1 //== TestAfterDivZeroChecker.cpp - Test after division by zero checker --*--==//
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 defines TestAfterDivZeroChecker, a builtin check that performs checks
10 //  for division by zero where the division occurs before comparison with zero.
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/PathSensitive/CallEvent.h"
18 #include "clang/StaticAnalyzer/Core/PathSensitive/CheckerContext.h"
19 #include "llvm/ADT/FoldingSet.h"
20 #include <optional>
21 
22 using namespace clang;
23 using namespace ento;
24 
25 namespace {
26 
27 class ZeroState {
28 private:
29   SymbolRef ZeroSymbol;
30   unsigned BlockID;
31   const StackFrameContext *SFC;
32 
33 public:
34   ZeroState(SymbolRef S, unsigned B, const StackFrameContext *SFC)
35       : ZeroSymbol(S), BlockID(B), SFC(SFC) {}
36 
37   const StackFrameContext *getStackFrameContext() const { return SFC; }
38 
39   bool operator==(const ZeroState &X) const {
40     return BlockID == X.BlockID && SFC == X.SFC && ZeroSymbol == X.ZeroSymbol;
41   }
42 
43   bool operator<(const ZeroState &X) const {
44     if (BlockID != X.BlockID)
45       return BlockID < X.BlockID;
46     if (SFC != X.SFC)
47       return SFC < X.SFC;
48     return ZeroSymbol < X.ZeroSymbol;
49   }
50 
51   void Profile(llvm::FoldingSetNodeID &ID) const {
52     ID.AddInteger(BlockID);
53     ID.AddPointer(SFC);
54     ID.AddPointer(ZeroSymbol);
55   }
56 };
57 
58 class DivisionBRVisitor : public BugReporterVisitor {
59 private:
60   SymbolRef ZeroSymbol;
61   const StackFrameContext *SFC;
62   bool Satisfied;
63 
64 public:
65   DivisionBRVisitor(SymbolRef ZeroSymbol, const StackFrameContext *SFC)
66       : ZeroSymbol(ZeroSymbol), SFC(SFC), Satisfied(false) {}
67 
68   void Profile(llvm::FoldingSetNodeID &ID) const override {
69     ID.Add(ZeroSymbol);
70     ID.Add(SFC);
71   }
72 
73   PathDiagnosticPieceRef VisitNode(const ExplodedNode *Succ,
74                                    BugReporterContext &BRC,
75                                    PathSensitiveBugReport &BR) override;
76 };
77 
78 class TestAfterDivZeroChecker
79     : public Checker<check::PreStmt<BinaryOperator>, check::BranchCondition,
80                      check::EndFunction> {
81   const BugType DivZeroBug{this, "Division by zero"};
82   void reportBug(SVal Val, CheckerContext &C) const;
83 
84 public:
85   void checkPreStmt(const BinaryOperator *B, CheckerContext &C) const;
86   void checkBranchCondition(const Stmt *Condition, CheckerContext &C) const;
87   void checkEndFunction(const ReturnStmt *RS, CheckerContext &C) const;
88   void setDivZeroMap(SVal Var, CheckerContext &C) const;
89   bool hasDivZeroMap(SVal Var, const CheckerContext &C) const;
90   bool isZero(SVal S, CheckerContext &C) const;
91 };
92 } // end anonymous namespace
93 
94 REGISTER_SET_WITH_PROGRAMSTATE(DivZeroMap, ZeroState)
95 
96 PathDiagnosticPieceRef
97 DivisionBRVisitor::VisitNode(const ExplodedNode *Succ, BugReporterContext &BRC,
98                              PathSensitiveBugReport &BR) {
99   if (Satisfied)
100     return nullptr;
101 
102   const Expr *E = nullptr;
103 
104   if (std::optional<PostStmt> P = Succ->getLocationAs<PostStmt>())
105     if (const BinaryOperator *BO = P->getStmtAs<BinaryOperator>()) {
106       BinaryOperator::Opcode Op = BO->getOpcode();
107       if (Op == BO_Div || Op == BO_Rem || Op == BO_DivAssign ||
108           Op == BO_RemAssign) {
109         E = BO->getRHS();
110       }
111     }
112 
113   if (!E)
114     return nullptr;
115 
116   SVal S = Succ->getSVal(E);
117   if (ZeroSymbol == S.getAsSymbol() && SFC == Succ->getStackFrame()) {
118     Satisfied = true;
119 
120     // Construct a new PathDiagnosticPiece.
121     ProgramPoint P = Succ->getLocation();
122     PathDiagnosticLocation L =
123         PathDiagnosticLocation::create(P, BRC.getSourceManager());
124 
125     if (!L.isValid() || !L.asLocation().isValid())
126       return nullptr;
127 
128     return std::make_shared<PathDiagnosticEventPiece>(
129         L, "Division with compared value made here");
130   }
131 
132   return nullptr;
133 }
134 
135 bool TestAfterDivZeroChecker::isZero(SVal S, CheckerContext &C) const {
136   std::optional<DefinedSVal> DSV = S.getAs<DefinedSVal>();
137 
138   if (!DSV)
139     return false;
140 
141   ConstraintManager &CM = C.getConstraintManager();
142   return !CM.assume(C.getState(), *DSV, true);
143 }
144 
145 void TestAfterDivZeroChecker::setDivZeroMap(SVal Var, CheckerContext &C) const {
146   SymbolRef SR = Var.getAsSymbol();
147   if (!SR)
148     return;
149 
150   ProgramStateRef State = C.getState();
151   State =
152       State->add<DivZeroMap>(ZeroState(SR, C.getBlockID(), C.getStackFrame()));
153   C.addTransition(State);
154 }
155 
156 bool TestAfterDivZeroChecker::hasDivZeroMap(SVal Var,
157                                             const CheckerContext &C) const {
158   SymbolRef SR = Var.getAsSymbol();
159   if (!SR)
160     return false;
161 
162   ZeroState ZS(SR, C.getBlockID(), C.getStackFrame());
163   return C.getState()->contains<DivZeroMap>(ZS);
164 }
165 
166 void TestAfterDivZeroChecker::reportBug(SVal Val, CheckerContext &C) const {
167   if (ExplodedNode *N = C.generateErrorNode(C.getState())) {
168     auto R = std::make_unique<PathSensitiveBugReport>(
169         DivZeroBug,
170         "Value being compared against zero has already been used "
171         "for division",
172         N);
173 
174     R->addVisitor(std::make_unique<DivisionBRVisitor>(Val.getAsSymbol(),
175                                                        C.getStackFrame()));
176     C.emitReport(std::move(R));
177   }
178 }
179 
180 void TestAfterDivZeroChecker::checkEndFunction(const ReturnStmt *,
181                                                CheckerContext &C) const {
182   ProgramStateRef State = C.getState();
183 
184   DivZeroMapTy DivZeroes = State->get<DivZeroMap>();
185   if (DivZeroes.isEmpty())
186     return;
187 
188   DivZeroMapTy::Factory &F = State->get_context<DivZeroMap>();
189   for (const ZeroState &ZS : DivZeroes) {
190     if (ZS.getStackFrameContext() == C.getStackFrame())
191       DivZeroes = F.remove(DivZeroes, ZS);
192   }
193   C.addTransition(State->set<DivZeroMap>(DivZeroes));
194 }
195 
196 void TestAfterDivZeroChecker::checkPreStmt(const BinaryOperator *B,
197                                            CheckerContext &C) const {
198   BinaryOperator::Opcode Op = B->getOpcode();
199   if (Op == BO_Div || Op == BO_Rem || Op == BO_DivAssign ||
200       Op == BO_RemAssign) {
201     SVal S = C.getSVal(B->getRHS());
202 
203     if (!isZero(S, C))
204       setDivZeroMap(S, C);
205   }
206 }
207 
208 void TestAfterDivZeroChecker::checkBranchCondition(const Stmt *Condition,
209                                                    CheckerContext &C) const {
210   if (const BinaryOperator *B = dyn_cast<BinaryOperator>(Condition)) {
211     if (B->isComparisonOp()) {
212       const IntegerLiteral *IntLiteral = dyn_cast<IntegerLiteral>(B->getRHS());
213       bool LRHS = true;
214       if (!IntLiteral) {
215         IntLiteral = dyn_cast<IntegerLiteral>(B->getLHS());
216         LRHS = false;
217       }
218 
219       if (!IntLiteral || IntLiteral->getValue() != 0)
220         return;
221 
222       SVal Val = C.getSVal(LRHS ? B->getLHS() : B->getRHS());
223       if (hasDivZeroMap(Val, C))
224         reportBug(Val, C);
225     }
226   } else if (const UnaryOperator *U = dyn_cast<UnaryOperator>(Condition)) {
227     if (U->getOpcode() == UO_LNot) {
228       SVal Val;
229       if (const ImplicitCastExpr *I =
230               dyn_cast<ImplicitCastExpr>(U->getSubExpr()))
231         Val = C.getSVal(I->getSubExpr());
232 
233       if (hasDivZeroMap(Val, C))
234         reportBug(Val, C);
235       else {
236         Val = C.getSVal(U->getSubExpr());
237         if (hasDivZeroMap(Val, C))
238           reportBug(Val, C);
239       }
240     }
241   } else if (const ImplicitCastExpr *IE =
242                  dyn_cast<ImplicitCastExpr>(Condition)) {
243     SVal Val = C.getSVal(IE->getSubExpr());
244 
245     if (hasDivZeroMap(Val, C))
246       reportBug(Val, C);
247     else {
248       SVal Val = C.getSVal(Condition);
249 
250       if (hasDivZeroMap(Val, C))
251         reportBug(Val, C);
252     }
253   }
254 }
255 
256 void ento::registerTestAfterDivZeroChecker(CheckerManager &mgr) {
257   mgr.registerChecker<TestAfterDivZeroChecker>();
258 }
259 
260 bool ento::shouldRegisterTestAfterDivZeroChecker(const CheckerManager &mgr) {
261   return true;
262 }
263