| //== ArrayBoundCheckerV2.cpp ------------------------------------*- C++ -*--==// |
| // |
| // The LLVM Compiler Infrastructure |
| // |
| // This file is distributed under the University of Illinois Open Source |
| // License. See LICENSE.TXT for details. |
| // |
| //===----------------------------------------------------------------------===// |
| // |
| // This file defines ArrayBoundCheckerV2, which is a path-sensitive check |
| // which looks for an out-of-bound array element access. |
| // |
| //===----------------------------------------------------------------------===// |
| |
| #include "ClangSACheckers.h" |
| #include "clang/StaticAnalyzer/Core/Checker.h" |
| #include "clang/StaticAnalyzer/Core/CheckerManager.h" |
| #include "clang/StaticAnalyzer/Core/PathSensitive/CheckerContext.h" |
| #include "clang/StaticAnalyzer/Core/BugReporter/BugType.h" |
| #include "clang/StaticAnalyzer/Core/PathSensitive/ExprEngine.h" |
| #include "clang/AST/CharUnits.h" |
| |
| using namespace clang; |
| using namespace ento; |
| |
| namespace { |
| class ArrayBoundCheckerV2 : |
| public Checker<check::Location> { |
| mutable llvm::OwningPtr<BuiltinBug> BT; |
| |
| enum OOB_Kind { OOB_Precedes, OOB_Excedes }; |
| |
| void reportOOB(CheckerContext &C, const GRState *errorState, |
| OOB_Kind kind) const; |
| |
| public: |
| void checkLocation(SVal l, bool isLoad, CheckerContext &C) const; |
| }; |
| |
| // FIXME: Eventually replace RegionRawOffset with this class. |
| class RegionRawOffsetV2 { |
| private: |
| const SubRegion *baseRegion; |
| SVal byteOffset; |
| |
| RegionRawOffsetV2() |
| : baseRegion(0), byteOffset(UnknownVal()) {} |
| |
| public: |
| RegionRawOffsetV2(const SubRegion* base, SVal offset) |
| : baseRegion(base), byteOffset(offset) {} |
| |
| NonLoc getByteOffset() const { return cast<NonLoc>(byteOffset); } |
| const SubRegion *getRegion() const { return baseRegion; } |
| |
| static RegionRawOffsetV2 computeOffset(const GRState *state, |
| SValBuilder &svalBuilder, |
| SVal location); |
| |
| void dump() const; |
| void dumpToStream(raw_ostream &os) const; |
| }; |
| } |
| |
| static SVal computeExtentBegin(SValBuilder &svalBuilder, |
| const MemRegion *region) { |
| while (true) |
| switch (region->getKind()) { |
| default: |
| return svalBuilder.makeZeroArrayIndex(); |
| case MemRegion::SymbolicRegionKind: |
| // FIXME: improve this later by tracking symbolic lower bounds |
| // for symbolic regions. |
| return UnknownVal(); |
| case MemRegion::ElementRegionKind: |
| region = cast<SubRegion>(region)->getSuperRegion(); |
| continue; |
| } |
| } |
| |
| void ArrayBoundCheckerV2::checkLocation(SVal location, bool isLoad, |
| CheckerContext &checkerContext) const { |
| |
| // NOTE: Instead of using GRState::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. |
| const GRState *state = checkerContext.getState(); |
| const GRState *originalState = state; |
| |
| SValBuilder &svalBuilder = checkerContext.getSValBuilder(); |
| const RegionRawOffsetV2 &rawOffset = |
| RegionRawOffsetV2::computeOffset(state, svalBuilder, location); |
| |
| if (!rawOffset.getRegion()) |
| return; |
| |
| // 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 (isa<NonLoc>(extentBegin)) { |
| SVal lowerBound |
| = svalBuilder.evalBinOpNN(state, BO_LT, rawOffset.getByteOffset(), |
| cast<NonLoc>(extentBegin), |
| svalBuilder.getConditionType()); |
| |
| NonLoc *lowerBoundToCheck = dyn_cast<NonLoc>(&lowerBound); |
| if (!lowerBoundToCheck) |
| return; |
| |
| const GRState *state_precedesLowerBound, *state_withinLowerBound; |
| llvm::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 >= extent(baseRegion)? If so, |
| // we are doing a load/store after the last valid offset. |
| DefinedOrUnknownSVal extentVal = |
| rawOffset.getRegion()->getExtent(svalBuilder); |
| if (!isa<NonLoc>(extentVal)) |
| break; |
| |
| SVal upperbound |
| = svalBuilder.evalBinOpNN(state, BO_GE, rawOffset.getByteOffset(), |
| cast<NonLoc>(extentVal), |
| svalBuilder.getConditionType()); |
| |
| NonLoc *upperboundToCheck = dyn_cast<NonLoc>(&upperbound); |
| if (!upperboundToCheck) |
| break; |
| |
| const GRState *state_exceedsUpperBound, *state_withinUpperBound; |
| llvm::tie(state_exceedsUpperBound, state_withinUpperBound) = |
| state->assume(*upperboundToCheck); |
| |
| // Are we constrained enough to definitely exceed the upper bound? |
| if (state_exceedsUpperBound && !state_withinUpperBound) { |
| reportOOB(checkerContext, state_exceedsUpperBound, OOB_Excedes); |
| return; |
| } |
| |
| assert(state_withinUpperBound); |
| state = state_withinUpperBound; |
| } |
| while (false); |
| |
| if (state != originalState) |
| checkerContext.generateNode(state); |
| } |
| |
| void ArrayBoundCheckerV2::reportOOB(CheckerContext &checkerContext, |
| const GRState *errorState, |
| OOB_Kind kind) const { |
| |
| ExplodedNode *errorNode = checkerContext.generateSink(errorState); |
| if (!errorNode) |
| return; |
| |
| if (!BT) |
| BT.reset(new BuiltinBug("Out-of-bound access")); |
| |
| // FIXME: This diagnostics are preliminary. We should get far better |
| // diagnostics for explaining buffer overruns. |
| |
| llvm::SmallString<256> buf; |
| llvm::raw_svector_ostream os(buf); |
| os << "Out of bound memory access " |
| << (kind == OOB_Precedes ? "(accessed memory precedes memory block)" |
| : "(access exceeds upper limit of memory block)"); |
| |
| checkerContext.EmitReport(new RangedBugReport(*BT, os.str(), errorNode)); |
| } |
| |
| void RegionRawOffsetV2::dump() const { |
| dumpToStream(llvm::errs()); |
| } |
| |
| void RegionRawOffsetV2::dumpToStream(raw_ostream &os) const { |
| os << "raw_offset_v2{" << getRegion() << ',' << getByteOffset() << '}'; |
| } |
| |
| // FIXME: Merge with the implementation of the same method in Store.cpp |
| static bool IsCompleteType(ASTContext &Ctx, QualType Ty) { |
| if (const RecordType *RT = Ty->getAs<RecordType>()) { |
| const RecordDecl *D = RT->getDecl(); |
| if (!D->getDefinition()) |
| return false; |
| } |
| |
| return true; |
| } |
| |
| |
| // 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 isa<UndefinedVal>(val) ? 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(const GRState *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(const GRState *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, |
| cast<NonLoc>(x), cast<NonLoc>(y), |
| svalBuilder.getArrayIndexType()); |
| } |
| |
| /// Compute a raw byte offset from a base region. Used for array bounds |
| /// checking. |
| RegionRawOffsetV2 RegionRawOffsetV2::computeOffset(const GRState *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 (!isa<NonLoc>(index)) |
| return RegionRawOffsetV2(); |
| QualType elemType = elemReg->getElementType(); |
| // If the element is an incomplete type, go no further. |
| ASTContext &astContext = svalBuilder.getContext(); |
| if (!IsCompleteType(astContext, elemType)) |
| return RegionRawOffsetV2(); |
| |
| // Update the offset. |
| offset = addValue(state, |
| getValue(offset, svalBuilder), |
| scaleValue(state, |
| cast<NonLoc>(index), |
| astContext.getTypeSizeInChars(elemType), |
| svalBuilder), |
| svalBuilder); |
| |
| if (offset.isUnknownOrUndef()) |
| return RegionRawOffsetV2(); |
| |
| region = elemReg->getSuperRegion(); |
| continue; |
| } |
| } |
| } |
| return RegionRawOffsetV2(); |
| } |
| |
| |
| void ento::registerArrayBoundCheckerV2(CheckerManager &mgr) { |
| mgr.registerChecker<ArrayBoundCheckerV2>(); |
| } |