// MmapWriteExecChecker.cpp - Check for the prot argument -----------------===//

//

// 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 checker tests the 3rd argument of mmap's calls to check if

// it is writable and executable in the same time. It's somehow

// an optional checker since for example in JIT libraries it is pretty common.

//

//===----------------------------------------------------------------------===//

#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/CallDescription.h"

#include "clang/StaticAnalyzer/Core/PathSensitive/CallEvent.h"

#include "clang/StaticAnalyzer/Core/PathSensitive/CheckerContext.h"

using namespace clang;

using namespace ento;

namespace {

class MmapWriteExecChecker : public Checker<check::PreCall> {

  CallDescription MmapFn;

  CallDescription MprotectFn;

  static int ProtWrite;

  static int ProtExec;

  static int ProtRead;

  mutable std::unique_ptr<BugType> BT;

public:

  MmapWriteExecChecker() : MmapFn({"mmap"}, 6), MprotectFn({"mprotect"}, 3) {}

  void checkPreCall(const CallEvent &Call, CheckerContext &C) const;

  int ProtExecOv;

  int ProtReadOv;

};

}

int MmapWriteExecChecker::ProtWrite = 0x02;

int MmapWriteExecChecker::ProtExec  = 0x04;

int MmapWriteExecChecker::ProtRead  = 0x01;

void MmapWriteExecChecker::checkPreCall(const CallEvent &Call,

                                         CheckerContext &C) const {

  if (matchesAny(Call, MmapFn, MprotectFn)) {

    SVal ProtVal = Call.getArgSVal(2);

    auto ProtLoc = ProtVal.getAs<nonloc::ConcreteInt>();

    if (!ProtLoc)

      return;

    int64_t Prot = ProtLoc->getValue().getSExtValue();

    if (ProtExecOv != ProtExec)

      ProtExec = ProtExecOv;

    if (ProtReadOv != ProtRead)

      ProtRead = ProtReadOv;

    // Wrong settings

    if (ProtRead == ProtExec)

      return;

    if ((Prot & (ProtWrite | ProtExec)) == (ProtWrite | ProtExec)) {

      if (!BT)

        BT.reset(new BugType(this, "W^X check fails, Write Exec prot flags set", "Security"));

      ExplodedNode *N = C.generateNonFatalErrorNode();

      if (!N)

        return;

      auto Report = std::make_unique<PathSensitiveBugReport>(

          *BT, "Both PROT_WRITE and PROT_EXEC flags are set. This can "

               "lead to exploitable memory regions, which could be overwritten "

               "with malicious code", N);

      Report->addRange(Call.getArgSourceRange(2));

      C.emitReport(std::move(Report));

    }

  }

}

void ento::registerMmapWriteExecChecker(CheckerManager &mgr) {

  MmapWriteExecChecker *Mwec =

      mgr.registerChecker<MmapWriteExecChecker>();

  Mwec->ProtExecOv =

    mgr.getAnalyzerOptions()

      .getCheckerIntegerOption(Mwec, "MmapProtExec");

  Mwec->ProtReadOv =

    mgr.getAnalyzerOptions()

      .getCheckerIntegerOption(Mwec, "MmapProtRead");

}

bool ento::shouldRegisterMmapWriteExecChecker(const CheckerManager &mgr) {

  return true;

}