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 call expression is the call of 270 /// *the* library function to which this specification applies. 271 bool matchesCall(const FunctionDecl *FD) const; 272 }; 273 274 // The same function (as in, function identifier) may have different 275 // summaries assigned to it, with different argument and return value types. 276 // We call these "variants" of the function. This can be useful for handling 277 // C++ function overloads, and also it can be used when the same function 278 // may have different definitions on different platforms. 279 typedef std::vector<Summary> Summaries; 280 281 // The map of all functions supported by the checker. It is initialized 282 // lazily, and it doesn't change after initialization. 283 mutable llvm::StringMap<Summaries> FunctionSummaryMap; 284 285 mutable std::unique_ptr<BugType> BT_InvalidArg; 286 287 // Auxiliary functions to support ArgNo within all structures 288 // in a unified manner. 289 static QualType getArgType(const Summary &Summary, ArgNo ArgN) { 290 return Summary.getArgType(ArgN); 291 } 292 static QualType getArgType(const CallEvent &Call, ArgNo ArgN) { 293 return ArgN == Ret ? Call.getResultType().getCanonicalType() 294 : Call.getArgExpr(ArgN)->getType().getCanonicalType(); 295 } 296 static QualType getArgType(const CallExpr *CE, ArgNo ArgN) { 297 return ArgN == Ret ? CE->getType().getCanonicalType() 298 : CE->getArg(ArgN)->getType().getCanonicalType(); 299 } 300 static SVal getArgSVal(const CallEvent &Call, ArgNo ArgN) { 301 return ArgN == Ret ? Call.getReturnValue() : Call.getArgSVal(ArgN); 302 } 303 304 public: 305 void checkPreCall(const CallEvent &Call, CheckerContext &C) const; 306 void checkPostCall(const CallEvent &Call, CheckerContext &C) const; 307 bool evalCall(const CallEvent &Call, CheckerContext &C) const; 308 309 enum CheckKind { 310 CK_StdCLibraryFunctionArgsChecker, 311 CK_StdCLibraryFunctionsTesterChecker, 312 CK_NumCheckKinds 313 }; 314 DefaultBool ChecksEnabled[CK_NumCheckKinds]; 315 CheckerNameRef CheckNames[CK_NumCheckKinds]; 316 317 private: 318 Optional<Summary> findFunctionSummary(const FunctionDecl *FD, 319 CheckerContext &C) const; 320 Optional<Summary> findFunctionSummary(const CallEvent &Call, 321 CheckerContext &C) const; 322 323 void initFunctionSummaries(CheckerContext &C) const; 324 325 void reportBug(const CallEvent &Call, ExplodedNode *N, 326 CheckerContext &C) const { 327 if (!ChecksEnabled[CK_StdCLibraryFunctionArgsChecker]) 328 return; 329 // TODO Add detailed diagnostic. 330 StringRef Msg = "Function argument constraint is not satisfied"; 331 if (!BT_InvalidArg) 332 BT_InvalidArg = std::make_unique<BugType>( 333 CheckNames[CK_StdCLibraryFunctionArgsChecker], 334 "Unsatisfied argument constraints", categories::LogicError); 335 auto R = std::make_unique<PathSensitiveBugReport>(*BT_InvalidArg, Msg, N); 336 bugreporter::trackExpressionValue(N, Call.getArgExpr(0), *R); 337 C.emitReport(std::move(R)); 338 } 339 }; 340 341 const StdLibraryFunctionsChecker::ArgNo StdLibraryFunctionsChecker::Ret = 342 std::numeric_limits<ArgNo>::max(); 343 344 } // end of anonymous namespace 345 346 ProgramStateRef StdLibraryFunctionsChecker::RangeConstraint::applyAsOutOfRange( 347 ProgramStateRef State, const CallEvent &Call, 348 const Summary &Summary) const { 349 350 ProgramStateManager &Mgr = State->getStateManager(); 351 SValBuilder &SVB = Mgr.getSValBuilder(); 352 BasicValueFactory &BVF = SVB.getBasicValueFactory(); 353 ConstraintManager &CM = Mgr.getConstraintManager(); 354 QualType T = getArgType(Summary, getArgNo()); 355 SVal V = getArgSVal(Call, getArgNo()); 356 357 if (auto N = V.getAs<NonLoc>()) { 358 const IntRangeVector &R = getRanges(); 359 size_t E = R.size(); 360 for (size_t I = 0; I != E; ++I) { 361 const llvm::APSInt &Min = BVF.getValue(R[I].first, T); 362 const llvm::APSInt &Max = BVF.getValue(R[I].second, T); 363 assert(Min <= Max); 364 State = CM.assumeInclusiveRange(State, *N, Min, Max, false); 365 if (!State) 366 break; 367 } 368 } 369 370 return State; 371 } 372 373 ProgramStateRef StdLibraryFunctionsChecker::RangeConstraint::applyAsWithinRange( 374 ProgramStateRef State, const CallEvent &Call, 375 const Summary &Summary) const { 376 377 ProgramStateManager &Mgr = State->getStateManager(); 378 SValBuilder &SVB = Mgr.getSValBuilder(); 379 BasicValueFactory &BVF = SVB.getBasicValueFactory(); 380 ConstraintManager &CM = Mgr.getConstraintManager(); 381 QualType T = getArgType(Summary, getArgNo()); 382 SVal V = getArgSVal(Call, getArgNo()); 383 384 // "WithinRange R" is treated as "outside [T_MIN, T_MAX] \ R". 385 // We cut off [T_MIN, min(R) - 1] and [max(R) + 1, T_MAX] if necessary, 386 // and then cut away all holes in R one by one. 387 // 388 // E.g. consider a range list R as [A, B] and [C, D] 389 // -------+--------+------------------+------------+-----------> 390 // A B C D 391 // Then we assume that the value is not in [-inf, A - 1], 392 // then not in [D + 1, +inf], then not in [B + 1, C - 1] 393 if (auto N = V.getAs<NonLoc>()) { 394 const IntRangeVector &R = getRanges(); 395 size_t E = R.size(); 396 397 const llvm::APSInt &MinusInf = BVF.getMinValue(T); 398 const llvm::APSInt &PlusInf = BVF.getMaxValue(T); 399 400 const llvm::APSInt &Left = BVF.getValue(R[0].first - 1ULL, T); 401 if (Left != PlusInf) { 402 assert(MinusInf <= Left); 403 State = CM.assumeInclusiveRange(State, *N, MinusInf, Left, false); 404 if (!State) 405 return nullptr; 406 } 407 408 const llvm::APSInt &Right = BVF.getValue(R[E - 1].second + 1ULL, T); 409 if (Right != MinusInf) { 410 assert(Right <= PlusInf); 411 State = CM.assumeInclusiveRange(State, *N, Right, PlusInf, false); 412 if (!State) 413 return nullptr; 414 } 415 416 for (size_t I = 1; I != E; ++I) { 417 const llvm::APSInt &Min = BVF.getValue(R[I - 1].second + 1ULL, T); 418 const llvm::APSInt &Max = BVF.getValue(R[I].first - 1ULL, T); 419 if (Min <= Max) { 420 State = CM.assumeInclusiveRange(State, *N, Min, Max, false); 421 if (!State) 422 return nullptr; 423 } 424 } 425 } 426 427 return State; 428 } 429 430 ProgramStateRef StdLibraryFunctionsChecker::ComparisonConstraint::apply( 431 ProgramStateRef State, const CallEvent &Call, 432 const Summary &Summary) const { 433 434 ProgramStateManager &Mgr = State->getStateManager(); 435 SValBuilder &SVB = Mgr.getSValBuilder(); 436 QualType CondT = SVB.getConditionType(); 437 QualType T = getArgType(Summary, getArgNo()); 438 SVal V = getArgSVal(Call, getArgNo()); 439 440 BinaryOperator::Opcode Op = getOpcode(); 441 ArgNo OtherArg = getOtherArgNo(); 442 SVal OtherV = getArgSVal(Call, OtherArg); 443 QualType OtherT = getArgType(Call, OtherArg); 444 // Note: we avoid integral promotion for comparison. 445 OtherV = SVB.evalCast(OtherV, T, OtherT); 446 if (auto CompV = SVB.evalBinOp(State, Op, V, OtherV, CondT) 447 .getAs<DefinedOrUnknownSVal>()) 448 State = State->assume(*CompV, true); 449 return State; 450 } 451 452 void StdLibraryFunctionsChecker::checkPreCall(const CallEvent &Call, 453 CheckerContext &C) const { 454 Optional<Summary> FoundSummary = findFunctionSummary(Call, C); 455 if (!FoundSummary) 456 return; 457 458 const Summary &Summary = *FoundSummary; 459 ProgramStateRef State = C.getState(); 460 461 ProgramStateRef NewState = State; 462 for (const ValueConstraintPtr& VC : Summary.ArgConstraints) { 463 ProgramStateRef SuccessSt = VC->apply(NewState, Call, Summary); 464 ProgramStateRef FailureSt = VC->negate()->apply(NewState, Call, Summary); 465 // The argument constraint is not satisfied. 466 if (FailureSt && !SuccessSt) { 467 if (ExplodedNode *N = C.generateErrorNode(NewState)) 468 reportBug(Call, N, C); 469 break; 470 } else { 471 // We will apply the constraint even if we cannot reason about the 472 // argument. This means both SuccessSt and FailureSt can be true. If we 473 // weren't applying the constraint that would mean that symbolic 474 // execution continues on a code whose behaviour is undefined. 475 assert(SuccessSt); 476 NewState = SuccessSt; 477 } 478 } 479 if (NewState && NewState != State) 480 C.addTransition(NewState); 481 } 482 483 void StdLibraryFunctionsChecker::checkPostCall(const CallEvent &Call, 484 CheckerContext &C) const { 485 Optional<Summary> FoundSummary = findFunctionSummary(Call, C); 486 if (!FoundSummary) 487 return; 488 489 // Now apply the constraints. 490 const Summary &Summary = *FoundSummary; 491 ProgramStateRef State = C.getState(); 492 493 // Apply case/branch specifications. 494 for (const auto &VRS : Summary.CaseConstraints) { 495 ProgramStateRef NewState = State; 496 for (const auto &VR: VRS) { 497 NewState = VR->apply(NewState, Call, Summary); 498 if (!NewState) 499 break; 500 } 501 502 if (NewState && NewState != State) 503 C.addTransition(NewState); 504 } 505 } 506 507 bool StdLibraryFunctionsChecker::evalCall(const CallEvent &Call, 508 CheckerContext &C) const { 509 Optional<Summary> FoundSummary = findFunctionSummary(Call, C); 510 if (!FoundSummary) 511 return false; 512 513 const Summary &Summary = *FoundSummary; 514 switch (Summary.InvalidationKd) { 515 case EvalCallAsPure: { 516 ProgramStateRef State = C.getState(); 517 const LocationContext *LC = C.getLocationContext(); 518 const auto *CE = cast_or_null<CallExpr>(Call.getOriginExpr()); 519 SVal V = C.getSValBuilder().conjureSymbolVal( 520 CE, LC, CE->getType().getCanonicalType(), C.blockCount()); 521 State = State->BindExpr(CE, LC, V); 522 C.addTransition(State); 523 return true; 524 } 525 case NoEvalCall: 526 // Summary tells us to avoid performing eval::Call. The function is possibly 527 // evaluated by another checker, or evaluated conservatively. 528 return false; 529 } 530 llvm_unreachable("Unknown invalidation kind!"); 531 } 532 533 bool StdLibraryFunctionsChecker::Summary::matchesCall( 534 const FunctionDecl *FD) const { 535 // Check number of arguments: 536 if (FD->param_size() != ArgTys.size()) 537 return false; 538 539 // Check return type if relevant: 540 if (!RetTy.isNull() && RetTy != FD->getReturnType().getCanonicalType()) 541 return false; 542 543 // Check argument types when relevant: 544 for (size_t I = 0, E = ArgTys.size(); I != E; ++I) { 545 QualType FormalT = ArgTys[I]; 546 // Null type marks irrelevant arguments. 547 if (FormalT.isNull()) 548 continue; 549 550 assertTypeSuitableForSummary(FormalT); 551 552 QualType ActualT = FD->getParamDecl(I)->getType().getCanonicalType(); 553 if (ActualT != FormalT) 554 return false; 555 } 556 557 return true; 558 } 559 560 Optional<StdLibraryFunctionsChecker::Summary> 561 StdLibraryFunctionsChecker::findFunctionSummary(const FunctionDecl *FD, 562 CheckerContext &C) const { 563 if (!FD) 564 return None; 565 566 initFunctionSummaries(C); 567 568 IdentifierInfo *II = FD->getIdentifier(); 569 if (!II) 570 return None; 571 StringRef Name = II->getName(); 572 if (Name.empty() || !C.isCLibraryFunction(FD, Name)) 573 return None; 574 575 auto FSMI = FunctionSummaryMap.find(Name); 576 if (FSMI == FunctionSummaryMap.end()) 577 return None; 578 579 // Verify that function signature matches the spec in advance. 580 // Otherwise we might be modeling the wrong function. 581 // Strict checking is important because we will be conducting 582 // very integral-type-sensitive operations on arguments and 583 // return values. 584 const Summaries &SpecVariants = FSMI->second; 585 for (const Summary &Spec : SpecVariants) 586 if (Spec.matchesCall(FD)) 587 return Spec; 588 589 return None; 590 } 591 592 Optional<StdLibraryFunctionsChecker::Summary> 593 StdLibraryFunctionsChecker::findFunctionSummary(const CallEvent &Call, 594 CheckerContext &C) const { 595 const FunctionDecl *FD = dyn_cast_or_null<FunctionDecl>(Call.getDecl()); 596 if (!FD) 597 return None; 598 return findFunctionSummary(FD, C); 599 } 600 601 void StdLibraryFunctionsChecker::initFunctionSummaries( 602 CheckerContext &C) const { 603 if (!FunctionSummaryMap.empty()) 604 return; 605 606 SValBuilder &SVB = C.getSValBuilder(); 607 BasicValueFactory &BVF = SVB.getBasicValueFactory(); 608 const ASTContext &ACtx = BVF.getContext(); 609 610 // These types are useful for writing specifications quickly, 611 // New specifications should probably introduce more types. 612 // Some types are hard to obtain from the AST, eg. "ssize_t". 613 // In such cases it should be possible to provide multiple variants 614 // of function summary for common cases (eg. ssize_t could be int or long 615 // or long long, so three summary variants would be enough). 616 // Of course, function variants are also useful for C++ overloads. 617 const QualType 618 Irrelevant{}; // A placeholder, whenever we do not care about the type. 619 const QualType IntTy = ACtx.IntTy; 620 const QualType LongTy = ACtx.LongTy; 621 const QualType LongLongTy = ACtx.LongLongTy; 622 const QualType SizeTy = ACtx.getSizeType(); 623 const QualType VoidPtrTy = ACtx.VoidPtrTy; // void * 624 const QualType VoidPtrRestrictTy = 625 ACtx.getRestrictType(VoidPtrTy); // void *restrict 626 const QualType ConstVoidPtrTy = 627 ACtx.getPointerType(ACtx.VoidTy.withConst()); // const void * 628 const QualType ConstCharPtrTy = 629 ACtx.getPointerType(ACtx.CharTy.withConst()); // const char * 630 const QualType ConstVoidPtrRestrictTy = 631 ACtx.getRestrictType(ConstVoidPtrTy); // const void *restrict 632 633 const RangeInt IntMax = BVF.getMaxValue(IntTy).getLimitedValue(); 634 const RangeInt LongMax = BVF.getMaxValue(LongTy).getLimitedValue(); 635 const RangeInt LongLongMax = BVF.getMaxValue(LongLongTy).getLimitedValue(); 636 637 // Set UCharRangeMax to min of int or uchar maximum value. 638 // The C standard states that the arguments of functions like isalpha must 639 // be representable as an unsigned char. Their type is 'int', so the max 640 // value of the argument should be min(UCharMax, IntMax). This just happen 641 // to be true for commonly used and well tested instruction set 642 // architectures, but not for others. 643 const RangeInt UCharRangeMax = 644 std::min(BVF.getMaxValue(ACtx.UnsignedCharTy).getLimitedValue(), IntMax); 645 646 // The platform dependent value of EOF. 647 // Try our best to parse this from the Preprocessor, otherwise fallback to -1. 648 const auto EOFv = [&C]() -> RangeInt { 649 if (const llvm::Optional<int> OptInt = 650 tryExpandAsInteger("EOF", C.getPreprocessor())) 651 return *OptInt; 652 return -1; 653 }(); 654 655 // We are finally ready to define specifications for all supported functions. 656 // 657 // The signature needs to have the correct number of arguments. 658 // However, we insert `Irrelevant' when the type is insignificant. 659 // 660 // Argument ranges should always cover all variants. If return value 661 // is completely unknown, omit it from the respective range set. 662 // 663 // All types in the spec need to be canonical. 664 // 665 // Every item in the list of range sets represents a particular 666 // execution path the analyzer would need to explore once 667 // the call is modeled - a new program state is constructed 668 // for every range set, and each range line in the range set 669 // corresponds to a specific constraint within this state. 670 // 671 // Upon comparing to another argument, the other argument is casted 672 // to the current argument's type. This avoids proper promotion but 673 // seems useful. For example, read() receives size_t argument, 674 // and its return value, which is of type ssize_t, cannot be greater 675 // than this argument. If we made a promotion, and the size argument 676 // is equal to, say, 10, then we'd impose a range of [0, 10] on the 677 // return value, however the correct range is [-1, 10]. 678 // 679 // Please update the list of functions in the header after editing! 680 // 681 682 // Below are helpers functions to create the summaries. 683 auto ArgumentCondition = [](ArgNo ArgN, RangeKind Kind, 684 IntRangeVector Ranges) { 685 return std::make_shared<RangeConstraint>(ArgN, Kind, Ranges); 686 }; 687 struct { 688 auto operator()(RangeKind Kind, IntRangeVector Ranges) { 689 return std::make_shared<RangeConstraint>(Ret, Kind, Ranges); 690 } 691 auto operator()(BinaryOperator::Opcode Op, ArgNo OtherArgN) { 692 return std::make_shared<ComparisonConstraint>(Ret, Op, OtherArgN); 693 } 694 } ReturnValueCondition; 695 auto Range = [](RangeInt b, RangeInt e) { 696 return IntRangeVector{std::pair<RangeInt, RangeInt>{b, e}}; 697 }; 698 auto SingleValue = [](RangeInt v) { 699 return IntRangeVector{std::pair<RangeInt, RangeInt>{v, v}}; 700 }; 701 auto LessThanOrEq = BO_LE; 702 auto NotNull = [&](ArgNo ArgN) { 703 return std::make_shared<NotNullConstraint>(ArgN); 704 }; 705 706 using RetType = QualType; 707 // Templates for summaries that are reused by many functions. 708 auto Getc = [&]() { 709 return Summary(ArgTypes{Irrelevant}, RetType{IntTy}, NoEvalCall) 710 .Case({ReturnValueCondition(WithinRange, 711 {{EOFv, EOFv}, {0, UCharRangeMax}})}); 712 }; 713 auto Read = [&](RetType R, RangeInt Max) { 714 return Summary(ArgTypes{Irrelevant, Irrelevant, SizeTy}, RetType{R}, 715 NoEvalCall) 716 .Case({ReturnValueCondition(LessThanOrEq, ArgNo(2)), 717 ReturnValueCondition(WithinRange, Range(-1, Max))}); 718 }; 719 auto Fread = [&]() { 720 return Summary(ArgTypes{VoidPtrRestrictTy, Irrelevant, SizeTy, Irrelevant}, 721 RetType{SizeTy}, NoEvalCall) 722 .Case({ 723 ReturnValueCondition(LessThanOrEq, ArgNo(2)), 724 }) 725 .ArgConstraint(NotNull(ArgNo(0))); 726 }; 727 auto Fwrite = [&]() { 728 return Summary( 729 ArgTypes{ConstVoidPtrRestrictTy, Irrelevant, SizeTy, Irrelevant}, 730 RetType{SizeTy}, NoEvalCall) 731 .Case({ 732 ReturnValueCondition(LessThanOrEq, ArgNo(2)), 733 }) 734 .ArgConstraint(NotNull(ArgNo(0))); 735 }; 736 auto Getline = [&](RetType R, RangeInt Max) { 737 return Summary(ArgTypes{Irrelevant, Irrelevant, Irrelevant}, RetType{R}, 738 NoEvalCall) 739 .Case({ReturnValueCondition(WithinRange, {{-1, -1}, {1, Max}})}); 740 }; 741 742 FunctionSummaryMap = { 743 // The isascii() family of functions. 744 // The behavior is undefined if the value of the argument is not 745 // representable as unsigned char or is not equal to EOF. See e.g. C99 746 // 7.4.1.2 The isalpha function (p: 181-182). 747 { 748 "isalnum", 749 Summaries{ 750 Summary(ArgTypes{IntTy}, RetType{IntTy}, EvalCallAsPure) 751 // Boils down to isupper() or islower() or isdigit(). 752 .Case( 753 {ArgumentCondition(0U, WithinRange, 754 {{'0', '9'}, {'A', 'Z'}, {'a', 'z'}}), 755 ReturnValueCondition(OutOfRange, SingleValue(0))}) 756 // The locale-specific range. 757 // No post-condition. We are completely unaware of 758 // locale-specific return values. 759 .Case({ArgumentCondition(0U, WithinRange, 760 {{128, UCharRangeMax}})}) 761 .Case({ArgumentCondition(0U, OutOfRange, 762 {{'0', '9'}, 763 {'A', 'Z'}, 764 {'a', 'z'}, 765 {128, UCharRangeMax}}), 766 ReturnValueCondition(WithinRange, SingleValue(0))}) 767 .ArgConstraint(ArgumentCondition( 768 0U, WithinRange, {{EOFv, EOFv}, {0, UCharRangeMax}}))}, 769 }, 770 { 771 "isalpha", 772 Summaries{ 773 Summary(ArgTypes{IntTy}, RetType{IntTy}, EvalCallAsPure) 774 .Case({ArgumentCondition(0U, WithinRange, 775 {{'A', 'Z'}, {'a', 'z'}}), 776 ReturnValueCondition(OutOfRange, SingleValue(0))}) 777 // The locale-specific range. 778 .Case({ArgumentCondition(0U, WithinRange, 779 {{128, UCharRangeMax}})}) 780 .Case({ArgumentCondition( 781 0U, OutOfRange, 782 {{'A', 'Z'}, {'a', 'z'}, {128, UCharRangeMax}}), 783 ReturnValueCondition(WithinRange, SingleValue(0))})}, 784 }, 785 { 786 "isascii", 787 Summaries{ 788 Summary(ArgTypes{IntTy}, RetType{IntTy}, EvalCallAsPure) 789 .Case({ArgumentCondition(0U, WithinRange, Range(0, 127)), 790 ReturnValueCondition(OutOfRange, SingleValue(0))}) 791 .Case({ArgumentCondition(0U, OutOfRange, Range(0, 127)), 792 ReturnValueCondition(WithinRange, SingleValue(0))})}, 793 }, 794 { 795 "isblank", 796 Summaries{ 797 Summary(ArgTypes{IntTy}, RetType{IntTy}, EvalCallAsPure) 798 .Case({ArgumentCondition(0U, WithinRange, 799 {{'\t', '\t'}, {' ', ' '}}), 800 ReturnValueCondition(OutOfRange, SingleValue(0))}) 801 .Case({ArgumentCondition(0U, OutOfRange, 802 {{'\t', '\t'}, {' ', ' '}}), 803 ReturnValueCondition(WithinRange, SingleValue(0))})}, 804 }, 805 { 806 "iscntrl", 807 Summaries{ 808 Summary(ArgTypes{IntTy}, RetType{IntTy}, EvalCallAsPure) 809 .Case({ArgumentCondition(0U, WithinRange, 810 {{0, 32}, {127, 127}}), 811 ReturnValueCondition(OutOfRange, SingleValue(0))}) 812 .Case( 813 {ArgumentCondition(0U, OutOfRange, {{0, 32}, {127, 127}}), 814 ReturnValueCondition(WithinRange, SingleValue(0))})}, 815 }, 816 { 817 "isdigit", 818 Summaries{ 819 Summary(ArgTypes{IntTy}, RetType{IntTy}, EvalCallAsPure) 820 .Case({ArgumentCondition(0U, WithinRange, Range('0', '9')), 821 ReturnValueCondition(OutOfRange, SingleValue(0))}) 822 .Case({ArgumentCondition(0U, OutOfRange, Range('0', '9')), 823 ReturnValueCondition(WithinRange, SingleValue(0))})}, 824 }, 825 { 826 "isgraph", 827 Summaries{ 828 Summary(ArgTypes{IntTy}, RetType{IntTy}, EvalCallAsPure) 829 .Case({ArgumentCondition(0U, WithinRange, Range(33, 126)), 830 ReturnValueCondition(OutOfRange, SingleValue(0))}) 831 .Case({ArgumentCondition(0U, OutOfRange, Range(33, 126)), 832 ReturnValueCondition(WithinRange, SingleValue(0))})}, 833 }, 834 { 835 "islower", 836 Summaries{ 837 Summary(ArgTypes{IntTy}, RetType{IntTy}, EvalCallAsPure) 838 // Is certainly lowercase. 839 .Case({ArgumentCondition(0U, WithinRange, Range('a', 'z')), 840 ReturnValueCondition(OutOfRange, SingleValue(0))}) 841 // Is ascii but not lowercase. 842 .Case({ArgumentCondition(0U, WithinRange, Range(0, 127)), 843 ArgumentCondition(0U, OutOfRange, Range('a', 'z')), 844 ReturnValueCondition(WithinRange, SingleValue(0))}) 845 // The locale-specific range. 846 .Case({ArgumentCondition(0U, WithinRange, 847 {{128, UCharRangeMax}})}) 848 // Is not an unsigned char. 849 .Case({ArgumentCondition(0U, OutOfRange, 850 Range(0, UCharRangeMax)), 851 ReturnValueCondition(WithinRange, SingleValue(0))})}, 852 }, 853 { 854 "isprint", 855 Summaries{ 856 Summary(ArgTypes{IntTy}, RetType{IntTy}, EvalCallAsPure) 857 .Case({ArgumentCondition(0U, WithinRange, Range(32, 126)), 858 ReturnValueCondition(OutOfRange, SingleValue(0))}) 859 .Case({ArgumentCondition(0U, OutOfRange, Range(32, 126)), 860 ReturnValueCondition(WithinRange, SingleValue(0))})}, 861 }, 862 { 863 "ispunct", 864 Summaries{ 865 Summary(ArgTypes{IntTy}, RetType{IntTy}, EvalCallAsPure) 866 .Case({ArgumentCondition( 867 0U, WithinRange, 868 {{'!', '/'}, {':', '@'}, {'[', '`'}, {'{', '~'}}), 869 ReturnValueCondition(OutOfRange, SingleValue(0))}) 870 .Case({ArgumentCondition( 871 0U, OutOfRange, 872 {{'!', '/'}, {':', '@'}, {'[', '`'}, {'{', '~'}}), 873 ReturnValueCondition(WithinRange, SingleValue(0))})}, 874 }, 875 { 876 "isspace", 877 Summaries{ 878 Summary(ArgTypes{IntTy}, RetType{IntTy}, EvalCallAsPure) 879 // Space, '\f', '\n', '\r', '\t', '\v'. 880 .Case({ArgumentCondition(0U, WithinRange, 881 {{9, 13}, {' ', ' '}}), 882 ReturnValueCondition(OutOfRange, SingleValue(0))}) 883 // The locale-specific range. 884 .Case({ArgumentCondition(0U, WithinRange, 885 {{128, UCharRangeMax}})}) 886 .Case({ArgumentCondition( 887 0U, OutOfRange, 888 {{9, 13}, {' ', ' '}, {128, UCharRangeMax}}), 889 ReturnValueCondition(WithinRange, SingleValue(0))})}, 890 }, 891 { 892 "isupper", 893 Summaries{ 894 Summary(ArgTypes{IntTy}, RetType{IntTy}, EvalCallAsPure) 895 // Is certainly uppercase. 896 .Case({ArgumentCondition(0U, WithinRange, Range('A', 'Z')), 897 ReturnValueCondition(OutOfRange, SingleValue(0))}) 898 // The locale-specific range. 899 .Case({ArgumentCondition(0U, WithinRange, 900 {{128, UCharRangeMax}})}) 901 // Other. 902 .Case({ArgumentCondition(0U, OutOfRange, 903 {{'A', 'Z'}, {128, UCharRangeMax}}), 904 ReturnValueCondition(WithinRange, SingleValue(0))})}, 905 }, 906 { 907 "isxdigit", 908 Summaries{ 909 Summary(ArgTypes{IntTy}, RetType{IntTy}, EvalCallAsPure) 910 .Case( 911 {ArgumentCondition(0U, WithinRange, 912 {{'0', '9'}, {'A', 'F'}, {'a', 'f'}}), 913 ReturnValueCondition(OutOfRange, SingleValue(0))}) 914 .Case( 915 {ArgumentCondition(0U, OutOfRange, 916 {{'0', '9'}, {'A', 'F'}, {'a', 'f'}}), 917 ReturnValueCondition(WithinRange, SingleValue(0))})}, 918 }, 919 920 // The getc() family of functions that returns either a char or an EOF. 921 {"getc", Summaries{Getc()}}, 922 {"fgetc", Summaries{Getc()}}, 923 {"getchar", 924 Summaries{Summary(ArgTypes{}, RetType{IntTy}, NoEvalCall) 925 .Case({ReturnValueCondition( 926 WithinRange, {{EOFv, EOFv}, {0, UCharRangeMax}})})}}, 927 928 // read()-like functions that never return more than buffer size. 929 // We are not sure how ssize_t is defined on every platform, so we 930 // provide three variants that should cover common cases. 931 {"read", Summaries{Read(IntTy, IntMax), Read(LongTy, LongMax), 932 Read(LongLongTy, LongLongMax)}}, 933 {"write", Summaries{Read(IntTy, IntMax), Read(LongTy, LongMax), 934 Read(LongLongTy, LongLongMax)}}, 935 {"fread", Summaries{Fread()}}, 936 {"fwrite", Summaries{Fwrite()}}, 937 // getline()-like functions either fail or read at least the delimiter. 938 {"getline", Summaries{Getline(IntTy, IntMax), Getline(LongTy, LongMax), 939 Getline(LongLongTy, LongLongMax)}}, 940 {"getdelim", Summaries{Getline(IntTy, IntMax), Getline(LongTy, LongMax), 941 Getline(LongLongTy, LongLongMax)}}, 942 }; 943 944 // Functions for testing. 945 if (ChecksEnabled[CK_StdCLibraryFunctionsTesterChecker]) { 946 llvm::StringMap<Summaries> TestFunctionSummaryMap = { 947 {"__two_constrained_args", 948 Summaries{ 949 Summary(ArgTypes{IntTy, IntTy}, RetType{IntTy}, EvalCallAsPure) 950 .ArgConstraint( 951 ArgumentCondition(0U, WithinRange, SingleValue(1))) 952 .ArgConstraint( 953 ArgumentCondition(1U, WithinRange, SingleValue(1)))}}, 954 {"__arg_constrained_twice", 955 Summaries{Summary(ArgTypes{IntTy}, RetType{IntTy}, EvalCallAsPure) 956 .ArgConstraint( 957 ArgumentCondition(0U, OutOfRange, SingleValue(1))) 958 .ArgConstraint( 959 ArgumentCondition(0U, OutOfRange, SingleValue(2)))}}, 960 {"__defaultparam", Summaries{Summary(ArgTypes{Irrelevant, IntTy}, 961 RetType{IntTy}, EvalCallAsPure) 962 .ArgConstraint(NotNull(ArgNo(0)))}}, 963 {"__variadic", Summaries{Summary(ArgTypes{VoidPtrTy, ConstCharPtrTy}, 964 RetType{IntTy}, EvalCallAsPure) 965 .ArgConstraint(NotNull(ArgNo(0))) 966 .ArgConstraint(NotNull(ArgNo(1)))}}}; 967 for (auto &E : TestFunctionSummaryMap) { 968 auto InsertRes = 969 FunctionSummaryMap.insert({std::string(E.getKey()), E.getValue()}); 970 assert(InsertRes.second && 971 "Test functions must not clash with modeled functions"); 972 (void)InsertRes; 973 } 974 } 975 } 976 977 void ento::registerStdCLibraryFunctionsChecker(CheckerManager &mgr) { 978 mgr.registerChecker<StdLibraryFunctionsChecker>(); 979 } 980 981 bool ento::shouldRegisterStdCLibraryFunctionsChecker(const CheckerManager &mgr) { 982 return true; 983 } 984 985 #define REGISTER_CHECKER(name) \ 986 void ento::register##name(CheckerManager &mgr) { \ 987 StdLibraryFunctionsChecker *checker = \ 988 mgr.getChecker<StdLibraryFunctionsChecker>(); \ 989 checker->ChecksEnabled[StdLibraryFunctionsChecker::CK_##name] = true; \ 990 checker->CheckNames[StdLibraryFunctionsChecker::CK_##name] = \ 991 mgr.getCurrentCheckerName(); \ 992 } \ 993 \ 994 bool ento::shouldRegister##name(const CheckerManager &mgr) { return true; } 995 996 REGISTER_CHECKER(StdCLibraryFunctionArgsChecker) 997 REGISTER_CHECKER(StdCLibraryFunctionsTesterChecker) 998