StackAddrEscapeChecker.cpp source code [clang_source_code/lib/StaticAnalyzer/Checkers/StackAddrEscapeChecker.cpp]

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

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