318 lines
11 KiB
C++
318 lines
11 KiB
C++
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//== ArrayBoundCheckerV2.cpp ------------------------------------*- C++ -*--==//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// This file defines ArrayBoundCheckerV2, which is a path-sensitive check
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// which looks for an out-of-bound array element access.
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//
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//===----------------------------------------------------------------------===//
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#include "ClangSACheckers.h"
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#include "clang/AST/CharUnits.h"
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#include "clang/StaticAnalyzer/Core/BugReporter/BugType.h"
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#include "clang/StaticAnalyzer/Core/Checker.h"
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#include "clang/StaticAnalyzer/Core/CheckerManager.h"
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#include "clang/StaticAnalyzer/Core/PathSensitive/CheckerContext.h"
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#include "clang/StaticAnalyzer/Core/PathSensitive/ExprEngine.h"
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#include "llvm/ADT/SmallString.h"
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#include "llvm/Support/raw_ostream.h"
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using namespace clang;
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using namespace ento;
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namespace {
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class ArrayBoundCheckerV2 :
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public Checker<check::Location> {
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mutable OwningPtr<BuiltinBug> BT;
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enum OOB_Kind { OOB_Precedes, OOB_Excedes, OOB_Tainted };
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void reportOOB(CheckerContext &C, ProgramStateRef errorState,
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OOB_Kind kind) const;
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public:
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void checkLocation(SVal l, bool isLoad, const Stmt*S,
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CheckerContext &C) const;
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};
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// FIXME: Eventually replace RegionRawOffset with this class.
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class RegionRawOffsetV2 {
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private:
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const SubRegion *baseRegion;
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SVal byteOffset;
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RegionRawOffsetV2()
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: baseRegion(0), byteOffset(UnknownVal()) {}
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public:
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RegionRawOffsetV2(const SubRegion* base, SVal offset)
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: baseRegion(base), byteOffset(offset) {}
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NonLoc getByteOffset() const { return byteOffset.castAs<NonLoc>(); }
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const SubRegion *getRegion() const { return baseRegion; }
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static RegionRawOffsetV2 computeOffset(ProgramStateRef state,
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SValBuilder &svalBuilder,
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SVal location);
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void dump() const;
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void dumpToStream(raw_ostream &os) const;
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};
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}
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static SVal computeExtentBegin(SValBuilder &svalBuilder,
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const MemRegion *region) {
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while (true)
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switch (region->getKind()) {
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default:
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return svalBuilder.makeZeroArrayIndex();
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case MemRegion::SymbolicRegionKind:
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// FIXME: improve this later by tracking symbolic lower bounds
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// for symbolic regions.
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return UnknownVal();
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case MemRegion::ElementRegionKind:
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region = cast<SubRegion>(region)->getSuperRegion();
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continue;
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}
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}
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void ArrayBoundCheckerV2::checkLocation(SVal location, bool isLoad,
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const Stmt* LoadS,
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CheckerContext &checkerContext) const {
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// NOTE: Instead of using ProgramState::assumeInBound(), we are prototyping
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// some new logic here that reasons directly about memory region extents.
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// Once that logic is more mature, we can bring it back to assumeInBound()
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// for all clients to use.
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//
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// The algorithm we are using here for bounds checking is to see if the
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// memory access is within the extent of the base region. Since we
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// have some flexibility in defining the base region, we can achieve
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// various levels of conservatism in our buffer overflow checking.
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ProgramStateRef state = checkerContext.getState();
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ProgramStateRef originalState = state;
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SValBuilder &svalBuilder = checkerContext.getSValBuilder();
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const RegionRawOffsetV2 &rawOffset =
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RegionRawOffsetV2::computeOffset(state, svalBuilder, location);
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if (!rawOffset.getRegion())
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return;
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// CHECK LOWER BOUND: Is byteOffset < extent begin?
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// If so, we are doing a load/store
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// before the first valid offset in the memory region.
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SVal extentBegin = computeExtentBegin(svalBuilder, rawOffset.getRegion());
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if (Optional<NonLoc> NV = extentBegin.getAs<NonLoc>()) {
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SVal lowerBound =
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svalBuilder.evalBinOpNN(state, BO_LT, rawOffset.getByteOffset(), *NV,
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svalBuilder.getConditionType());
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Optional<NonLoc> lowerBoundToCheck = lowerBound.getAs<NonLoc>();
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if (!lowerBoundToCheck)
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return;
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ProgramStateRef state_precedesLowerBound, state_withinLowerBound;
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llvm::tie(state_precedesLowerBound, state_withinLowerBound) =
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state->assume(*lowerBoundToCheck);
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// Are we constrained enough to definitely precede the lower bound?
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if (state_precedesLowerBound && !state_withinLowerBound) {
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reportOOB(checkerContext, state_precedesLowerBound, OOB_Precedes);
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return;
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}
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// Otherwise, assume the constraint of the lower bound.
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assert(state_withinLowerBound);
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state = state_withinLowerBound;
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}
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do {
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// CHECK UPPER BOUND: Is byteOffset >= extent(baseRegion)? If so,
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// we are doing a load/store after the last valid offset.
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DefinedOrUnknownSVal extentVal =
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rawOffset.getRegion()->getExtent(svalBuilder);
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if (!extentVal.getAs<NonLoc>())
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break;
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SVal upperbound
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= svalBuilder.evalBinOpNN(state, BO_GE, rawOffset.getByteOffset(),
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extentVal.castAs<NonLoc>(),
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svalBuilder.getConditionType());
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Optional<NonLoc> upperboundToCheck = upperbound.getAs<NonLoc>();
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if (!upperboundToCheck)
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break;
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ProgramStateRef state_exceedsUpperBound, state_withinUpperBound;
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llvm::tie(state_exceedsUpperBound, state_withinUpperBound) =
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state->assume(*upperboundToCheck);
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// If we are under constrained and the index variables are tainted, report.
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if (state_exceedsUpperBound && state_withinUpperBound) {
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if (state->isTainted(rawOffset.getByteOffset()))
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reportOOB(checkerContext, state_exceedsUpperBound, OOB_Tainted);
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return;
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}
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// If we are constrained enough to definitely exceed the upper bound, report.
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if (state_exceedsUpperBound) {
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assert(!state_withinUpperBound);
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reportOOB(checkerContext, state_exceedsUpperBound, OOB_Excedes);
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return;
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}
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assert(state_withinUpperBound);
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state = state_withinUpperBound;
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}
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while (false);
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if (state != originalState)
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checkerContext.addTransition(state);
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}
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void ArrayBoundCheckerV2::reportOOB(CheckerContext &checkerContext,
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ProgramStateRef errorState,
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OOB_Kind kind) const {
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ExplodedNode *errorNode = checkerContext.generateSink(errorState);
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if (!errorNode)
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return;
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if (!BT)
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BT.reset(new BuiltinBug("Out-of-bound access"));
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// FIXME: This diagnostics are preliminary. We should get far better
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// diagnostics for explaining buffer overruns.
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SmallString<256> buf;
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llvm::raw_svector_ostream os(buf);
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os << "Out of bound memory access ";
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switch (kind) {
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case OOB_Precedes:
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os << "(accessed memory precedes memory block)";
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break;
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case OOB_Excedes:
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os << "(access exceeds upper limit of memory block)";
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break;
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case OOB_Tainted:
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os << "(index is tainted)";
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break;
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}
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checkerContext.emitReport(new BugReport(*BT, os.str(), errorNode));
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}
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void RegionRawOffsetV2::dump() const {
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dumpToStream(llvm::errs());
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}
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void RegionRawOffsetV2::dumpToStream(raw_ostream &os) const {
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os << "raw_offset_v2{" << getRegion() << ',' << getByteOffset() << '}';
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}
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// FIXME: Merge with the implementation of the same method in Store.cpp
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static bool IsCompleteType(ASTContext &Ctx, QualType Ty) {
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if (const RecordType *RT = Ty->getAs<RecordType>()) {
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const RecordDecl *D = RT->getDecl();
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if (!D->getDefinition())
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return false;
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}
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return true;
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}
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// Lazily computes a value to be used by 'computeOffset'. If 'val'
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// is unknown or undefined, we lazily substitute '0'. Otherwise,
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// return 'val'.
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static inline SVal getValue(SVal val, SValBuilder &svalBuilder) {
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return val.getAs<UndefinedVal>() ? svalBuilder.makeArrayIndex(0) : val;
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}
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// Scale a base value by a scaling factor, and return the scaled
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// value as an SVal. Used by 'computeOffset'.
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static inline SVal scaleValue(ProgramStateRef state,
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NonLoc baseVal, CharUnits scaling,
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SValBuilder &sb) {
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return sb.evalBinOpNN(state, BO_Mul, baseVal,
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sb.makeArrayIndex(scaling.getQuantity()),
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sb.getArrayIndexType());
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}
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// Add an SVal to another, treating unknown and undefined values as
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// summing to UnknownVal. Used by 'computeOffset'.
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static SVal addValue(ProgramStateRef state, SVal x, SVal y,
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SValBuilder &svalBuilder) {
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// We treat UnknownVals and UndefinedVals the same here because we
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// only care about computing offsets.
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if (x.isUnknownOrUndef() || y.isUnknownOrUndef())
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return UnknownVal();
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return svalBuilder.evalBinOpNN(state, BO_Add, x.castAs<NonLoc>(),
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y.castAs<NonLoc>(),
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svalBuilder.getArrayIndexType());
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}
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/// Compute a raw byte offset from a base region. Used for array bounds
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/// checking.
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RegionRawOffsetV2 RegionRawOffsetV2::computeOffset(ProgramStateRef state,
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SValBuilder &svalBuilder,
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SVal location)
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{
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const MemRegion *region = location.getAsRegion();
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SVal offset = UndefinedVal();
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while (region) {
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switch (region->getKind()) {
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default: {
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if (const SubRegion *subReg = dyn_cast<SubRegion>(region)) {
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offset = getValue(offset, svalBuilder);
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if (!offset.isUnknownOrUndef())
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return RegionRawOffsetV2(subReg, offset);
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}
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return RegionRawOffsetV2();
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}
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case MemRegion::ElementRegionKind: {
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const ElementRegion *elemReg = cast<ElementRegion>(region);
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SVal index = elemReg->getIndex();
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if (!index.getAs<NonLoc>())
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return RegionRawOffsetV2();
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QualType elemType = elemReg->getElementType();
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// If the element is an incomplete type, go no further.
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ASTContext &astContext = svalBuilder.getContext();
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if (!IsCompleteType(astContext, elemType))
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return RegionRawOffsetV2();
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// Update the offset.
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offset = addValue(state,
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getValue(offset, svalBuilder),
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scaleValue(state,
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index.castAs<NonLoc>(),
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astContext.getTypeSizeInChars(elemType),
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svalBuilder),
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svalBuilder);
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if (offset.isUnknownOrUndef())
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return RegionRawOffsetV2();
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region = elemReg->getSuperRegion();
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continue;
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}
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}
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}
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return RegionRawOffsetV2();
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}
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void ento::registerArrayBoundCheckerV2(CheckerManager &mgr) {
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mgr.registerChecker<ArrayBoundCheckerV2>();
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}
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