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/AST/ExprCXX.h"
15#include "clang/Basic/SourceManager.h"
16#include "clang/StaticAnalyzer/Checkers/BuiltinCheckerRegistration.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"
25using namespace clang;
26using namespace ento;
27
28namespace {
29class 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
38public:
39  enum CheckKind {
40    CK_StackAddrEscapeChecker,
41    CK_StackAddrAsyncEscapeChecker,
42    CK_NumCheckKinds
43  };
44
45  bool ChecksEnabled[CK_NumCheckKinds] = {false};
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
52private:
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 isNotInCurrentFrame(const MemRegion *R, CheckerContext &C);
65};
66} // namespace
67
68SourceRange 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
112bool StackAddrEscapeChecker::isNotInCurrentFrame(const MemRegion *R,
113                                                 CheckerContext &C) {
114  const StackSpaceRegion *S = cast<StackSpaceRegion>(R->getMemorySpace());
115  return S->getStackFrame() != C.getStackFrame();
116}
117
118bool StackAddrEscapeChecker::isSemaphoreCaptured(const BlockDecl &B) const {
119  if (!dispatch_semaphore_tII)
120    dispatch_semaphore_tII = &B.getASTContext().Idents.get("dispatch_semaphore_t");
121  for (const auto &C : B.captures()) {
122    const auto *T = C.getVariable()->getType()->getAs<TypedefType>();
123    if (T && T->getDecl()->getIdentifier() == dispatch_semaphore_tII)
124      return true;
125  }
126  return false;
127}
128
129SmallVector<const MemRegion *, 4>
130StackAddrEscapeChecker::getCapturedStackRegions(const BlockDataRegion &B,
131                                                CheckerContext &C) {
132  SmallVector<const MemRegion *, 4> Regions;
133  BlockDataRegion::referenced_vars_iterator I = B.referenced_vars_begin();
134  BlockDataRegion::referenced_vars_iterator E = B.referenced_vars_end();
135  for (; I != E; ++I) {
136    SVal Val = C.getState()->getSVal(I.getCapturedRegion());
137    const MemRegion *Region = Val.getAsRegion();
138    if (Region && isa<StackSpaceRegion>(Region->getMemorySpace()))
139      Regions.push_back(Region);
140  }
141  return Regions;
142}
143
144void StackAddrEscapeChecker::EmitStackError(CheckerContext &C,
145                                            const MemRegion *R,
146                                            const Expr *RetE) const {
147  ExplodedNode *N = C.generateNonFatalErrorNode();
148  if (!N)
149    return;
150  if (!BT_returnstack)
151    BT_returnstack = std::make_unique<BuiltinBug>(
152        CheckNames[CK_StackAddrEscapeChecker],
153        "Return of address to stack-allocated memory");
154  // Generate a report for this bug.
155  SmallString<128> buf;
156  llvm::raw_svector_ostream os(buf);
157  SourceRange range = genName(os, R, C.getASTContext());
158  os << " returned to caller";
159  auto report =
160      std::make_unique<PathSensitiveBugReport>(*BT_returnstack, os.str(), N);
161  report->addRange(RetE->getSourceRange());
162  if (range.isValid())
163    report->addRange(range);
164  C.emitReport(std::move(report));
165}
166
167void StackAddrEscapeChecker::checkAsyncExecutedBlockCaptures(
168    const BlockDataRegion &B, CheckerContext &C) const {
169  // There is a not-too-uncommon idiom
170  // where a block passed to dispatch_async captures a semaphore
171  // and then the thread (which called dispatch_async) is blocked on waiting
172  // for the completion of the execution of the block
173  // via dispatch_semaphore_wait. To avoid false-positives (for now)
174  // we ignore all the blocks which have captured
175  // a variable of the type "dispatch_semaphore_t".
176  if (isSemaphoreCaptured(*B.getDecl()))
177    return;
178  for (const MemRegion *Region : getCapturedStackRegions(B, C)) {
179    // The block passed to dispatch_async may capture another block
180    // created on the stack. However, there is no leak in this situaton,
181    // no matter if ARC or no ARC is enabled:
182    // dispatch_async copies the passed "outer" block (via Block_copy)
183    // and if the block has captured another "inner" block,
184    // the "inner" block will be copied as well.
185    if (isa<BlockDataRegion>(Region))
186      continue;
187    ExplodedNode *N = C.generateNonFatalErrorNode();
188    if (!N)
189      continue;
190    if (!BT_capturedstackasync)
191      BT_capturedstackasync = std::make_unique<BuiltinBug>(
192          CheckNames[CK_StackAddrAsyncEscapeChecker],
193          "Address of stack-allocated memory is captured");
194    SmallString<128> Buf;
195    llvm::raw_svector_ostream Out(Buf);
196    SourceRange Range = genName(Out, Region, C.getASTContext());
197    Out << " is captured by an asynchronously-executed block";
198    auto Report = std::make_unique<PathSensitiveBugReport>(
199        *BT_capturedstackasync, Out.str(), N);
200    if (Range.isValid())
201      Report->addRange(Range);
202    C.emitReport(std::move(Report));
203  }
204}
205
206void StackAddrEscapeChecker::checkReturnedBlockCaptures(
207    const BlockDataRegion &B, CheckerContext &C) const {
208  for (const MemRegion *Region : getCapturedStackRegions(B, C)) {
209    if (isNotInCurrentFrame(Region, C))
210      continue;
211    ExplodedNode *N = C.generateNonFatalErrorNode();
212    if (!N)
213      continue;
214    if (!BT_capturedstackret)
215      BT_capturedstackret = std::make_unique<BuiltinBug>(
216          CheckNames[CK_StackAddrEscapeChecker],
217          "Address of stack-allocated memory is captured");
218    SmallString<128> Buf;
219    llvm::raw_svector_ostream Out(Buf);
220    SourceRange Range = genName(Out, Region, C.getASTContext());
221    Out << " is captured by a returned block";
222    auto Report = std::make_unique<PathSensitiveBugReport>(*BT_capturedstackret,
223                                                           Out.str(), N);
224    if (Range.isValid())
225      Report->addRange(Range);
226    C.emitReport(std::move(Report));
227  }
228}
229
230void StackAddrEscapeChecker::checkPreCall(const CallEvent &Call,
231                                          CheckerContext &C) const {
232  if (!ChecksEnabled[CK_StackAddrAsyncEscapeChecker])
233    return;
234  if (!Call.isGlobalCFunction("dispatch_after") &&
235      !Call.isGlobalCFunction("dispatch_async"))
236    return;
237  for (unsigned Idx = 0, NumArgs = Call.getNumArgs(); Idx < NumArgs; ++Idx) {
238    if (const BlockDataRegion *B = dyn_cast_or_null<BlockDataRegion>(
239            Call.getArgSVal(Idx).getAsRegion()))
240      checkAsyncExecutedBlockCaptures(*B, C);
241  }
242}
243
244void StackAddrEscapeChecker::checkPreStmt(const ReturnStmt *RS,
245                                          CheckerContext &C) const {
246  if (!ChecksEnabled[CK_StackAddrEscapeChecker])
247    return;
248
249  const Expr *RetE = RS->getRetValue();
250  if (!RetE)
251    return;
252  RetE = RetE->IgnoreParens();
253
254  SVal V = C.getSVal(RetE);
255  const MemRegion *R = V.getAsRegion();
256  if (!R)
257    return;
258
259  if (const BlockDataRegion *B = dyn_cast<BlockDataRegion>(R))
260    checkReturnedBlockCaptures(*B, C);
261
262  if (!isa<StackSpaceRegion>(R->getMemorySpace()) || isNotInCurrentFrame(R, C))
263    return;
264
265  // Returning a record by value is fine. (In this case, the returned
266  // expression will be a copy-constructor, possibly wrapped in an
267  // ExprWithCleanups node.)
268  if (const ExprWithCleanups *Cleanup = dyn_cast<ExprWithCleanups>(RetE))
269    RetE = Cleanup->getSubExpr();
270  if (isa<CXXConstructExpr>(RetE) && RetE->getType()->isRecordType())
271    return;
272
273  // The CK_CopyAndAutoreleaseBlockObject cast causes the block to be copied
274  // so the stack address is not escaping here.
275  if (const auto *ICE = dyn_cast<ImplicitCastExpr>(RetE)) {
276    if (isa<BlockDataRegion>(R) &&
277        ICE->getCastKind() == CK_CopyAndAutoreleaseBlockObject) {
278      return;
279    }
280  }
281
282  EmitStackError(C, R, RetE);
283}
284
285void StackAddrEscapeChecker::checkEndFunction(const ReturnStmt *RS,
286                                              CheckerContext &Ctx) const {
287  if (!ChecksEnabled[CK_StackAddrEscapeChecker])
288    return;
289
290  ProgramStateRef State = Ctx.getState();
291
292  // Iterate over all bindings to global variables and see if it contains
293  // a memory region in the stack space.
294  class CallBack : public StoreManager::BindingsHandler {
295  private:
296    CheckerContext &Ctx;
297    const StackFrameContext *PoppedFrame;
298
299    /// Look for stack variables referring to popped stack variables.
300    /// Returns true only if it found some dangling stack variables
301    /// referred by an other stack variable from different stack frame.
302    bool checkForDanglingStackVariable(const MemRegion *Referrer,
303                                       const MemRegion *Referred) {
304      const auto *ReferrerMemSpace =
305          Referrer->getMemorySpace()->getAs<StackSpaceRegion>();
306      const auto *ReferredMemSpace =
307          Referred->getMemorySpace()->getAs<StackSpaceRegion>();
308
309      if (!ReferrerMemSpace || !ReferredMemSpace)
310        return false;
311
312      const auto *ReferrerFrame = ReferrerMemSpace->getStackFrame();
313      const auto *ReferredFrame = ReferredMemSpace->getStackFrame();
314
315      if (ReferrerMemSpace && ReferredMemSpace) {
316        if (ReferredFrame == PoppedFrame &&
317            ReferrerFrame->isParentOf(PoppedFrame)) {
318          V.emplace_back(Referrer, Referred);
319          return true;
320        }
321      }
322      return false;
323    }
324
325  public:
326    SmallVector<std::pair<const MemRegion *, const MemRegion *>, 10> V;
327
328    CallBack(CheckerContext &CC) : Ctx(CC), PoppedFrame(CC.getStackFrame()) {}
329
330    bool HandleBinding(StoreManager &SMgr, Store S, const MemRegion *Region,
331                       SVal Val) override {
332      const MemRegion *VR = Val.getAsRegion();
333      if (!VR)
334        return true;
335
336      if (checkForDanglingStackVariable(Region, VR))
337        return true;
338
339      // Check the globals for the same.
340      if (!isa<GlobalsSpaceRegion>(Region->getMemorySpace()))
341        return true;
342      if (VR && VR->hasStackStorage() && !isNotInCurrentFrame(VR, Ctx))
343        V.emplace_back(Region, VR);
344      return true;
345    }
346  };
347
348  CallBack Cb(Ctx);
349  State->getStateManager().getStoreManager().iterBindings(State->getStore(),
350                                                          Cb);
351
352  if (Cb.V.empty())
353    return;
354
355  // Generate an error node.
356  ExplodedNode *N = Ctx.generateNonFatalErrorNode(State);
357  if (!N)
358    return;
359
360  if (!BT_stackleak)
361    BT_stackleak = std::make_unique<BuiltinBug>(
362        CheckNames[CK_StackAddrEscapeChecker],
363        "Stack address stored into global variable",
364        "Stack address was saved into a global variable. "
365        "This is dangerous because the address will become "
366        "invalid after returning from the function");
367
368  for (const auto &P : Cb.V) {
369    const MemRegion *Referrer = P.first;
370    const MemRegion *Referred = P.second;
371
372    // Generate a report for this bug.
373    const StringRef CommonSuffix =
374        "upon returning to the caller.  This will be a dangling reference";
375    SmallString<128> Buf;
376    llvm::raw_svector_ostream Out(Buf);
377    const SourceRange Range = genName(Out, Referred, Ctx.getASTContext());
378
379    if (isa<CXXTempObjectRegion>(Referrer)) {
380      Out << " is still referred to by a temporary object on the stack "
381          << CommonSuffix;
382      auto Report =
383          std::make_unique<PathSensitiveBugReport>(*BT_stackleak, Out.str(), N);
384      Ctx.emitReport(std::move(Report));
385      return;
386    }
387
388    const StringRef ReferrerMemorySpace = [](const MemSpaceRegion *Space) {
389      if (isa<StaticGlobalSpaceRegion>(Space))
390        return "static";
391      if (isa<GlobalsSpaceRegion>(Space))
392        return "global";
393      assert(isa<StackSpaceRegion>(Space));
394      return "stack";
395    }(Referrer->getMemorySpace());
396
397    // This cast supposed to succeed.
398    const VarRegion *ReferrerVar = cast<VarRegion>(Referrer->getBaseRegion());
399    const std::string ReferrerVarName =
400        ReferrerVar->getDecl()->getDeclName().getAsString();
401
402    Out << " is still referred to by the " << ReferrerMemorySpace
403        << " variable '" << ReferrerVarName << "' " << CommonSuffix;
404    auto Report =
405        std::make_unique<PathSensitiveBugReport>(*BT_stackleak, Out.str(), N);
406    if (Range.isValid())
407      Report->addRange(Range);
408
409    Ctx.emitReport(std::move(Report));
410  }
411}
412
413void ento::registerStackAddrEscapeBase(CheckerManager &mgr) {
414  mgr.registerChecker<StackAddrEscapeChecker>();
415}
416
417bool ento::shouldRegisterStackAddrEscapeBase(const CheckerManager &mgr) {
418  return true;
419}
420
421#define REGISTER_CHECKER(name)                                                 \
422  void ento::register##name(CheckerManager &Mgr) {                             \
423    StackAddrEscapeChecker *Chk = Mgr.getChecker<StackAddrEscapeChecker>();    \
424    Chk->ChecksEnabled[StackAddrEscapeChecker::CK_##name] = true;              \
425    Chk->CheckNames[StackAddrEscapeChecker::CK_##name] =                       \
426        Mgr.getCurrentCheckerName();                                           \
427  }                                                                            \
428                                                                               \
429  bool ento::shouldRegister##name(const CheckerManager &mgr) { return true; }
430
431REGISTER_CHECKER(StackAddrEscapeChecker)
432REGISTER_CHECKER(StackAddrAsyncEscapeChecker)
433