1 //=== PointerArithChecker.cpp - Pointer arithmetic 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 PointerArithChecker, a builtin checker that checks for
10 // pointer arithmetic on locations other than array elements.
11 //
12 //===----------------------------------------------------------------------===//
13
14 #include "clang/AST/DeclCXX.h"
15 #include "clang/AST/ExprCXX.h"
16 #include "clang/StaticAnalyzer/Checkers/BuiltinCheckerRegistration.h"
17 #include "clang/StaticAnalyzer/Core/BugReporter/BugType.h"
18 #include "clang/StaticAnalyzer/Core/Checker.h"
19 #include "clang/StaticAnalyzer/Core/CheckerManager.h"
20 #include "clang/StaticAnalyzer/Core/PathSensitive/CheckerContext.h"
21 #include "llvm/ADT/StringRef.h"
22
23 using namespace clang;
24 using namespace ento;
25
26 namespace {
27 enum class AllocKind {
28 SingleObject,
29 Array,
30 Unknown,
31 Reinterpreted // Single object interpreted as an array.
32 };
33 } // end namespace
34
35 namespace llvm {
36 template <> struct FoldingSetTrait<AllocKind> {
Profilellvm::FoldingSetTrait37 static inline void Profile(AllocKind X, FoldingSetNodeID &ID) {
38 ID.AddInteger(static_cast<int>(X));
39 }
40 };
41 } // end namespace llvm
42
43 namespace {
44 class PointerArithChecker
45 : public Checker<
46 check::PreStmt<BinaryOperator>, check::PreStmt<UnaryOperator>,
47 check::PreStmt<ArraySubscriptExpr>, check::PreStmt<CastExpr>,
48 check::PostStmt<CastExpr>, check::PostStmt<CXXNewExpr>,
49 check::PostStmt<CallExpr>, check::DeadSymbols> {
50 AllocKind getKindOfNewOp(const CXXNewExpr *NE, const FunctionDecl *FD) const;
51 const MemRegion *getArrayRegion(const MemRegion *Region, bool &Polymorphic,
52 AllocKind &AKind, CheckerContext &C) const;
53 const MemRegion *getPointedRegion(const MemRegion *Region,
54 CheckerContext &C) const;
55 void reportPointerArithMisuse(const Expr *E, CheckerContext &C,
56 bool PointedNeeded = false) const;
57 void initAllocIdentifiers(ASTContext &C) const;
58
59 const BugType BT_pointerArith{this, "Dangerous pointer arithmetic"};
60 const BugType BT_polyArray{this, "Dangerous pointer arithmetic"};
61 mutable llvm::SmallSet<IdentifierInfo *, 8> AllocFunctions;
62
63 public:
64 void checkPreStmt(const UnaryOperator *UOp, CheckerContext &C) const;
65 void checkPreStmt(const BinaryOperator *BOp, CheckerContext &C) const;
66 void checkPreStmt(const ArraySubscriptExpr *SubExpr, CheckerContext &C) const;
67 void checkPreStmt(const CastExpr *CE, CheckerContext &C) const;
68 void checkPostStmt(const CastExpr *CE, CheckerContext &C) const;
69 void checkPostStmt(const CXXNewExpr *NE, CheckerContext &C) const;
70 void checkPostStmt(const CallExpr *CE, CheckerContext &C) const;
71 void checkDeadSymbols(SymbolReaper &SR, CheckerContext &C) const;
72 };
73 } // end namespace
74
REGISTER_MAP_WITH_PROGRAMSTATE(RegionState,const MemRegion *,AllocKind)75 REGISTER_MAP_WITH_PROGRAMSTATE(RegionState, const MemRegion *, AllocKind)
76
77 void PointerArithChecker::checkDeadSymbols(SymbolReaper &SR,
78 CheckerContext &C) const {
79 // TODO: intentional leak. Some information is garbage collected too early,
80 // see http://reviews.llvm.org/D14203 for further information.
81 /*ProgramStateRef State = C.getState();
82 RegionStateTy RegionStates = State->get<RegionState>();
83 for (const MemRegion *Reg: llvm::make_first_range(RegionStates)) {
84 if (!SR.isLiveRegion(Reg))
85 State = State->remove<RegionState>(Reg);
86 }
87 C.addTransition(State);*/
88 }
89
getKindOfNewOp(const CXXNewExpr * NE,const FunctionDecl * FD) const90 AllocKind PointerArithChecker::getKindOfNewOp(const CXXNewExpr *NE,
91 const FunctionDecl *FD) const {
92 // This checker try not to assume anything about placement and overloaded
93 // new to avoid false positives.
94 if (isa<CXXMethodDecl>(FD))
95 return AllocKind::Unknown;
96 if (FD->getNumParams() != 1 || FD->isVariadic())
97 return AllocKind::Unknown;
98 if (NE->isArray())
99 return AllocKind::Array;
100
101 return AllocKind::SingleObject;
102 }
103
104 const MemRegion *
getPointedRegion(const MemRegion * Region,CheckerContext & C) const105 PointerArithChecker::getPointedRegion(const MemRegion *Region,
106 CheckerContext &C) const {
107 assert(Region);
108 ProgramStateRef State = C.getState();
109 SVal S = State->getSVal(Region);
110 return S.getAsRegion();
111 }
112
113 /// Checks whether a region is the part of an array.
114 /// In case there is a derived to base cast above the array element, the
115 /// Polymorphic output value is set to true. AKind output value is set to the
116 /// allocation kind of the inspected region.
getArrayRegion(const MemRegion * Region,bool & Polymorphic,AllocKind & AKind,CheckerContext & C) const117 const MemRegion *PointerArithChecker::getArrayRegion(const MemRegion *Region,
118 bool &Polymorphic,
119 AllocKind &AKind,
120 CheckerContext &C) const {
121 assert(Region);
122 while (const auto *BaseRegion = dyn_cast<CXXBaseObjectRegion>(Region)) {
123 Region = BaseRegion->getSuperRegion();
124 Polymorphic = true;
125 }
126 if (const auto *ElemRegion = dyn_cast<ElementRegion>(Region)) {
127 Region = ElemRegion->getSuperRegion();
128 }
129
130 ProgramStateRef State = C.getState();
131 if (const AllocKind *Kind = State->get<RegionState>(Region)) {
132 AKind = *Kind;
133 if (*Kind == AllocKind::Array)
134 return Region;
135 else
136 return nullptr;
137 }
138 // When the region is symbolic and we do not have any information about it,
139 // assume that this is an array to avoid false positives.
140 if (isa<SymbolicRegion>(Region))
141 return Region;
142
143 // No AllocKind stored and not symbolic, assume that it points to a single
144 // object.
145 return nullptr;
146 }
147
reportPointerArithMisuse(const Expr * E,CheckerContext & C,bool PointedNeeded) const148 void PointerArithChecker::reportPointerArithMisuse(const Expr *E,
149 CheckerContext &C,
150 bool PointedNeeded) const {
151 SourceRange SR = E->getSourceRange();
152 if (SR.isInvalid())
153 return;
154
155 ProgramStateRef State = C.getState();
156 const MemRegion *Region = C.getSVal(E).getAsRegion();
157 if (!Region)
158 return;
159 if (PointedNeeded)
160 Region = getPointedRegion(Region, C);
161 if (!Region)
162 return;
163
164 bool IsPolymorphic = false;
165 AllocKind Kind = AllocKind::Unknown;
166 if (const MemRegion *ArrayRegion =
167 getArrayRegion(Region, IsPolymorphic, Kind, C)) {
168 if (!IsPolymorphic)
169 return;
170 if (ExplodedNode *N = C.generateNonFatalErrorNode()) {
171 constexpr llvm::StringLiteral Msg =
172 "Pointer arithmetic on a pointer to base class is dangerous "
173 "because derived and base class may have different size.";
174 auto R = std::make_unique<PathSensitiveBugReport>(BT_polyArray, Msg, N);
175 R->addRange(E->getSourceRange());
176 R->markInteresting(ArrayRegion);
177 C.emitReport(std::move(R));
178 }
179 return;
180 }
181
182 if (Kind == AllocKind::Reinterpreted)
183 return;
184
185 // We might not have enough information about symbolic regions.
186 if (Kind != AllocKind::SingleObject &&
187 Region->getKind() == MemRegion::Kind::SymbolicRegionKind)
188 return;
189
190 if (ExplodedNode *N = C.generateNonFatalErrorNode()) {
191 constexpr llvm::StringLiteral Msg =
192 "Pointer arithmetic on non-array variables relies on memory layout, "
193 "which is dangerous.";
194 auto R = std::make_unique<PathSensitiveBugReport>(BT_pointerArith, Msg, N);
195 R->addRange(SR);
196 R->markInteresting(Region);
197 C.emitReport(std::move(R));
198 }
199 }
200
initAllocIdentifiers(ASTContext & C) const201 void PointerArithChecker::initAllocIdentifiers(ASTContext &C) const {
202 if (!AllocFunctions.empty())
203 return;
204 AllocFunctions.insert(&C.Idents.get("alloca"));
205 AllocFunctions.insert(&C.Idents.get("malloc"));
206 AllocFunctions.insert(&C.Idents.get("realloc"));
207 AllocFunctions.insert(&C.Idents.get("calloc"));
208 AllocFunctions.insert(&C.Idents.get("valloc"));
209 }
210
checkPostStmt(const CallExpr * CE,CheckerContext & C) const211 void PointerArithChecker::checkPostStmt(const CallExpr *CE,
212 CheckerContext &C) const {
213 ProgramStateRef State = C.getState();
214 const FunctionDecl *FD = C.getCalleeDecl(CE);
215 if (!FD)
216 return;
217 IdentifierInfo *FunI = FD->getIdentifier();
218 initAllocIdentifiers(C.getASTContext());
219 if (AllocFunctions.count(FunI) == 0)
220 return;
221
222 SVal SV = C.getSVal(CE);
223 const MemRegion *Region = SV.getAsRegion();
224 if (!Region)
225 return;
226 // Assume that C allocation functions allocate arrays to avoid false
227 // positives.
228 // TODO: Add heuristics to distinguish alloc calls that allocates single
229 // objecs.
230 State = State->set<RegionState>(Region, AllocKind::Array);
231 C.addTransition(State);
232 }
233
checkPostStmt(const CXXNewExpr * NE,CheckerContext & C) const234 void PointerArithChecker::checkPostStmt(const CXXNewExpr *NE,
235 CheckerContext &C) const {
236 const FunctionDecl *FD = NE->getOperatorNew();
237 if (!FD)
238 return;
239
240 AllocKind Kind = getKindOfNewOp(NE, FD);
241
242 ProgramStateRef State = C.getState();
243 SVal AllocedVal = C.getSVal(NE);
244 const MemRegion *Region = AllocedVal.getAsRegion();
245 if (!Region)
246 return;
247 State = State->set<RegionState>(Region, Kind);
248 C.addTransition(State);
249 }
250
checkPostStmt(const CastExpr * CE,CheckerContext & C) const251 void PointerArithChecker::checkPostStmt(const CastExpr *CE,
252 CheckerContext &C) const {
253 if (CE->getCastKind() != CastKind::CK_BitCast)
254 return;
255
256 const Expr *CastedExpr = CE->getSubExpr();
257 ProgramStateRef State = C.getState();
258 SVal CastedVal = C.getSVal(CastedExpr);
259
260 const MemRegion *Region = CastedVal.getAsRegion();
261 if (!Region)
262 return;
263
264 // Suppress reinterpret casted hits.
265 State = State->set<RegionState>(Region, AllocKind::Reinterpreted);
266 C.addTransition(State);
267 }
268
checkPreStmt(const CastExpr * CE,CheckerContext & C) const269 void PointerArithChecker::checkPreStmt(const CastExpr *CE,
270 CheckerContext &C) const {
271 if (CE->getCastKind() != CastKind::CK_ArrayToPointerDecay)
272 return;
273
274 const Expr *CastedExpr = CE->getSubExpr();
275 ProgramStateRef State = C.getState();
276 SVal CastedVal = C.getSVal(CastedExpr);
277
278 const MemRegion *Region = CastedVal.getAsRegion();
279 if (!Region)
280 return;
281
282 if (const AllocKind *Kind = State->get<RegionState>(Region)) {
283 if (*Kind == AllocKind::Array || *Kind == AllocKind::Reinterpreted)
284 return;
285 }
286 State = State->set<RegionState>(Region, AllocKind::Array);
287 C.addTransition(State);
288 }
289
checkPreStmt(const UnaryOperator * UOp,CheckerContext & C) const290 void PointerArithChecker::checkPreStmt(const UnaryOperator *UOp,
291 CheckerContext &C) const {
292 if (!UOp->isIncrementDecrementOp() || !UOp->getType()->isPointerType())
293 return;
294 reportPointerArithMisuse(UOp->getSubExpr(), C, true);
295 }
296
checkPreStmt(const ArraySubscriptExpr * SubsExpr,CheckerContext & C) const297 void PointerArithChecker::checkPreStmt(const ArraySubscriptExpr *SubsExpr,
298 CheckerContext &C) const {
299 SVal Idx = C.getSVal(SubsExpr->getIdx());
300
301 // Indexing with 0 is OK.
302 if (Idx.isZeroConstant())
303 return;
304
305 // Indexing vector-type expressions is also OK.
306 if (SubsExpr->getBase()->getType()->isVectorType())
307 return;
308 reportPointerArithMisuse(SubsExpr->getBase(), C);
309 }
310
checkPreStmt(const BinaryOperator * BOp,CheckerContext & C) const311 void PointerArithChecker::checkPreStmt(const BinaryOperator *BOp,
312 CheckerContext &C) const {
313 BinaryOperatorKind OpKind = BOp->getOpcode();
314 if (!BOp->isAdditiveOp() && OpKind != BO_AddAssign && OpKind != BO_SubAssign)
315 return;
316
317 const Expr *Lhs = BOp->getLHS();
318 const Expr *Rhs = BOp->getRHS();
319 ProgramStateRef State = C.getState();
320
321 if (Rhs->getType()->isIntegerType() && Lhs->getType()->isPointerType()) {
322 SVal RHSVal = C.getSVal(Rhs);
323 if (State->isNull(RHSVal).isConstrainedTrue())
324 return;
325 reportPointerArithMisuse(Lhs, C, !BOp->isAdditiveOp());
326 }
327 // The int += ptr; case is not valid C++.
328 if (Lhs->getType()->isIntegerType() && Rhs->getType()->isPointerType()) {
329 SVal LHSVal = C.getSVal(Lhs);
330 if (State->isNull(LHSVal).isConstrainedTrue())
331 return;
332 reportPointerArithMisuse(Rhs, C);
333 }
334 }
335
registerPointerArithChecker(CheckerManager & mgr)336 void ento::registerPointerArithChecker(CheckerManager &mgr) {
337 mgr.registerChecker<PointerArithChecker>();
338 }
339
shouldRegisterPointerArithChecker(const CheckerManager & mgr)340 bool ento::shouldRegisterPointerArithChecker(const CheckerManager &mgr) {
341 return true;
342 }
343