StackAddrEscapeChecker.cpp revision 4e4d08403ca5cfd4d558fa2936215d3a4e5a528d 
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/StaticAnalyzer/Core/Checker.h"
17#include "clang/StaticAnalyzer/Core/CheckerManager.h"
18#include "clang/StaticAnalyzer/Core/PathSensitive/CheckerContext.h"
19#include "clang/StaticAnalyzer/Core/BugReporter/BugType.h"
20#include "clang/StaticAnalyzer/Core/PathSensitive/ProgramState.h"
21#include "clang/Basic/SourceManager.h"
22#include "llvm/ADT/SmallString.h"
23using namespace clang;
24using namespace ento;
25
26namespace {
27class StackAddrEscapeChecker : public Checker< check::PreStmt<ReturnStmt>,
28                                               check::EndPath > {
29  mutable OwningPtr<BuiltinBug> BT_stackleak;
30  mutable OwningPtr<BuiltinBug> BT_returnstack;
31
32public:
33  void checkPreStmt(const ReturnStmt *RS, CheckerContext &C) const;
34  void checkEndPath(CheckerContext &Ctx) const;
35private:
36  void EmitStackError(CheckerContext &C, const MemRegion *R,
37                      const Expr *RetE) const;
38  static SourceRange GenName(raw_ostream &os, const MemRegion *R,
39                             SourceManager &SM);
40};
41}
42
43SourceRange StackAddrEscapeChecker::GenName(raw_ostream &os,
44                                          const MemRegion *R,
45                                          SourceManager &SM) {
46    // Get the base region, stripping away fields and elements.
47  R = R->getBaseRegion();
48  SourceRange range;
49  os << "Address of ";
50
51  // Check if the region is a compound literal.
52  if (const CompoundLiteralRegion* CR = dyn_cast<CompoundLiteralRegion>(R)) {
53    const CompoundLiteralExpr *CL = CR->getLiteralExpr();
54    os << "stack memory associated with a compound literal "
55          "declared on line "
56        << SM.getExpansionLineNumber(CL->getLocStart())
57        << " returned to caller";
58    range = CL->getSourceRange();
59  }
60  else if (const AllocaRegion* AR = dyn_cast<AllocaRegion>(R)) {
61    const Expr *ARE = AR->getExpr();
62    SourceLocation L = ARE->getLocStart();
63    range = ARE->getSourceRange();
64    os << "stack memory allocated by call to alloca() on line "
65       << SM.getExpansionLineNumber(L);
66  }
67  else if (const BlockDataRegion *BR = dyn_cast<BlockDataRegion>(R)) {
68    const BlockDecl *BD = BR->getCodeRegion()->getDecl();
69    SourceLocation L = BD->getLocStart();
70    range = BD->getSourceRange();
71    os << "stack-allocated block declared on line "
72       << SM.getExpansionLineNumber(L);
73  }
74  else if (const VarRegion *VR = dyn_cast<VarRegion>(R)) {
75    os << "stack memory associated with local variable '"
76       << VR->getString() << '\'';
77    range = VR->getDecl()->getSourceRange();
78  }
79  else if (const CXXTempObjectRegion *TOR = dyn_cast<CXXTempObjectRegion>(R)) {
80    os << "stack memory associated with temporary object of type '"
81       << TOR->getValueType().getAsString() << '\'';
82    range = TOR->getExpr()->getSourceRange();
83  }
84  else {
85    llvm_unreachable("Invalid region in ReturnStackAddressChecker.");
86  }
87
88  return range;
89}
90
91void StackAddrEscapeChecker::EmitStackError(CheckerContext &C, const MemRegion *R,
92                                          const Expr *RetE) const {
93  ExplodedNode *N = C.generateSink();
94
95  if (!N)
96    return;
97
98  if (!BT_returnstack)
99   BT_returnstack.reset(
100                 new BuiltinBug("Return of address to stack-allocated memory"));
101
102  // Generate a report for this bug.
103  SmallString<512> buf;
104  llvm::raw_svector_ostream os(buf);
105  SourceRange range = GenName(os, R, C.getSourceManager());
106  os << " returned to caller";
107  BugReport *report = new BugReport(*BT_returnstack, os.str(), N);
108  report->addRange(RetE->getSourceRange());
109  if (range.isValid())
110    report->addRange(range);
111
112  C.EmitReport(report);
113}
114
115void StackAddrEscapeChecker::checkPreStmt(const ReturnStmt *RS,
116                                          CheckerContext &C) const {
117
118  const Expr *RetE = RS->getRetValue();
119  if (!RetE)
120    return;
121
122  SVal V = C.getState()->getSVal(RetE, C.getLocationContext());
123  const MemRegion *R = V.getAsRegion();
124
125  if (!R)
126    return;
127
128  const StackSpaceRegion *SS =
129    dyn_cast_or_null<StackSpaceRegion>(R->getMemorySpace());
130
131  if (!SS)
132    return;
133
134  // Return stack memory in an ancestor stack frame is fine.
135  const StackFrameContext *SFC = SS->getStackFrame();
136  if (SFC != C.getLocationContext()->getCurrentStackFrame())
137    return;
138
139  // Automatic reference counting automatically copies blocks.
140  if (C.getASTContext().getLangOpts().ObjCAutoRefCount &&
141      isa<BlockDataRegion>(R))
142    return;
143
144  EmitStackError(C, R, RetE);
145}
146
147void StackAddrEscapeChecker::checkEndPath(CheckerContext &Ctx) const {
148  ProgramStateRef state = Ctx.getState();
149
150  // Iterate over all bindings to global variables and see if it contains
151  // a memory region in the stack space.
152  class CallBack : public StoreManager::BindingsHandler {
153  private:
154    CheckerContext &Ctx;
155    const StackFrameContext *CurSFC;
156  public:
157    SmallVector<std::pair<const MemRegion*, const MemRegion*>, 10> V;
158
159    CallBack(CheckerContext &CC) :
160      Ctx(CC),
161      CurSFC(CC.getLocationContext()->getCurrentStackFrame())
162    {}
163
164    bool HandleBinding(StoreManager &SMgr, Store store,
165                       const MemRegion *region, SVal val) {
166
167      if (!isa<GlobalsSpaceRegion>(region->getMemorySpace()))
168        return true;
169
170      const MemRegion *vR = val.getAsRegion();
171      if (!vR)
172        return true;
173
174      // Under automated retain release, it is okay to assign a block
175      // directly to a global variable.
176      if (Ctx.getASTContext().getLangOpts().ObjCAutoRefCount &&
177          isa<BlockDataRegion>(vR))
178        return true;
179
180      if (const StackSpaceRegion *SSR =
181          dyn_cast<StackSpaceRegion>(vR->getMemorySpace())) {
182        // If the global variable holds a location in the current stack frame,
183        // record the binding to emit a warning.
184        if (SSR->getStackFrame() == CurSFC)
185          V.push_back(std::make_pair(region, vR));
186      }
187
188      return true;
189    }
190  };
191
192  CallBack cb(Ctx);
193  state->getStateManager().getStoreManager().iterBindings(state->getStore(),cb);
194
195  if (cb.V.empty())
196    return;
197
198  // Generate an error node.
199  ExplodedNode *N = Ctx.addTransition(state);
200  if (!N)
201    return;
202
203  if (!BT_stackleak)
204    BT_stackleak.reset(
205      new BuiltinBug("Stack address stored into global variable",
206                     "Stack address was saved into a global variable. "
207                     "This is dangerous because the address will become "
208                     "invalid after returning from the function"));
209
210  for (unsigned i = 0, e = cb.V.size(); i != e; ++i) {
211    // Generate a report for this bug.
212    SmallString<512> buf;
213    llvm::raw_svector_ostream os(buf);
214    SourceRange range = GenName(os, cb.V[i].second,
215                                Ctx.getSourceManager());
216    os << " is still referred to by the global variable '";
217    const VarRegion *VR = cast<VarRegion>(cb.V[i].first->getBaseRegion());
218    os << *VR->getDecl()
219       << "' upon returning to the caller.  This will be a dangling reference";
220    BugReport *report = new BugReport(*BT_stackleak, os.str(), N);
221    if (range.isValid())
222      report->addRange(range);
223
224    Ctx.EmitReport(report);
225  }
226}
227
228void ento::registerStackAddrEscapeChecker(CheckerManager &mgr) {
229  mgr.registerChecker<StackAddrEscapeChecker>();
230}
231