clang  9.0.0
StackAddrEscapeChecker.cpp
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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 
15 #include "clang/AST/ExprCXX.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 
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();
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 
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 
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 
125 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>
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 
151 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 = llvm::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 = llvm::make_unique<BugReport>(*BT_returnstack, os.str(), N);
166  report->addRange(RetE->getSourceRange());
167  if (range.isValid())
168  report->addRange(range);
169  C.emitReport(std::move(report));
170 }
171 
172 void StackAddrEscapeChecker::checkAsyncExecutedBlockCaptures(
173  const BlockDataRegion &B, CheckerContext &C) const {
174  // There is a not-too-uncommon idiom
175  // where a block passed to dispatch_async captures a semaphore
176  // and then the thread (which called dispatch_async) is blocked on waiting
177  // for the completion of the execution of the block
178  // via dispatch_semaphore_wait. To avoid false-positives (for now)
179  // we ignore all the blocks which have captured
180  // a variable of the type "dispatch_semaphore_t".
181  if (isSemaphoreCaptured(*B.getDecl()))
182  return;
183  for (const MemRegion *Region : getCapturedStackRegions(B, C)) {
184  // The block passed to dispatch_async may capture another block
185  // created on the stack. However, there is no leak in this situaton,
186  // no matter if ARC or no ARC is enabled:
187  // dispatch_async copies the passed "outer" block (via Block_copy)
188  // and if the block has captured another "inner" block,
189  // the "inner" block will be copied as well.
190  if (isa<BlockDataRegion>(Region))
191  continue;
192  ExplodedNode *N = C.generateNonFatalErrorNode();
193  if (!N)
194  continue;
195  if (!BT_capturedstackasync)
196  BT_capturedstackasync = llvm::make_unique<BuiltinBug>(
197  this, "Address of stack-allocated memory is captured");
198  SmallString<128> Buf;
199  llvm::raw_svector_ostream Out(Buf);
200  SourceRange Range = genName(Out, Region, C.getASTContext());
201  Out << " is captured by an asynchronously-executed block";
202  auto Report =
203  llvm::make_unique<BugReport>(*BT_capturedstackasync, Out.str(), N);
204  if (Range.isValid())
205  Report->addRange(Range);
206  C.emitReport(std::move(Report));
207  }
208 }
209 
210 void StackAddrEscapeChecker::checkReturnedBlockCaptures(
211  const BlockDataRegion &B, CheckerContext &C) const {
212  for (const MemRegion *Region : getCapturedStackRegions(B, C)) {
213  if (isArcManagedBlock(Region, C) || isNotInCurrentFrame(Region, C))
214  continue;
215  ExplodedNode *N = C.generateNonFatalErrorNode();
216  if (!N)
217  continue;
218  if (!BT_capturedstackret)
219  BT_capturedstackret = llvm::make_unique<BuiltinBug>(
220  this, "Address of stack-allocated memory is captured");
221  SmallString<128> Buf;
222  llvm::raw_svector_ostream Out(Buf);
223  SourceRange Range = genName(Out, Region, C.getASTContext());
224  Out << " is captured by a returned block";
225  auto Report =
226  llvm::make_unique<BugReport>(*BT_capturedstackret, Out.str(), N);
227  if (Range.isValid())
228  Report->addRange(Range);
229  C.emitReport(std::move(Report));
230  }
231 }
232 
233 void StackAddrEscapeChecker::checkPreCall(const CallEvent &Call,
234  CheckerContext &C) const {
235  if (!ChecksEnabled[CK_StackAddrAsyncEscapeChecker])
236  return;
237  if (!Call.isGlobalCFunction("dispatch_after") &&
238  !Call.isGlobalCFunction("dispatch_async"))
239  return;
240  for (unsigned Idx = 0, NumArgs = Call.getNumArgs(); Idx < NumArgs; ++Idx) {
241  if (const BlockDataRegion *B = dyn_cast_or_null<BlockDataRegion>(
242  Call.getArgSVal(Idx).getAsRegion()))
243  checkAsyncExecutedBlockCaptures(*B, C);
244  }
245 }
246 
247 void StackAddrEscapeChecker::checkPreStmt(const ReturnStmt *RS,
248  CheckerContext &C) const {
249  if (!ChecksEnabled[CK_StackAddrEscapeChecker])
250  return;
251 
252  const Expr *RetE = RS->getRetValue();
253  if (!RetE)
254  return;
255  RetE = RetE->IgnoreParens();
256 
257  SVal V = C.getSVal(RetE);
258  const MemRegion *R = V.getAsRegion();
259  if (!R)
260  return;
261 
262  if (const BlockDataRegion *B = dyn_cast<BlockDataRegion>(R))
263  checkReturnedBlockCaptures(*B, C);
264 
265  if (!isa<StackSpaceRegion>(R->getMemorySpace()) ||
266  isNotInCurrentFrame(R, C) || isArcManagedBlock(R, C))
267  return;
268 
269  // Returning a record by value is fine. (In this case, the returned
270  // expression will be a copy-constructor, possibly wrapped in an
271  // ExprWithCleanups node.)
272  if (const ExprWithCleanups *Cleanup = dyn_cast<ExprWithCleanups>(RetE))
273  RetE = Cleanup->getSubExpr();
274  if (isa<CXXConstructExpr>(RetE) && RetE->getType()->isRecordType())
275  return;
276 
277  // The CK_CopyAndAutoreleaseBlockObject cast causes the block to be copied
278  // so the stack address is not escaping here.
279  if (auto *ICE = dyn_cast<ImplicitCastExpr>(RetE)) {
280  if (isa<BlockDataRegion>(R) &&
281  ICE->getCastKind() == CK_CopyAndAutoreleaseBlockObject) {
282  return;
283  }
284  }
285 
286  EmitStackError(C, R, RetE);
287 }
288 
289 void StackAddrEscapeChecker::checkEndFunction(const ReturnStmt *RS,
290  CheckerContext &Ctx) const {
291  if (!ChecksEnabled[CK_StackAddrEscapeChecker])
292  return;
293 
294  ProgramStateRef State = Ctx.getState();
295 
296  // Iterate over all bindings to global variables and see if it contains
297  // a memory region in the stack space.
298  class CallBack : public StoreManager::BindingsHandler {
299  private:
300  CheckerContext &Ctx;
301  const StackFrameContext *CurSFC;
302 
303  public:
304  SmallVector<std::pair<const MemRegion *, const MemRegion *>, 10> V;
305 
306  CallBack(CheckerContext &CC) : Ctx(CC), CurSFC(CC.getStackFrame()) {}
307 
308  bool HandleBinding(StoreManager &SMgr, Store S, const MemRegion *Region,
309  SVal Val) override {
310 
311  if (!isa<GlobalsSpaceRegion>(Region->getMemorySpace()))
312  return true;
313  const MemRegion *VR = Val.getAsRegion();
314  if (VR && isa<StackSpaceRegion>(VR->getMemorySpace()) &&
315  !isArcManagedBlock(VR, Ctx) && !isNotInCurrentFrame(VR, Ctx))
316  V.emplace_back(Region, VR);
317  return true;
318  }
319  };
320 
321  CallBack Cb(Ctx);
322  State->getStateManager().getStoreManager().iterBindings(State->getStore(),
323  Cb);
324 
325  if (Cb.V.empty())
326  return;
327 
328  // Generate an error node.
329  ExplodedNode *N = Ctx.generateNonFatalErrorNode(State);
330  if (!N)
331  return;
332 
333  if (!BT_stackleak)
334  BT_stackleak = llvm::make_unique<BuiltinBug>(
335  this, "Stack address stored into global variable",
336  "Stack address was saved into a global variable. "
337  "This is dangerous because the address will become "
338  "invalid after returning from the function");
339 
340  for (const auto &P : Cb.V) {
341  // Generate a report for this bug.
342  SmallString<128> Buf;
343  llvm::raw_svector_ostream Out(Buf);
344  SourceRange Range = genName(Out, P.second, Ctx.getASTContext());
345  Out << " is still referred to by the ";
346  if (isa<StaticGlobalSpaceRegion>(P.first->getMemorySpace()))
347  Out << "static";
348  else
349  Out << "global";
350  Out << " variable '";
351  const VarRegion *VR = cast<VarRegion>(P.first->getBaseRegion());
352  Out << *VR->getDecl()
353  << "' upon returning to the caller. This will be a dangling reference";
354  auto Report = llvm::make_unique<BugReport>(*BT_stackleak, Out.str(), N);
355  if (Range.isValid())
356  Report->addRange(Range);
357 
358  Ctx.emitReport(std::move(Report));
359  }
360 }
361 
362 void ento::registerStackAddrEscapeBase(CheckerManager &mgr) {
363  mgr.registerChecker<StackAddrEscapeChecker>();
364 }
365 
366 bool ento::shouldRegisterStackAddrEscapeBase(const LangOptions &LO) {
367  return true;
368 }
369 
370 #define REGISTER_CHECKER(name) \
371  void ento::register##name(CheckerManager &Mgr) { \
372  StackAddrEscapeChecker *Chk = \
373  Mgr.getChecker<StackAddrEscapeChecker>(); \
374  Chk->ChecksEnabled[StackAddrEscapeChecker::CK_##name] = true; \
375  } \
376  \
377  bool ento::shouldRegister##name(const LangOptions &LO) { \
378  return true; \
379  }
380 
381 REGISTER_CHECKER(StackAddrEscapeChecker)
382 REGISTER_CHECKER(StackAddrAsyncEscapeChecker)
A (possibly-)qualified type.
Definition: Type.h:643
Defines the SourceManager interface.
bool isRecordType() const
Definition: Type.h:6464
SourceLocation getBeginLoc() const LLVM_READONLY
Definition: DeclBase.h:421
IntrusiveRefCntPtr< const ProgramState > ProgramStateRef
StringRef P
CompoundLiteralExpr - [C99 6.5.2.5].
Definition: Expr.h:3048
const void * Store
Store - This opaque type encapsulates an immutable mapping from locations to values.
Definition: StoreRef.h:27
RangeSelector range(RangeSelector Begin, RangeSelector End)
Selects from the start of Begin and to the end of End.
Represents an expression – generally a full-expression – that introduces cleanups to be run at the ...
Definition: ExprCXX.h:3212
Defines the clang::Expr interface and subclasses for C++ expressions.
SourceLocation getBeginLoc() const LLVM_READONLY
Definition: Expr.h:3091
One of these records is kept for each identifier that is lexed.
Holds long-lived AST nodes (such as types and decls) that can be referred to throughout the semantic ...
Definition: ASTContext.h:154
LineState State
SourceLocation getBeginLoc() const LLVM_READONLY
Definition: Stmt.cpp:263
Keeps track of the various options that can be enabled, which controls the dialect of C or C++ that i...
Definition: LangOptions.h:49
IdentifierTable & Idents
Definition: ASTContext.h:569
void print(raw_ostream &OS, const PrintingPolicy &Policy, const Twine &PlaceHolder=Twine(), unsigned Indentation=0) const
const clang::PrintingPolicy & getPrintingPolicy() const
Definition: ASTContext.h:657
Represents a block literal declaration, which is like an unnamed FunctionDecl.
Definition: Decl.h:3915
This represents one expression.
Definition: Expr.h:108
#define V(N, I)
Definition: ASTContext.h:2907
QualType getType() const
Definition: Expr.h:137
ReturnStmt - This represents a return, optionally of an expression: return; return 4;...
Definition: Stmt.h:2610
unsigned getExpansionLineNumber(SourceLocation Loc, bool *Invalid=nullptr) const
const SourceManager & SM
Definition: Format.cpp:1572
Encodes a location in the source.
IdentifierInfo & get(StringRef Name)
Return the identifier token info for the specified named identifier.
Expr * getRetValue()
Definition: Stmt.h:2643
ASTContext & getASTContext() const LLVM_READONLY
Definition: DeclBase.cpp:376
#define REGISTER_CHECKER(name)
Dataflow Directional Tag Classes.
ArrayRef< Capture > captures() const
Definition: Decl.h:4042
SourceManager & getSourceManager()
Definition: ASTContext.h:665
bool isValid() const
SourceRange getSourceRange() const override LLVM_READONLY
Source range that this declaration covers.
Definition: Decl.cpp:4455
SourceRange getSourceRange() const LLVM_READONLY
SourceLocation tokens are not useful in isolation - they are low level value objects created/interpre...
Definition: Stmt.cpp:251
A trivial tuple used to represent a source range.
This class handles loading and caching of source files into memory.
Expr * IgnoreParens() LLVM_READONLY
Skip past any parentheses which might surround this expression until reaching a fixed point...
Definition: Expr.cpp:2938