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//== 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;
}