1 //=== StdLibraryFunctionsChecker.cpp - Model standard functions -*- 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 checker improves modeling of a few simple library functions. 10 // 11 // This checker provides a specification format - `Summary' - and 12 // contains descriptions of some library functions in this format. Each 13 // specification contains a list of branches for splitting the program state 14 // upon call, and range constraints on argument and return-value symbols that 15 // are satisfied on each branch. This spec can be expanded to include more 16 // items, like external effects of the function. 17 // 18 // The main difference between this approach and the body farms technique is 19 // in more explicit control over how many branches are produced. For example, 20 // consider standard C function `ispunct(int x)', which returns a non-zero value 21 // iff `x' is a punctuation character, that is, when `x' is in range 22 // ['!', '/'] [':', '@'] U ['[', '\`'] U ['{', '~']. 23 // `Summary' provides only two branches for this function. However, 24 // any attempt to describe this range with if-statements in the body farm 25 // would result in many more branches. Because each branch needs to be analyzed 26 // independently, this significantly reduces performance. Additionally, 27 // once we consider a branch on which `x' is in range, say, ['!', '/'], 28 // we assume that such branch is an important separate path through the program, 29 // which may lead to false positives because considering this particular path 30 // was not consciously intended, and therefore it might have been unreachable. 31 // 32 // This checker uses eval::Call for modeling pure functions (functions without 33 // side effets), for which their `Summary' is a precise model. This avoids 34 // unnecessary invalidation passes. Conflicts with other checkers are unlikely 35 // because if the function has no other effects, other checkers would probably 36 // never want to improve upon the modeling done by this checker. 37 // 38 // Non-pure functions, for which only partial improvement over the default 39 // behavior is expected, are modeled via check::PostCall, non-intrusively. 40 // 41 // The following standard C functions are currently supported: 42 // 43 // fgetc getline isdigit isupper 44 // fread isalnum isgraph isxdigit 45 // fwrite isalpha islower read 46 // getc isascii isprint write 47 // getchar isblank ispunct 48 // getdelim iscntrl isspace 49 // 50 //===----------------------------------------------------------------------===// 51 52 #include "clang/StaticAnalyzer/Checkers/BuiltinCheckerRegistration.h" 53 #include "clang/StaticAnalyzer/Core/BugReporter/BugType.h" 54 #include "clang/StaticAnalyzer/Core/Checker.h" 55 #include "clang/StaticAnalyzer/Core/CheckerManager.h" 56 #include "clang/StaticAnalyzer/Core/PathSensitive/CallEvent.h" 57 #include "clang/StaticAnalyzer/Core/PathSensitive/CheckerContext.h" 58 #include "clang/StaticAnalyzer/Core/PathSensitive/CheckerHelpers.h" 59 60 using namespace clang; 61 using namespace clang::ento; 62 63 namespace { 64 class StdLibraryFunctionsChecker 65 : public Checker<check::PreCall, check::PostCall, eval::Call> { 66 /// Below is a series of typedefs necessary to define function specs. 67 /// We avoid nesting types here because each additional qualifier 68 /// would need to be repeated in every function spec. 69 struct Summary; 70 71 /// Specify how much the analyzer engine should entrust modeling this function 72 /// to us. If he doesn't, he performs additional invalidations. 73 enum InvalidationKind { NoEvalCall, EvalCallAsPure }; 74 75 // The universal integral type to use in value range descriptions. 76 // Unsigned to make sure overflows are well-defined. 77 typedef uint64_t RangeInt; 78 79 /// Normally, describes a single range constraint, eg. {{0, 1}, {3, 4}} is 80 /// a non-negative integer, which less than 5 and not equal to 2. For 81 /// `ComparesToArgument', holds information about how exactly to compare to 82 /// the argument. 83 typedef std::vector<std::pair<RangeInt, RangeInt>> IntRangeVector; 84 85 /// A reference to an argument or return value by its number. 86 /// ArgNo in CallExpr and CallEvent is defined as Unsigned, but 87 /// obviously uint32_t should be enough for all practical purposes. 88 typedef uint32_t ArgNo; 89 static const ArgNo Ret; 90 91 class ValueConstraint; 92 93 // Pointer to the ValueConstraint. We need a copyable, polymorphic and 94 // default initialize able type (vector needs that). A raw pointer was good, 95 // however, we cannot default initialize that. unique_ptr makes the Summary 96 // class non-copyable, therefore not an option. Releasing the copyability 97 // requirement would render the initialization of the Summary map infeasible. 98 using ValueConstraintPtr = std::shared_ptr<ValueConstraint>; 99 100 /// Polymorphic base class that represents a constraint on a given argument 101 /// (or return value) of a function. Derived classes implement different kind 102 /// of constraints, e.g range constraints or correlation between two 103 /// arguments. 104 class ValueConstraint { 105 public: 106 ValueConstraint(ArgNo ArgN) : ArgN(ArgN) {} 107 virtual ~ValueConstraint() {} 108 /// Apply the effects of the constraint on the given program state. If null 109 /// is returned then the constraint is not feasible. 110 virtual ProgramStateRef apply(ProgramStateRef State, const CallEvent &Call, 111 const Summary &Summary) const = 0; 112 virtual ValueConstraintPtr negate() const { 113 llvm_unreachable("Not implemented"); 114 }; 115 ArgNo getArgNo() const { return ArgN; } 116 117 protected: 118 ArgNo ArgN; // Argument to which we apply the constraint. 119 }; 120 121 /// Given a range, should the argument stay inside or outside this range? 122 enum RangeKind { OutOfRange, WithinRange }; 123 124 /// Encapsulates a single range on a single symbol within a branch. 125 class RangeConstraint : public ValueConstraint { 126 RangeKind Kind; // Kind of range definition. 127 IntRangeVector Args; // Polymorphic arguments. 128 129 public: 130 RangeConstraint(ArgNo ArgN, RangeKind Kind, const IntRangeVector &Args) 131 : ValueConstraint(ArgN), Kind(Kind), Args(Args) {} 132 133 const IntRangeVector &getRanges() const { 134 return Args; 135 } 136 137 private: 138 ProgramStateRef applyAsOutOfRange(ProgramStateRef State, 139 const CallEvent &Call, 140 const Summary &Summary) const; 141 ProgramStateRef applyAsWithinRange(ProgramStateRef State, 142 const CallEvent &Call, 143 const Summary &Summary) const; 144 public: 145 ProgramStateRef apply(ProgramStateRef State, const CallEvent &Call, 146 const Summary &Summary) const override { 147 switch (Kind) { 148 case OutOfRange: 149 return applyAsOutOfRange(State, Call, Summary); 150 case WithinRange: 151 return applyAsWithinRange(State, Call, Summary); 152 } 153 llvm_unreachable("Unknown range kind!"); 154 } 155 156 ValueConstraintPtr negate() const override { 157 RangeConstraint Tmp(*this); 158 switch (Kind) { 159 case OutOfRange: 160 Tmp.Kind = WithinRange; 161 break; 162 case WithinRange: 163 Tmp.Kind = OutOfRange; 164 break; 165 } 166 return std::make_shared<RangeConstraint>(Tmp); 167 } 168 }; 169 170 class ComparisonConstraint : public ValueConstraint { 171 BinaryOperator::Opcode Opcode; 172 ArgNo OtherArgN; 173 174 public: 175 ComparisonConstraint(ArgNo ArgN, BinaryOperator::Opcode Opcode, 176 ArgNo OtherArgN) 177 : ValueConstraint(ArgN), Opcode(Opcode), OtherArgN(OtherArgN) {} 178 ArgNo getOtherArgNo() const { return OtherArgN; } 179 BinaryOperator::Opcode getOpcode() const { return Opcode; } 180 ProgramStateRef apply(ProgramStateRef State, const CallEvent &Call, 181 const Summary &Summary) const override; 182 }; 183 184 class NotNullConstraint : public ValueConstraint { 185 using ValueConstraint::ValueConstraint; 186 // This variable has a role when we negate the constraint. 187 bool CannotBeNull = true; 188 189 public: 190 ProgramStateRef apply(ProgramStateRef State, const CallEvent &Call, 191 const Summary &Summary) const override { 192 SVal V = getArgSVal(Call, getArgNo()); 193 if (V.isUndef()) 194 return State; 195 196 DefinedOrUnknownSVal L = V.castAs<DefinedOrUnknownSVal>(); 197 if (!L.getAs<Loc>()) 198 return State; 199 200 return State->assume(L, CannotBeNull); 201 } 202 203 ValueConstraintPtr negate() const override { 204 NotNullConstraint Tmp(*this); 205 Tmp.CannotBeNull = !this->CannotBeNull; 206 return std::make_shared<NotNullConstraint>(Tmp); 207 } 208 }; 209 210 /// The complete list of constraints that defines a single branch. 211 typedef std::vector<ValueConstraintPtr> ConstraintSet; 212 213 using ArgTypes = std::vector<QualType>; 214 using Cases = std::vector<ConstraintSet>; 215 216 /// Includes information about 217 /// * function prototype (which is necessary to 218 /// ensure we're modeling the right function and casting values properly), 219 /// * approach to invalidation, 220 /// * a list of branches - a list of list of ranges - 221 /// A branch represents a path in the exploded graph of a function (which 222 /// is a tree). So, a branch is a series of assumptions. In other words, 223 /// branches represent split states and additional assumptions on top of 224 /// the splitting assumption. 225 /// For example, consider the branches in `isalpha(x)` 226 /// Branch 1) 227 /// x is in range ['A', 'Z'] or in ['a', 'z'] 228 /// then the return value is not 0. (I.e. out-of-range [0, 0]) 229 /// Branch 2) 230 /// x is out-of-range ['A', 'Z'] and out-of-range ['a', 'z'] 231 /// then the return value is 0. 232 /// * a list of argument constraints, that must be true on every branch. 233 /// If these constraints are not satisfied that means a fatal error 234 /// usually resulting in undefined behaviour. 235 struct Summary { 236 const ArgTypes ArgTys; 237 const QualType RetTy; 238 const InvalidationKind InvalidationKd; 239 Cases CaseConstraints; 240 ConstraintSet ArgConstraints; 241 242 Summary(ArgTypes ArgTys, QualType RetTy, InvalidationKind InvalidationKd) 243 : ArgTys(ArgTys), RetTy(RetTy), InvalidationKd(InvalidationKd) {} 244 245 Summary &Case(ConstraintSet&& CS) { 246 CaseConstraints.push_back(std::move(CS)); 247 return *this; 248 } 249 Summary &ArgConstraint(ValueConstraintPtr VC) { 250 ArgConstraints.push_back(VC); 251 return *this; 252 } 253 254 private: 255 static void assertTypeSuitableForSummary(QualType T) { 256 assert(!T->isVoidType() && 257 "We should have had no significant void types in the spec"); 258 assert(T.isCanonical() && 259 "We should only have canonical types in the spec"); 260 } 261 262 public: 263 QualType getArgType(ArgNo ArgN) const { 264 QualType T = (ArgN == Ret) ? RetTy : ArgTys[ArgN]; 265 assertTypeSuitableForSummary(T); 266 return T; 267 } 268 269 /// Try our best to figure out if the summary's signature matches 270 /// *the* library function to which this specification applies. 271 bool matchesSignature(const FunctionDecl *FD) const; 272 }; 273 274 // The map of all functions supported by the checker. It is initialized 275 // lazily, and it doesn't change after initialization. 276 using FunctionSummaryMapType = llvm::DenseMap<const FunctionDecl *, Summary>; 277 mutable FunctionSummaryMapType FunctionSummaryMap; 278 279 mutable std::unique_ptr<BugType> BT_InvalidArg; 280 281 // Auxiliary functions to support ArgNo within all structures 282 // in a unified manner. 283 static QualType getArgType(const Summary &Summary, ArgNo ArgN) { 284 return Summary.getArgType(ArgN); 285 } 286 static SVal getArgSVal(const CallEvent &Call, ArgNo ArgN) { 287 return ArgN == Ret ? Call.getReturnValue() : Call.getArgSVal(ArgN); 288 } 289 290 public: 291 void checkPreCall(const CallEvent &Call, CheckerContext &C) const; 292 void checkPostCall(const CallEvent &Call, CheckerContext &C) const; 293 bool evalCall(const CallEvent &Call, CheckerContext &C) const; 294 295 enum CheckKind { 296 CK_StdCLibraryFunctionArgsChecker, 297 CK_StdCLibraryFunctionsTesterChecker, 298 CK_NumCheckKinds 299 }; 300 DefaultBool ChecksEnabled[CK_NumCheckKinds]; 301 CheckerNameRef CheckNames[CK_NumCheckKinds]; 302 303 bool DisplayLoadedSummaries = false; 304 305 private: 306 Optional<Summary> findFunctionSummary(const FunctionDecl *FD, 307 CheckerContext &C) const; 308 Optional<Summary> findFunctionSummary(const CallEvent &Call, 309 CheckerContext &C) const; 310 311 void initFunctionSummaries(CheckerContext &C) const; 312 313 void reportBug(const CallEvent &Call, ExplodedNode *N, 314 CheckerContext &C) const { 315 if (!ChecksEnabled[CK_StdCLibraryFunctionArgsChecker]) 316 return; 317 // TODO Add detailed diagnostic. 318 StringRef Msg = "Function argument constraint is not satisfied"; 319 if (!BT_InvalidArg) 320 BT_InvalidArg = std::make_unique<BugType>( 321 CheckNames[CK_StdCLibraryFunctionArgsChecker], 322 "Unsatisfied argument constraints", categories::LogicError); 323 auto R = std::make_unique<PathSensitiveBugReport>(*BT_InvalidArg, Msg, N); 324 bugreporter::trackExpressionValue(N, Call.getArgExpr(0), *R); 325 C.emitReport(std::move(R)); 326 } 327 }; 328 329 const StdLibraryFunctionsChecker::ArgNo StdLibraryFunctionsChecker::Ret = 330 std::numeric_limits<ArgNo>::max(); 331 332 } // end of anonymous namespace 333 334 ProgramStateRef StdLibraryFunctionsChecker::RangeConstraint::applyAsOutOfRange( 335 ProgramStateRef State, const CallEvent &Call, 336 const Summary &Summary) const { 337 338 ProgramStateManager &Mgr = State->getStateManager(); 339 SValBuilder &SVB = Mgr.getSValBuilder(); 340 BasicValueFactory &BVF = SVB.getBasicValueFactory(); 341 ConstraintManager &CM = Mgr.getConstraintManager(); 342 QualType T = getArgType(Summary, getArgNo()); 343 SVal V = getArgSVal(Call, getArgNo()); 344 345 if (auto N = V.getAs<NonLoc>()) { 346 const IntRangeVector &R = getRanges(); 347 size_t E = R.size(); 348 for (size_t I = 0; I != E; ++I) { 349 const llvm::APSInt &Min = BVF.getValue(R[I].first, T); 350 const llvm::APSInt &Max = BVF.getValue(R[I].second, T); 351 assert(Min <= Max); 352 State = CM.assumeInclusiveRange(State, *N, Min, Max, false); 353 if (!State) 354 break; 355 } 356 } 357 358 return State; 359 } 360 361 ProgramStateRef StdLibraryFunctionsChecker::RangeConstraint::applyAsWithinRange( 362 ProgramStateRef State, const CallEvent &Call, 363 const Summary &Summary) const { 364 365 ProgramStateManager &Mgr = State->getStateManager(); 366 SValBuilder &SVB = Mgr.getSValBuilder(); 367 BasicValueFactory &BVF = SVB.getBasicValueFactory(); 368 ConstraintManager &CM = Mgr.getConstraintManager(); 369 QualType T = getArgType(Summary, getArgNo()); 370 SVal V = getArgSVal(Call, getArgNo()); 371 372 // "WithinRange R" is treated as "outside [T_MIN, T_MAX] \ R". 373 // We cut off [T_MIN, min(R) - 1] and [max(R) + 1, T_MAX] if necessary, 374 // and then cut away all holes in R one by one. 375 // 376 // E.g. consider a range list R as [A, B] and [C, D] 377 // -------+--------+------------------+------------+-----------> 378 // A B C D 379 // Then we assume that the value is not in [-inf, A - 1], 380 // then not in [D + 1, +inf], then not in [B + 1, C - 1] 381 if (auto N = V.getAs<NonLoc>()) { 382 const IntRangeVector &R = getRanges(); 383 size_t E = R.size(); 384 385 const llvm::APSInt &MinusInf = BVF.getMinValue(T); 386 const llvm::APSInt &PlusInf = BVF.getMaxValue(T); 387 388 const llvm::APSInt &Left = BVF.getValue(R[0].first - 1ULL, T); 389 if (Left != PlusInf) { 390 assert(MinusInf <= Left); 391 State = CM.assumeInclusiveRange(State, *N, MinusInf, Left, false); 392 if (!State) 393 return nullptr; 394 } 395 396 const llvm::APSInt &Right = BVF.getValue(R[E - 1].second + 1ULL, T); 397 if (Right != MinusInf) { 398 assert(Right <= PlusInf); 399 State = CM.assumeInclusiveRange(State, *N, Right, PlusInf, false); 400 if (!State) 401 return nullptr; 402 } 403 404 for (size_t I = 1; I != E; ++I) { 405 const llvm::APSInt &Min = BVF.getValue(R[I - 1].second + 1ULL, T); 406 const llvm::APSInt &Max = BVF.getValue(R[I].first - 1ULL, T); 407 if (Min <= Max) { 408 State = CM.assumeInclusiveRange(State, *N, Min, Max, false); 409 if (!State) 410 return nullptr; 411 } 412 } 413 } 414 415 return State; 416 } 417 418 ProgramStateRef StdLibraryFunctionsChecker::ComparisonConstraint::apply( 419 ProgramStateRef State, const CallEvent &Call, 420 const Summary &Summary) const { 421 422 ProgramStateManager &Mgr = State->getStateManager(); 423 SValBuilder &SVB = Mgr.getSValBuilder(); 424 QualType CondT = SVB.getConditionType(); 425 QualType T = getArgType(Summary, getArgNo()); 426 SVal V = getArgSVal(Call, getArgNo()); 427 428 BinaryOperator::Opcode Op = getOpcode(); 429 ArgNo OtherArg = getOtherArgNo(); 430 SVal OtherV = getArgSVal(Call, OtherArg); 431 QualType OtherT = getArgType(Summary, OtherArg); 432 // Note: we avoid integral promotion for comparison. 433 OtherV = SVB.evalCast(OtherV, T, OtherT); 434 if (auto CompV = SVB.evalBinOp(State, Op, V, OtherV, CondT) 435 .getAs<DefinedOrUnknownSVal>()) 436 State = State->assume(*CompV, true); 437 return State; 438 } 439 440 void StdLibraryFunctionsChecker::checkPreCall(const CallEvent &Call, 441 CheckerContext &C) const { 442 Optional<Summary> FoundSummary = findFunctionSummary(Call, C); 443 if (!FoundSummary) 444 return; 445 446 const Summary &Summary = *FoundSummary; 447 ProgramStateRef State = C.getState(); 448 449 ProgramStateRef NewState = State; 450 for (const ValueConstraintPtr& VC : Summary.ArgConstraints) { 451 ProgramStateRef SuccessSt = VC->apply(NewState, Call, Summary); 452 ProgramStateRef FailureSt = VC->negate()->apply(NewState, Call, Summary); 453 // The argument constraint is not satisfied. 454 if (FailureSt && !SuccessSt) { 455 if (ExplodedNode *N = C.generateErrorNode(NewState)) 456 reportBug(Call, N, C); 457 break; 458 } else { 459 // We will apply the constraint even if we cannot reason about the 460 // argument. This means both SuccessSt and FailureSt can be true. If we 461 // weren't applying the constraint that would mean that symbolic 462 // execution continues on a code whose behaviour is undefined. 463 assert(SuccessSt); 464 NewState = SuccessSt; 465 } 466 } 467 if (NewState && NewState != State) 468 C.addTransition(NewState); 469 } 470 471 void StdLibraryFunctionsChecker::checkPostCall(const CallEvent &Call, 472 CheckerContext &C) const { 473 Optional<Summary> FoundSummary = findFunctionSummary(Call, C); 474 if (!FoundSummary) 475 return; 476 477 // Now apply the constraints. 478 const Summary &Summary = *FoundSummary; 479 ProgramStateRef State = C.getState(); 480 481 // Apply case/branch specifications. 482 for (const auto &VRS : Summary.CaseConstraints) { 483 ProgramStateRef NewState = State; 484 for (const auto &VR: VRS) { 485 NewState = VR->apply(NewState, Call, Summary); 486 if (!NewState) 487 break; 488 } 489 490 if (NewState && NewState != State) 491 C.addTransition(NewState); 492 } 493 } 494 495 bool StdLibraryFunctionsChecker::evalCall(const CallEvent &Call, 496 CheckerContext &C) const { 497 Optional<Summary> FoundSummary = findFunctionSummary(Call, C); 498 if (!FoundSummary) 499 return false; 500 501 const Summary &Summary = *FoundSummary; 502 switch (Summary.InvalidationKd) { 503 case EvalCallAsPure: { 504 ProgramStateRef State = C.getState(); 505 const LocationContext *LC = C.getLocationContext(); 506 const auto *CE = cast_or_null<CallExpr>(Call.getOriginExpr()); 507 SVal V = C.getSValBuilder().conjureSymbolVal( 508 CE, LC, CE->getType().getCanonicalType(), C.blockCount()); 509 State = State->BindExpr(CE, LC, V); 510 C.addTransition(State); 511 return true; 512 } 513 case NoEvalCall: 514 // Summary tells us to avoid performing eval::Call. The function is possibly 515 // evaluated by another checker, or evaluated conservatively. 516 return false; 517 } 518 llvm_unreachable("Unknown invalidation kind!"); 519 } 520 521 bool StdLibraryFunctionsChecker::Summary::matchesSignature( 522 const FunctionDecl *FD) const { 523 // Check number of arguments: 524 if (FD->param_size() != ArgTys.size()) 525 return false; 526 527 // Check return type if relevant: 528 if (!RetTy.isNull() && RetTy != FD->getReturnType().getCanonicalType()) 529 return false; 530 531 // Check argument types when relevant: 532 for (size_t I = 0, E = ArgTys.size(); I != E; ++I) { 533 QualType FormalT = ArgTys[I]; 534 // Null type marks irrelevant arguments. 535 if (FormalT.isNull()) 536 continue; 537 538 assertTypeSuitableForSummary(FormalT); 539 540 QualType ActualT = FD->getParamDecl(I)->getType().getCanonicalType(); 541 if (ActualT != FormalT) 542 return false; 543 } 544 545 return true; 546 } 547 548 Optional<StdLibraryFunctionsChecker::Summary> 549 StdLibraryFunctionsChecker::findFunctionSummary(const FunctionDecl *FD, 550 CheckerContext &C) const { 551 if (!FD) 552 return None; 553 554 initFunctionSummaries(C); 555 556 auto FSMI = FunctionSummaryMap.find(FD->getCanonicalDecl()); 557 if (FSMI == FunctionSummaryMap.end()) 558 return None; 559 return FSMI->second; 560 } 561 562 Optional<StdLibraryFunctionsChecker::Summary> 563 StdLibraryFunctionsChecker::findFunctionSummary(const CallEvent &Call, 564 CheckerContext &C) const { 565 const FunctionDecl *FD = dyn_cast_or_null<FunctionDecl>(Call.getDecl()); 566 if (!FD) 567 return None; 568 return findFunctionSummary(FD, C); 569 } 570 571 void StdLibraryFunctionsChecker::initFunctionSummaries( 572 CheckerContext &C) const { 573 if (!FunctionSummaryMap.empty()) 574 return; 575 576 SValBuilder &SVB = C.getSValBuilder(); 577 BasicValueFactory &BVF = SVB.getBasicValueFactory(); 578 const ASTContext &ACtx = BVF.getContext(); 579 580 // These types are useful for writing specifications quickly, 581 // New specifications should probably introduce more types. 582 // Some types are hard to obtain from the AST, eg. "ssize_t". 583 // In such cases it should be possible to provide multiple variants 584 // of function summary for common cases (eg. ssize_t could be int or long 585 // or long long, so three summary variants would be enough). 586 // Of course, function variants are also useful for C++ overloads. 587 const QualType 588 Irrelevant{}; // A placeholder, whenever we do not care about the type. 589 const QualType IntTy = ACtx.IntTy; 590 const QualType LongTy = ACtx.LongTy; 591 const QualType LongLongTy = ACtx.LongLongTy; 592 const QualType SizeTy = ACtx.getSizeType(); 593 const QualType VoidPtrTy = ACtx.VoidPtrTy; // void * 594 const QualType VoidPtrRestrictTy = 595 ACtx.getRestrictType(VoidPtrTy); // void *restrict 596 const QualType ConstVoidPtrTy = 597 ACtx.getPointerType(ACtx.VoidTy.withConst()); // const void * 598 const QualType ConstCharPtrTy = 599 ACtx.getPointerType(ACtx.CharTy.withConst()); // const char * 600 const QualType ConstVoidPtrRestrictTy = 601 ACtx.getRestrictType(ConstVoidPtrTy); // const void *restrict 602 603 const RangeInt IntMax = BVF.getMaxValue(IntTy).getLimitedValue(); 604 const RangeInt LongMax = BVF.getMaxValue(LongTy).getLimitedValue(); 605 const RangeInt LongLongMax = BVF.getMaxValue(LongLongTy).getLimitedValue(); 606 607 // Set UCharRangeMax to min of int or uchar maximum value. 608 // The C standard states that the arguments of functions like isalpha must 609 // be representable as an unsigned char. Their type is 'int', so the max 610 // value of the argument should be min(UCharMax, IntMax). This just happen 611 // to be true for commonly used and well tested instruction set 612 // architectures, but not for others. 613 const RangeInt UCharRangeMax = 614 std::min(BVF.getMaxValue(ACtx.UnsignedCharTy).getLimitedValue(), IntMax); 615 616 // The platform dependent value of EOF. 617 // Try our best to parse this from the Preprocessor, otherwise fallback to -1. 618 const auto EOFv = [&C]() -> RangeInt { 619 if (const llvm::Optional<int> OptInt = 620 tryExpandAsInteger("EOF", C.getPreprocessor())) 621 return *OptInt; 622 return -1; 623 }(); 624 625 // Auxiliary class to aid adding summaries to the summary map. 626 struct AddToFunctionSummaryMap { 627 const ASTContext &ACtx; 628 FunctionSummaryMapType ⤅ 629 bool DisplayLoadedSummaries; 630 AddToFunctionSummaryMap(const ASTContext &ACtx, FunctionSummaryMapType &FSM, 631 bool DisplayLoadedSummaries) 632 : ACtx(ACtx), Map(FSM), DisplayLoadedSummaries(DisplayLoadedSummaries) { 633 } 634 635 // Add a summary to a FunctionDecl found by lookup. The lookup is performed 636 // by the given Name, and in the global scope. The summary will be attached 637 // to the found FunctionDecl only if the signatures match. 638 void operator()(StringRef Name, const Summary &S) { 639 IdentifierInfo &II = ACtx.Idents.get(Name); 640 auto LookupRes = ACtx.getTranslationUnitDecl()->lookup(&II); 641 if (LookupRes.size() == 0) 642 return; 643 for (Decl *D : LookupRes) { 644 if (auto *FD = dyn_cast<FunctionDecl>(D)) { 645 if (S.matchesSignature(FD)) { 646 auto Res = Map.insert({FD->getCanonicalDecl(), S}); 647 assert(Res.second && "Function already has a summary set!"); 648 (void)Res; 649 if (DisplayLoadedSummaries) { 650 llvm::errs() << "Loaded summary for: "; 651 FD->print(llvm::errs()); 652 llvm::errs() << "\n"; 653 } 654 return; 655 } 656 } 657 } 658 } 659 // Add several summaries for the given name. 660 void operator()(StringRef Name, const std::vector<Summary> &Summaries) { 661 for (const Summary &S : Summaries) 662 operator()(Name, S); 663 } 664 } addToFunctionSummaryMap(ACtx, FunctionSummaryMap, DisplayLoadedSummaries); 665 666 // We are finally ready to define specifications for all supported functions. 667 // 668 // The signature needs to have the correct number of arguments. 669 // However, we insert `Irrelevant' when the type is insignificant. 670 // 671 // Argument ranges should always cover all variants. If return value 672 // is completely unknown, omit it from the respective range set. 673 // 674 // All types in the spec need to be canonical. 675 // 676 // Every item in the list of range sets represents a particular 677 // execution path the analyzer would need to explore once 678 // the call is modeled - a new program state is constructed 679 // for every range set, and each range line in the range set 680 // corresponds to a specific constraint within this state. 681 // 682 // Upon comparing to another argument, the other argument is casted 683 // to the current argument's type. This avoids proper promotion but 684 // seems useful. For example, read() receives size_t argument, 685 // and its return value, which is of type ssize_t, cannot be greater 686 // than this argument. If we made a promotion, and the size argument 687 // is equal to, say, 10, then we'd impose a range of [0, 10] on the 688 // return value, however the correct range is [-1, 10]. 689 // 690 // Please update the list of functions in the header after editing! 691 692 // Below are helpers functions to create the summaries. 693 auto ArgumentCondition = [](ArgNo ArgN, RangeKind Kind, 694 IntRangeVector Ranges) { 695 return std::make_shared<RangeConstraint>(ArgN, Kind, Ranges); 696 }; 697 struct { 698 auto operator()(RangeKind Kind, IntRangeVector Ranges) { 699 return std::make_shared<RangeConstraint>(Ret, Kind, Ranges); 700 } 701 auto operator()(BinaryOperator::Opcode Op, ArgNo OtherArgN) { 702 return std::make_shared<ComparisonConstraint>(Ret, Op, OtherArgN); 703 } 704 } ReturnValueCondition; 705 auto Range = [](RangeInt b, RangeInt e) { 706 return IntRangeVector{std::pair<RangeInt, RangeInt>{b, e}}; 707 }; 708 auto SingleValue = [](RangeInt v) { 709 return IntRangeVector{std::pair<RangeInt, RangeInt>{v, v}}; 710 }; 711 auto LessThanOrEq = BO_LE; 712 auto NotNull = [&](ArgNo ArgN) { 713 return std::make_shared<NotNullConstraint>(ArgN); 714 }; 715 716 using RetType = QualType; 717 // Templates for summaries that are reused by many functions. 718 auto Getc = [&]() { 719 return Summary(ArgTypes{Irrelevant}, RetType{IntTy}, NoEvalCall) 720 .Case({ReturnValueCondition(WithinRange, 721 {{EOFv, EOFv}, {0, UCharRangeMax}})}); 722 }; 723 auto Read = [&](RetType R, RangeInt Max) { 724 return Summary(ArgTypes{Irrelevant, Irrelevant, SizeTy}, RetType{R}, 725 NoEvalCall) 726 .Case({ReturnValueCondition(LessThanOrEq, ArgNo(2)), 727 ReturnValueCondition(WithinRange, Range(-1, Max))}); 728 }; 729 auto Fread = [&]() { 730 return Summary(ArgTypes{VoidPtrRestrictTy, Irrelevant, SizeTy, Irrelevant}, 731 RetType{SizeTy}, NoEvalCall) 732 .Case({ 733 ReturnValueCondition(LessThanOrEq, ArgNo(2)), 734 }) 735 .ArgConstraint(NotNull(ArgNo(0))); 736 }; 737 auto Fwrite = [&]() { 738 return Summary( 739 ArgTypes{ConstVoidPtrRestrictTy, Irrelevant, SizeTy, Irrelevant}, 740 RetType{SizeTy}, NoEvalCall) 741 .Case({ 742 ReturnValueCondition(LessThanOrEq, ArgNo(2)), 743 }) 744 .ArgConstraint(NotNull(ArgNo(0))); 745 }; 746 auto Getline = [&](RetType R, RangeInt Max) { 747 return Summary(ArgTypes{Irrelevant, Irrelevant, Irrelevant}, RetType{R}, 748 NoEvalCall) 749 .Case({ReturnValueCondition(WithinRange, {{-1, -1}, {1, Max}})}); 750 }; 751 752 // The isascii() family of functions. 753 // The behavior is undefined if the value of the argument is not 754 // representable as unsigned char or is not equal to EOF. See e.g. C99 755 // 7.4.1.2 The isalpha function (p: 181-182). 756 addToFunctionSummaryMap( 757 "isalnum", 758 Summary(ArgTypes{IntTy}, RetType{IntTy}, EvalCallAsPure) 759 // Boils down to isupper() or islower() or isdigit(). 760 .Case({ArgumentCondition(0U, WithinRange, 761 {{'0', '9'}, {'A', 'Z'}, {'a', 'z'}}), 762 ReturnValueCondition(OutOfRange, SingleValue(0))}) 763 // The locale-specific range. 764 // No post-condition. We are completely unaware of 765 // locale-specific return values. 766 .Case({ArgumentCondition(0U, WithinRange, {{128, UCharRangeMax}})}) 767 .Case( 768 {ArgumentCondition( 769 0U, OutOfRange, 770 {{'0', '9'}, {'A', 'Z'}, {'a', 'z'}, {128, UCharRangeMax}}), 771 ReturnValueCondition(WithinRange, SingleValue(0))}) 772 .ArgConstraint(ArgumentCondition( 773 0U, WithinRange, {{EOFv, EOFv}, {0, UCharRangeMax}}))); 774 addToFunctionSummaryMap( 775 "isalpha", 776 Summary(ArgTypes{IntTy}, RetType{IntTy}, EvalCallAsPure) 777 .Case({ArgumentCondition(0U, WithinRange, {{'A', 'Z'}, {'a', 'z'}}), 778 ReturnValueCondition(OutOfRange, SingleValue(0))}) 779 // The locale-specific range. 780 .Case({ArgumentCondition(0U, WithinRange, {{128, UCharRangeMax}})}) 781 .Case({ArgumentCondition( 782 0U, OutOfRange, 783 {{'A', 'Z'}, {'a', 'z'}, {128, UCharRangeMax}}), 784 ReturnValueCondition(WithinRange, SingleValue(0))})); 785 addToFunctionSummaryMap( 786 "isascii", 787 Summary(ArgTypes{IntTy}, RetType{IntTy}, EvalCallAsPure) 788 .Case({ArgumentCondition(0U, WithinRange, Range(0, 127)), 789 ReturnValueCondition(OutOfRange, SingleValue(0))}) 790 .Case({ArgumentCondition(0U, OutOfRange, Range(0, 127)), 791 ReturnValueCondition(WithinRange, SingleValue(0))})); 792 addToFunctionSummaryMap( 793 "isblank", 794 Summary(ArgTypes{IntTy}, RetType{IntTy}, EvalCallAsPure) 795 .Case({ArgumentCondition(0U, WithinRange, {{'\t', '\t'}, {' ', ' '}}), 796 ReturnValueCondition(OutOfRange, SingleValue(0))}) 797 .Case({ArgumentCondition(0U, OutOfRange, {{'\t', '\t'}, {' ', ' '}}), 798 ReturnValueCondition(WithinRange, SingleValue(0))})); 799 addToFunctionSummaryMap( 800 "iscntrl", 801 Summary(ArgTypes{IntTy}, RetType{IntTy}, EvalCallAsPure) 802 .Case({ArgumentCondition(0U, WithinRange, {{0, 32}, {127, 127}}), 803 ReturnValueCondition(OutOfRange, SingleValue(0))}) 804 .Case({ArgumentCondition(0U, OutOfRange, {{0, 32}, {127, 127}}), 805 ReturnValueCondition(WithinRange, SingleValue(0))})); 806 addToFunctionSummaryMap( 807 "isdigit", 808 Summary(ArgTypes{IntTy}, RetType{IntTy}, EvalCallAsPure) 809 .Case({ArgumentCondition(0U, WithinRange, Range('0', '9')), 810 ReturnValueCondition(OutOfRange, SingleValue(0))}) 811 .Case({ArgumentCondition(0U, OutOfRange, Range('0', '9')), 812 ReturnValueCondition(WithinRange, SingleValue(0))})); 813 addToFunctionSummaryMap( 814 "isgraph", 815 Summary(ArgTypes{IntTy}, RetType{IntTy}, EvalCallAsPure) 816 .Case({ArgumentCondition(0U, WithinRange, Range(33, 126)), 817 ReturnValueCondition(OutOfRange, SingleValue(0))}) 818 .Case({ArgumentCondition(0U, OutOfRange, Range(33, 126)), 819 ReturnValueCondition(WithinRange, SingleValue(0))})); 820 addToFunctionSummaryMap( 821 "islower", 822 Summary(ArgTypes{IntTy}, RetType{IntTy}, EvalCallAsPure) 823 // Is certainly lowercase. 824 .Case({ArgumentCondition(0U, WithinRange, Range('a', 'z')), 825 ReturnValueCondition(OutOfRange, SingleValue(0))}) 826 // Is ascii but not lowercase. 827 .Case({ArgumentCondition(0U, WithinRange, Range(0, 127)), 828 ArgumentCondition(0U, OutOfRange, Range('a', 'z')), 829 ReturnValueCondition(WithinRange, SingleValue(0))}) 830 // The locale-specific range. 831 .Case({ArgumentCondition(0U, WithinRange, {{128, UCharRangeMax}})}) 832 // Is not an unsigned char. 833 .Case({ArgumentCondition(0U, OutOfRange, Range(0, UCharRangeMax)), 834 ReturnValueCondition(WithinRange, SingleValue(0))})); 835 addToFunctionSummaryMap( 836 "isprint", 837 Summary(ArgTypes{IntTy}, RetType{IntTy}, EvalCallAsPure) 838 .Case({ArgumentCondition(0U, WithinRange, Range(32, 126)), 839 ReturnValueCondition(OutOfRange, SingleValue(0))}) 840 .Case({ArgumentCondition(0U, OutOfRange, Range(32, 126)), 841 ReturnValueCondition(WithinRange, SingleValue(0))})); 842 addToFunctionSummaryMap( 843 "ispunct", 844 Summary(ArgTypes{IntTy}, RetType{IntTy}, EvalCallAsPure) 845 .Case({ArgumentCondition( 846 0U, WithinRange, 847 {{'!', '/'}, {':', '@'}, {'[', '`'}, {'{', '~'}}), 848 ReturnValueCondition(OutOfRange, SingleValue(0))}) 849 .Case({ArgumentCondition( 850 0U, OutOfRange, 851 {{'!', '/'}, {':', '@'}, {'[', '`'}, {'{', '~'}}), 852 ReturnValueCondition(WithinRange, SingleValue(0))})); 853 addToFunctionSummaryMap( 854 "isspace", 855 Summary(ArgTypes{IntTy}, RetType{IntTy}, EvalCallAsPure) 856 // Space, '\f', '\n', '\r', '\t', '\v'. 857 .Case({ArgumentCondition(0U, WithinRange, {{9, 13}, {' ', ' '}}), 858 ReturnValueCondition(OutOfRange, SingleValue(0))}) 859 // The locale-specific range. 860 .Case({ArgumentCondition(0U, WithinRange, {{128, UCharRangeMax}})}) 861 .Case({ArgumentCondition(0U, OutOfRange, 862 {{9, 13}, {' ', ' '}, {128, UCharRangeMax}}), 863 ReturnValueCondition(WithinRange, SingleValue(0))})); 864 addToFunctionSummaryMap( 865 "isupper", 866 Summary(ArgTypes{IntTy}, RetType{IntTy}, EvalCallAsPure) 867 // Is certainly uppercase. 868 .Case({ArgumentCondition(0U, WithinRange, Range('A', 'Z')), 869 ReturnValueCondition(OutOfRange, SingleValue(0))}) 870 // The locale-specific range. 871 .Case({ArgumentCondition(0U, WithinRange, {{128, UCharRangeMax}})}) 872 // Other. 873 .Case({ArgumentCondition(0U, OutOfRange, 874 {{'A', 'Z'}, {128, UCharRangeMax}}), 875 ReturnValueCondition(WithinRange, SingleValue(0))})); 876 addToFunctionSummaryMap( 877 "isxdigit", 878 Summary(ArgTypes{IntTy}, RetType{IntTy}, EvalCallAsPure) 879 .Case({ArgumentCondition(0U, WithinRange, 880 {{'0', '9'}, {'A', 'F'}, {'a', 'f'}}), 881 ReturnValueCondition(OutOfRange, SingleValue(0))}) 882 .Case({ArgumentCondition(0U, OutOfRange, 883 {{'0', '9'}, {'A', 'F'}, {'a', 'f'}}), 884 ReturnValueCondition(WithinRange, SingleValue(0))})); 885 886 // The getc() family of functions that returns either a char or an EOF. 887 addToFunctionSummaryMap("getc", Getc()); 888 addToFunctionSummaryMap("fgetc", Getc()); 889 addToFunctionSummaryMap( 890 "getchar", Summary(ArgTypes{}, RetType{IntTy}, NoEvalCall) 891 .Case({ReturnValueCondition( 892 WithinRange, {{EOFv, EOFv}, {0, UCharRangeMax}})})); 893 894 // read()-like functions that never return more than buffer size. 895 // We are not sure how ssize_t is defined on every platform, so we 896 // provide three variants that should cover common cases. 897 addToFunctionSummaryMap("read", {Read(IntTy, IntMax), Read(LongTy, LongMax), 898 Read(LongLongTy, LongLongMax)}); 899 addToFunctionSummaryMap("write", {Read(IntTy, IntMax), Read(LongTy, LongMax), 900 Read(LongLongTy, LongLongMax)}); 901 addToFunctionSummaryMap("fread", Fread()); 902 addToFunctionSummaryMap("fwrite", Fwrite()); 903 // getline()-like functions either fail or read at least the delimiter. 904 addToFunctionSummaryMap("getline", 905 {Getline(IntTy, IntMax), Getline(LongTy, LongMax), 906 Getline(LongLongTy, LongLongMax)}); 907 addToFunctionSummaryMap("getdelim", 908 {Getline(IntTy, IntMax), Getline(LongTy, LongMax), 909 Getline(LongLongTy, LongLongMax)}); 910 911 // Functions for testing. 912 if (ChecksEnabled[CK_StdCLibraryFunctionsTesterChecker]) { 913 addToFunctionSummaryMap( 914 "__two_constrained_args", 915 Summary(ArgTypes{IntTy, IntTy}, RetType{IntTy}, EvalCallAsPure) 916 .ArgConstraint(ArgumentCondition(0U, WithinRange, SingleValue(1))) 917 .ArgConstraint(ArgumentCondition(1U, WithinRange, SingleValue(1)))); 918 addToFunctionSummaryMap( 919 "__arg_constrained_twice", 920 Summary(ArgTypes{IntTy}, RetType{IntTy}, EvalCallAsPure) 921 .ArgConstraint(ArgumentCondition(0U, OutOfRange, SingleValue(1))) 922 .ArgConstraint(ArgumentCondition(0U, OutOfRange, SingleValue(2)))); 923 addToFunctionSummaryMap( 924 "__defaultparam", 925 Summary(ArgTypes{Irrelevant, IntTy}, RetType{IntTy}, EvalCallAsPure) 926 .ArgConstraint(NotNull(ArgNo(0)))); 927 addToFunctionSummaryMap("__variadic", 928 Summary(ArgTypes{VoidPtrTy, ConstCharPtrTy}, 929 RetType{IntTy}, EvalCallAsPure) 930 .ArgConstraint(NotNull(ArgNo(0))) 931 .ArgConstraint(NotNull(ArgNo(1)))); 932 } 933 } 934 935 void ento::registerStdCLibraryFunctionsChecker(CheckerManager &mgr) { 936 auto *Checker = mgr.registerChecker<StdLibraryFunctionsChecker>(); 937 Checker->DisplayLoadedSummaries = 938 mgr.getAnalyzerOptions().getCheckerBooleanOption( 939 Checker, "DisplayLoadedSummaries"); 940 } 941 942 bool ento::shouldRegisterStdCLibraryFunctionsChecker(const CheckerManager &mgr) { 943 return true; 944 } 945 946 #define REGISTER_CHECKER(name) \ 947 void ento::register##name(CheckerManager &mgr) { \ 948 StdLibraryFunctionsChecker *checker = \ 949 mgr.getChecker<StdLibraryFunctionsChecker>(); \ 950 checker->ChecksEnabled[StdLibraryFunctionsChecker::CK_##name] = true; \ 951 checker->CheckNames[StdLibraryFunctionsChecker::CK_##name] = \ 952 mgr.getCurrentCheckerName(); \ 953 } \ 954 \ 955 bool ento::shouldRegister##name(const CheckerManager &mgr) { return true; } 956 957 REGISTER_CHECKER(StdCLibraryFunctionArgsChecker) 958 REGISTER_CHECKER(StdCLibraryFunctionsTesterChecker) 959