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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"
25 using namespace clang;
26 using namespace ento;
27 
28 namespace {
29 class 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 
34 public:
35   void checkPreStmt(const ReturnStmt *RS, CheckerContext &C) const;
36   void checkEndFunction(CheckerContext &Ctx) const;
37 private:
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 
genName(raw_ostream & os,const MemRegion * R,ASTContext & Ctx)45 SourceRange 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 
EmitStackError(CheckerContext & C,const MemRegion * R,const Expr * RetE) const95 void 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 
checkPreStmt(const ReturnStmt * RS,CheckerContext & C) const119 void 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 
checkEndFunction(CheckerContext & Ctx) const171 void 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 
registerStackAddrEscapeChecker(CheckerManager & mgr)256 void ento::registerStackAddrEscapeChecker(CheckerManager &mgr) {
257   mgr.registerChecker<StackAddrEscapeChecker>();
258 }
259