1 //=== UndefBranchChecker.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 UndefBranchChecker, which checks for undefined branch
10 // condition.
11 //
12 //===----------------------------------------------------------------------===//
13
14 #include "clang/AST/StmtObjC.h"
15 #include "clang/AST/Type.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 <utility>
22
23 using namespace clang;
24 using namespace ento;
25
26 namespace {
27
28 class UndefBranchChecker : public Checker<check::BranchCondition> {
29 mutable std::unique_ptr<BuiltinBug> BT;
30
31 struct FindUndefExpr {
32 ProgramStateRef St;
33 const LocationContext *LCtx;
34
FindUndefExpr__anonae1f902e0111::UndefBranchChecker::FindUndefExpr35 FindUndefExpr(ProgramStateRef S, const LocationContext *L)
36 : St(std::move(S)), LCtx(L) {}
37
FindExpr__anonae1f902e0111::UndefBranchChecker::FindUndefExpr38 const Expr *FindExpr(const Expr *Ex) {
39 if (!MatchesCriteria(Ex))
40 return nullptr;
41
42 for (const Stmt *SubStmt : Ex->children())
43 if (const Expr *ExI = dyn_cast_or_null<Expr>(SubStmt))
44 if (const Expr *E2 = FindExpr(ExI))
45 return E2;
46
47 return Ex;
48 }
49
MatchesCriteria__anonae1f902e0111::UndefBranchChecker::FindUndefExpr50 bool MatchesCriteria(const Expr *Ex) {
51 return St->getSVal(Ex, LCtx).isUndef();
52 }
53 };
54
55 public:
56 void checkBranchCondition(const Stmt *Condition, CheckerContext &Ctx) const;
57 };
58
59 } // namespace
60
checkBranchCondition(const Stmt * Condition,CheckerContext & Ctx) const61 void UndefBranchChecker::checkBranchCondition(const Stmt *Condition,
62 CheckerContext &Ctx) const {
63 // ObjCForCollection is a loop, but has no actual condition.
64 if (isa<ObjCForCollectionStmt>(Condition))
65 return;
66 SVal X = Ctx.getSVal(Condition);
67 if (X.isUndef()) {
68 // Generate a sink node, which implicitly marks both outgoing branches as
69 // infeasible.
70 ExplodedNode *N = Ctx.generateErrorNode();
71 if (N) {
72 if (!BT)
73 BT.reset(new BuiltinBug(
74 this, "Branch condition evaluates to a garbage value"));
75
76 // What's going on here: we want to highlight the subexpression of the
77 // condition that is the most likely source of the "uninitialized
78 // branch condition." We do a recursive walk of the condition's
79 // subexpressions and roughly look for the most nested subexpression
80 // that binds to Undefined. We then highlight that expression's range.
81
82 // Get the predecessor node and check if is a PostStmt with the Stmt
83 // being the terminator condition. We want to inspect the state
84 // of that node instead because it will contain main information about
85 // the subexpressions.
86
87 // Note: any predecessor will do. They should have identical state,
88 // since all the BlockEdge did was act as an error sink since the value
89 // had to already be undefined.
90 assert (!N->pred_empty());
91 const Expr *Ex = cast<Expr>(Condition);
92 ExplodedNode *PrevN = *N->pred_begin();
93 ProgramPoint P = PrevN->getLocation();
94 ProgramStateRef St = N->getState();
95
96 if (Optional<PostStmt> PS = P.getAs<PostStmt>())
97 if (PS->getStmt() == Ex)
98 St = PrevN->getState();
99
100 FindUndefExpr FindIt(St, Ctx.getLocationContext());
101 Ex = FindIt.FindExpr(Ex);
102
103 // Emit the bug report.
104 auto R = std::make_unique<PathSensitiveBugReport>(
105 *BT, BT->getDescription(), N);
106 bugreporter::trackExpressionValue(N, Ex, *R);
107 R->addRange(Ex->getSourceRange());
108
109 Ctx.emitReport(std::move(R));
110 }
111 }
112 }
113
registerUndefBranchChecker(CheckerManager & mgr)114 void ento::registerUndefBranchChecker(CheckerManager &mgr) {
115 mgr.registerChecker<UndefBranchChecker>();
116 }
117
shouldRegisterUndefBranchChecker(const CheckerManager & mgr)118 bool ento::shouldRegisterUndefBranchChecker(const CheckerManager &mgr) {
119 return true;
120 }
121