1 //== ArrayBoundChecker.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 file defines ArrayBoundChecker, which is a path-sensitive check
10 // which looks for an out-of-bound array element access.
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/ExprEngine.h"
20 
21 using namespace clang;
22 using namespace ento;
23 
24 namespace {
25 class ArrayBoundChecker :
26     public Checker<check::Location> {
27   mutable std::unique_ptr<BuiltinBug> BT;
28 
29 public:
30   void checkLocation(SVal l, bool isLoad, const Stmt* S,
31                      CheckerContext &C) const;
32 };
33 }
34 
35 void ArrayBoundChecker::checkLocation(SVal l, bool isLoad, const Stmt* LoadS,
36                                       CheckerContext &C) const {
37   // Check for out of bound array element access.
38   const MemRegion *R = l.getAsRegion();
39   if (!R)
40     return;
41 
42   const ElementRegion *ER = dyn_cast<ElementRegion>(R);
43   if (!ER)
44     return;
45 
46   // Get the index of the accessed element.
47   DefinedOrUnknownSVal Idx = ER->getIndex().castAs<DefinedOrUnknownSVal>();
48 
49   // Zero index is always in bound, this also passes ElementRegions created for
50   // pointer casts.
51   if (Idx.isZeroConstant())
52     return;
53 
54   ProgramStateRef state = C.getState();
55 
56   // Get the size of the array.
57   DefinedOrUnknownSVal NumElements
58     = C.getStoreManager().getSizeInElements(state, ER->getSuperRegion(),
59                                             ER->getValueType());
60 
61   ProgramStateRef StInBound = state->assumeInBound(Idx, NumElements, true);
62   ProgramStateRef StOutBound = state->assumeInBound(Idx, NumElements, false);
63   if (StOutBound && !StInBound) {
64     ExplodedNode *N = C.generateErrorNode(StOutBound);
65     if (!N)
66       return;
67 
68     if (!BT)
69       BT.reset(new BuiltinBug(
70           this, "Out-of-bound array access",
71           "Access out-of-bound array element (buffer overflow)"));
72 
73     // FIXME: It would be nice to eventually make this diagnostic more clear,
74     // e.g., by referencing the original declaration or by saying *why* this
75     // reference is outside the range.
76 
77     // Generate a report for this bug.
78     auto report = llvm::make_unique<BugReport>(*BT, BT->getDescription(), N);
79 
80     report->addRange(LoadS->getSourceRange());
81     C.emitReport(std::move(report));
82     return;
83   }
84 
85   // Array bound check succeeded.  From this point forward the array bound
86   // should always succeed.
87   C.addTransition(StInBound);
88 }
89 
90 void ento::registerArrayBoundChecker(CheckerManager &mgr) {
91   mgr.registerChecker<ArrayBoundChecker>();
92 }
93 
94 bool ento::shouldRegisterArrayBoundChecker(const LangOptions &LO) {
95   return true;
96 }
97