1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
|
//=== UndefResultChecker.cpp ------------------------------------*- C++ -*-===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This defines UndefResultChecker, a builtin check in ExprEngine that
// performs checks for undefined results of non-assignment binary operators.
//
//===----------------------------------------------------------------------===//
#include "clang/StaticAnalyzer/Checkers/BuiltinCheckerRegistration.h"
#include "clang/StaticAnalyzer/Core/BugReporter/BugType.h"
#include "clang/StaticAnalyzer/Core/Checker.h"
#include "clang/StaticAnalyzer/Core/CheckerManager.h"
#include "clang/StaticAnalyzer/Core/PathSensitive/CheckerContext.h"
#include "clang/StaticAnalyzer/Core/PathSensitive/ExprEngine.h"
#include "llvm/ADT/SmallString.h"
#include "llvm/Support/raw_ostream.h"
using namespace clang;
using namespace ento;
namespace {
class UndefResultChecker
: public Checker< check::PostStmt<BinaryOperator> > {
mutable std::unique_ptr<BugType> BT;
public:
void checkPostStmt(const BinaryOperator *B, CheckerContext &C) const;
};
} // end anonymous namespace
static bool isArrayIndexOutOfBounds(CheckerContext &C, const Expr *Ex) {
ProgramStateRef state = C.getState();
if (!isa<ArraySubscriptExpr>(Ex))
return false;
SVal Loc = C.getSVal(Ex);
if (!Loc.isValid())
return false;
const MemRegion *MR = Loc.castAs<loc::MemRegionVal>().getRegion();
const ElementRegion *ER = dyn_cast<ElementRegion>(MR);
if (!ER)
return false;
DefinedOrUnknownSVal Idx = ER->getIndex().castAs<DefinedOrUnknownSVal>();
DefinedOrUnknownSVal NumElements = C.getStoreManager().getSizeInElements(
state, ER->getSuperRegion(), ER->getValueType());
ProgramStateRef StInBound = state->assumeInBound(Idx, NumElements, true);
ProgramStateRef StOutBound = state->assumeInBound(Idx, NumElements, false);
return StOutBound && !StInBound;
}
static bool isShiftOverflow(const BinaryOperator *B, CheckerContext &C) {
return C.isGreaterOrEqual(
B->getRHS(), C.getASTContext().getIntWidth(B->getLHS()->getType()));
}
static bool isLeftShiftResultUnrepresentable(const BinaryOperator *B,
CheckerContext &C) {
SValBuilder &SB = C.getSValBuilder();
ProgramStateRef State = C.getState();
const llvm::APSInt *LHS = SB.getKnownValue(State, C.getSVal(B->getLHS()));
const llvm::APSInt *RHS = SB.getKnownValue(State, C.getSVal(B->getRHS()));
assert(LHS && RHS && "Values unknown, inconsistent state");
return (unsigned)RHS->getZExtValue() > LHS->countLeadingZeros();
}
void UndefResultChecker::checkPostStmt(const BinaryOperator *B,
CheckerContext &C) const {
if (C.getSVal(B).isUndef()) {
// Do not report assignments of uninitialized values inside swap functions.
// This should allow to swap partially uninitialized structs
// (radar://14129997)
if (const FunctionDecl *EnclosingFunctionDecl =
dyn_cast<FunctionDecl>(C.getStackFrame()->getDecl()))
if (C.getCalleeName(EnclosingFunctionDecl) == "swap")
return;
// Generate an error node.
ExplodedNode *N = C.generateErrorNode();
if (!N)
return;
if (!BT)
BT.reset(
new BuiltinBug(this, "Result of operation is garbage or undefined"));
SmallString<256> sbuf;
llvm::raw_svector_ostream OS(sbuf);
const Expr *Ex = nullptr;
bool isLeft = true;
if (C.getSVal(B->getLHS()).isUndef()) {
Ex = B->getLHS()->IgnoreParenCasts();
isLeft = true;
}
else if (C.getSVal(B->getRHS()).isUndef()) {
Ex = B->getRHS()->IgnoreParenCasts();
isLeft = false;
}
if (Ex) {
OS << "The " << (isLeft ? "left" : "right") << " operand of '"
<< BinaryOperator::getOpcodeStr(B->getOpcode())
<< "' is a garbage value";
if (isArrayIndexOutOfBounds(C, Ex))
OS << " due to array index out of bounds";
} else {
// Neither operand was undefined, but the result is undefined.
if ((B->getOpcode() == BinaryOperatorKind::BO_Shl ||
B->getOpcode() == BinaryOperatorKind::BO_Shr) &&
C.isNegative(B->getRHS())) {
OS << "The result of the "
<< ((B->getOpcode() == BinaryOperatorKind::BO_Shl) ? "left"
: "right")
<< " shift is undefined because the right operand is negative";
Ex = B->getRHS();
} else if ((B->getOpcode() == BinaryOperatorKind::BO_Shl ||
B->getOpcode() == BinaryOperatorKind::BO_Shr) &&
isShiftOverflow(B, C)) {
OS << "The result of the "
<< ((B->getOpcode() == BinaryOperatorKind::BO_Shl) ? "left"
: "right")
<< " shift is undefined due to shifting by ";
Ex = B->getRHS();
SValBuilder &SB = C.getSValBuilder();
const llvm::APSInt *I =
SB.getKnownValue(C.getState(), C.getSVal(B->getRHS()));
if (!I)
OS << "a value that is";
else if (I->isUnsigned())
OS << '\'' << I->getZExtValue() << "\', which is";
else
OS << '\'' << I->getSExtValue() << "\', which is";
OS << " greater or equal to the width of type '"
<< B->getLHS()->getType().getAsString() << "'.";
} else if (B->getOpcode() == BinaryOperatorKind::BO_Shl &&
C.isNegative(B->getLHS())) {
OS << "The result of the left shift is undefined because the left "
"operand is negative";
Ex = B->getLHS();
} else if (B->getOpcode() == BinaryOperatorKind::BO_Shl &&
isLeftShiftResultUnrepresentable(B, C)) {
ProgramStateRef State = C.getState();
SValBuilder &SB = C.getSValBuilder();
const llvm::APSInt *LHS =
SB.getKnownValue(State, C.getSVal(B->getLHS()));
const llvm::APSInt *RHS =
SB.getKnownValue(State, C.getSVal(B->getRHS()));
OS << "The result of the left shift is undefined due to shifting \'"
<< LHS->getSExtValue() << "\' by \'" << RHS->getZExtValue()
<< "\', which is unrepresentable in the unsigned version of "
<< "the return type \'" << B->getLHS()->getType().getAsString()
<< "\'";
Ex = B->getLHS();
} else {
OS << "The result of the '"
<< BinaryOperator::getOpcodeStr(B->getOpcode())
<< "' expression is undefined";
}
}
auto report = llvm::make_unique<BugReport>(*BT, OS.str(), N);
if (Ex) {
report->addRange(Ex->getSourceRange());
bugreporter::trackExpressionValue(N, Ex, *report);
}
else
bugreporter::trackExpressionValue(N, B, *report);
C.emitReport(std::move(report));
}
}
void ento::registerUndefResultChecker(CheckerManager &mgr) {
mgr.registerChecker<UndefResultChecker>();
}
|
