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