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 "clang/StaticAnalyzer/Checkers/BuiltinCheckerRegistration.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/CallEvent.h"
22 #include "clang/StaticAnalyzer/Core/PathSensitive/CheckerContext.h"
23 #include "clang/StaticAnalyzer/Core/PathSensitive/ProgramState.h"
24 #include "llvm/ADT/SmallString.h"
25 #include "llvm/Support/raw_ostream.h"
26 using namespace clang;
27 using namespace ento;
28 
29 namespace {
30 class StackAddrEscapeChecker
31     : public Checker<check::PreCall, check::PreStmt<ReturnStmt>,
32                      check::EndFunction> {
33   mutable IdentifierInfo *dispatch_semaphore_tII;
34   mutable std::unique_ptr<BuiltinBug> BT_stackleak;
35   mutable std::unique_ptr<BuiltinBug> BT_returnstack;
36   mutable std::unique_ptr<BuiltinBug> BT_capturedstackasync;
37   mutable std::unique_ptr<BuiltinBug> BT_capturedstackret;
38 
39 public:
40   enum CheckKind {
41     CK_StackAddrEscapeChecker,
42     CK_StackAddrAsyncEscapeChecker,
43     CK_NumCheckKinds
44   };
45 
46   DefaultBool ChecksEnabled[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 = llvm::make_unique<BuiltinBug>(
160         this, "Return of address to stack-allocated memory");
161   // Generate a report for this bug.
162   SmallString<128> buf;
163   llvm::raw_svector_ostream os(buf);
164   SourceRange range = genName(os, R, C.getASTContext());
165   os << " returned to caller";
166   auto report = llvm::make_unique<BugReport>(*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 = llvm::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 =
204         llvm::make_unique<BugReport>(*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 = llvm::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 =
227         llvm::make_unique<BugReport>(*BT_capturedstackret, 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 = llvm::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 = llvm::make_unique<BugReport>(*BT_stackleak, Out.str(), N);
356     if (Range.isValid())
357       Report->addRange(Range);
358 
359     Ctx.emitReport(std::move(Report));
360   }
361 }
362 
363 #define REGISTER_CHECKER(name) \
364   void ento::register##name(CheckerManager &Mgr) { \
365     StackAddrEscapeChecker *Chk = \
366         Mgr.registerChecker<StackAddrEscapeChecker>(); \
367     Chk->ChecksEnabled[StackAddrEscapeChecker::CK_##name] = true; \
368   }
369 
370 REGISTER_CHECKER(StackAddrEscapeChecker)
371 REGISTER_CHECKER(StackAddrAsyncEscapeChecker)
372