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"
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  DefaultBool ChecksEnabled[CK_NumCheckKinds];
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 isArcManagedBlock(const MemRegion *R, CheckerContext &C);
65  static bool isNotInCurrentFrame(const MemRegion *R, CheckerContext &C);
66};
67} // namespace
68
69SourceRange 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
113bool 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
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  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
152void 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 = std::make_unique<BuiltinBug>(
160        CheckNames[CK_StackAddrEscapeChecker],
161        "Return of address to stack-allocated memory");
162  // Generate a report for this bug.
163  SmallString<128> buf;
164  llvm::raw_svector_ostream os(buf);
165  SourceRange range = genName(os, R, C.getASTContext());
166  os << " returned to caller";
167  auto report =
168      std::make_unique<PathSensitiveBugReport>(*BT_returnstack, os.str(), N);
169  report->addRange(RetE->getSourceRange());
170  if (range.isValid())
171    report->addRange(range);
172  C.emitReport(std::move(report));
173}
174
175void StackAddrEscapeChecker::checkAsyncExecutedBlockCaptures(
176    const BlockDataRegion &B, CheckerContext &C) const {
177  // There is a not-too-uncommon idiom
178  // where a block passed to dispatch_async captures a semaphore
179  // and then the thread (which called dispatch_async) is blocked on waiting
180  // for the completion of the execution of the block
181  // via dispatch_semaphore_wait. To avoid false-positives (for now)
182  // we ignore all the blocks which have captured
183  // a variable of the type "dispatch_semaphore_t".
184  if (isSemaphoreCaptured(*B.getDecl()))
185    return;
186  for (const MemRegion *Region : getCapturedStackRegions(B, C)) {
187    // The block passed to dispatch_async may capture another block
188    // created on the stack. However, there is no leak in this situaton,
189    // no matter if ARC or no ARC is enabled:
190    // dispatch_async copies the passed "outer" block (via Block_copy)
191    // and if the block has captured another "inner" block,
192    // the "inner" block will be copied as well.
193    if (isa<BlockDataRegion>(Region))
194      continue;
195    ExplodedNode *N = C.generateNonFatalErrorNode();
196    if (!N)
197      continue;
198    if (!BT_capturedstackasync)
199      BT_capturedstackasync = std::make_unique<BuiltinBug>(
200          CheckNames[CK_StackAddrAsyncEscapeChecker],
201          "Address of stack-allocated memory is captured");
202    SmallString<128> Buf;
203    llvm::raw_svector_ostream Out(Buf);
204    SourceRange Range = genName(Out, Region, C.getASTContext());
205    Out << " is captured by an asynchronously-executed block";
206    auto Report = std::make_unique<PathSensitiveBugReport>(
207        *BT_capturedstackasync, Out.str(), N);
208    if (Range.isValid())
209      Report->addRange(Range);
210    C.emitReport(std::move(Report));
211  }
212}
213
214void StackAddrEscapeChecker::checkReturnedBlockCaptures(
215    const BlockDataRegion &B, CheckerContext &C) const {
216  for (const MemRegion *Region : getCapturedStackRegions(B, C)) {
217    if (isArcManagedBlock(Region, C) || isNotInCurrentFrame(Region, C))
218      continue;
219    ExplodedNode *N = C.generateNonFatalErrorNode();
220    if (!N)
221      continue;
222    if (!BT_capturedstackret)
223      BT_capturedstackret = std::make_unique<BuiltinBug>(
224          CheckNames[CK_StackAddrEscapeChecker],
225          "Address of stack-allocated memory is captured");
226    SmallString<128> Buf;
227    llvm::raw_svector_ostream Out(Buf);
228    SourceRange Range = genName(Out, Region, C.getASTContext());
229    Out << " is captured by a returned block";
230    auto Report = std::make_unique<PathSensitiveBugReport>(*BT_capturedstackret,
231                                                           Out.str(), N);
232    if (Range.isValid())
233      Report->addRange(Range);
234    C.emitReport(std::move(Report));
235  }
236}
237
238void StackAddrEscapeChecker::checkPreCall(const CallEvent &Call,
239                                          CheckerContext &C) const {
240  if (!ChecksEnabled[CK_StackAddrAsyncEscapeChecker])
241    return;
242  if (!Call.isGlobalCFunction("dispatch_after") &&
243      !Call.isGlobalCFunction("dispatch_async"))
244    return;
245  for (unsigned Idx = 0, NumArgs = Call.getNumArgs(); Idx < NumArgs; ++Idx) {
246    if (const BlockDataRegion *B = dyn_cast_or_null<BlockDataRegion>(
247            Call.getArgSVal(Idx).getAsRegion()))
248      checkAsyncExecutedBlockCaptures(*B, C);
249  }
250}
251
252void StackAddrEscapeChecker::checkPreStmt(const ReturnStmt *RS,
253                                          CheckerContext &C) const {
254  if (!ChecksEnabled[CK_StackAddrEscapeChecker])
255    return;
256
257  const Expr *RetE = RS->getRetValue();
258  if (!RetE)
259    return;
260  RetE = RetE->IgnoreParens();
261
262  SVal V = C.getSVal(RetE);
263  const MemRegion *R = V.getAsRegion();
264  if (!R)
265    return;
266
267  if (const BlockDataRegion *B = dyn_cast<BlockDataRegion>(R))
268    checkReturnedBlockCaptures(*B, C);
269
270  if (!isa<StackSpaceRegion>(R->getMemorySpace()) ||
271      isNotInCurrentFrame(R, C) || isArcManagedBlock(R, C))
272    return;
273
274  // Returning a record by value is fine. (In this case, the returned
275  // expression will be a copy-constructor, possibly wrapped in an
276  // ExprWithCleanups node.)
277  if (const ExprWithCleanups *Cleanup = dyn_cast<ExprWithCleanups>(RetE))
278    RetE = Cleanup->getSubExpr();
279  if (isa<CXXConstructExpr>(RetE) && RetE->getType()->isRecordType())
280    return;
281
282  // The CK_CopyAndAutoreleaseBlockObject cast causes the block to be copied
283  // so the stack address is not escaping here.
284  if (const auto *ICE = dyn_cast<ImplicitCastExpr>(RetE)) {
285    if (isa<BlockDataRegion>(R) &&
286        ICE->getCastKind() == CK_CopyAndAutoreleaseBlockObject) {
287      return;
288    }
289  }
290
291  EmitStackError(C, R, RetE);
292}
293
294void StackAddrEscapeChecker::checkEndFunction(const ReturnStmt *RS,
295                                              CheckerContext &Ctx) const {
296  if (!ChecksEnabled[CK_StackAddrEscapeChecker])
297    return;
298
299  ProgramStateRef State = Ctx.getState();
300
301  // Iterate over all bindings to global variables and see if it contains
302  // a memory region in the stack space.
303  class CallBack : public StoreManager::BindingsHandler {
304  private:
305    CheckerContext &Ctx;
306    const StackFrameContext *CurSFC;
307
308  public:
309    SmallVector<std::pair<const MemRegion *, const MemRegion *>, 10> V;
310
311    CallBack(CheckerContext &CC) : Ctx(CC), CurSFC(CC.getStackFrame()) {}
312
313    bool HandleBinding(StoreManager &SMgr, Store S, const MemRegion *Region,
314                       SVal Val) override {
315
316      if (!isa<GlobalsSpaceRegion>(Region->getMemorySpace()))
317        return true;
318      const MemRegion *VR = Val.getAsRegion();
319      if (VR && isa<StackSpaceRegion>(VR->getMemorySpace()) &&
320          !isArcManagedBlock(VR, Ctx) && !isNotInCurrentFrame(VR, Ctx))
321        V.emplace_back(Region, VR);
322      return true;
323    }
324  };
325
326  CallBack Cb(Ctx);
327  State->getStateManager().getStoreManager().iterBindings(State->getStore(),
328                                                          Cb);
329
330  if (Cb.V.empty())
331    return;
332
333  // Generate an error node.
334  ExplodedNode *N = Ctx.generateNonFatalErrorNode(State);
335  if (!N)
336    return;
337
338  if (!BT_stackleak)
339    BT_stackleak = std::make_unique<BuiltinBug>(
340        CheckNames[CK_StackAddrEscapeChecker],
341        "Stack address stored into global variable",
342        "Stack address was saved into a global variable. "
343        "This is dangerous because the address will become "
344        "invalid after returning from the function");
345
346  for (const auto &P : Cb.V) {
347    // Generate a report for this bug.
348    SmallString<128> Buf;
349    llvm::raw_svector_ostream Out(Buf);
350    SourceRange Range = genName(Out, P.second, Ctx.getASTContext());
351    Out << " is still referred to by the ";
352    if (isa<StaticGlobalSpaceRegion>(P.first->getMemorySpace()))
353      Out << "static";
354    else
355      Out << "global";
356    Out << " variable '";
357    const VarRegion *VR = cast<VarRegion>(P.first->getBaseRegion());
358    Out << *VR->getDecl()
359        << "' upon returning to the caller.  This will be a dangling reference";
360    auto Report =
361        std::make_unique<PathSensitiveBugReport>(*BT_stackleak, Out.str(), N);
362    if (Range.isValid())
363      Report->addRange(Range);
364
365    Ctx.emitReport(std::move(Report));
366  }
367}
368
369void ento::registerStackAddrEscapeBase(CheckerManager &mgr) {
370  mgr.registerChecker<StackAddrEscapeChecker>();
371}
372
373bool ento::shouldRegisterStackAddrEscapeBase(const CheckerManager &mgr) {
374  return true;
375}
376
377#define REGISTER_CHECKER(name)                                                 \
378  void ento::register##name(CheckerManager &Mgr) {                             \
379    StackAddrEscapeChecker *Chk = Mgr.getChecker<StackAddrEscapeChecker>();    \
380    Chk->ChecksEnabled[StackAddrEscapeChecker::CK_##name] = true;              \
381    Chk->CheckNames[StackAddrEscapeChecker::CK_##name] =                       \
382        Mgr.getCurrentCheckerName();                                           \
383  }                                                                            \
384                                                                               \
385  bool ento::shouldRegister##name(const CheckerManager &mgr) { return true; }
386
387REGISTER_CHECKER(StackAddrEscapeChecker)
388REGISTER_CHECKER(StackAddrAsyncEscapeChecker)
389