1 //=== StackAddrEscapeChecker.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 stack address leak checker, which checks if an invalid
10 // stack address is stored into a global or heap location. See CERT DCL30-C.
11 //
12 //===----------------------------------------------------------------------===//
13
14 #include "clang/StaticAnalyzer/Checkers/BuiltinCheckerRegistration.h"
15 #include "clang/AST/ExprCXX.h"
16 #include "clang/Basic/SourceManager.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/CallEvent.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
30 : public Checker<check::PreCall, check::PreStmt<ReturnStmt>,
31 check::EndFunction> {
32 mutable IdentifierInfo *dispatch_semaphore_tII;
33 mutable std::unique_ptr<BuiltinBug> BT_stackleak;
34 mutable std::unique_ptr<BuiltinBug> BT_returnstack;
35 mutable std::unique_ptr<BuiltinBug> BT_capturedstackasync;
36 mutable std::unique_ptr<BuiltinBug> BT_capturedstackret;
37
38 public:
39 enum CheckKind {
40 CK_StackAddrEscapeChecker,
41 CK_StackAddrAsyncEscapeChecker,
42 CK_NumCheckKinds
43 };
44
45 DefaultBool ChecksEnabled[CK_NumCheckKinds];
46 CheckerNameRef CheckNames[CK_NumCheckKinds];
47
48 void checkPreCall(const CallEvent &Call, CheckerContext &C) const;
49 void checkPreStmt(const ReturnStmt *RS, CheckerContext &C) const;
50 void checkEndFunction(const ReturnStmt *RS, CheckerContext &Ctx) const;
51
52 private:
53 void checkReturnedBlockCaptures(const BlockDataRegion &B,
54 CheckerContext &C) const;
55 void checkAsyncExecutedBlockCaptures(const BlockDataRegion &B,
56 CheckerContext &C) const;
57 void EmitStackError(CheckerContext &C, const MemRegion *R,
58 const Expr *RetE) const;
59 bool isSemaphoreCaptured(const BlockDecl &B) const;
60 static SourceRange genName(raw_ostream &os, const MemRegion *R,
61 ASTContext &Ctx);
62 static SmallVector<const MemRegion *, 4>
63 getCapturedStackRegions(const BlockDataRegion &B, CheckerContext &C);
64 static bool isArcManagedBlock(const MemRegion *R, CheckerContext &C);
65 static bool isNotInCurrentFrame(const MemRegion *R, CheckerContext &C);
66 };
67 } // namespace
68
genName(raw_ostream & os,const MemRegion * R,ASTContext & Ctx)69 SourceRange StackAddrEscapeChecker::genName(raw_ostream &os, const MemRegion *R,
70 ASTContext &Ctx) {
71 // Get the base region, stripping away fields and elements.
72 R = R->getBaseRegion();
73 SourceManager &SM = Ctx.getSourceManager();
74 SourceRange range;
75 os << "Address of ";
76
77 // Check if the region is a compound literal.
78 if (const auto *CR = dyn_cast<CompoundLiteralRegion>(R)) {
79 const CompoundLiteralExpr *CL = CR->getLiteralExpr();
80 os << "stack memory associated with a compound literal "
81 "declared on line "
82 << SM.getExpansionLineNumber(CL->getBeginLoc()) << " returned to caller";
83 range = CL->getSourceRange();
84 } else if (const auto *AR = dyn_cast<AllocaRegion>(R)) {
85 const Expr *ARE = AR->getExpr();
86 SourceLocation L = ARE->getBeginLoc();
87 range = ARE->getSourceRange();
88 os << "stack memory allocated by call to alloca() on line "
89 << SM.getExpansionLineNumber(L);
90 } else if (const auto *BR = dyn_cast<BlockDataRegion>(R)) {
91 const BlockDecl *BD = BR->getCodeRegion()->getDecl();
92 SourceLocation L = BD->getBeginLoc();
93 range = BD->getSourceRange();
94 os << "stack-allocated block declared on line "
95 << SM.getExpansionLineNumber(L);
96 } else if (const auto *VR = dyn_cast<VarRegion>(R)) {
97 os << "stack memory associated with local variable '" << VR->getString()
98 << '\'';
99 range = VR->getDecl()->getSourceRange();
100 } else if (const auto *TOR = dyn_cast<CXXTempObjectRegion>(R)) {
101 QualType Ty = TOR->getValueType().getLocalUnqualifiedType();
102 os << "stack memory associated with temporary object of type '";
103 Ty.print(os, Ctx.getPrintingPolicy());
104 os << "'";
105 range = TOR->getExpr()->getSourceRange();
106 } else {
107 llvm_unreachable("Invalid region in ReturnStackAddressChecker.");
108 }
109
110 return range;
111 }
112
isArcManagedBlock(const MemRegion * R,CheckerContext & C)113 bool StackAddrEscapeChecker::isArcManagedBlock(const MemRegion *R,
114 CheckerContext &C) {
115 assert(R && "MemRegion should not be null");
116 return C.getASTContext().getLangOpts().ObjCAutoRefCount &&
117 isa<BlockDataRegion>(R);
118 }
119
isNotInCurrentFrame(const MemRegion * R,CheckerContext & C)120 bool StackAddrEscapeChecker::isNotInCurrentFrame(const MemRegion *R,
121 CheckerContext &C) {
122 const StackSpaceRegion *S = cast<StackSpaceRegion>(R->getMemorySpace());
123 return S->getStackFrame() != C.getStackFrame();
124 }
125
isSemaphoreCaptured(const BlockDecl & B) const126 bool StackAddrEscapeChecker::isSemaphoreCaptured(const BlockDecl &B) const {
127 if (!dispatch_semaphore_tII)
128 dispatch_semaphore_tII = &B.getASTContext().Idents.get("dispatch_semaphore_t");
129 for (const auto &C : B.captures()) {
130 const auto *T = C.getVariable()->getType()->getAs<TypedefType>();
131 if (T && T->getDecl()->getIdentifier() == dispatch_semaphore_tII)
132 return true;
133 }
134 return false;
135 }
136
137 SmallVector<const MemRegion *, 4>
getCapturedStackRegions(const BlockDataRegion & B,CheckerContext & C)138 StackAddrEscapeChecker::getCapturedStackRegions(const BlockDataRegion &B,
139 CheckerContext &C) {
140 SmallVector<const MemRegion *, 4> Regions;
141 BlockDataRegion::referenced_vars_iterator I = B.referenced_vars_begin();
142 BlockDataRegion::referenced_vars_iterator E = B.referenced_vars_end();
143 for (; I != E; ++I) {
144 SVal Val = C.getState()->getSVal(I.getCapturedRegion());
145 const MemRegion *Region = Val.getAsRegion();
146 if (Region && isa<StackSpaceRegion>(Region->getMemorySpace()))
147 Regions.push_back(Region);
148 }
149 return Regions;
150 }
151
EmitStackError(CheckerContext & C,const MemRegion * R,const Expr * RetE) const152 void StackAddrEscapeChecker::EmitStackError(CheckerContext &C,
153 const MemRegion *R,
154 const Expr *RetE) const {
155 ExplodedNode *N = C.generateNonFatalErrorNode();
156 if (!N)
157 return;
158 if (!BT_returnstack)
159 BT_returnstack = std::make_unique<BuiltinBug>(
160 CheckNames[CK_StackAddrEscapeChecker],
161 "Return of address to stack-allocated memory");
162 // Generate a report for this bug.
163 SmallString<128> buf;
164 llvm::raw_svector_ostream os(buf);
165 SourceRange range = genName(os, R, C.getASTContext());
166 os << " returned to caller";
167 auto report =
168 std::make_unique<PathSensitiveBugReport>(*BT_returnstack, os.str(), N);
169 report->addRange(RetE->getSourceRange());
170 if (range.isValid())
171 report->addRange(range);
172 C.emitReport(std::move(report));
173 }
174
checkAsyncExecutedBlockCaptures(const BlockDataRegion & B,CheckerContext & C) const175 void StackAddrEscapeChecker::checkAsyncExecutedBlockCaptures(
176 const BlockDataRegion &B, CheckerContext &C) const {
177 // There is a not-too-uncommon idiom
178 // where a block passed to dispatch_async captures a semaphore
179 // and then the thread (which called dispatch_async) is blocked on waiting
180 // for the completion of the execution of the block
181 // via dispatch_semaphore_wait. To avoid false-positives (for now)
182 // we ignore all the blocks which have captured
183 // a variable of the type "dispatch_semaphore_t".
184 if (isSemaphoreCaptured(*B.getDecl()))
185 return;
186 for (const MemRegion *Region : getCapturedStackRegions(B, C)) {
187 // The block passed to dispatch_async may capture another block
188 // created on the stack. However, there is no leak in this situaton,
189 // no matter if ARC or no ARC is enabled:
190 // dispatch_async copies the passed "outer" block (via Block_copy)
191 // and if the block has captured another "inner" block,
192 // the "inner" block will be copied as well.
193 if (isa<BlockDataRegion>(Region))
194 continue;
195 ExplodedNode *N = C.generateNonFatalErrorNode();
196 if (!N)
197 continue;
198 if (!BT_capturedstackasync)
199 BT_capturedstackasync = std::make_unique<BuiltinBug>(
200 CheckNames[CK_StackAddrAsyncEscapeChecker],
201 "Address of stack-allocated memory is captured");
202 SmallString<128> Buf;
203 llvm::raw_svector_ostream Out(Buf);
204 SourceRange Range = genName(Out, Region, C.getASTContext());
205 Out << " is captured by an asynchronously-executed block";
206 auto Report = std::make_unique<PathSensitiveBugReport>(
207 *BT_capturedstackasync, Out.str(), N);
208 if (Range.isValid())
209 Report->addRange(Range);
210 C.emitReport(std::move(Report));
211 }
212 }
213
checkReturnedBlockCaptures(const BlockDataRegion & B,CheckerContext & C) const214 void StackAddrEscapeChecker::checkReturnedBlockCaptures(
215 const BlockDataRegion &B, CheckerContext &C) const {
216 for (const MemRegion *Region : getCapturedStackRegions(B, C)) {
217 if (isArcManagedBlock(Region, C) || isNotInCurrentFrame(Region, C))
218 continue;
219 ExplodedNode *N = C.generateNonFatalErrorNode();
220 if (!N)
221 continue;
222 if (!BT_capturedstackret)
223 BT_capturedstackret = std::make_unique<BuiltinBug>(
224 CheckNames[CK_StackAddrEscapeChecker],
225 "Address of stack-allocated memory is captured");
226 SmallString<128> Buf;
227 llvm::raw_svector_ostream Out(Buf);
228 SourceRange Range = genName(Out, Region, C.getASTContext());
229 Out << " is captured by a returned block";
230 auto Report = std::make_unique<PathSensitiveBugReport>(*BT_capturedstackret,
231 Out.str(), N);
232 if (Range.isValid())
233 Report->addRange(Range);
234 C.emitReport(std::move(Report));
235 }
236 }
237
checkPreCall(const CallEvent & Call,CheckerContext & C) const238 void StackAddrEscapeChecker::checkPreCall(const CallEvent &Call,
239 CheckerContext &C) const {
240 if (!ChecksEnabled[CK_StackAddrAsyncEscapeChecker])
241 return;
242 if (!Call.isGlobalCFunction("dispatch_after") &&
243 !Call.isGlobalCFunction("dispatch_async"))
244 return;
245 for (unsigned Idx = 0, NumArgs = Call.getNumArgs(); Idx < NumArgs; ++Idx) {
246 if (const BlockDataRegion *B = dyn_cast_or_null<BlockDataRegion>(
247 Call.getArgSVal(Idx).getAsRegion()))
248 checkAsyncExecutedBlockCaptures(*B, C);
249 }
250 }
251
checkPreStmt(const ReturnStmt * RS,CheckerContext & C) const252 void StackAddrEscapeChecker::checkPreStmt(const ReturnStmt *RS,
253 CheckerContext &C) const {
254 if (!ChecksEnabled[CK_StackAddrEscapeChecker])
255 return;
256
257 const Expr *RetE = RS->getRetValue();
258 if (!RetE)
259 return;
260 RetE = RetE->IgnoreParens();
261
262 SVal V = C.getSVal(RetE);
263 const MemRegion *R = V.getAsRegion();
264 if (!R)
265 return;
266
267 if (const BlockDataRegion *B = dyn_cast<BlockDataRegion>(R))
268 checkReturnedBlockCaptures(*B, C);
269
270 if (!isa<StackSpaceRegion>(R->getMemorySpace()) ||
271 isNotInCurrentFrame(R, C) || isArcManagedBlock(R, C))
272 return;
273
274 // Returning a record by value is fine. (In this case, the returned
275 // expression will be a copy-constructor, possibly wrapped in an
276 // ExprWithCleanups node.)
277 if (const ExprWithCleanups *Cleanup = dyn_cast<ExprWithCleanups>(RetE))
278 RetE = Cleanup->getSubExpr();
279 if (isa<CXXConstructExpr>(RetE) && RetE->getType()->isRecordType())
280 return;
281
282 // The CK_CopyAndAutoreleaseBlockObject cast causes the block to be copied
283 // so the stack address is not escaping here.
284 if (const auto *ICE = dyn_cast<ImplicitCastExpr>(RetE)) {
285 if (isa<BlockDataRegion>(R) &&
286 ICE->getCastKind() == CK_CopyAndAutoreleaseBlockObject) {
287 return;
288 }
289 }
290
291 EmitStackError(C, R, RetE);
292 }
293
checkEndFunction(const ReturnStmt * RS,CheckerContext & Ctx) const294 void StackAddrEscapeChecker::checkEndFunction(const ReturnStmt *RS,
295 CheckerContext &Ctx) const {
296 if (!ChecksEnabled[CK_StackAddrEscapeChecker])
297 return;
298
299 ProgramStateRef State = Ctx.getState();
300
301 // Iterate over all bindings to global variables and see if it contains
302 // a memory region in the stack space.
303 class CallBack : public StoreManager::BindingsHandler {
304 private:
305 CheckerContext &Ctx;
306 const StackFrameContext *CurSFC;
307
308 public:
309 SmallVector<std::pair<const MemRegion *, const MemRegion *>, 10> V;
310
311 CallBack(CheckerContext &CC) : Ctx(CC), CurSFC(CC.getStackFrame()) {}
312
313 bool HandleBinding(StoreManager &SMgr, Store S, const MemRegion *Region,
314 SVal Val) override {
315
316 if (!isa<GlobalsSpaceRegion>(Region->getMemorySpace()))
317 return true;
318 const MemRegion *VR = Val.getAsRegion();
319 if (VR && isa<StackSpaceRegion>(VR->getMemorySpace()) &&
320 !isArcManagedBlock(VR, Ctx) && !isNotInCurrentFrame(VR, Ctx))
321 V.emplace_back(Region, VR);
322 return true;
323 }
324 };
325
326 CallBack Cb(Ctx);
327 State->getStateManager().getStoreManager().iterBindings(State->getStore(),
328 Cb);
329
330 if (Cb.V.empty())
331 return;
332
333 // Generate an error node.
334 ExplodedNode *N = Ctx.generateNonFatalErrorNode(State);
335 if (!N)
336 return;
337
338 if (!BT_stackleak)
339 BT_stackleak = std::make_unique<BuiltinBug>(
340 CheckNames[CK_StackAddrEscapeChecker],
341 "Stack address stored into global variable",
342 "Stack address was saved into a global variable. "
343 "This is dangerous because the address will become "
344 "invalid after returning from the function");
345
346 for (const auto &P : Cb.V) {
347 // Generate a report for this bug.
348 SmallString<128> Buf;
349 llvm::raw_svector_ostream Out(Buf);
350 SourceRange Range = genName(Out, P.second, Ctx.getASTContext());
351 Out << " is still referred to by the ";
352 if (isa<StaticGlobalSpaceRegion>(P.first->getMemorySpace()))
353 Out << "static";
354 else
355 Out << "global";
356 Out << " variable '";
357 const VarRegion *VR = cast<VarRegion>(P.first->getBaseRegion());
358 Out << *VR->getDecl()
359 << "' upon returning to the caller. This will be a dangling reference";
360 auto Report =
361 std::make_unique<PathSensitiveBugReport>(*BT_stackleak, Out.str(), N);
362 if (Range.isValid())
363 Report->addRange(Range);
364
365 Ctx.emitReport(std::move(Report));
366 }
367 }
368
registerStackAddrEscapeBase(CheckerManager & mgr)369 void ento::registerStackAddrEscapeBase(CheckerManager &mgr) {
370 mgr.registerChecker<StackAddrEscapeChecker>();
371 }
372
shouldRegisterStackAddrEscapeBase(const CheckerManager & mgr)373 bool ento::shouldRegisterStackAddrEscapeBase(const CheckerManager &mgr) {
374 return true;
375 }
376
377 #define REGISTER_CHECKER(name) \
378 void ento::register##name(CheckerManager &Mgr) { \
379 StackAddrEscapeChecker *Chk = Mgr.getChecker<StackAddrEscapeChecker>(); \
380 Chk->ChecksEnabled[StackAddrEscapeChecker::CK_##name] = true; \
381 Chk->CheckNames[StackAddrEscapeChecker::CK_##name] = \
382 Mgr.getCurrentCheckerName(); \
383 } \
384 \
385 bool ento::shouldRegister##name(const CheckerManager &mgr) { return true; }
386
387 REGISTER_CHECKER(StackAddrEscapeChecker)
388 REGISTER_CHECKER(StackAddrAsyncEscapeChecker)
389