Ex) { 92 OS << "The " << (isLeft ? "left" : "right") << " operand of '" 93 << BinaryOperator::getOpcodeStr(B->getOpcode()) 94 << "' is a garbage value"; 95 if (isArrayIndexOutOfBounds(C, Ex)) 96 OS << " due to array index out of bounds"; 97 } else { 98 // Neither operand was undefined, but the result is undefined. 99 OS << "The result of the '" 100 << BinaryOperator::getOpcodeStr(B->getOpcode()) 101 << "' expression is undefined"; 102 } 103 auto report = std::make_unique<PathSensitiveBugReport>(BT, OS.str(), N); 104 if (Ex) { 105 report->addRange(Ex->getSourceRange()); 106 bugreporter::trackExpressionValue(N, Ex, *report); 107 } 108 else 109 bugreporter::trackExpressionValue(N, B, *report); 110 111 C.emitReport(std::move(report)); 112 } 113 } 114 115 void ento::registerUndefResultChecker(CheckerManager &mgr) { 116 mgr.registerChecker<UndefResultChecker>(); 117 } 118 119 bool ento::shouldRegisterUndefResultChecker(const CheckerManager &mgr) { 120 return true; 121 } 122