362 lines
13 KiB
C++
362 lines
13 KiB
C++
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//== ArrayBoundCheckerV2.cpp ------------------------------------*- C++ -*--==//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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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 "Taint.h"
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#include "clang/AST/CharUnits.h"
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#include "clang/StaticAnalyzer/Checkers/BuiltinCheckerRegistration.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/APSIntType.h"
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#include "clang/StaticAnalyzer/Core/PathSensitive/CheckerContext.h"
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#include "clang/StaticAnalyzer/Core/PathSensitive/DynamicSize.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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using namespace taint;
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namespace {
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class ArrayBoundCheckerV2 :
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public Checker<check::Location> {
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mutable std::unique_ptr<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, OOB_Kind kind,
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std::unique_ptr<BugReporterVisitor> Visitor = nullptr) 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(nullptr), 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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const MemSpaceRegion *SR = region->getMemorySpace();
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if (SR->getKind() == MemRegion::UnknownSpaceRegionKind)
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return UnknownVal();
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else
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return svalBuilder.makeZeroArrayIndex();
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}
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// TODO: once the constraint manager is smart enough to handle non simplified
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// symbolic expressions remove this function. Note that this can not be used in
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// the constraint manager as is, since this does not handle overflows. It is
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// safe to assume, however, that memory offsets will not overflow.
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static std::pair<NonLoc, nonloc::ConcreteInt>
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getSimplifiedOffsets(NonLoc offset, nonloc::ConcreteInt extent,
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SValBuilder &svalBuilder) {
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Optional<nonloc::SymbolVal> SymVal = offset.getAs<nonloc::SymbolVal>();
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if (SymVal && SymVal->isExpression()) {
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if (const SymIntExpr *SIE = dyn_cast<SymIntExpr>(SymVal->getSymbol())) {
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llvm::APSInt constant =
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APSIntType(extent.getValue()).convert(SIE->getRHS());
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switch (SIE->getOpcode()) {
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case BO_Mul:
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// The constant should never be 0 here, since it the result of scaling
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// based on the size of a type which is never 0.
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if ((extent.getValue() % constant) != 0)
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return std::pair<NonLoc, nonloc::ConcreteInt>(offset, extent);
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else
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return getSimplifiedOffsets(
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nonloc::SymbolVal(SIE->getLHS()),
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svalBuilder.makeIntVal(extent.getValue() / constant),
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svalBuilder);
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case BO_Add:
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return getSimplifiedOffsets(
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nonloc::SymbolVal(SIE->getLHS()),
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svalBuilder.makeIntVal(extent.getValue() - constant), svalBuilder);
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default:
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break;
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}
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}
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}
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return std::pair<NonLoc, nonloc::ConcreteInt>(offset, extent);
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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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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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NonLoc rawOffsetVal = rawOffset.getByteOffset();
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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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if (NV->getAs<nonloc::ConcreteInt>()) {
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std::pair<NonLoc, nonloc::ConcreteInt> simplifiedOffsets =
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getSimplifiedOffsets(rawOffset.getByteOffset(),
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NV->castAs<nonloc::ConcreteInt>(),
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svalBuilder);
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rawOffsetVal = simplifiedOffsets.first;
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*NV = simplifiedOffsets.second;
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}
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SVal lowerBound = svalBuilder.evalBinOpNN(state, BO_LT, rawOffsetVal, *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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std::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 >= size(baseRegion)? If so,
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// we are doing a load/store after the last valid offset.
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const MemRegion *MR = rawOffset.getRegion();
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DefinedOrUnknownSVal Size = getDynamicSize(state, MR, svalBuilder);
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if (!Size.getAs<NonLoc>())
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break;
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if (Size.getAs<nonloc::ConcreteInt>()) {
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std::pair<NonLoc, nonloc::ConcreteInt> simplifiedOffsets =
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getSimplifiedOffsets(rawOffset.getByteOffset(),
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Size.castAs<nonloc::ConcreteInt>(), svalBuilder);
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rawOffsetVal = simplifiedOffsets.first;
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Size = simplifiedOffsets.second;
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}
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SVal upperbound = svalBuilder.evalBinOpNN(state, BO_GE, rawOffsetVal,
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Size.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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std::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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SVal ByteOffset = rawOffset.getByteOffset();
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if (isTainted(state, ByteOffset)) {
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reportOOB(checkerContext, state_exceedsUpperBound, OOB_Tainted,
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std::make_unique<TaintBugVisitor>(ByteOffset));
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return;
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}
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} else if (state_exceedsUpperBound) {
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// If we are constrained enough to definitely exceed the upper bound,
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// report.
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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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checkerContext.addTransition(state);
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}
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void ArrayBoundCheckerV2::reportOOB(
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CheckerContext &checkerContext, ProgramStateRef errorState, OOB_Kind kind,
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std::unique_ptr<BugReporterVisitor> Visitor) const {
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ExplodedNode *errorNode = checkerContext.generateErrorNode(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(this, "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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auto BR = std::make_unique<PathSensitiveBugReport>(*BT, os.str(), errorNode);
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BR->addVisitor(std::move(Visitor));
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checkerContext.emitReport(std::move(BR));
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}
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#ifndef NDEBUG
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LLVM_DUMP_METHOD 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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#endif
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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 (elemType->isIncompleteType())
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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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bool ento::shouldRegisterArrayBoundCheckerV2(const CheckerManager &mgr) {
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return true;
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}
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