1 //=== PointerSubChecker.cpp - Pointer subtraction checker ------*- 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 files defines PointerSubChecker, a builtin checker that checks for 10 // pointer subtractions on two pointers pointing to different memory chunks. 11 // This check corresponds to CWE-469. 12 // 13 //===----------------------------------------------------------------------===// 14 15 #include "clang/StaticAnalyzer/Checkers/BuiltinCheckerRegistration.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 "llvm/ADT/StringRef.h" 21 22 using namespace clang; 23 using namespace ento; 24 25 namespace { 26 class PointerSubChecker 27 : public Checker< check::PreStmt<BinaryOperator> > { 28 const BugType BT{this, "Pointer subtraction"}; 29 30 public: 31 void checkPreStmt(const BinaryOperator *B, CheckerContext &C) const; 32 }; 33 } 34 35 void PointerSubChecker::checkPreStmt(const BinaryOperator *B, 36 CheckerContext &C) const { 37 // When doing pointer subtraction, if the two pointers do not point to the 38 // same memory chunk, emit a warning. 39 if (B->getOpcode() != BO_Sub) 40 return; 41 42 SVal LV = C.getSVal(B->getLHS()); 43 SVal RV = C.getSVal(B->getRHS()); 44 45 const MemRegion *LR = LV.getAsRegion(); 46 const MemRegion *RR = RV.getAsRegion(); 47 48 if (!(LR && RR)) 49 return; 50 51 const MemRegion *BaseLR = LR->getBaseRegion(); 52 const MemRegion *BaseRR = RR->getBaseRegion(); 53 54 if (BaseLR == BaseRR) 55 return; 56 57 // Allow arithmetic on different symbolic regions. 58 if (isa<SymbolicRegion>(BaseLR) || isa<SymbolicRegion>(BaseRR)) 59 return; 60 61 if (ExplodedNode *N = C.generateNonFatalErrorNode()) { 62 constexpr llvm::StringLiteral Msg = 63 "Subtraction of two pointers that do not point to the same memory " 64 "chunk may cause incorrect result."; 65 auto R = std::make_unique<PathSensitiveBugReport>(BT, Msg, N); 66 R->addRange(B->getSourceRange()); 67 C.emitReport(std::move(R)); 68 } 69 } 70 71 void ento::registerPointerSubChecker(CheckerManager &mgr) { 72 mgr.registerChecker<PointerSubChecker>(); 73 } 74 75 bool ento::shouldRegisterPointerSubChecker(const CheckerManager &mgr) { 76 return true; 77 } 78