e607360fcd
At pointer subtraction only pointers are allowed that point into an array (or one after the end), this fact was checker by the checker. This check is now removed because it is a special case of array indexing error that is handled by different checkers (like ArrayBoundsV2).
122 lines
4.1 KiB
C++
122 lines
4.1 KiB
C++
//=== PointerSubChecker.cpp - Pointer subtraction checker ------*- 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 files defines PointerSubChecker, a builtin checker that checks for
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// pointer subtractions on two pointers pointing to different memory chunks.
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// This check corresponds to CWE-469.
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//
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//===----------------------------------------------------------------------===//
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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/CheckerContext.h"
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#include "clang/StaticAnalyzer/Core/PathSensitive/DynamicExtent.h"
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#include "llvm/ADT/StringRef.h"
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#include "llvm/Support/FormatVariadic.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 PointerSubChecker
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: public Checker< check::PreStmt<BinaryOperator> > {
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const BugType BT{this, "Pointer subtraction"};
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const llvm::StringLiteral Msg_MemRegionDifferent =
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"Subtraction of two pointers that do not point into the same array "
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"is undefined behavior.";
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public:
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void checkPreStmt(const BinaryOperator *B, CheckerContext &C) const;
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};
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}
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void PointerSubChecker::checkPreStmt(const BinaryOperator *B,
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CheckerContext &C) const {
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// When doing pointer subtraction, if the two pointers do not point to the
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// same array, emit a warning.
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if (B->getOpcode() != BO_Sub)
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return;
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SVal LV = C.getSVal(B->getLHS());
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SVal RV = C.getSVal(B->getRHS());
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const MemRegion *LR = LV.getAsRegion();
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const MemRegion *RR = RV.getAsRegion();
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if (!LR || !RR)
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return;
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// Allow subtraction of identical pointers.
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if (LR == RR)
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return;
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// No warning if one operand is unknown or resides in a region that could be
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// equal to the other.
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if (LR->getSymbolicBase() || RR->getSymbolicBase())
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return;
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const auto *ElemLR = dyn_cast<ElementRegion>(LR);
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const auto *ElemRR = dyn_cast<ElementRegion>(RR);
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// Allow cases like "(&x + 1) - &x".
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if (ElemLR && ElemLR->getSuperRegion() == RR)
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return;
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// Allow cases like "&x - (&x + 1)".
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if (ElemRR && ElemRR->getSuperRegion() == LR)
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return;
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const ValueDecl *DiffDeclL = nullptr;
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const ValueDecl *DiffDeclR = nullptr;
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if (ElemLR && ElemRR) {
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const MemRegion *SuperLR = ElemLR->getSuperRegion();
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const MemRegion *SuperRR = ElemRR->getSuperRegion();
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if (SuperLR == SuperRR)
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return;
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// Allow arithmetic on different symbolic regions.
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if (isa<SymbolicRegion>(SuperLR) || isa<SymbolicRegion>(SuperRR))
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return;
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if (const auto *SuperDLR = dyn_cast<DeclRegion>(SuperLR))
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DiffDeclL = SuperDLR->getDecl();
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if (const auto *SuperDRR = dyn_cast<DeclRegion>(SuperRR))
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DiffDeclR = SuperDRR->getDecl();
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}
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if (ExplodedNode *N = C.generateNonFatalErrorNode()) {
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auto R =
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std::make_unique<PathSensitiveBugReport>(BT, Msg_MemRegionDifferent, N);
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R->addRange(B->getSourceRange());
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// The declarations may be identical even if the regions are different:
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// struct { int array[10]; } a, b;
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// do_something(&a.array[5] - &b.array[5]);
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// In this case don't emit notes.
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if (DiffDeclL != DiffDeclR) {
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auto AddNote = [&R, &C](const ValueDecl *D, StringRef SideStr) {
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if (D) {
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std::string Msg = llvm::formatv(
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"{0} at the {1}-hand side of subtraction",
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D->getType()->isArrayType() ? "Array" : "Object", SideStr);
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R->addNote(Msg, {D, C.getSourceManager()});
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}
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};
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AddNote(DiffDeclL, "left");
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AddNote(DiffDeclR, "right");
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}
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C.emitReport(std::move(R));
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}
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}
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void ento::registerPointerSubChecker(CheckerManager &mgr) {
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mgr.registerChecker<PointerSubChecker>();
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}
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bool ento::shouldRegisterPointerSubChecker(const CheckerManager &mgr) {
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return true;
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}
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