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 = nullptr;
33  mutable std::unique_ptr<BugType> BT_stackleak;
34  mutable std::unique_ptr<BugType> BT_returnstack;
35  mutable std::unique_ptr<BugType> BT_capturedstackasync;
36  mutable std::unique_ptr<BugType> 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 *LER = dyn_cast<CXXLifetimeExtendedObjectRegion>(R)) {
100    QualType Ty = LER->getValueType().getLocalUnqualifiedType();
101    os << "stack memory associated with temporary object of type '";
102    Ty.print(os, Ctx.getPrintingPolicy());
103    os << "' lifetime extended by local variable";
104    if (const IdentifierInfo *ID = LER->getExtendingDecl()->getIdentifier())
105      os << " '" << ID->getName() << '\'';
106    range = LER->getExpr()->getSourceRange();
107  } else if (const auto *TOR = dyn_cast<CXXTempObjectRegion>(R)) {
108    QualType Ty = TOR->getValueType().getLocalUnqualifiedType();
109    os << "stack memory associated with temporary object of type '";
110    Ty.print(os, Ctx.getPrintingPolicy());
111    os << "'";
112    range = TOR->getExpr()->getSourceRange();
113  } else {
114    llvm_unreachable("Invalid region in ReturnStackAddressChecker.");
115  }
116
117  return range;
118}
119
120bool StackAddrEscapeChecker::isNotInCurrentFrame(const MemRegion *R,
121                                                 CheckerContext &C) {
122  const StackSpaceRegion *S = cast<StackSpaceRegion>(R->getMemorySpace());
123  return S->getStackFrame() != C.getStackFrame();
124}
125
126bool 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
137SmallVector<const MemRegion *, 4>
138StackAddrEscapeChecker::getCapturedStackRegions(const BlockDataRegion &B,
139                                                CheckerContext &C) {
140  SmallVector<const MemRegion *, 4> Regions;
141  for (auto Var : B.referenced_vars()) {
142    SVal Val = C.getState()->getSVal(Var.getCapturedRegion());
143    const MemRegion *Region = Val.getAsRegion();
144    if (Region && isa<StackSpaceRegion>(Region->getMemorySpace()))
145      Regions.push_back(Region);
146  }
147  return Regions;
148}
149
150void StackAddrEscapeChecker::EmitStackError(CheckerContext &C,
151                                            const MemRegion *R,
152                                            const Expr *RetE) const {
153  ExplodedNode *N = C.generateNonFatalErrorNode();
154  if (!N)
155    return;
156  if (!BT_returnstack)
157    BT_returnstack = std::make_unique<BugType>(
158        CheckNames[CK_StackAddrEscapeChecker],
159        "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
173void 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<BugType>(
198          CheckNames[CK_StackAddrAsyncEscapeChecker],
199          "Address of stack-allocated memory is captured");
200    SmallString<128> Buf;
201    llvm::raw_svector_ostream Out(Buf);
202    SourceRange Range = genName(Out, Region, C.getASTContext());
203    Out << " is captured by an asynchronously-executed block";
204    auto Report = std::make_unique<PathSensitiveBugReport>(
205        *BT_capturedstackasync, Out.str(), N);
206    if (Range.isValid())
207      Report->addRange(Range);
208    C.emitReport(std::move(Report));
209  }
210}
211
212void StackAddrEscapeChecker::checkReturnedBlockCaptures(
213    const BlockDataRegion &B, CheckerContext &C) const {
214  for (const MemRegion *Region : getCapturedStackRegions(B, C)) {
215    if (isNotInCurrentFrame(Region, C))
216      continue;
217    ExplodedNode *N = C.generateNonFatalErrorNode();
218    if (!N)
219      continue;
220    if (!BT_capturedstackret)
221      BT_capturedstackret = std::make_unique<BugType>(
222          CheckNames[CK_StackAddrEscapeChecker],
223          "Address of stack-allocated memory is captured");
224    SmallString<128> Buf;
225    llvm::raw_svector_ostream Out(Buf);
226    SourceRange Range = genName(Out, Region, C.getASTContext());
227    Out << " is captured by a returned block";
228    auto Report = std::make_unique<PathSensitiveBugReport>(*BT_capturedstackret,
229                                                           Out.str(), N);
230    if (Range.isValid())
231      Report->addRange(Range);
232    C.emitReport(std::move(Report));
233  }
234}
235
236void StackAddrEscapeChecker::checkPreCall(const CallEvent &Call,
237                                          CheckerContext &C) const {
238  if (!ChecksEnabled[CK_StackAddrAsyncEscapeChecker])
239    return;
240  if (!Call.isGlobalCFunction("dispatch_after") &&
241      !Call.isGlobalCFunction("dispatch_async"))
242    return;
243  for (unsigned Idx = 0, NumArgs = Call.getNumArgs(); Idx < NumArgs; ++Idx) {
244    if (const BlockDataRegion *B = dyn_cast_or_null<BlockDataRegion>(
245            Call.getArgSVal(Idx).getAsRegion()))
246      checkAsyncExecutedBlockCaptures(*B, C);
247  }
248}
249
250void StackAddrEscapeChecker::checkPreStmt(const ReturnStmt *RS,
251                                          CheckerContext &C) const {
252  if (!ChecksEnabled[CK_StackAddrEscapeChecker])
253    return;
254
255  const Expr *RetE = RS->getRetValue();
256  if (!RetE)
257    return;
258  RetE = RetE->IgnoreParens();
259
260  SVal V = C.getSVal(RetE);
261  const MemRegion *R = V.getAsRegion();
262  if (!R)
263    return;
264
265  if (const BlockDataRegion *B = dyn_cast<BlockDataRegion>(R))
266    checkReturnedBlockCaptures(*B, C);
267
268  if (!isa<StackSpaceRegion>(R->getMemorySpace()) || isNotInCurrentFrame(R, C))
269    return;
270
271  // Returning a record by value is fine. (In this case, the returned
272  // expression will be a copy-constructor, possibly wrapped in an
273  // ExprWithCleanups node.)
274  if (const ExprWithCleanups *Cleanup = dyn_cast<ExprWithCleanups>(RetE))
275    RetE = Cleanup->getSubExpr();
276  if (isa<CXXConstructExpr>(RetE) && RetE->getType()->isRecordType())
277    return;
278
279  // The CK_CopyAndAutoreleaseBlockObject cast causes the block to be copied
280  // so the stack address is not escaping here.
281  if (const auto *ICE = dyn_cast<ImplicitCastExpr>(RetE)) {
282    if (isa<BlockDataRegion>(R) &&
283        ICE->getCastKind() == CK_CopyAndAutoreleaseBlockObject) {
284      return;
285    }
286  }
287
288  EmitStackError(C, R, RetE);
289}
290
291void StackAddrEscapeChecker::checkEndFunction(const ReturnStmt *RS,
292                                              CheckerContext &Ctx) const {
293  if (!ChecksEnabled[CK_StackAddrEscapeChecker])
294    return;
295
296  ProgramStateRef State = Ctx.getState();
297
298  // Iterate over all bindings to global variables and see if it contains
299  // a memory region in the stack space.
300  class CallBack : public StoreManager::BindingsHandler {
301  private:
302    CheckerContext &Ctx;
303    const StackFrameContext *PoppedFrame;
304
305    /// Look for stack variables referring to popped stack variables.
306    /// Returns true only if it found some dangling stack variables
307    /// referred by an other stack variable from different stack frame.
308    bool checkForDanglingStackVariable(const MemRegion *Referrer,
309                                       const MemRegion *Referred) {
310      const auto *ReferrerMemSpace =
311          Referrer->getMemorySpace()->getAs<StackSpaceRegion>();
312      const auto *ReferredMemSpace =
313          Referred->getMemorySpace()->getAs<StackSpaceRegion>();
314
315      if (!ReferrerMemSpace || !ReferredMemSpace)
316        return false;
317
318      const auto *ReferrerFrame = ReferrerMemSpace->getStackFrame();
319      const auto *ReferredFrame = ReferredMemSpace->getStackFrame();
320
321      if (ReferrerMemSpace && ReferredMemSpace) {
322        if (ReferredFrame == PoppedFrame &&
323            ReferrerFrame->isParentOf(PoppedFrame)) {
324          V.emplace_back(Referrer, Referred);
325          return true;
326        }
327      }
328      return false;
329    }
330
331  public:
332    SmallVector<std::pair<const MemRegion *, const MemRegion *>, 10> V;
333
334    CallBack(CheckerContext &CC) : Ctx(CC), PoppedFrame(CC.getStackFrame()) {}
335
336    bool HandleBinding(StoreManager &SMgr, Store S, const MemRegion *Region,
337                       SVal Val) override {
338      const MemRegion *VR = Val.getAsRegion();
339      if (!VR)
340        return true;
341
342      if (checkForDanglingStackVariable(Region, VR))
343        return true;
344
345      // Check the globals for the same.
346      if (!isa<GlobalsSpaceRegion>(Region->getMemorySpace()))
347        return true;
348      if (VR && VR->hasStackStorage() && !isNotInCurrentFrame(VR, Ctx))
349        V.emplace_back(Region, VR);
350      return true;
351    }
352  };
353
354  CallBack Cb(Ctx);
355  State->getStateManager().getStoreManager().iterBindings(State->getStore(),
356                                                          Cb);
357
358  if (Cb.V.empty())
359    return;
360
361  // Generate an error node.
362  ExplodedNode *N = Ctx.generateNonFatalErrorNode(State);
363  if (!N)
364    return;
365
366  if (!BT_stackleak)
367    BT_stackleak =
368        std::make_unique<BugType>(CheckNames[CK_StackAddrEscapeChecker],
369                                  "Stack address stored into global variable");
370
371  for (const auto &P : Cb.V) {
372    const MemRegion *Referrer = P.first->getBaseRegion();
373    const MemRegion *Referred = P.second;
374
375    // Generate a report for this bug.
376    const StringRef CommonSuffix =
377        "upon returning to the caller.  This will be a dangling reference";
378    SmallString<128> Buf;
379    llvm::raw_svector_ostream Out(Buf);
380    const SourceRange Range = genName(Out, Referred, Ctx.getASTContext());
381
382    if (isa<CXXTempObjectRegion, CXXLifetimeExtendedObjectRegion>(Referrer)) {
383      Out << " is still referred to by a temporary object on the stack "
384          << CommonSuffix;
385      auto Report =
386          std::make_unique<PathSensitiveBugReport>(*BT_stackleak, Out.str(), N);
387      if (Range.isValid())
388        Report->addRange(Range);
389      Ctx.emitReport(std::move(Report));
390      return;
391    }
392
393    const StringRef ReferrerMemorySpace = [](const MemSpaceRegion *Space) {
394      if (isa<StaticGlobalSpaceRegion>(Space))
395        return "static";
396      if (isa<GlobalsSpaceRegion>(Space))
397        return "global";
398      assert(isa<StackSpaceRegion>(Space));
399      return "stack";
400    }(Referrer->getMemorySpace());
401
402    // We should really only have VarRegions here.
403    // Anything else is really surprising, and we should get notified if such
404    // ever happens.
405    const auto *ReferrerVar = dyn_cast<VarRegion>(Referrer);
406    if (!ReferrerVar) {
407      assert(false && "We should have a VarRegion here");
408      continue; // Defensively skip this one.
409    }
410    const std::string ReferrerVarName =
411        ReferrerVar->getDecl()->getDeclName().getAsString();
412
413    Out << " is still referred to by the " << ReferrerMemorySpace
414        << " variable '" << ReferrerVarName << "' " << CommonSuffix;
415    auto Report =
416        std::make_unique<PathSensitiveBugReport>(*BT_stackleak, Out.str(), N);
417    if (Range.isValid())
418      Report->addRange(Range);
419
420    Ctx.emitReport(std::move(Report));
421  }
422}
423
424void ento::registerStackAddrEscapeBase(CheckerManager &mgr) {
425  mgr.registerChecker<StackAddrEscapeChecker>();
426}
427
428bool ento::shouldRegisterStackAddrEscapeBase(const CheckerManager &mgr) {
429  return true;
430}
431
432#define REGISTER_CHECKER(name)                                                 \
433  void ento::register##name(CheckerManager &Mgr) {                             \
434    StackAddrEscapeChecker *Chk = Mgr.getChecker<StackAddrEscapeChecker>();    \
435    Chk->ChecksEnabled[StackAddrEscapeChecker::CK_##name] = true;              \
436    Chk->CheckNames[StackAddrEscapeChecker::CK_##name] =                       \
437        Mgr.getCurrentCheckerName();                                           \
438  }                                                                            \
439                                                                               \
440  bool ento::shouldRegister##name(const CheckerManager &mgr) { return true; }
441
442REGISTER_CHECKER(StackAddrEscapeChecker)
443REGISTER_CHECKER(StackAddrAsyncEscapeChecker)
444