1 //=== UndefResultChecker.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 defines UndefResultChecker, a builtin check in ExprEngine that
10 // performs checks for undefined results of non-assignment binary operators.
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/DynamicExtent.h"
20 #include "clang/StaticAnalyzer/Core/PathSensitive/ExprEngine.h"
21 #include "llvm/ADT/SmallString.h"
22 #include "llvm/Support/raw_ostream.h"
23 
24 using namespace clang;
25 using namespace ento;
26 
27 namespace {
28 class UndefResultChecker
29   : public Checker< check::PostStmt<BinaryOperator> > {
30 
31   const BugType BT{this, "Result of operation is garbage or undefined"};
32 
33 public:
34   void checkPostStmt(const BinaryOperator *B, CheckerContext &C) const;
35 };
36 } // end anonymous namespace
37 
38 static bool isArrayIndexOutOfBounds(CheckerContext &C, const Expr *Ex) {
39   ProgramStateRef state = C.getState();
40 
41   if (!isa<ArraySubscriptExpr>(Ex))
42     return false;
43 
44   SVal Loc = C.getSVal(Ex);
45   if (!Loc.isValid())
46     return false;
47 
48   const MemRegion *MR = Loc.castAs<loc::MemRegionVal>().getRegion();
49   const ElementRegion *ER = dyn_cast<ElementRegion>(MR);
50   if (!ER)
51     return false;
52 
53   DefinedOrUnknownSVal Idx = ER->getIndex().castAs<DefinedOrUnknownSVal>();
54   DefinedOrUnknownSVal ElementCount = getDynamicElementCount(
55       state, ER->getSuperRegion(), C.getSValBuilder(), ER->getValueType());
56   ProgramStateRef StInBound, StOutBound;
57   std::tie(StInBound, StOutBound) = state->assumeInBoundDual(Idx, ElementCount);
58   return StOutBound && !StInBound;
59 }
60 
61 void UndefResultChecker::checkPostStmt(const BinaryOperator *B,
62                                        CheckerContext &C) const {
63   if (C.getSVal(B).isUndef()) {
64 
65     // Do not report assignments of uninitialized values inside swap functions.
66     // This should allow to swap partially uninitialized structs
67     if (const FunctionDecl *EnclosingFunctionDecl =
68         dyn_cast<FunctionDecl>(C.getStackFrame()->getDecl()))
69       if (C.getCalleeName(EnclosingFunctionDecl) == "swap")
70         return;
71 
72     // Generate an error node.
73     ExplodedNode *N = C.generateErrorNode();
74     if (!N)
75       return;
76 
77     SmallString<256> sbuf;
78     llvm::raw_svector_ostream OS(sbuf);
79     const Expr *Ex = nullptr;
80     bool isLeft = true;
81 
82     if (C.getSVal(B->getLHS()).isUndef()) {
83       Ex = B->getLHS()->IgnoreParenCasts();
84       isLeft = true;
85     }
86     else if (C.getSVal(B->getRHS()).isUndef()) {
87       Ex = B->getRHS()->IgnoreParenCasts();
88       isLeft = false;
89     }
90 
91     if (Ex) {
92       OS << "The " << (isLeft ? "left" : "right") << " operand of '"
93          << BinaryOperator::getOpcodeStr(B->getOpcode())
94          << "' is a garbage value";
95       if (isArrayIndexOutOfBounds(C, Ex))
96         OS << " due to array index out of bounds";
97     } else {
98       // Neither operand was undefined, but the result is undefined.
99       OS << "The result of the '"
100          << BinaryOperator::getOpcodeStr(B->getOpcode())
101          << "' expression is undefined";
102     }
103     auto report = std::make_unique<PathSensitiveBugReport>(BT, OS.str(), N);
104     if (Ex) {
105       report->addRange(Ex->getSourceRange());
106       bugreporter::trackExpressionValue(N, Ex, *report);
107     }
108     else
109       bugreporter::trackExpressionValue(N, B, *report);
110 
111     C.emitReport(std::move(report));
112   }
113 }
114 
115 void ento::registerUndefResultChecker(CheckerManager &mgr) {
116   mgr.registerChecker<UndefResultChecker>();
117 }
118 
119 bool ento::shouldRegisterUndefResultChecker(const CheckerManager &mgr) {
120   return true;
121 }
122