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
checkPreStmt(const BinaryOperator * B,CheckerContext & C) const35 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
registerPointerSubChecker(CheckerManager & mgr)71 void ento::registerPointerSubChecker(CheckerManager &mgr) {
72 mgr.registerChecker<PointerSubChecker>();
73 }
74
shouldRegisterPointerSubChecker(const CheckerManager & mgr)75 bool ento::shouldRegisterPointerSubChecker(const CheckerManager &mgr) {
76 return true;
77 }
78