| //== 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 "Taint.h" |
| #include "clang/AST/CharUnits.h" |
| #include "clang/StaticAnalyzer/Checkers/BuiltinCheckerRegistration.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" |
| |
| using namespace clang; |
| using namespace ento; |
| using namespace taint; |
| |
| namespace { |
| class ArrayBoundCheckerV2 : |
| public Checker<check::Location> { |
| mutable std::unique_ptr<BuiltinBug> BT; |
| |
| enum OOB_Kind { OOB_Precedes, OOB_Excedes, OOB_Tainted }; |
| |
| void reportOOB(CheckerContext &C, ProgramStateRef errorState, OOB_Kind kind, |
| std::unique_ptr<BugReporterVisitor> Visitor = nullptr) const; |
| |
| 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; |
| SVal byteOffset; |
| |
| RegionRawOffsetV2() |
| : baseRegion(nullptr), byteOffset(UnknownVal()) {} |
| |
| public: |
| RegionRawOffsetV2(const SubRegion* base, SVal offset) |
| : baseRegion(base), byteOffset(offset) {} |
| |
| NonLoc getByteOffset() const { return byteOffset.castAs<NonLoc>(); } |
| const SubRegion *getRegion() const { return baseRegion; } |
| |
| static RegionRawOffsetV2 computeOffset(ProgramStateRef state, |
| SValBuilder &svalBuilder, |
| SVal location); |
| |
| void dump() const; |
| void dumpToStream(raw_ostream &os) const; |
| }; |
| } |
| |
| static SVal computeExtentBegin(SValBuilder &svalBuilder, |
| const MemRegion *region) { |
| const MemSpaceRegion *SR = region->getMemorySpace(); |
| if (SR->getKind() == MemRegion::UnknownSpaceRegionKind) |
| return UnknownVal(); |
| else |
| return svalBuilder.makeZeroArrayIndex(); |
| } |
| |
| // 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. |
| static std::pair<NonLoc, nonloc::ConcreteInt> |
| getSimplifiedOffsets(NonLoc offset, nonloc::ConcreteInt extent, |
| SValBuilder &svalBuilder) { |
| Optional<nonloc::SymbolVal> SymVal = offset.getAs<nonloc::SymbolVal>(); |
| if (SymVal && SymVal->isExpression()) { |
| 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); |
| } |
| |
| 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. |
| ProgramStateRef state = checkerContext.getState(); |
| |
| SValBuilder &svalBuilder = checkerContext.getSValBuilder(); |
| const RegionRawOffsetV2 &rawOffset = |
| RegionRawOffsetV2::computeOffset(state, svalBuilder, location); |
| |
| if (!rawOffset.getRegion()) |
| return; |
| |
| NonLoc rawOffsetVal = rawOffset.getByteOffset(); |
| |
| // CHECK LOWER BOUND: Is byteOffset < extent begin? |
| // If so, we are doing a load/store |
| // before the first valid offset in the memory region. |
| |
| SVal extentBegin = computeExtentBegin(svalBuilder, rawOffset.getRegion()); |
| |
| if (Optional<NonLoc> NV = extentBegin.getAs<NonLoc>()) { |
| if (NV->getAs<nonloc::ConcreteInt>()) { |
| std::pair<NonLoc, nonloc::ConcreteInt> simplifiedOffsets = |
| getSimplifiedOffsets(rawOffset.getByteOffset(), |
| NV->castAs<nonloc::ConcreteInt>(), |
| svalBuilder); |
| rawOffsetVal = simplifiedOffsets.first; |
| *NV = simplifiedOffsets.second; |
| } |
| |
| SVal lowerBound = svalBuilder.evalBinOpNN(state, BO_LT, rawOffsetVal, *NV, |
| svalBuilder.getConditionType()); |
| |
| Optional<NonLoc> lowerBoundToCheck = lowerBound.getAs<NonLoc>(); |
| if (!lowerBoundToCheck) |
| return; |
| |
| ProgramStateRef state_precedesLowerBound, state_withinLowerBound; |
| std::tie(state_precedesLowerBound, state_withinLowerBound) = |
| state->assume(*lowerBoundToCheck); |
| |
| // Are we constrained enough to definitely precede the lower bound? |
| if (state_precedesLowerBound && !state_withinLowerBound) { |
| reportOOB(checkerContext, state_precedesLowerBound, OOB_Precedes); |
| return; |
| } |
| |
| // Otherwise, assume the constraint of the lower bound. |
| assert(state_withinLowerBound); |
| state = state_withinLowerBound; |
| } |
| |
| do { |
| // CHECK UPPER BOUND: Is byteOffset >= size(baseRegion)? If so, |
| // we are doing a load/store after the last valid offset. |
| const MemRegion *MR = rawOffset.getRegion(); |
| DefinedOrUnknownSVal Size = getDynamicExtent(state, MR, svalBuilder); |
| if (!Size.getAs<NonLoc>()) |
| break; |
| |
| if (Size.getAs<nonloc::ConcreteInt>()) { |
| std::pair<NonLoc, nonloc::ConcreteInt> simplifiedOffsets = |
| getSimplifiedOffsets(rawOffset.getByteOffset(), |
| Size.castAs<nonloc::ConcreteInt>(), svalBuilder); |
| rawOffsetVal = simplifiedOffsets.first; |
| Size = simplifiedOffsets.second; |
| } |
| |
| SVal upperbound = svalBuilder.evalBinOpNN(state, BO_GE, rawOffsetVal, |
| Size.castAs<NonLoc>(), |
| svalBuilder.getConditionType()); |
| |
| Optional<NonLoc> upperboundToCheck = upperbound.getAs<NonLoc>(); |
| if (!upperboundToCheck) |
| break; |
| |
| ProgramStateRef state_exceedsUpperBound, state_withinUpperBound; |
| std::tie(state_exceedsUpperBound, state_withinUpperBound) = |
| state->assume(*upperboundToCheck); |
| |
| // If we are under constrained and the index variables are tainted, report. |
| if (state_exceedsUpperBound && state_withinUpperBound) { |
| SVal ByteOffset = rawOffset.getByteOffset(); |
| if (isTainted(state, ByteOffset)) { |
| reportOOB(checkerContext, state_exceedsUpperBound, OOB_Tainted, |
| std::make_unique<TaintBugVisitor>(ByteOffset)); |
| return; |
| } |
| } else if (state_exceedsUpperBound) { |
| // If we are constrained enough to definitely exceed the upper bound, |
| // report. |
| assert(!state_withinUpperBound); |
| reportOOB(checkerContext, state_exceedsUpperBound, OOB_Excedes); |
| return; |
| } |
| |
| assert(state_withinUpperBound); |
| state = state_withinUpperBound; |
| } |
| while (false); |
| |
| checkerContext.addTransition(state); |
| } |
| |
| void ArrayBoundCheckerV2::reportOOB( |
| CheckerContext &checkerContext, ProgramStateRef errorState, OOB_Kind kind, |
| std::unique_ptr<BugReporterVisitor> Visitor) const { |
| |
| ExplodedNode *errorNode = checkerContext.generateErrorNode(errorState); |
| if (!errorNode) |
| return; |
| |
| if (!BT) |
| BT.reset(new BuiltinBug(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; |
| case OOB_Tainted: |
| os << "(index is tainted)"; |
| break; |
| } |
| |
| auto BR = std::make_unique<PathSensitiveBugReport>(*BT, os.str(), errorNode); |
| BR->addVisitor(std::move(Visitor)); |
| checkerContext.emitReport(std::move(BR)); |
| } |
| |
| #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 |
| |
| // Lazily computes a value to be used by 'computeOffset'. If 'val' |
| // is unknown or undefined, we lazily substitute '0'. Otherwise, |
| // return 'val'. |
| static inline SVal getValue(SVal val, SValBuilder &svalBuilder) { |
| return val.getAs<UndefinedVal>() ? svalBuilder.makeArrayIndex(0) : val; |
| } |
| |
| // Scale a base value by a scaling factor, and return the scaled |
| // value as an SVal. Used by 'computeOffset'. |
| static inline SVal scaleValue(ProgramStateRef state, |
| NonLoc baseVal, CharUnits scaling, |
| SValBuilder &sb) { |
| return sb.evalBinOpNN(state, BO_Mul, baseVal, |
| sb.makeArrayIndex(scaling.getQuantity()), |
| sb.getArrayIndexType()); |
| } |
| |
| // Add an SVal to another, treating unknown and undefined values as |
| // summing to UnknownVal. Used by 'computeOffset'. |
| static SVal addValue(ProgramStateRef state, SVal x, SVal y, |
| SValBuilder &svalBuilder) { |
| // We treat UnknownVals and UndefinedVals the same here because we |
| // only care about computing offsets. |
| if (x.isUnknownOrUndef() || y.isUnknownOrUndef()) |
| return UnknownVal(); |
| |
| return svalBuilder.evalBinOpNN(state, BO_Add, x.castAs<NonLoc>(), |
| y.castAs<NonLoc>(), |
| svalBuilder.getArrayIndexType()); |
| } |
| |
| /// Compute a raw byte offset from a base region. Used for array bounds |
| /// checking. |
| RegionRawOffsetV2 RegionRawOffsetV2::computeOffset(ProgramStateRef state, |
| SValBuilder &svalBuilder, |
| SVal location) |
| { |
| const MemRegion *region = location.getAsRegion(); |
| SVal offset = UndefinedVal(); |
| |
| while (region) { |
| switch (region->getKind()) { |
| default: { |
| if (const SubRegion *subReg = dyn_cast<SubRegion>(region)) { |
| offset = getValue(offset, svalBuilder); |
| if (!offset.isUnknownOrUndef()) |
| return RegionRawOffsetV2(subReg, offset); |
| } |
| return RegionRawOffsetV2(); |
| } |
| case MemRegion::ElementRegionKind: { |
| const ElementRegion *elemReg = cast<ElementRegion>(region); |
| SVal index = elemReg->getIndex(); |
| if (!index.getAs<NonLoc>()) |
| return RegionRawOffsetV2(); |
| QualType elemType = elemReg->getElementType(); |
| // If the element is an incomplete type, go no further. |
| ASTContext &astContext = svalBuilder.getContext(); |
| if (elemType->isIncompleteType()) |
| return RegionRawOffsetV2(); |
| |
| // Update the offset. |
| offset = addValue(state, |
| getValue(offset, svalBuilder), |
| scaleValue(state, |
| index.castAs<NonLoc>(), |
| astContext.getTypeSizeInChars(elemType), |
| svalBuilder), |
| svalBuilder); |
| |
| if (offset.isUnknownOrUndef()) |
| return RegionRawOffsetV2(); |
| |
| region = elemReg->getSuperRegion(); |
| continue; |
| } |
| } |
| } |
| return RegionRawOffsetV2(); |
| } |
| |
| void ento::registerArrayBoundCheckerV2(CheckerManager &mgr) { |
| mgr.registerChecker<ArrayBoundCheckerV2>(); |
| } |
| |
| bool ento::shouldRegisterArrayBoundCheckerV2(const CheckerManager &mgr) { |
| return true; |
| } |