125 lines · cpp
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-exception6//7//===----------------------------------------------------------------------===//8//9// This files defines PointerSubChecker, a builtin checker that checks for10// 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#include "llvm/Support/FormatVariadic.h"22 23using namespace clang;24using namespace ento;25 26namespace {27class PointerSubChecker28 : public Checker< check::PreStmt<BinaryOperator> > {29 const BugType BT{this, "Pointer subtraction"};30 const llvm::StringLiteral Msg_MemRegionDifferent =31 "Subtraction of two pointers that do not point into the same array "32 "is undefined behavior.";33 34public:35 void checkPreStmt(const BinaryOperator *B, CheckerContext &C) const;36};37}38 39void PointerSubChecker::checkPreStmt(const BinaryOperator *B,40 CheckerContext &C) const {41 // When doing pointer subtraction, if the two pointers do not point to the42 // same array, emit a warning.43 if (B->getOpcode() != BO_Sub)44 return;45 46 SVal LV = C.getSVal(B->getLHS());47 SVal RV = C.getSVal(B->getRHS());48 49 const MemRegion *LR = LV.getAsRegion();50 const MemRegion *RR = RV.getAsRegion();51 if (!LR || !RR)52 return;53 54 // Allow subtraction of identical pointers.55 if (LR == RR)56 return;57 58 // No warning if one operand is unknown or resides in a region that could be59 // equal to the other.60 if (LR->getSymbolicBase() || RR->getSymbolicBase())61 return;62 63 if (!B->getLHS()->getType()->isPointerType() ||64 !B->getRHS()->getType()->isPointerType())65 return;66 67 const auto *ElemLR = dyn_cast<ElementRegion>(LR);68 const auto *ElemRR = dyn_cast<ElementRegion>(RR);69 70 // Allow cases like "(&x + 1) - &x".71 if (ElemLR && ElemLR->getSuperRegion() == RR)72 return;73 // Allow cases like "&x - (&x + 1)".74 if (ElemRR && ElemRR->getSuperRegion() == LR)75 return;76 77 const ValueDecl *DiffDeclL = nullptr;78 const ValueDecl *DiffDeclR = nullptr;79 80 if (ElemLR && ElemRR) {81 const MemRegion *SuperLR = ElemLR->getSuperRegion();82 const MemRegion *SuperRR = ElemRR->getSuperRegion();83 if (SuperLR == SuperRR)84 return;85 // Allow arithmetic on different symbolic regions.86 if (isa<SymbolicRegion>(SuperLR) || isa<SymbolicRegion>(SuperRR))87 return;88 if (const auto *SuperDLR = dyn_cast<DeclRegion>(SuperLR))89 DiffDeclL = SuperDLR->getDecl();90 if (const auto *SuperDRR = dyn_cast<DeclRegion>(SuperRR))91 DiffDeclR = SuperDRR->getDecl();92 }93 94 if (ExplodedNode *N = C.generateNonFatalErrorNode()) {95 auto R =96 std::make_unique<PathSensitiveBugReport>(BT, Msg_MemRegionDifferent, N);97 R->addRange(B->getSourceRange());98 // The declarations may be identical even if the regions are different:99 // struct { int array[10]; } a, b;100 // do_something(&a.array[5] - &b.array[5]);101 // In this case don't emit notes.102 if (DiffDeclL != DiffDeclR) {103 auto AddNote = [&R, &C](const ValueDecl *D, StringRef SideStr) {104 if (D) {105 std::string Msg = llvm::formatv(106 "{0} at the {1}-hand side of subtraction",107 D->getType()->isArrayType() ? "Array" : "Object", SideStr);108 R->addNote(Msg, {D, C.getSourceManager()});109 }110 };111 AddNote(DiffDeclL, "left");112 AddNote(DiffDeclR, "right");113 }114 C.emitReport(std::move(R));115 }116}117 118void ento::registerPointerSubChecker(CheckerManager &mgr) {119 mgr.registerChecker<PointerSubChecker>();120}121 122bool ento::shouldRegisterPointerSubChecker(const CheckerManager &mgr) {123 return true;124}125