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
genName(raw_ostream & os,const MemRegion * R,ASTContext & Ctx)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
isArcManagedBlock(const MemRegion * R,CheckerContext & C)112 bool StackAddrEscapeChecker::isArcManagedBlock(const MemRegion *R,
113 CheckerContext &C) {
114 assert(R && "MemRegion should not be null");
115 return C.getASTContext().getLangOpts().ObjCAutoRefCount &&
116 isa<BlockDataRegion>(R);
117 }
118
isNotInCurrentFrame(const MemRegion * R,CheckerContext & C)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
isSemaphoreCaptured(const BlockDecl & B) const125 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>
getCapturedStackRegions(const BlockDataRegion & B,CheckerContext & C)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
EmitStackError(CheckerContext & C,const MemRegion * R,const Expr * RetE) const151 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 = std::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 =
166 std::make_unique<PathSensitiveBugReport>(*BT_returnstack, os.str(), N);
167 report->addRange(RetE->getSourceRange());
168 if (range.isValid())
169 report->addRange(range);
170 C.emitReport(std::move(report));
171 }
172
checkAsyncExecutedBlockCaptures(const BlockDataRegion & B,CheckerContext & C) const173 void StackAddrEscapeChecker::checkAsyncExecutedBlockCaptures(
174 const BlockDataRegion &B, CheckerContext &C) const {
175 // There is a not-too-uncommon idiom
176 // where a block passed to dispatch_async captures a semaphore
177 // and then the thread (which called dispatch_async) is blocked on waiting
178 // for the completion of the execution of the block
179 // via dispatch_semaphore_wait. To avoid false-positives (for now)
180 // we ignore all the blocks which have captured
181 // a variable of the type "dispatch_semaphore_t".
182 if (isSemaphoreCaptured(*B.getDecl()))
183 return;
184 for (const MemRegion *Region : getCapturedStackRegions(B, C)) {
185 // The block passed to dispatch_async may capture another block
186 // created on the stack. However, there is no leak in this situaton,
187 // no matter if ARC or no ARC is enabled:
188 // dispatch_async copies the passed "outer" block (via Block_copy)
189 // and if the block has captured another "inner" block,
190 // the "inner" block will be copied as well.
191 if (isa<BlockDataRegion>(Region))
192 continue;
193 ExplodedNode *N = C.generateNonFatalErrorNode();
194 if (!N)
195 continue;
196 if (!BT_capturedstackasync)
197 BT_capturedstackasync = std::make_unique<BuiltinBug>(
198 this, "Address of stack-allocated memory is captured");
199 SmallString<128> Buf;
200 llvm::raw_svector_ostream Out(Buf);
201 SourceRange Range = genName(Out, Region, C.getASTContext());
202 Out << " is captured by an asynchronously-executed block";
203 auto Report = std::make_unique<PathSensitiveBugReport>(
204 *BT_capturedstackasync, Out.str(), N);
205 if (Range.isValid())
206 Report->addRange(Range);
207 C.emitReport(std::move(Report));
208 }
209 }
210
checkReturnedBlockCaptures(const BlockDataRegion & B,CheckerContext & C) const211 void StackAddrEscapeChecker::checkReturnedBlockCaptures(
212 const BlockDataRegion &B, CheckerContext &C) const {
213 for (const MemRegion *Region : getCapturedStackRegions(B, C)) {
214 if (isArcManagedBlock(Region, C) || isNotInCurrentFrame(Region, C))
215 continue;
216 ExplodedNode *N = C.generateNonFatalErrorNode();
217 if (!N)
218 continue;
219 if (!BT_capturedstackret)
220 BT_capturedstackret = std::make_unique<BuiltinBug>(
221 this, "Address of stack-allocated memory is captured");
222 SmallString<128> Buf;
223 llvm::raw_svector_ostream Out(Buf);
224 SourceRange Range = genName(Out, Region, C.getASTContext());
225 Out << " is captured by a returned block";
226 auto Report = std::make_unique<PathSensitiveBugReport>(*BT_capturedstackret,
227 Out.str(), N);
228 if (Range.isValid())
229 Report->addRange(Range);
230 C.emitReport(std::move(Report));
231 }
232 }
233
checkPreCall(const CallEvent & Call,CheckerContext & C) const234 void StackAddrEscapeChecker::checkPreCall(const CallEvent &Call,
235 CheckerContext &C) const {
236 if (!ChecksEnabled[CK_StackAddrAsyncEscapeChecker])
237 return;
238 if (!Call.isGlobalCFunction("dispatch_after") &&
239 !Call.isGlobalCFunction("dispatch_async"))
240 return;
241 for (unsigned Idx = 0, NumArgs = Call.getNumArgs(); Idx < NumArgs; ++Idx) {
242 if (const BlockDataRegion *B = dyn_cast_or_null<BlockDataRegion>(
243 Call.getArgSVal(Idx).getAsRegion()))
244 checkAsyncExecutedBlockCaptures(*B, C);
245 }
246 }
247
checkPreStmt(const ReturnStmt * RS,CheckerContext & C) const248 void StackAddrEscapeChecker::checkPreStmt(const ReturnStmt *RS,
249 CheckerContext &C) const {
250 if (!ChecksEnabled[CK_StackAddrEscapeChecker])
251 return;
252
253 const Expr *RetE = RS->getRetValue();
254 if (!RetE)
255 return;
256 RetE = RetE->IgnoreParens();
257
258 SVal V = C.getSVal(RetE);
259 const MemRegion *R = V.getAsRegion();
260 if (!R)
261 return;
262
263 if (const BlockDataRegion *B = dyn_cast<BlockDataRegion>(R))
264 checkReturnedBlockCaptures(*B, C);
265
266 if (!isa<StackSpaceRegion>(R->getMemorySpace()) ||
267 isNotInCurrentFrame(R, C) || isArcManagedBlock(R, C))
268 return;
269
270 // Returning a record by value is fine. (In this case, the returned
271 // expression will be a copy-constructor, possibly wrapped in an
272 // ExprWithCleanups node.)
273 if (const ExprWithCleanups *Cleanup = dyn_cast<ExprWithCleanups>(RetE))
274 RetE = Cleanup->getSubExpr();
275 if (isa<CXXConstructExpr>(RetE) && RetE->getType()->isRecordType())
276 return;
277
278 // The CK_CopyAndAutoreleaseBlockObject cast causes the block to be copied
279 // so the stack address is not escaping here.
280 if (auto *ICE = dyn_cast<ImplicitCastExpr>(RetE)) {
281 if (isa<BlockDataRegion>(R) &&
282 ICE->getCastKind() == CK_CopyAndAutoreleaseBlockObject) {
283 return;
284 }
285 }
286
287 EmitStackError(C, R, RetE);
288 }
289
checkEndFunction(const ReturnStmt * RS,CheckerContext & Ctx) const290 void StackAddrEscapeChecker::checkEndFunction(const ReturnStmt *RS,
291 CheckerContext &Ctx) const {
292 if (!ChecksEnabled[CK_StackAddrEscapeChecker])
293 return;
294
295 ProgramStateRef State = Ctx.getState();
296
297 // Iterate over all bindings to global variables and see if it contains
298 // a memory region in the stack space.
299 class CallBack : public StoreManager::BindingsHandler {
300 private:
301 CheckerContext &Ctx;
302 const StackFrameContext *CurSFC;
303
304 public:
305 SmallVector<std::pair<const MemRegion *, const MemRegion *>, 10> V;
306
307 CallBack(CheckerContext &CC) : Ctx(CC), CurSFC(CC.getStackFrame()) {}
308
309 bool HandleBinding(StoreManager &SMgr, Store S, const MemRegion *Region,
310 SVal Val) override {
311
312 if (!isa<GlobalsSpaceRegion>(Region->getMemorySpace()))
313 return true;
314 const MemRegion *VR = Val.getAsRegion();
315 if (VR && isa<StackSpaceRegion>(VR->getMemorySpace()) &&
316 !isArcManagedBlock(VR, Ctx) && !isNotInCurrentFrame(VR, Ctx))
317 V.emplace_back(Region, VR);
318 return true;
319 }
320 };
321
322 CallBack Cb(Ctx);
323 State->getStateManager().getStoreManager().iterBindings(State->getStore(),
324 Cb);
325
326 if (Cb.V.empty())
327 return;
328
329 // Generate an error node.
330 ExplodedNode *N = Ctx.generateNonFatalErrorNode(State);
331 if (!N)
332 return;
333
334 if (!BT_stackleak)
335 BT_stackleak = std::make_unique<BuiltinBug>(
336 this, "Stack address stored into global variable",
337 "Stack address was saved into a global variable. "
338 "This is dangerous because the address will become "
339 "invalid after returning from the function");
340
341 for (const auto &P : Cb.V) {
342 // Generate a report for this bug.
343 SmallString<128> Buf;
344 llvm::raw_svector_ostream Out(Buf);
345 SourceRange Range = genName(Out, P.second, Ctx.getASTContext());
346 Out << " is still referred to by the ";
347 if (isa<StaticGlobalSpaceRegion>(P.first->getMemorySpace()))
348 Out << "static";
349 else
350 Out << "global";
351 Out << " variable '";
352 const VarRegion *VR = cast<VarRegion>(P.first->getBaseRegion());
353 Out << *VR->getDecl()
354 << "' upon returning to the caller. This will be a dangling reference";
355 auto Report =
356 std::make_unique<PathSensitiveBugReport>(*BT_stackleak, Out.str(), N);
357 if (Range.isValid())
358 Report->addRange(Range);
359
360 Ctx.emitReport(std::move(Report));
361 }
362 }
363
registerStackAddrEscapeBase(CheckerManager & mgr)364 void ento::registerStackAddrEscapeBase(CheckerManager &mgr) {
365 mgr.registerChecker<StackAddrEscapeChecker>();
366 }
367
shouldRegisterStackAddrEscapeBase(const LangOptions & LO)368 bool ento::shouldRegisterStackAddrEscapeBase(const LangOptions &LO) {
369 return true;
370 }
371
372 #define REGISTER_CHECKER(name) \
373 void ento::register##name(CheckerManager &Mgr) { \
374 StackAddrEscapeChecker *Chk = \
375 Mgr.getChecker<StackAddrEscapeChecker>(); \
376 Chk->ChecksEnabled[StackAddrEscapeChecker::CK_##name] = true; \
377 } \
378 \
379 bool ento::shouldRegister##name(const LangOptions &LO) { \
380 return true; \
381 }
382
383 REGISTER_CHECKER(StackAddrEscapeChecker)
384 REGISTER_CHECKER(StackAddrAsyncEscapeChecker)
385