Add WIP prototype of a new buffer overflow

checker based on using raw (symbolic) byte offsets
from a base region.

llvm-svn: 122469

clang/include/clang/Driver/CC1Options.td

@@ -70,6 +70,8 @@ def analysis_WarnIdempotentOps : Flag<"-analyzer-check-idempotent-operations">,
   HelpText<"Warn about idempotent operations">;
 def analysis_AnalyzerStats : Flag<"-analyzer-stats">,
   HelpText<"Emit warnings with analyzer statistics">;
+def analysis_WarnBufferOverflows : Flag<"-analyzer-check-buffer-overflows">,
+  HelpText<"Warn about buffer overflows">;
 
 def analyzer_store : Separate<"-analyzer-store">,
   HelpText<"Source Code Analysis - Abstract Memory Store Models">;

clang/include/clang/Frontend/AnalyzerOptions.h

@@ -68,6 +68,7 @@ public:
   unsigned AnalyzerStats : 1;
   unsigned EagerlyAssume : 1;
   unsigned IdempotentOps : 1;
+  unsigned BufferOverflows : 1;
   unsigned PurgeDead : 1;
   unsigned TrimGraph : 1;
   unsigned VisualizeEGDot : 1;
@@ -89,6 +90,8 @@ public:
     AnalyzeNestedBlocks = 0;
     AnalyzerStats = 0;
     EagerlyAssume = 0;
+    IdempotentOps = 0;
+    BufferOverflows = 0;    
     PurgeDead = 1;
     TrimGraph = 0;
     VisualizeEGDot = 0;

clang/lib/Frontend/CompilerInvocation.cpp

@@ -117,7 +117,9 @@ static void AnalyzerOptsToArgs(const AnalyzerOptions &Opts,
   if (Opts.EnableExperimentalInternalChecks)
     Res.push_back("-analyzer-experimental-internal-checks");
   if (Opts.IdempotentOps)
-      Res.push_back("-analyzer-check-idempotent-operations");
+    Res.push_back("-analyzer-check-idempotent-operations");
+  if (Opts.BufferOverflows)
+    Res.push_back("-analyzer-check-buffer-overflows");
 }
 
 static void CodeGenOptsToArgs(const CodeGenOptions &Opts,
@@ -857,6 +859,7 @@ static void ParseAnalyzerArgs(AnalyzerOptions &Opts, ArgList &Args,
   Opts.MaxLoop = Args.getLastArgIntValue(OPT_analyzer_max_loop, 4, Diags);
   Opts.InlineCall = Args.hasArg(OPT_analyzer_inline_call);
   Opts.IdempotentOps = Args.hasArg(OPT_analysis_WarnIdempotentOps);
+  Opts.BufferOverflows = Args.hasArg(OPT_analysis_WarnBufferOverflows);
 }
 
 static void ParseCodeGenArgs(CodeGenOptions &Opts, ArgList &Args, InputKind IK,

clang/lib/GR/Checkers/AnalysisConsumer.cpp

@@ -354,6 +354,9 @@ static void ActionExprEngine(AnalysisConsumer &C, AnalysisManager& mgr,
   if (C.Opts.IdempotentOps || C.Opts.EnableExperimentalChecks
       || C.Opts.EnableExperimentalInternalChecks)
     RegisterIdempotentOperationChecker(Eng);
+  
+  if (C.Opts.BufferOverflows)
+    RegisterArrayBoundCheckerV2(Eng);
 
   // Enable AnalyzerStatsChecker if it was given as an argument
   if (C.Opts.AnalyzerStats)

clang/lib/GR/Checkers/ArrayBoundCheckerV2.cpp

@@ -0,0 +1,277 @@
+//== 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 "ExprEngineInternalChecks.h"
+#include "clang/GR/BugReporter/BugType.h"
+#include "clang/GR/PathSensitive/CheckerVisitor.h"
+#include "clang/GR/PathSensitive/ExprEngine.h"
+#include "clang/AST/CharUnits.h"
+
+using namespace clang;
+using namespace GR;
+
+namespace {
+class ArrayBoundCheckerV2 : 
+    public CheckerVisitor<ArrayBoundCheckerV2> {      
+  BuiltinBug *BT;
+      
+  enum OOB_Kind { OOB_Precedes, OOB_Excedes };
+  
+  void reportOOB(CheckerContext &C, const GRState *errorState,
+                 OOB_Kind kind);
+      
+public:
+  ArrayBoundCheckerV2() : BT(0) {}
+  static void *getTag() { static int x = 0; return &x; }
+  void visitLocation(CheckerContext &C, const Stmt *S, SVal l);      
+};
+
+// 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(llvm::raw_ostream& os) const;
+};
+}
+
+void GR::RegisterArrayBoundCheckerV2(ExprEngine &Eng) {
+  Eng.registerCheck(new ArrayBoundCheckerV2());
+}
+
+void ArrayBoundCheckerV2::visitLocation(CheckerContext &checkerContext,
+                                        const Stmt *S,
+                                        SVal location) {
+
+  // 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 < 0?  If so, we are doing a load/store
+  //  before the first valid offset in the memory region.
+
+  SVal lowerBound
+    = svalBuilder.evalBinOpNN(state, BO_LT, rawOffset.getByteOffset(),
+                              svalBuilder.makeZeroArrayIndex(),
+                              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) {
+  
+  ExplodedNode *errorNode = checkerContext.generateSink(errorState);
+  if (!errorNode)
+    return;
+
+  if (!BT)
+    BT = 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(llvm::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))
+          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();
+}
+
+
+

clang/lib/GR/Checkers/CMakeLists.txt

@@ -2,9 +2,11 @@ add_clang_library(clangGRCheckers
   AdjustedReturnValueChecker.cpp
   AnalysisConsumer.cpp
   ArrayBoundChecker.cpp
+  ArrayBoundCheckerV2.cpp
   AttrNonNullChecker.cpp
   BasicObjCFoundationChecks.cpp
   BuiltinFunctionChecker.cpp
+  CStringChecker.cpp
   CallAndMessageChecker.cpp
   CastSizeChecker.cpp
   CastToStructChecker.cpp
@@ -14,7 +16,6 @@ add_clang_library(clangGRCheckers
   CheckSecuritySyntaxOnly.cpp
   CheckSizeofPointer.cpp
   ChrootChecker.cpp
-  CStringChecker.cpp
   DereferenceChecker.cpp
   DivZeroChecker.cpp
   ExprEngine.cpp

clang/lib/GR/Checkers/ExprEngineInternalChecks.h

@@ -24,6 +24,7 @@ class ExprEngine;
 // Foundational checks that handle basic semantics.
 void RegisterAdjustedReturnValueChecker(ExprEngine &Eng);
 void RegisterArrayBoundChecker(ExprEngine &Eng);
+void RegisterArrayBoundCheckerV2(ExprEngine &Eng);
 void RegisterAttrNonNullChecker(ExprEngine &Eng);
 void RegisterBuiltinFunctionChecker(ExprEngine &Eng);
 void RegisterCallAndMessageChecker(ExprEngine &Eng);

clang/test/Analysis/out-of-bounds.c

@@ -0,0 +1,132 @@
+// RUN: %clang_cc1 -analyze -analyzer-check-objc-mem -analyzer-check-buffer-overflows -verify
+
+// Tests doing an out-of-bounds access after the end of an array using:
+// - constant integer index
+// - constant integer size for buffer
+void test1(int x) {
+  int buf[100];
+  buf[100] = 1; // expected-warning{{Out of bound memory access}}
+}
+
+void test1_ok(int x) {
+  int buf[100];
+  buf[99] = 1; // no-warning
+}
+
+// Tests doing an out-of-bounds access after the end of an array using:
+// - indirect pointer to buffer
+// - constant integer index
+// - constant integer size for buffer
+void test1_ptr(int x) {
+  int buf[100];
+  int *p = buf;
+  p[101] = 1; // expected-warning{{Out of bound memory access}}
+}
+
+void test1_ptr_ok(int x) {
+  int buf[100];
+  int *p = buf;
+  p[99] = 1; // expected-warning{{Out of bound memory access}}
+}
+
+// Tests doing an out-of-bounds access before the start of an array using:
+// - indirect pointer to buffer, manipulated using simple pointer arithmetic
+// - constant integer index
+// - constant integer size for buffer
+void test1_ptr_arith(int x) {
+  int buf[100];
+  int *p = buf;
+  p = p + 100;
+  p[0] = 1; // expected-warning{{Out of bound memory access}}
+}
+
+void test1_ptr_arith_ok(int x) {
+  int buf[100];
+  int *p = buf;
+  p = p + 99;
+  p[0] = 1; // no-warning
+}
+
+void test1_ptr_arith_bad(int x) {
+  int buf[100];
+  int *p = buf;
+  p = p + 99;
+  p[1] = 1; // expected-warning{{Out of bound memory access}}
+}
+
+void test1_ptr_arith_ok2(int x) {
+  int buf[100];
+  int *p = buf;
+  p = p + 100;
+  p[-1] = 1; // no-warning
+}
+
+// Tests doing an out-of-bounds access before the start of an array using:
+// - constant integer index
+// - constant integer size for buffer
+void test2(int x) {
+  int buf[100];
+  buf[-1] = 1; // expected-warning{{Out of bound memory access}}
+}
+
+// Tests doing an out-of-bounds access before the start of an array using:
+// - indirect pointer to buffer
+// - constant integer index
+// - constant integer size for buffer
+void test2_ptr(int x) {
+  int buf[100];
+  int *p = buf;
+  p[-1] = 1; // expected-warning{{Out of bound memory access}}
+}
+
+// Tests doing an out-of-bounds access before the start of an array using:
+// - indirect pointer to buffer, manipulated using simple pointer arithmetic
+// - constant integer index
+// - constant integer size for buffer
+void test2_ptr_arith(int x) {
+  int buf[100];
+  int *p = buf;
+  --p;
+  p[0] = 1; // expected-warning{{Out of bound memory access}}
+}
+
+// Tests doing an out-of-bounds access before the start of a multi-dimensional
+// array using:
+// - constant integer indices
+// - constant integer sizes for the array
+void test2_multi(int x) {
+  int buf[100][100];
+  buf[0][-1] = 1; // expected-warning{{Out of bound memory access}}
+}
+
+// Tests doing an out-of-bounds access before the start of a multi-dimensional
+// array using:
+// - constant integer indices
+// - constant integer sizes for the array
+void test2_multi_b(int x) {
+  int buf[100][100];
+  buf[-1][0] = 1; // expected-warning{{Out of bound memory access}}
+}
+
+void test2_multi_ok(int x) {
+  int buf[100][100];
+  buf[0][0] = 1; // no-warning
+}
+
+// *** FIXME ***
+// We don't get a warning here yet because our symbolic constraint solving
+// doesn't handle:  (symbol * constant) < constant
+void test3(int x) {
+  int buf[100];
+  if (x < 0)
+    buf[x] = 1; 
+}
+
+// *** FIXME ***
+// We don't get a warning here yet because our symbolic constraint solving
+// doesn't handle:  (symbol * constant) < constant
+void test4(int x) {
+  int buf[100];
+  if (x > 99)
+    buf[x] = 1; 
+}