clang  11.0.0git
ArrayBoundCheckerV2.cpp
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1 //== ArrayBoundCheckerV2.cpp ------------------------------------*- C++ -*--==//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 //
9 // This file defines ArrayBoundCheckerV2, which is a path-sensitive check
10 // which looks for an out-of-bound array element access.
11 //
12 //===----------------------------------------------------------------------===//
13 
14 #include "Taint.h"
15 #include "clang/AST/CharUnits.h"
24 #include "llvm/ADT/SmallString.h"
25 #include "llvm/Support/raw_ostream.h"
26 
27 using namespace clang;
28 using namespace ento;
29 using namespace taint;
30 
31 namespace {
32 class ArrayBoundCheckerV2 :
33  public Checker<check::Location> {
34  mutable std::unique_ptr<BuiltinBug> BT;
35 
36  enum OOB_Kind { OOB_Precedes, OOB_Excedes, OOB_Tainted };
37 
38  void reportOOB(CheckerContext &C, ProgramStateRef errorState, OOB_Kind kind,
39  std::unique_ptr<BugReporterVisitor> Visitor = nullptr) const;
40 
41 public:
42  void checkLocation(SVal l, bool isLoad, const Stmt*S,
43  CheckerContext &C) const;
44 };
45 
46 // FIXME: Eventually replace RegionRawOffset with this class.
47 class RegionRawOffsetV2 {
48 private:
49  const SubRegion *baseRegion;
50  SVal byteOffset;
51 
52  RegionRawOffsetV2()
53  : baseRegion(nullptr), byteOffset(UnknownVal()) {}
54 
55 public:
56  RegionRawOffsetV2(const SubRegion* base, SVal offset)
57  : baseRegion(base), byteOffset(offset) {}
58 
59  NonLoc getByteOffset() const { return byteOffset.castAs<NonLoc>(); }
60  const SubRegion *getRegion() const { return baseRegion; }
61 
62  static RegionRawOffsetV2 computeOffset(ProgramStateRef state,
63  SValBuilder &svalBuilder,
64  SVal location);
65 
66  void dump() const;
67  void dumpToStream(raw_ostream &os) const;
68 };
69 }
70 
71 static SVal computeExtentBegin(SValBuilder &svalBuilder,
72  const MemRegion *region) {
73  const MemSpaceRegion *SR = region->getMemorySpace();
74  if (SR->getKind() == MemRegion::UnknownSpaceRegionKind)
75  return UnknownVal();
76  else
77  return svalBuilder.makeZeroArrayIndex();
78 }
79 
80 // TODO: once the constraint manager is smart enough to handle non simplified
81 // symbolic expressions remove this function. Note that this can not be used in
82 // the constraint manager as is, since this does not handle overflows. It is
83 // safe to assume, however, that memory offsets will not overflow.
84 static std::pair<NonLoc, nonloc::ConcreteInt>
85 getSimplifiedOffsets(NonLoc offset, nonloc::ConcreteInt extent,
86  SValBuilder &svalBuilder) {
87  Optional<nonloc::SymbolVal> SymVal = offset.getAs<nonloc::SymbolVal>();
88  if (SymVal && SymVal->isExpression()) {
89  if (const SymIntExpr *SIE = dyn_cast<SymIntExpr>(SymVal->getSymbol())) {
90  llvm::APSInt constant =
91  APSIntType(extent.getValue()).convert(SIE->getRHS());
92  switch (SIE->getOpcode()) {
93  case BO_Mul:
94  // The constant should never be 0 here, since it the result of scaling
95  // based on the size of a type which is never 0.
96  if ((extent.getValue() % constant) != 0)
97  return std::pair<NonLoc, nonloc::ConcreteInt>(offset, extent);
98  else
99  return getSimplifiedOffsets(
100  nonloc::SymbolVal(SIE->getLHS()),
101  svalBuilder.makeIntVal(extent.getValue() / constant),
102  svalBuilder);
103  case BO_Add:
104  return getSimplifiedOffsets(
105  nonloc::SymbolVal(SIE->getLHS()),
106  svalBuilder.makeIntVal(extent.getValue() - constant), svalBuilder);
107  default:
108  break;
109  }
110  }
111  }
112 
113  return std::pair<NonLoc, nonloc::ConcreteInt>(offset, extent);
114 }
115 
116 void ArrayBoundCheckerV2::checkLocation(SVal location, bool isLoad,
117  const Stmt* LoadS,
118  CheckerContext &checkerContext) const {
119 
120  // NOTE: Instead of using ProgramState::assumeInBound(), we are prototyping
121  // some new logic here that reasons directly about memory region extents.
122  // Once that logic is more mature, we can bring it back to assumeInBound()
123  // for all clients to use.
124  //
125  // The algorithm we are using here for bounds checking is to see if the
126  // memory access is within the extent of the base region. Since we
127  // have some flexibility in defining the base region, we can achieve
128  // various levels of conservatism in our buffer overflow checking.
129  ProgramStateRef state = checkerContext.getState();
130 
131  SValBuilder &svalBuilder = checkerContext.getSValBuilder();
132  const RegionRawOffsetV2 &rawOffset =
133  RegionRawOffsetV2::computeOffset(state, svalBuilder, location);
134 
135  if (!rawOffset.getRegion())
136  return;
137 
138  NonLoc rawOffsetVal = rawOffset.getByteOffset();
139 
140  // CHECK LOWER BOUND: Is byteOffset < extent begin?
141  // If so, we are doing a load/store
142  // before the first valid offset in the memory region.
143 
144  SVal extentBegin = computeExtentBegin(svalBuilder, rawOffset.getRegion());
145 
146  if (Optional<NonLoc> NV = extentBegin.getAs<NonLoc>()) {
147  if (NV->getAs<nonloc::ConcreteInt>()) {
148  std::pair<NonLoc, nonloc::ConcreteInt> simplifiedOffsets =
149  getSimplifiedOffsets(rawOffset.getByteOffset(),
150  NV->castAs<nonloc::ConcreteInt>(),
151  svalBuilder);
152  rawOffsetVal = simplifiedOffsets.first;
153  *NV = simplifiedOffsets.second;
154  }
155 
156  SVal lowerBound = svalBuilder.evalBinOpNN(state, BO_LT, rawOffsetVal, *NV,
157  svalBuilder.getConditionType());
158 
159  Optional<NonLoc> lowerBoundToCheck = lowerBound.getAs<NonLoc>();
160  if (!lowerBoundToCheck)
161  return;
162 
163  ProgramStateRef state_precedesLowerBound, state_withinLowerBound;
164  std::tie(state_precedesLowerBound, state_withinLowerBound) =
165  state->assume(*lowerBoundToCheck);
166 
167  // Are we constrained enough to definitely precede the lower bound?
168  if (state_precedesLowerBound && !state_withinLowerBound) {
169  reportOOB(checkerContext, state_precedesLowerBound, OOB_Precedes);
170  return;
171  }
172 
173  // Otherwise, assume the constraint of the lower bound.
174  assert(state_withinLowerBound);
175  state = state_withinLowerBound;
176  }
177 
178  do {
179  // CHECK UPPER BOUND: Is byteOffset >= size(baseRegion)? If so,
180  // we are doing a load/store after the last valid offset.
181  const MemRegion *MR = rawOffset.getRegion();
182  DefinedOrUnknownSVal Size = getDynamicSize(state, MR, svalBuilder);
183  if (!Size.getAs<NonLoc>())
184  break;
185 
186  if (Size.getAs<nonloc::ConcreteInt>()) {
187  std::pair<NonLoc, nonloc::ConcreteInt> simplifiedOffsets =
188  getSimplifiedOffsets(rawOffset.getByteOffset(),
189  Size.castAs<nonloc::ConcreteInt>(), svalBuilder);
190  rawOffsetVal = simplifiedOffsets.first;
191  Size = simplifiedOffsets.second;
192  }
193 
194  SVal upperbound = svalBuilder.evalBinOpNN(state, BO_GE, rawOffsetVal,
195  Size.castAs<NonLoc>(),
196  svalBuilder.getConditionType());
197 
198  Optional<NonLoc> upperboundToCheck = upperbound.getAs<NonLoc>();
199  if (!upperboundToCheck)
200  break;
201 
202  ProgramStateRef state_exceedsUpperBound, state_withinUpperBound;
203  std::tie(state_exceedsUpperBound, state_withinUpperBound) =
204  state->assume(*upperboundToCheck);
205 
206  // If we are under constrained and the index variables are tainted, report.
207  if (state_exceedsUpperBound && state_withinUpperBound) {
208  SVal ByteOffset = rawOffset.getByteOffset();
209  if (isTainted(state, ByteOffset)) {
210  reportOOB(checkerContext, state_exceedsUpperBound, OOB_Tainted,
211  std::make_unique<TaintBugVisitor>(ByteOffset));
212  return;
213  }
214  } else if (state_exceedsUpperBound) {
215  // If we are constrained enough to definitely exceed the upper bound,
216  // report.
217  assert(!state_withinUpperBound);
218  reportOOB(checkerContext, state_exceedsUpperBound, OOB_Excedes);
219  return;
220  }
221 
222  assert(state_withinUpperBound);
223  state = state_withinUpperBound;
224  }
225  while (false);
226 
227  checkerContext.addTransition(state);
228 }
229 
230 void ArrayBoundCheckerV2::reportOOB(
231  CheckerContext &checkerContext, ProgramStateRef errorState, OOB_Kind kind,
232  std::unique_ptr<BugReporterVisitor> Visitor) const {
233 
234  ExplodedNode *errorNode = checkerContext.generateErrorNode(errorState);
235  if (!errorNode)
236  return;
237 
238  if (!BT)
239  BT.reset(new BuiltinBug(this, "Out-of-bound access"));
240 
241  // FIXME: This diagnostics are preliminary. We should get far better
242  // diagnostics for explaining buffer overruns.
243 
244  SmallString<256> buf;
245  llvm::raw_svector_ostream os(buf);
246  os << "Out of bound memory access ";
247  switch (kind) {
248  case OOB_Precedes:
249  os << "(accessed memory precedes memory block)";
250  break;
251  case OOB_Excedes:
252  os << "(access exceeds upper limit of memory block)";
253  break;
254  case OOB_Tainted:
255  os << "(index is tainted)";
256  break;
257  }
258 
259  auto BR = std::make_unique<PathSensitiveBugReport>(*BT, os.str(), errorNode);
260  BR->addVisitor(std::move(Visitor));
261  checkerContext.emitReport(std::move(BR));
262 }
263 
264 #ifndef NDEBUG
265 LLVM_DUMP_METHOD void RegionRawOffsetV2::dump() const {
266  dumpToStream(llvm::errs());
267 }
268 
269 void RegionRawOffsetV2::dumpToStream(raw_ostream &os) const {
270  os << "raw_offset_v2{" << getRegion() << ',' << getByteOffset() << '}';
271 }
272 #endif
273 
274 // Lazily computes a value to be used by 'computeOffset'. If 'val'
275 // is unknown or undefined, we lazily substitute '0'. Otherwise,
276 // return 'val'.
277 static inline SVal getValue(SVal val, SValBuilder &svalBuilder) {
278  return val.getAs<UndefinedVal>() ? svalBuilder.makeArrayIndex(0) : val;
279 }
280 
281 // Scale a base value by a scaling factor, and return the scaled
282 // value as an SVal. Used by 'computeOffset'.
283 static inline SVal scaleValue(ProgramStateRef state,
284  NonLoc baseVal, CharUnits scaling,
285  SValBuilder &sb) {
286  return sb.evalBinOpNN(state, BO_Mul, baseVal,
287  sb.makeArrayIndex(scaling.getQuantity()),
288  sb.getArrayIndexType());
289 }
290 
291 // Add an SVal to another, treating unknown and undefined values as
292 // summing to UnknownVal. Used by 'computeOffset'.
293 static SVal addValue(ProgramStateRef state, SVal x, SVal y,
294  SValBuilder &svalBuilder) {
295  // We treat UnknownVals and UndefinedVals the same here because we
296  // only care about computing offsets.
297  if (x.isUnknownOrUndef() || y.isUnknownOrUndef())
298  return UnknownVal();
299 
300  return svalBuilder.evalBinOpNN(state, BO_Add, x.castAs<NonLoc>(),
301  y.castAs<NonLoc>(),
302  svalBuilder.getArrayIndexType());
303 }
304 
305 /// Compute a raw byte offset from a base region. Used for array bounds
306 /// checking.
307 RegionRawOffsetV2 RegionRawOffsetV2::computeOffset(ProgramStateRef state,
308  SValBuilder &svalBuilder,
309  SVal location)
310 {
311  const MemRegion *region = location.getAsRegion();
312  SVal offset = UndefinedVal();
313 
314  while (region) {
315  switch (region->getKind()) {
316  default: {
317  if (const SubRegion *subReg = dyn_cast<SubRegion>(region)) {
318  offset = getValue(offset, svalBuilder);
319  if (!offset.isUnknownOrUndef())
320  return RegionRawOffsetV2(subReg, offset);
321  }
322  return RegionRawOffsetV2();
323  }
324  case MemRegion::ElementRegionKind: {
325  const ElementRegion *elemReg = cast<ElementRegion>(region);
326  SVal index = elemReg->getIndex();
327  if (!index.getAs<NonLoc>())
328  return RegionRawOffsetV2();
329  QualType elemType = elemReg->getElementType();
330  // If the element is an incomplete type, go no further.
331  ASTContext &astContext = svalBuilder.getContext();
332  if (elemType->isIncompleteType())
333  return RegionRawOffsetV2();
334 
335  // Update the offset.
336  offset = addValue(state,
337  getValue(offset, svalBuilder),
339  index.castAs<NonLoc>(),
340  astContext.getTypeSizeInChars(elemType),
341  svalBuilder),
342  svalBuilder);
343 
344  if (offset.isUnknownOrUndef())
345  return RegionRawOffsetV2();
346 
347  region = elemReg->getSuperRegion();
348  continue;
349  }
350  }
351  }
352  return RegionRawOffsetV2();
353 }
354 
355 void ento::registerArrayBoundCheckerV2(CheckerManager &mgr) {
356  mgr.registerChecker<ArrayBoundCheckerV2>();
357 }
358 
359 bool ento::shouldRegisterArrayBoundCheckerV2(const CheckerManager &mgr) {
360  return true;
361 }
A (possibly-)qualified type.
Definition: Type.h:655
static SVal addValue(ProgramStateRef state, SVal x, SVal y, SValBuilder &svalBuilder)
Stmt - This represents one statement.
Definition: Stmt.h:68
IntrusiveRefCntPtr< const ProgramState > ProgramStateRef
Holds long-lived AST nodes (such as types and decls) that can be referred to throughout the semantic ...
Definition: ASTContext.h:174
i32 captured_struct **param SharedsTy A type which contains references the shared variables *param Shareds Context with the list of shared variables from the p *TaskFunction *param Data Additional data for task generation like final * state
CharUnits - This is an opaque type for sizes expressed in character units.
Definition: CharUnits.h:38
static void dump(llvm::raw_ostream &OS, StringRef FunctionName, ArrayRef< CounterExpression > Expressions, ArrayRef< CounterMappingRegion > Regions)
static SVal computeExtentBegin(SValBuilder &svalBuilder, const MemRegion *region)
QuantityType getQuantity() const
getQuantity - Get the raw integer representation of this quantity.
Definition: CharUnits.h:179
static SVal getValue(SVal val, SValBuilder &svalBuilder)
DefinedOrUnknownSVal getDynamicSize(ProgramStateRef State, const MemRegion *MR, SValBuilder &SVB)
Get the stored dynamic size for the region MR.
Definition: DynamicSize.cpp:25
llvm::APSInt APSInt
bool isTainted(ProgramStateRef State, const Stmt *S, const LocationContext *LCtx, TaintTagType Kind=TaintTagGeneric)
Check if the statement has a tainted value in the given state.
static SVal scaleValue(ProgramStateRef state, NonLoc baseVal, CharUnits scaling, SValBuilder &sb)
Dataflow Directional Tag Classes.
BinarySymExprImpl< const SymExpr *, const llvm::APSInt &, SymExpr::Kind::SymIntExprKind > SymIntExpr
Represents a symbolic expression like &#39;x&#39; + 3.
bool isIncompleteType(NamedDecl **Def=nullptr) const
Types are partitioned into 3 broad categories (C99 6.2.5p1): object types, function types...
Definition: Type.cpp:2211
unsigned kind
All of the diagnostics that can be emitted by the frontend.
Definition: DiagnosticIDs.h:60
static std::pair< NonLoc, nonloc::ConcreteInt > getSimplifiedOffsets(NonLoc offset, nonloc::ConcreteInt extent, SValBuilder &svalBuilder)
CharUnits getTypeSizeInChars(QualType T) const
Return the size of the specified (complete) type T, in characters.