1 //=== StackAddrEscapeChecker.cpp ----------------------------------*- C++ -*--//
2 //
3 // The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 //
10 // This file defines stack address leak checker, which checks if an invalid
11 // stack address is stored into a global or heap location. See CERT DCL30-C.
12 //
13 //===----------------------------------------------------------------------===//
14
15 #include "ClangSACheckers.h"
16 #include "clang/AST/ExprCXX.h"
17 #include "clang/Basic/SourceManager.h"
18 #include "clang/StaticAnalyzer/Core/BugReporter/BugType.h"
19 #include "clang/StaticAnalyzer/Core/Checker.h"
20 #include "clang/StaticAnalyzer/Core/CheckerManager.h"
21 #include "clang/StaticAnalyzer/Core/PathSensitive/CheckerContext.h"
22 #include "clang/StaticAnalyzer/Core/PathSensitive/ProgramState.h"
23 #include "llvm/ADT/SmallString.h"
24 #include "llvm/Support/raw_ostream.h"
25 using namespace clang;
26 using namespace ento;
27
28 namespace {
29 class StackAddrEscapeChecker : public Checker< check::PreStmt<ReturnStmt>,
30 check::EndFunction > {
31 mutable std::unique_ptr<BuiltinBug> BT_stackleak;
32 mutable std::unique_ptr<BuiltinBug> BT_returnstack;
33
34 public:
35 void checkPreStmt(const ReturnStmt *RS, CheckerContext &C) const;
36 void checkEndFunction(CheckerContext &Ctx) const;
37 private:
38 void EmitStackError(CheckerContext &C, const MemRegion *R,
39 const Expr *RetE) const;
40 static SourceRange genName(raw_ostream &os, const MemRegion *R,
41 ASTContext &Ctx);
42 };
43 }
44
genName(raw_ostream & os,const MemRegion * R,ASTContext & Ctx)45 SourceRange StackAddrEscapeChecker::genName(raw_ostream &os, const MemRegion *R,
46 ASTContext &Ctx) {
47 // Get the base region, stripping away fields and elements.
48 R = R->getBaseRegion();
49 SourceManager &SM = Ctx.getSourceManager();
50 SourceRange range;
51 os << "Address of ";
52
53 // Check if the region is a compound literal.
54 if (const CompoundLiteralRegion* CR = dyn_cast<CompoundLiteralRegion>(R)) {
55 const CompoundLiteralExpr *CL = CR->getLiteralExpr();
56 os << "stack memory associated with a compound literal "
57 "declared on line "
58 << SM.getExpansionLineNumber(CL->getLocStart())
59 << " returned to caller";
60 range = CL->getSourceRange();
61 }
62 else if (const AllocaRegion* AR = dyn_cast<AllocaRegion>(R)) {
63 const Expr *ARE = AR->getExpr();
64 SourceLocation L = ARE->getLocStart();
65 range = ARE->getSourceRange();
66 os << "stack memory allocated by call to alloca() on line "
67 << SM.getExpansionLineNumber(L);
68 }
69 else if (const BlockDataRegion *BR = dyn_cast<BlockDataRegion>(R)) {
70 const BlockDecl *BD = BR->getCodeRegion()->getDecl();
71 SourceLocation L = BD->getLocStart();
72 range = BD->getSourceRange();
73 os << "stack-allocated block declared on line "
74 << SM.getExpansionLineNumber(L);
75 }
76 else if (const VarRegion *VR = dyn_cast<VarRegion>(R)) {
77 os << "stack memory associated with local variable '"
78 << VR->getString() << '\'';
79 range = VR->getDecl()->getSourceRange();
80 }
81 else if (const CXXTempObjectRegion *TOR = dyn_cast<CXXTempObjectRegion>(R)) {
82 QualType Ty = TOR->getValueType().getLocalUnqualifiedType();
83 os << "stack memory associated with temporary object of type '";
84 Ty.print(os, Ctx.getPrintingPolicy());
85 os << "'";
86 range = TOR->getExpr()->getSourceRange();
87 }
88 else {
89 llvm_unreachable("Invalid region in ReturnStackAddressChecker.");
90 }
91
92 return range;
93 }
94
EmitStackError(CheckerContext & C,const MemRegion * R,const Expr * RetE) const95 void StackAddrEscapeChecker::EmitStackError(CheckerContext &C, const MemRegion *R,
96 const Expr *RetE) const {
97 ExplodedNode *N = C.generateErrorNode();
98
99 if (!N)
100 return;
101
102 if (!BT_returnstack)
103 BT_returnstack.reset(
104 new BuiltinBug(this, "Return of address to stack-allocated memory"));
105
106 // Generate a report for this bug.
107 SmallString<512> buf;
108 llvm::raw_svector_ostream os(buf);
109 SourceRange range = genName(os, R, C.getASTContext());
110 os << " returned to caller";
111 auto report = llvm::make_unique<BugReport>(*BT_returnstack, os.str(), N);
112 report->addRange(RetE->getSourceRange());
113 if (range.isValid())
114 report->addRange(range);
115
116 C.emitReport(std::move(report));
117 }
118
checkPreStmt(const ReturnStmt * RS,CheckerContext & C) const119 void StackAddrEscapeChecker::checkPreStmt(const ReturnStmt *RS,
120 CheckerContext &C) const {
121
122 const Expr *RetE = RS->getRetValue();
123 if (!RetE)
124 return;
125 RetE = RetE->IgnoreParens();
126
127 const LocationContext *LCtx = C.getLocationContext();
128 SVal V = C.getState()->getSVal(RetE, LCtx);
129 const MemRegion *R = V.getAsRegion();
130
131 if (!R)
132 return;
133
134 const StackSpaceRegion *SS =
135 dyn_cast_or_null<StackSpaceRegion>(R->getMemorySpace());
136
137 if (!SS)
138 return;
139
140 // Return stack memory in an ancestor stack frame is fine.
141 const StackFrameContext *CurFrame = LCtx->getCurrentStackFrame();
142 const StackFrameContext *MemFrame = SS->getStackFrame();
143 if (MemFrame != CurFrame)
144 return;
145
146 // Automatic reference counting automatically copies blocks.
147 if (C.getASTContext().getLangOpts().ObjCAutoRefCount &&
148 isa<BlockDataRegion>(R))
149 return;
150
151 // Returning a record by value is fine. (In this case, the returned
152 // expression will be a copy-constructor, possibly wrapped in an
153 // ExprWithCleanups node.)
154 if (const ExprWithCleanups *Cleanup = dyn_cast<ExprWithCleanups>(RetE))
155 RetE = Cleanup->getSubExpr();
156 if (isa<CXXConstructExpr>(RetE) && RetE->getType()->isRecordType())
157 return;
158
159 // The CK_CopyAndAutoreleaseBlockObject cast causes the block to be copied
160 // so the stack address is not escaping here.
161 if (auto *ICE = dyn_cast<ImplicitCastExpr>(RetE)) {
162 if (isa<BlockDataRegion>(R) &&
163 ICE->getCastKind() == CK_CopyAndAutoreleaseBlockObject) {
164 return;
165 }
166 }
167
168 EmitStackError(C, R, RetE);
169 }
170
checkEndFunction(CheckerContext & Ctx) const171 void StackAddrEscapeChecker::checkEndFunction(CheckerContext &Ctx) const {
172 ProgramStateRef state = Ctx.getState();
173
174 // Iterate over all bindings to global variables and see if it contains
175 // a memory region in the stack space.
176 class CallBack : public StoreManager::BindingsHandler {
177 private:
178 CheckerContext &Ctx;
179 const StackFrameContext *CurSFC;
180 public:
181 SmallVector<std::pair<const MemRegion*, const MemRegion*>, 10> V;
182
183 CallBack(CheckerContext &CC) :
184 Ctx(CC),
185 CurSFC(CC.getLocationContext()->getCurrentStackFrame())
186 {}
187
188 bool HandleBinding(StoreManager &SMgr, Store store,
189 const MemRegion *region, SVal val) override {
190
191 if (!isa<GlobalsSpaceRegion>(region->getMemorySpace()))
192 return true;
193
194 const MemRegion *vR = val.getAsRegion();
195 if (!vR)
196 return true;
197
198 // Under automated retain release, it is okay to assign a block
199 // directly to a global variable.
200 if (Ctx.getASTContext().getLangOpts().ObjCAutoRefCount &&
201 isa<BlockDataRegion>(vR))
202 return true;
203
204 if (const StackSpaceRegion *SSR =
205 dyn_cast<StackSpaceRegion>(vR->getMemorySpace())) {
206 // If the global variable holds a location in the current stack frame,
207 // record the binding to emit a warning.
208 if (SSR->getStackFrame() == CurSFC)
209 V.push_back(std::make_pair(region, vR));
210 }
211
212 return true;
213 }
214 };
215
216 CallBack cb(Ctx);
217 state->getStateManager().getStoreManager().iterBindings(state->getStore(),cb);
218
219 if (cb.V.empty())
220 return;
221
222 // Generate an error node.
223 ExplodedNode *N = Ctx.generateNonFatalErrorNode(state);
224 if (!N)
225 return;
226
227 if (!BT_stackleak)
228 BT_stackleak.reset(
229 new BuiltinBug(this, "Stack address stored into global variable",
230 "Stack address was saved into a global variable. "
231 "This is dangerous because the address will become "
232 "invalid after returning from the function"));
233
234 for (unsigned i = 0, e = cb.V.size(); i != e; ++i) {
235 // Generate a report for this bug.
236 SmallString<512> buf;
237 llvm::raw_svector_ostream os(buf);
238 SourceRange range = genName(os, cb.V[i].second, Ctx.getASTContext());
239 os << " is still referred to by the global variable '";
240 const VarRegion *VR = cast<VarRegion>(cb.V[i].first->getBaseRegion());
241 os << *VR->getDecl()
242 << "' upon returning to the caller. This will be a dangling reference";
243 auto report = llvm::make_unique<BugReport>(*BT_stackleak, os.str(), N);
244 if (range.isValid())
245 report->addRange(range);
246
247 Ctx.emitReport(std::move(report));
248 }
249 }
250
registerStackAddrEscapeChecker(CheckerManager & mgr)251 void ento::registerStackAddrEscapeChecker(CheckerManager &mgr) {
252 mgr.registerChecker<StackAddrEscapeChecker>();
253 }
254