forked from OSchip/llvm-project
186 lines
5.8 KiB
C++
186 lines
5.8 KiB
C++
//=== VLASizeChecker.cpp - Undefined dereference checker --------*- 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 defines VLASizeChecker, a builtin check in ExprEngine that
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// performs checks for declaration of VLA of undefined or zero size.
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// In addition, VLASizeChecker is responsible for defining the extent
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// of the MemRegion that represents a VLA.
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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 "llvm/ADT/STLExtras.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 VLASizeChecker : public Checker< check::PreStmt<DeclStmt> > {
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mutable std::unique_ptr<BugType> BT;
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enum VLASize_Kind { VLA_Garbage, VLA_Zero, VLA_Tainted, VLA_Negative };
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void reportBug(VLASize_Kind Kind, const Expr *SizeE, ProgramStateRef State,
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CheckerContext &C,
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std::unique_ptr<BugReporterVisitor> Visitor = nullptr) const;
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public:
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void checkPreStmt(const DeclStmt *DS, CheckerContext &C) const;
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};
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} // end anonymous namespace
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void VLASizeChecker::reportBug(
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VLASize_Kind Kind, const Expr *SizeE, ProgramStateRef State,
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CheckerContext &C, std::unique_ptr<BugReporterVisitor> Visitor) const {
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// Generate an error node.
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ExplodedNode *N = C.generateErrorNode(State);
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if (!N)
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return;
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if (!BT)
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BT.reset(new BuiltinBug(
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this, "Dangerous variable-length array (VLA) declaration"));
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SmallString<256> buf;
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llvm::raw_svector_ostream os(buf);
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os << "Declared variable-length array (VLA) ";
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switch (Kind) {
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case VLA_Garbage:
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os << "uses a garbage value as its size";
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break;
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case VLA_Zero:
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os << "has zero size";
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break;
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case VLA_Tainted:
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os << "has tainted size";
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break;
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case VLA_Negative:
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os << "has negative size";
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break;
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}
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auto report = llvm::make_unique<BugReport>(*BT, os.str(), N);
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report->addVisitor(std::move(Visitor));
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report->addRange(SizeE->getSourceRange());
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bugreporter::trackNullOrUndefValue(N, SizeE, *report);
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C.emitReport(std::move(report));
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}
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void VLASizeChecker::checkPreStmt(const DeclStmt *DS, CheckerContext &C) const {
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if (!DS->isSingleDecl())
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return;
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const VarDecl *VD = dyn_cast<VarDecl>(DS->getSingleDecl());
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if (!VD)
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return;
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ASTContext &Ctx = C.getASTContext();
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const VariableArrayType *VLA = Ctx.getAsVariableArrayType(VD->getType());
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if (!VLA)
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return;
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// FIXME: Handle multi-dimensional VLAs.
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const Expr *SE = VLA->getSizeExpr();
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ProgramStateRef state = C.getState();
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SVal sizeV = C.getSVal(SE);
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if (sizeV.isUndef()) {
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reportBug(VLA_Garbage, SE, state, C);
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return;
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}
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// See if the size value is known. It can't be undefined because we would have
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// warned about that already.
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if (sizeV.isUnknown())
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return;
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// Check if the size is tainted.
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if (state->isTainted(sizeV)) {
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reportBug(VLA_Tainted, SE, nullptr, C,
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llvm::make_unique<TaintBugVisitor>(sizeV));
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return;
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}
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// Check if the size is zero.
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DefinedSVal sizeD = sizeV.castAs<DefinedSVal>();
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ProgramStateRef stateNotZero, stateZero;
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std::tie(stateNotZero, stateZero) = state->assume(sizeD);
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if (stateZero && !stateNotZero) {
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reportBug(VLA_Zero, SE, stateZero, C);
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return;
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}
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// From this point on, assume that the size is not zero.
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state = stateNotZero;
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// VLASizeChecker is responsible for defining the extent of the array being
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// declared. We do this by multiplying the array length by the element size,
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// then matching that with the array region's extent symbol.
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// Check if the size is negative.
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SValBuilder &svalBuilder = C.getSValBuilder();
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QualType Ty = SE->getType();
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DefinedOrUnknownSVal Zero = svalBuilder.makeZeroVal(Ty);
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SVal LessThanZeroVal = svalBuilder.evalBinOp(state, BO_LT, sizeD, Zero, Ty);
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if (Optional<DefinedSVal> LessThanZeroDVal =
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LessThanZeroVal.getAs<DefinedSVal>()) {
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ConstraintManager &CM = C.getConstraintManager();
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ProgramStateRef StatePos, StateNeg;
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std::tie(StateNeg, StatePos) = CM.assumeDual(state, *LessThanZeroDVal);
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if (StateNeg && !StatePos) {
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reportBug(VLA_Negative, SE, state, C);
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return;
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}
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state = StatePos;
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}
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// Convert the array length to size_t.
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QualType SizeTy = Ctx.getSizeType();
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NonLoc ArrayLength =
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svalBuilder.evalCast(sizeD, SizeTy, SE->getType()).castAs<NonLoc>();
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// Get the element size.
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CharUnits EleSize = Ctx.getTypeSizeInChars(VLA->getElementType());
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SVal EleSizeVal = svalBuilder.makeIntVal(EleSize.getQuantity(), SizeTy);
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// Multiply the array length by the element size.
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SVal ArraySizeVal = svalBuilder.evalBinOpNN(
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state, BO_Mul, ArrayLength, EleSizeVal.castAs<NonLoc>(), SizeTy);
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// Finally, assume that the array's extent matches the given size.
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const LocationContext *LC = C.getLocationContext();
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DefinedOrUnknownSVal Extent =
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state->getRegion(VD, LC)->getExtent(svalBuilder);
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DefinedOrUnknownSVal ArraySize = ArraySizeVal.castAs<DefinedOrUnknownSVal>();
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DefinedOrUnknownSVal sizeIsKnown =
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svalBuilder.evalEQ(state, Extent, ArraySize);
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state = state->assume(sizeIsKnown, true);
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// Assume should not fail at this point.
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assert(state);
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// Remember our assumptions!
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C.addTransition(state);
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}
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void ento::registerVLASizeChecker(CheckerManager &mgr) {
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mgr.registerChecker<VLASizeChecker>();
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}
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