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 
21 using namespace clang;
22 using namespace ento;
23 
24 namespace {
25 class PointerSubChecker
26   : public Checker< check::PreStmt<BinaryOperator> > {
27   mutable std::unique_ptr<BuiltinBug> BT;
28 
29 public:
30   void checkPreStmt(const BinaryOperator *B, CheckerContext &C) const;
31 };
32 }
33 
34 void PointerSubChecker::checkPreStmt(const BinaryOperator *B,
35                                      CheckerContext &C) const {
36   // When doing pointer subtraction, if the two pointers do not point to the
37   // same memory chunk, emit a warning.
38   if (B->getOpcode() != BO_Sub)
39     return;
40 
41   SVal LV = C.getSVal(B->getLHS());
42   SVal RV = C.getSVal(B->getRHS());
43 
44   const MemRegion *LR = LV.getAsRegion();
45   const MemRegion *RR = RV.getAsRegion();
46 
47   if (!(LR && RR))
48     return;
49 
50   const MemRegion *BaseLR = LR->getBaseRegion();
51   const MemRegion *BaseRR = RR->getBaseRegion();
52 
53   if (BaseLR == BaseRR)
54     return;
55 
56   // Allow arithmetic on different symbolic regions.
57   if (isa<SymbolicRegion>(BaseLR) || isa<SymbolicRegion>(BaseRR))
58     return;
59 
60   if (ExplodedNode *N = C.generateNonFatalErrorNode()) {
61     if (!BT)
62       BT.reset(
63           new BuiltinBug(this, "Pointer subtraction",
64                          "Subtraction of two pointers that do not point to "
65                          "the same memory chunk may cause incorrect result."));
66     auto R =
67         std::make_unique<PathSensitiveBugReport>(*BT, BT->getDescription(), N);
68     R->addRange(B->getSourceRange());
69     C.emitReport(std::move(R));
70   }
71 }
72 
73 void ento::registerPointerSubChecker(CheckerManager &mgr) {
74   mgr.registerChecker<PointerSubChecker>();
75 }
76 
77 bool ento::shouldRegisterPointerSubChecker(const CheckerManager &mgr) {
78   return true;
79 }
80