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/CallEvent.h" 22 #include "clang/StaticAnalyzer/Core/PathSensitive/CheckerContext.h" 23 #include "clang/StaticAnalyzer/Core/PathSensitive/ProgramState.h" 24 #include "llvm/ADT/SmallString.h" 25 #include "llvm/Support/raw_ostream.h" 26 using namespace clang; 27 using namespace ento; 28 29 namespace { 30 class StackAddrEscapeChecker 31 : public Checker<check::PreCall, check::PreStmt<ReturnStmt>, 32 check::EndFunction> { 33 mutable IdentifierInfo *dispatch_semaphore_tII; 34 mutable std::unique_ptr<BuiltinBug> BT_stackleak; 35 mutable std::unique_ptr<BuiltinBug> BT_returnstack; 36 mutable std::unique_ptr<BuiltinBug> BT_capturedstackasync; 37 mutable std::unique_ptr<BuiltinBug> BT_capturedstackret; 38 39 public: 40 void checkPreCall(const CallEvent &Call, CheckerContext &C) const; 41 void checkPreStmt(const ReturnStmt *RS, CheckerContext &C) const; 42 void checkEndFunction(CheckerContext &Ctx) const; 43 44 private: 45 void checkReturnedBlockCaptures(const BlockDataRegion &B, 46 CheckerContext &C) const; 47 void checkAsyncExecutedBlockCaptures(const BlockDataRegion &B, 48 CheckerContext &C) const; 49 void EmitStackError(CheckerContext &C, const MemRegion *R, 50 const Expr *RetE) const; 51 bool isSemaphoreCaptured(const BlockDecl &B) const; 52 static SourceRange genName(raw_ostream &os, const MemRegion *R, 53 ASTContext &Ctx); 54 static SmallVector<const MemRegion *, 4> 55 getCapturedStackRegions(const BlockDataRegion &B, CheckerContext &C); 56 static bool isArcManagedBlock(const MemRegion *R, CheckerContext &C); 57 static bool isNotInCurrentFrame(const MemRegion *R, CheckerContext &C); 58 }; 59 } // namespace 60 61 SourceRange StackAddrEscapeChecker::genName(raw_ostream &os, const MemRegion *R, 62 ASTContext &Ctx) { 63 // Get the base region, stripping away fields and elements. 64 R = R->getBaseRegion(); 65 SourceManager &SM = Ctx.getSourceManager(); 66 SourceRange range; 67 os << "Address of "; 68 69 // Check if the region is a compound literal. 70 if (const auto *CR = dyn_cast<CompoundLiteralRegion>(R)) { 71 const CompoundLiteralExpr *CL = CR->getLiteralExpr(); 72 os << "stack memory associated with a compound literal " 73 "declared on line " 74 << SM.getExpansionLineNumber(CL->getLocStart()) << " returned to caller"; 75 range = CL->getSourceRange(); 76 } else if (const auto *AR = dyn_cast<AllocaRegion>(R)) { 77 const Expr *ARE = AR->getExpr(); 78 SourceLocation L = ARE->getLocStart(); 79 range = ARE->getSourceRange(); 80 os << "stack memory allocated by call to alloca() on line " 81 << SM.getExpansionLineNumber(L); 82 } else if (const auto *BR = dyn_cast<BlockDataRegion>(R)) { 83 const BlockDecl *BD = BR->getCodeRegion()->getDecl(); 84 SourceLocation L = BD->getLocStart(); 85 range = BD->getSourceRange(); 86 os << "stack-allocated block declared on line " 87 << SM.getExpansionLineNumber(L); 88 } else if (const auto *VR = dyn_cast<VarRegion>(R)) { 89 os << "stack memory associated with local variable '" << VR->getString() 90 << '\''; 91 range = VR->getDecl()->getSourceRange(); 92 } else if (const auto *TOR = dyn_cast<CXXTempObjectRegion>(R)) { 93 QualType Ty = TOR->getValueType().getLocalUnqualifiedType(); 94 os << "stack memory associated with temporary object of type '"; 95 Ty.print(os, Ctx.getPrintingPolicy()); 96 os << "'"; 97 range = TOR->getExpr()->getSourceRange(); 98 } else { 99 llvm_unreachable("Invalid region in ReturnStackAddressChecker."); 100 } 101 102 return range; 103 } 104 105 bool StackAddrEscapeChecker::isArcManagedBlock(const MemRegion *R, 106 CheckerContext &C) { 107 assert(R && "MemRegion should not be null"); 108 return C.getASTContext().getLangOpts().ObjCAutoRefCount && 109 isa<BlockDataRegion>(R); 110 } 111 112 bool StackAddrEscapeChecker::isNotInCurrentFrame(const MemRegion *R, 113 CheckerContext &C) { 114 const StackSpaceRegion *S = cast<StackSpaceRegion>(R->getMemorySpace()); 115 return S->getStackFrame() != C.getLocationContext()->getCurrentStackFrame(); 116 } 117 118 bool StackAddrEscapeChecker::isSemaphoreCaptured(const BlockDecl &B) const { 119 if (!dispatch_semaphore_tII) 120 dispatch_semaphore_tII = &B.getASTContext().Idents.get("dispatch_semaphore_t"); 121 for (const auto &C : B.captures()) { 122 const auto *T = C.getVariable()->getType()->getAs<TypedefType>(); 123 if (T && T->getDecl()->getIdentifier() == dispatch_semaphore_tII) 124 return true; 125 } 126 return false; 127 } 128 129 SmallVector<const MemRegion *, 4> 130 StackAddrEscapeChecker::getCapturedStackRegions(const BlockDataRegion &B, 131 CheckerContext &C) { 132 SmallVector<const MemRegion *, 4> Regions; 133 BlockDataRegion::referenced_vars_iterator I = B.referenced_vars_begin(); 134 BlockDataRegion::referenced_vars_iterator E = B.referenced_vars_end(); 135 for (; I != E; ++I) { 136 SVal Val = C.getState()->getSVal(I.getCapturedRegion()); 137 const MemRegion *Region = Val.getAsRegion(); 138 if (Region && isa<StackSpaceRegion>(Region->getMemorySpace())) 139 Regions.push_back(Region); 140 } 141 return Regions; 142 } 143 144 void StackAddrEscapeChecker::EmitStackError(CheckerContext &C, 145 const MemRegion *R, 146 const Expr *RetE) const { 147 ExplodedNode *N = C.generateNonFatalErrorNode(); 148 if (!N) 149 return; 150 if (!BT_returnstack) 151 BT_returnstack = llvm::make_unique<BuiltinBug>( 152 this, "Return of address to stack-allocated memory"); 153 // Generate a report for this bug. 154 SmallString<128> buf; 155 llvm::raw_svector_ostream os(buf); 156 SourceRange range = genName(os, R, C.getASTContext()); 157 os << " returned to caller"; 158 auto report = llvm::make_unique<BugReport>(*BT_returnstack, os.str(), N); 159 report->addRange(RetE->getSourceRange()); 160 if (range.isValid()) 161 report->addRange(range); 162 C.emitReport(std::move(report)); 163 } 164 165 void StackAddrEscapeChecker::checkAsyncExecutedBlockCaptures( 166 const BlockDataRegion &B, CheckerContext &C) const { 167 // There is a not-too-uncommon idiom 168 // where a block passed to dispatch_async captures a semaphore 169 // and then the thread (which called dispatch_async) is blocked on waiting 170 // for the completion of the execution of the block 171 // via dispatch_semaphore_wait. To avoid false-positives (for now) 172 // we ignore all the blocks which have captured 173 // a variable of the type "dispatch_semaphore_t". 174 if (isSemaphoreCaptured(*B.getDecl())) 175 return; 176 for (const MemRegion *Region : getCapturedStackRegions(B, C)) { 177 // The block passed to dispatch_async may capture another block 178 // created on the stack. However, there is no leak in this situaton, 179 // no matter if ARC or no ARC is enabled: 180 // dispatch_async copies the passed "outer" block (via Block_copy) 181 // and if the block has captured another "inner" block, 182 // the "inner" block will be copied as well. 183 if (isa<BlockDataRegion>(Region)) 184 continue; 185 ExplodedNode *N = C.generateNonFatalErrorNode(); 186 if (!N) 187 continue; 188 if (!BT_capturedstackasync) 189 BT_capturedstackasync = llvm::make_unique<BuiltinBug>( 190 this, "Address of stack-allocated memory is captured"); 191 SmallString<128> Buf; 192 llvm::raw_svector_ostream Out(Buf); 193 SourceRange Range = genName(Out, Region, C.getASTContext()); 194 Out << " is captured by an asynchronously-executed block"; 195 auto Report = 196 llvm::make_unique<BugReport>(*BT_capturedstackasync, Out.str(), N); 197 if (Range.isValid()) 198 Report->addRange(Range); 199 C.emitReport(std::move(Report)); 200 } 201 } 202 203 void StackAddrEscapeChecker::checkReturnedBlockCaptures( 204 const BlockDataRegion &B, CheckerContext &C) const { 205 for (const MemRegion *Region : getCapturedStackRegions(B, C)) { 206 if (isArcManagedBlock(Region, C) || isNotInCurrentFrame(Region, C)) 207 continue; 208 ExplodedNode *N = C.generateNonFatalErrorNode(); 209 if (!N) 210 continue; 211 if (!BT_capturedstackret) 212 BT_capturedstackret = llvm::make_unique<BuiltinBug>( 213 this, "Address of stack-allocated memory is captured"); 214 SmallString<128> Buf; 215 llvm::raw_svector_ostream Out(Buf); 216 SourceRange Range = genName(Out, Region, C.getASTContext()); 217 Out << " is captured by a returned block"; 218 auto Report = 219 llvm::make_unique<BugReport>(*BT_capturedstackret, Out.str(), N); 220 if (Range.isValid()) 221 Report->addRange(Range); 222 C.emitReport(std::move(Report)); 223 } 224 } 225 226 void StackAddrEscapeChecker::checkPreCall(const CallEvent &Call, 227 CheckerContext &C) const { 228 if (!Call.isGlobalCFunction("dispatch_after") && 229 !Call.isGlobalCFunction("dispatch_async")) 230 return; 231 for (unsigned Idx = 0, NumArgs = Call.getNumArgs(); Idx < NumArgs; ++Idx) { 232 if (const BlockDataRegion *B = dyn_cast_or_null<BlockDataRegion>( 233 Call.getArgSVal(Idx).getAsRegion())) 234 checkAsyncExecutedBlockCaptures(*B, C); 235 } 236 } 237 238 void StackAddrEscapeChecker::checkPreStmt(const ReturnStmt *RS, 239 CheckerContext &C) const { 240 241 const Expr *RetE = RS->getRetValue(); 242 if (!RetE) 243 return; 244 RetE = RetE->IgnoreParens(); 245 246 const LocationContext *LCtx = C.getLocationContext(); 247 SVal V = C.getState()->getSVal(RetE, LCtx); 248 const MemRegion *R = V.getAsRegion(); 249 if (!R) 250 return; 251 252 if (const BlockDataRegion *B = dyn_cast<BlockDataRegion>(R)) 253 checkReturnedBlockCaptures(*B, C); 254 255 if (!isa<StackSpaceRegion>(R->getMemorySpace()) || 256 isNotInCurrentFrame(R, C) || isArcManagedBlock(R, C)) 257 return; 258 259 // Returning a record by value is fine. (In this case, the returned 260 // expression will be a copy-constructor, possibly wrapped in an 261 // ExprWithCleanups node.) 262 if (const ExprWithCleanups *Cleanup = dyn_cast<ExprWithCleanups>(RetE)) 263 RetE = Cleanup->getSubExpr(); 264 if (isa<CXXConstructExpr>(RetE) && RetE->getType()->isRecordType()) 265 return; 266 267 // The CK_CopyAndAutoreleaseBlockObject cast causes the block to be copied 268 // so the stack address is not escaping here. 269 if (auto *ICE = dyn_cast<ImplicitCastExpr>(RetE)) { 270 if (isa<BlockDataRegion>(R) && 271 ICE->getCastKind() == CK_CopyAndAutoreleaseBlockObject) { 272 return; 273 } 274 } 275 276 EmitStackError(C, R, RetE); 277 } 278 279 void StackAddrEscapeChecker::checkEndFunction(CheckerContext &Ctx) const { 280 ProgramStateRef State = Ctx.getState(); 281 282 // Iterate over all bindings to global variables and see if it contains 283 // a memory region in the stack space. 284 class CallBack : public StoreManager::BindingsHandler { 285 private: 286 CheckerContext &Ctx; 287 const StackFrameContext *CurSFC; 288 289 public: 290 SmallVector<std::pair<const MemRegion *, const MemRegion *>, 10> V; 291 292 CallBack(CheckerContext &CC) 293 : Ctx(CC), CurSFC(CC.getLocationContext()->getCurrentStackFrame()) {} 294 295 bool HandleBinding(StoreManager &SMgr, Store S, const MemRegion *Region, 296 SVal Val) override { 297 298 if (!isa<GlobalsSpaceRegion>(Region->getMemorySpace())) 299 return true; 300 const MemRegion *VR = Val.getAsRegion(); 301 if (VR && isa<StackSpaceRegion>(VR->getMemorySpace()) && 302 !isArcManagedBlock(VR, Ctx) && !isNotInCurrentFrame(VR, Ctx)) 303 V.emplace_back(Region, VR); 304 return true; 305 } 306 }; 307 308 CallBack Cb(Ctx); 309 State->getStateManager().getStoreManager().iterBindings(State->getStore(), 310 Cb); 311 312 if (Cb.V.empty()) 313 return; 314 315 // Generate an error node. 316 ExplodedNode *N = Ctx.generateNonFatalErrorNode(State); 317 if (!N) 318 return; 319 320 if (!BT_stackleak) 321 BT_stackleak = llvm::make_unique<BuiltinBug>( 322 this, "Stack address stored into global variable", 323 "Stack address was saved into a global variable. " 324 "This is dangerous because the address will become " 325 "invalid after returning from the function"); 326 327 for (const auto &P : Cb.V) { 328 // Generate a report for this bug. 329 SmallString<128> Buf; 330 llvm::raw_svector_ostream Out(Buf); 331 SourceRange Range = genName(Out, P.second, Ctx.getASTContext()); 332 Out << " is still referred to by the "; 333 if (isa<StaticGlobalSpaceRegion>(P.first->getMemorySpace())) 334 Out << "static"; 335 else 336 Out << "global"; 337 Out << " variable '"; 338 const VarRegion *VR = cast<VarRegion>(P.first->getBaseRegion()); 339 Out << *VR->getDecl() 340 << "' upon returning to the caller. This will be a dangling reference"; 341 auto Report = llvm::make_unique<BugReport>(*BT_stackleak, Out.str(), N); 342 if (Range.isValid()) 343 Report->addRange(Range); 344 345 Ctx.emitReport(std::move(Report)); 346 } 347 } 348 349 void ento::registerStackAddrEscapeChecker(CheckerManager &Mgr) { 350 Mgr.registerChecker<StackAddrEscapeChecker>(); 351 } 352