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 "ClangSACheckers.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/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 : public Checker< check::PreStmt<ReturnStmt>,
30                                               check::EndFunction > {
31  mutable std::unique_ptr<BuiltinBug> BT_stackleak;
32  mutable std::unique_ptr<BuiltinBug> BT_returnstack;
33
34public:
35  void checkPreStmt(const ReturnStmt *RS, CheckerContext &C) const;
36  void checkEndFunction(CheckerContext &Ctx) const;
37private:
38  void EmitStackError(CheckerContext &C, const MemRegion *R,
39                      const Expr *RetE) const;
40  static SourceRange genName(raw_ostream &os, const MemRegion *R,
41                             ASTContext &Ctx);
42};
43}
44
45SourceRange StackAddrEscapeChecker::genName(raw_ostream &os, const MemRegion *R,
46                                            ASTContext &Ctx) {
47    // Get the base region, stripping away fields and elements.
48  R = R->getBaseRegion();
49  SourceManager &SM = Ctx.getSourceManager();
50  SourceRange range;
51  os << "Address of ";
52
53  // Check if the region is a compound literal.
54  if (const CompoundLiteralRegion* CR = dyn_cast<CompoundLiteralRegion>(R)) {
55    const CompoundLiteralExpr *CL = CR->getLiteralExpr();
56    os << "stack memory associated with a compound literal "
57          "declared on line "
58        << SM.getExpansionLineNumber(CL->getLocStart())
59        << " returned to caller";
60    range = CL->getSourceRange();
61  }
62  else if (const AllocaRegion* AR = dyn_cast<AllocaRegion>(R)) {
63    const Expr *ARE = AR->getExpr();
64    SourceLocation L = ARE->getLocStart();
65    range = ARE->getSourceRange();
66    os << "stack memory allocated by call to alloca() on line "
67       << SM.getExpansionLineNumber(L);
68  }
69  else if (const BlockDataRegion *BR = dyn_cast<BlockDataRegion>(R)) {
70    const BlockDecl *BD = BR->getCodeRegion()->getDecl();
71    SourceLocation L = BD->getLocStart();
72    range = BD->getSourceRange();
73    os << "stack-allocated block declared on line "
74       << SM.getExpansionLineNumber(L);
75  }
76  else if (const VarRegion *VR = dyn_cast<VarRegion>(R)) {
77    os << "stack memory associated with local variable '"
78       << VR->getString() << '\'';
79    range = VR->getDecl()->getSourceRange();
80  }
81  else if (const CXXTempObjectRegion *TOR = dyn_cast<CXXTempObjectRegion>(R)) {
82    QualType Ty = TOR->getValueType().getLocalUnqualifiedType();
83    os << "stack memory associated with temporary object of type '";
84    Ty.print(os, Ctx.getPrintingPolicy());
85    os << "'";
86    range = TOR->getExpr()->getSourceRange();
87  }
88  else {
89    llvm_unreachable("Invalid region in ReturnStackAddressChecker.");
90  }
91
92  return range;
93}
94
95void StackAddrEscapeChecker::EmitStackError(CheckerContext &C, const MemRegion *R,
96                                          const Expr *RetE) const {
97  ExplodedNode *N = C.generateErrorNode();
98
99  if (!N)
100    return;
101
102  if (!BT_returnstack)
103    BT_returnstack.reset(
104        new BuiltinBug(this, "Return of address to stack-allocated memory"));
105
106  // Generate a report for this bug.
107  SmallString<512> buf;
108  llvm::raw_svector_ostream os(buf);
109  SourceRange range = genName(os, R, C.getASTContext());
110  os << " returned to caller";
111  auto report = llvm::make_unique<BugReport>(*BT_returnstack, os.str(), N);
112  report->addRange(RetE->getSourceRange());
113  if (range.isValid())
114    report->addRange(range);
115
116  C.emitReport(std::move(report));
117}
118
119void StackAddrEscapeChecker::checkPreStmt(const ReturnStmt *RS,
120                                          CheckerContext &C) const {
121
122  const Expr *RetE = RS->getRetValue();
123  if (!RetE)
124    return;
125  RetE = RetE->IgnoreParens();
126
127  const LocationContext *LCtx = C.getLocationContext();
128  SVal V = C.getState()->getSVal(RetE, LCtx);
129  const MemRegion *R = V.getAsRegion();
130
131  if (!R)
132    return;
133
134  const StackSpaceRegion *SS =
135    dyn_cast_or_null<StackSpaceRegion>(R->getMemorySpace());
136
137  if (!SS)
138    return;
139
140  // Return stack memory in an ancestor stack frame is fine.
141  const StackFrameContext *CurFrame = LCtx->getCurrentStackFrame();
142  const StackFrameContext *MemFrame = SS->getStackFrame();
143  if (MemFrame != CurFrame)
144    return;
145
146  // Automatic reference counting automatically copies blocks.
147  if (C.getASTContext().getLangOpts().ObjCAutoRefCount &&
148      isa<BlockDataRegion>(R))
149    return;
150
151  // Returning a record by value is fine. (In this case, the returned
152  // expression will be a copy-constructor, possibly wrapped in an
153  // ExprWithCleanups node.)
154  if (const ExprWithCleanups *Cleanup = dyn_cast<ExprWithCleanups>(RetE))
155    RetE = Cleanup->getSubExpr();
156  if (isa<CXXConstructExpr>(RetE) && RetE->getType()->isRecordType())
157    return;
158
159  // The CK_CopyAndAutoreleaseBlockObject cast causes the block to be copied
160  // so the stack address is not escaping here.
161  if (auto *ICE = dyn_cast<ImplicitCastExpr>(RetE)) {
162    if (isa<BlockDataRegion>(R) &&
163        ICE->getCastKind() == CK_CopyAndAutoreleaseBlockObject) {
164      return;
165    }
166  }
167
168  EmitStackError(C, R, RetE);
169}
170
171void StackAddrEscapeChecker::checkEndFunction(CheckerContext &Ctx) const {
172  ProgramStateRef state = Ctx.getState();
173
174  // Iterate over all bindings to global variables and see if it contains
175  // a memory region in the stack space.
176  class CallBack : public StoreManager::BindingsHandler {
177  private:
178    CheckerContext &Ctx;
179    const StackFrameContext *CurSFC;
180  public:
181    SmallVector<std::pair<const MemRegion*, const MemRegion*>, 10> V;
182
183    CallBack(CheckerContext &CC) :
184      Ctx(CC),
185      CurSFC(CC.getLocationContext()->getCurrentStackFrame())
186    {}
187
188    bool HandleBinding(StoreManager &SMgr, Store store,
189                       const MemRegion *region, SVal val) override {
190
191      if (!isa<GlobalsSpaceRegion>(region->getMemorySpace()))
192        return true;
193
194      const MemRegion *vR = val.getAsRegion();
195      if (!vR)
196        return true;
197
198      // Under automated retain release, it is okay to assign a block
199      // directly to a global variable.
200      if (Ctx.getASTContext().getLangOpts().ObjCAutoRefCount &&
201          isa<BlockDataRegion>(vR))
202        return true;
203
204      if (const StackSpaceRegion *SSR =
205          dyn_cast<StackSpaceRegion>(vR->getMemorySpace())) {
206        // If the global variable holds a location in the current stack frame,
207        // record the binding to emit a warning.
208        if (SSR->getStackFrame() == CurSFC)
209          V.push_back(std::make_pair(region, vR));
210      }
211
212      return true;
213    }
214  };
215
216  CallBack cb(Ctx);
217  state->getStateManager().getStoreManager().iterBindings(state->getStore(),cb);
218
219  if (cb.V.empty())
220    return;
221
222  // Generate an error node.
223  ExplodedNode *N = Ctx.generateNonFatalErrorNode(state);
224  if (!N)
225    return;
226
227  if (!BT_stackleak)
228    BT_stackleak.reset(
229        new BuiltinBug(this, "Stack address stored into global variable",
230                       "Stack address was saved into a global variable. "
231                       "This is dangerous because the address will become "
232                       "invalid after returning from the function"));
233
234  for (unsigned i = 0, e = cb.V.size(); i != e; ++i) {
235    // Generate a report for this bug.
236    SmallString<512> buf;
237    llvm::raw_svector_ostream os(buf);
238    SourceRange range = genName(os, cb.V[i].second, Ctx.getASTContext());
239    os << " is still referred to by the ";
240    if (isa<StaticGlobalSpaceRegion>(cb.V[i].first->getMemorySpace()))
241      os << "static";
242    else
243      os << "global";
244    os << " variable '";
245    const VarRegion *VR = cast<VarRegion>(cb.V[i].first->getBaseRegion());
246    os << *VR->getDecl()
247       << "' upon returning to the caller.  This will be a dangling reference";
248    auto report = llvm::make_unique<BugReport>(*BT_stackleak, os.str(), N);
249    if (range.isValid())
250      report->addRange(range);
251
252    Ctx.emitReport(std::move(report));
253  }
254}
255
256void ento::registerStackAddrEscapeChecker(CheckerManager &mgr) {
257  mgr.registerChecker<StackAddrEscapeChecker>();
258}
259