//== ArrayBoundCheckerV2.cpp ------------------------------------*- C++ -*--==//

//

// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.

// See https://llvm.org/LICENSE.txt for license information.

// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception

//

//===----------------------------------------------------------------------===//

//

// This file defines ArrayBoundCheckerV2, which is a path-sensitive check

// which looks for an out-of-bound array element access.

//

//===----------------------------------------------------------------------===//

#include "clang/AST/CharUnits.h"

#include "clang/StaticAnalyzer/Checkers/BuiltinCheckerRegistration.h"

#include "clang/StaticAnalyzer/Checkers/Taint.h"

#include "clang/StaticAnalyzer/Core/BugReporter/BugType.h"

#include "clang/StaticAnalyzer/Core/Checker.h"

#include "clang/StaticAnalyzer/Core/CheckerManager.h"

#include "clang/StaticAnalyzer/Core/PathSensitive/APSIntType.h"

#include "clang/StaticAnalyzer/Core/PathSensitive/CheckerContext.h"

#include "clang/StaticAnalyzer/Core/PathSensitive/DynamicExtent.h"

#include "clang/StaticAnalyzer/Core/PathSensitive/ExprEngine.h"

#include "llvm/ADT/SmallString.h"

#include "llvm/Support/raw_ostream.h"

#include <optional>

using namespace clang;

using namespace ento;

using namespace taint;

namespace {

class ArrayBoundCheckerV2 :

    public Checker<check::Location> {

  mutable std::unique_ptr<BugType> BT;

  mutable std::unique_ptr<BugType> TaintBT;

  enum OOB_Kind { OOB_Precedes, OOB_Excedes };

  void reportOOB(CheckerContext &C, ProgramStateRef errorState,

                 OOB_Kind kind) const;

  void reportTaintOOB(CheckerContext &C, ProgramStateRef errorState,

                      SVal TaintedSVal) const;

  static bool isFromCtypeMacro(const Stmt *S, ASTContext &AC);

public:

  void checkLocation(SVal l, bool isLoad, const Stmt *S,

                     CheckerContext &C) const;

};

// FIXME: Eventually replace RegionRawOffset with this class.

class RegionRawOffsetV2 {

private:

  const SubRegion *baseRegion;

  NonLoc byteOffset;

public:

  RegionRawOffsetV2(const SubRegion *base, NonLoc offset)

      : baseRegion(base), byteOffset(offset) { assert(base); }

  NonLoc getByteOffset() const { return byteOffset; }

  const SubRegion *getRegion() const { return baseRegion; }

  static std::optional<RegionRawOffsetV2>

  computeOffset(ProgramStateRef State, SValBuilder &SVB, SVal Location);

  void dump() const;

  void dumpToStream(raw_ostream &os) const;

};

}

// TODO: once the constraint manager is smart enough to handle non simplified

// symbolic expressions remove this function. Note that this can not be used in

// the constraint manager as is, since this does not handle overflows. It is

// safe to assume, however, that memory offsets will not overflow.

// NOTE: callers of this function need to be aware of the effects of overflows

// and signed<->unsigned conversions!

static std::pair<NonLoc, nonloc::ConcreteInt>

getSimplifiedOffsets(NonLoc offset, nonloc::ConcreteInt extent,

                     SValBuilder &svalBuilder) {

  std::optional<nonloc::SymbolVal> SymVal = offset.getAs<nonloc::SymbolVal>();

  if (SymVal && 
SymVal->isExpression()180
) {

    if (const SymIntExpr *SIE = dyn_cast<SymIntExpr>(SymVal->getSymbol())) {

      llvm::APSInt constant =

          APSIntType(extent.getValue()).convert(SIE->getRHS());

      switch (SIE->getOpcode()) {

      case BO_Mul:

        // The constant should never be 0 here, since it the result of scaling

        // based on the size of a type which is never 0.

        if ((extent.getValue() % constant) != 0)

          return std::pair<NonLoc, nonloc::ConcreteInt>(offset, extent);

        else

          return getSimplifiedOffsets(

              nonloc::SymbolVal(SIE->getLHS()),

              svalBuilder.makeIntVal(extent.getValue() / constant),

              svalBuilder);

      case BO_Add:

        return getSimplifiedOffsets(

            nonloc::SymbolVal(SIE->getLHS()),

            svalBuilder.makeIntVal(extent.getValue() - constant), svalBuilder);

      default:

        break;

      }

    }

  }

  return std::pair<NonLoc, nonloc::ConcreteInt>(offset, extent);

}

// Evaluate the comparison Value < Threshold with the help of the custom

// simplification algorithm defined for this checker. Return a pair of states,

// where the first one corresponds to "value below threshold" and the second

// corresponds to "value at or above threshold". Returns {nullptr, nullptr} in

// the case when the evaluation fails.

static std::pair<ProgramStateRef, ProgramStateRef>

compareValueToThreshold(ProgramStateRef State, NonLoc Value, NonLoc Threshold,

                        SValBuilder &SVB) {

  if (auto ConcreteThreshold = Threshold.getAs<nonloc::ConcreteInt>()) {

    std::tie(Value, Threshold) = getSimplifiedOffsets(Value, *ConcreteThreshold, SVB);

  }

  if (auto ConcreteThreshold = Threshold.getAs<nonloc::ConcreteInt>()) {

    QualType T = Value.getType(SVB.getContext());

    if (T->isUnsignedIntegerType() && 
ConcreteThreshold->getValue().isNegative()12
) {

      // In this case we reduced the bound check to a comparison of the form

      //   (symbol or value with unsigned type) < (negative number)

      // which is always false. We are handling these cases separately because

      // evalBinOpNN can perform a signed->unsigned conversion that turns the

      // negative number into a huge positive value and leads to wildly

      // inaccurate conclusions.

      return {nullptr, State};

    }

  }

  auto BelowThreshold =

      SVB.evalBinOpNN(State, BO_LT, Value, Threshold, SVB.getConditionType()).getAs<NonLoc>();

  if (BelowThreshold)

    return State->assume(*BelowThreshold);

  return {nullptr, nullptr};

}

void ArrayBoundCheckerV2::checkLocation(SVal location, bool isLoad,

                                        const Stmt* LoadS,

                                        CheckerContext &checkerContext) const {

  // NOTE: Instead of using ProgramState::assumeInBound(), we are prototyping

  // some new logic here that reasons directly about memory region extents.

  // Once that logic is more mature, we can bring it back to assumeInBound()

  // for all clients to use.

  //

  // The algorithm we are using here for bounds checking is to see if the

  // memory access is within the extent of the base region.  Since we

  // have some flexibility in defining the base region, we can achieve

  // various levels of conservatism in our buffer overflow checking.

  // The header ctype.h (from e.g. glibc) implements the isXXXXX() macros as

  //   #define isXXXXX(arg) (LOOKUP_TABLE[arg] & BITMASK_FOR_XXXXX)

  // and incomplete analysis of these leads to false positives. As even

  // accurate reports would be confusing for the users, just disable reports

  // from these macros:

  if (isFromCtypeMacro(LoadS, checkerContext.getASTContext()))

    return;

  ProgramStateRef state = checkerContext.getState();

  SValBuilder &svalBuilder = checkerContext.getSValBuilder();

  const std::optional<RegionRawOffsetV2> &RawOffset =

      RegionRawOffsetV2::computeOffset(state, svalBuilder, location);

  if (!RawOffset)

    return;

  NonLoc ByteOffset = RawOffset->getByteOffset();

  const SubRegion *Reg = RawOffset->getRegion();

  // CHECK LOWER BOUND

  const MemSpaceRegion *Space = Reg->getMemorySpace();

  if (!(isa<SymbolicRegion>(Reg) && 
isa<UnknownSpaceRegion>(Space)8.32k
)) {

    // A symbolic region in unknown space represents an unknown pointer that

    // may point into the middle of an array, so we don't look for underflows.

    // Both conditions are significant because we want to check underflows in

    // symbolic regions on the heap (which may be introduced by checkers like

    // MallocChecker that call SValBuilder::getConjuredHeapSymbolVal()) and

    // non-symbolic regions (e.g. a field subregion of a symbolic region) in

    // unknown space.

    auto [state_precedesLowerBound, state_withinLowerBound] =

        compareValueToThreshold(state, ByteOffset,

                                svalBuilder.makeZeroArrayIndex(), svalBuilder);

    if (state_precedesLowerBound && 
!state_withinLowerBound55
) {

      // We know that the index definitely precedes the lower bound.

      reportOOB(checkerContext, state_precedesLowerBound, OOB_Precedes);

      return;

    }

    if (state_withinLowerBound)

      state = state_withinLowerBound;

  }

  // CHECK UPPER BOUND

  DefinedOrUnknownSVal Size = getDynamicExtent(state, Reg, svalBuilder);

  if (auto KnownSize = Size.getAs<NonLoc>()) {

    auto [state_withinUpperBound, state_exceedsUpperBound] =

        compareValueToThreshold(state, ByteOffset, *KnownSize, svalBuilder);

    if (state_exceedsUpperBound) {

      if (!state_withinUpperBound) {

        // We know that the index definitely exceeds the upper bound.

        reportOOB(checkerContext, state_exceedsUpperBound, OOB_Excedes);

        return;

      }

      if (isTainted(state, ByteOffset)) {

        // Both cases are possible, but the index is tainted, so report.

        reportTaintOOB(checkerContext, state_exceedsUpperBound, ByteOffset);

        return;

      }

    }

    if (state_withinUpperBound)

      state = state_withinUpperBound;

  }

  checkerContext.addTransition(state);

}

void ArrayBoundCheckerV2::reportTaintOOB(CheckerContext &checkerContext,

                                         ProgramStateRef errorState,

                                         SVal TaintedSVal) const {

  ExplodedNode *errorNode = checkerContext.generateErrorNode(errorState);

  if (!errorNode)

    return;

  if (!TaintBT)

    TaintBT.reset(

        new BugType(this, "Out-of-bound access", categories::TaintedData));

  SmallString<256> buf;

  llvm::raw_svector_ostream os(buf);

  os << "Out of bound memory access (index is tainted)";

  auto BR =

      std::make_unique<PathSensitiveBugReport>(*TaintBT, os.str(), errorNode);

  // Track back the propagation of taintedness.

  for (SymbolRef Sym : getTaintedSymbols(errorState, TaintedSVal)) {

    BR->markInteresting(Sym);

  }

  checkerContext.emitReport(std::move(BR));

}

void ArrayBoundCheckerV2::reportOOB(CheckerContext &checkerContext,

                                    ProgramStateRef errorState,

                                    OOB_Kind kind) const {

  ExplodedNode *errorNode = checkerContext.generateErrorNode(errorState);

  if (!errorNode)

    return;

  if (!BT)

    BT.reset(new BugType(this, "Out-of-bound access"));

  // FIXME: This diagnostics are preliminary.  We should get far better

  // diagnostics for explaining buffer overruns.

  SmallString<256> buf;

  llvm::raw_svector_ostream os(buf);

  os << "Out of bound memory access ";

  switch (kind) {

  case OOB_Precedes:

    os << "(accessed memory precedes memory block)";

    break;

  case OOB_Excedes:

    os << "(access exceeds upper limit of memory block)";

    break;

  }

  auto BR = std::make_unique<PathSensitiveBugReport>(*BT, os.str(), errorNode);

  checkerContext.emitReport(std::move(BR));

}

bool ArrayBoundCheckerV2::isFromCtypeMacro(const Stmt *S, ASTContext &ACtx) {

  SourceLocation Loc = S->getBeginLoc();

  if (!Loc.isMacroID())

    return false;

  StringRef MacroName = Lexer::getImmediateMacroName(

      Loc, ACtx.getSourceManager(), ACtx.getLangOpts());

  if (MacroName.size() < 7 || MacroName[0] != 'i' || 
MacroName[1] != 's'6
)

    return false;

  return ((MacroName == "isalnum") || (MacroName == "isalpha") ||

          (MacroName == "isblank") || (MacroName == "isdigit") ||

          
(MacroName == "isgraph")0
 || 
(MacroName == "islower")0
 ||

          
(MacroName == "isnctrl")0
 || 
(MacroName == "isprint")0
 ||

          
(MacroName == "ispunct")0
 || 
(MacroName == "isspace")0
 ||

          
(MacroName == "isupper")0
 || 
(MacroName == "isxdigit")0
);

}

#ifndef NDEBUG

LLVM_DUMP_METHOD void RegionRawOffsetV2::dump() const {

  dumpToStream(llvm::errs());

}

void RegionRawOffsetV2::dumpToStream(raw_ostream &os) const {

  os << "raw_offset_v2{" << getRegion() << ',' << getByteOffset() << '}';

}

#endif

/// For a given Location that can be represented as a symbolic expression

/// Arr[Idx] (or perhaps Arr[Idx1][Idx2] etc.), return the parent memory block

/// Arr and the distance of Location from the beginning of Arr (expressed in a

/// NonLoc that specifies the number of CharUnits). Returns nullopt when these

/// cannot be determined.

std::optional<RegionRawOffsetV2>

RegionRawOffsetV2::computeOffset(ProgramStateRef State, SValBuilder &SVB,

                                 SVal Location) {

  QualType T = SVB.getArrayIndexType();

  auto Calc = [&SVB, State, T](BinaryOperatorKind Op, NonLoc LHS, NonLoc RHS) {

    // We will use this utility to add and multiply values.

    return SVB.evalBinOpNN(State, Op, LHS, RHS, T).getAs<NonLoc>();

  };

  const MemRegion *Region = Location.getAsRegion();

  NonLoc Offset = SVB.makeZeroArrayIndex();

  while (Region) {

    if (const auto *ERegion = dyn_cast<ElementRegion>(Region)) {

      if (const auto Index = ERegion->getIndex().getAs<NonLoc>()) {

        QualType ElemType = ERegion->getElementType();

        // If the element is an incomplete type, go no further.

        if (ElemType->isIncompleteType())

          return std::nullopt;

        // Perform Offset += Index * sizeof(ElemType); then continue the offset

        // calculations with SuperRegion:

        NonLoc Size = SVB.makeArrayIndex(

            SVB.getContext().getTypeSizeInChars(ElemType).getQuantity());

        if (auto Delta = Calc(BO_Mul, *Index, Size)) {

          if (auto NewOffset = Calc(BO_Add, Offset, *Delta)) {

            Offset = *NewOffset;

            Region = ERegion->getSuperRegion();

            continue;

          }

        }

      }

    } else if (const auto *SRegion = dyn_cast<SubRegion>(Region)) {

      // NOTE: The dyn_cast<>() is expected to succeed, it'd be very surprising

      // to see a MemSpaceRegion at this point.

      // FIXME: We may return with {<Region>, 0} even if we didn't handle any

      // ElementRegion layers. I think that this behavior was introduced

      // accidentally by 8a4c760c204546aba566e302f299f7ed2e00e287 in 2011, so

      // it may be useful to review it in the future.

      return RegionRawOffsetV2(SRegion, Offset);

    }

    return std::nullopt;

  }

  return std::nullopt;

}

void ento::registerArrayBoundCheckerV2(CheckerManager &mgr) {

  mgr.registerChecker<ArrayBoundCheckerV2>();

}

bool ento::shouldRegisterArrayBoundCheckerV2(const CheckerManager &mgr) {

  return true;

}