/**
 * Copyright (C) 2018 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
#define _GNU_SOURCE
#include <sys/types.h>
#include <sys/wait.h>
#include <errno.h>
#include <fcntl.h>
#include <stdlib.h>
#include <sys/mman.h>
#include <sys/ptrace.h>
#include <sys/stat.h>
#include <unistd.h>
#include <../includes/common.h>

volatile char *mem = 0;

// child
int check_zero_page() {
  char *temp =
      (char *)mmap(0, 4096, PROT_READ, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
  int zeropage = *(int *)temp;
  munmap(temp, 4096);
  return zeropage;
}

// child
int do_child(int val) {
  // enable tracing and wait until parent is finished unlocking zero page
  ptrace(PTRACE_TRACEME, 0, 0, 0);
  sleep(2);

  mprotect((void *)mem, 4096, PROT_READ | PROT_WRITE);

  // try to corrupt zero page
  mem[0] = val;

  int zeropage = check_zero_page();
  return zeropage ? EXIT_VULNERABLE : 0;
}

// parent
int do_trace(pid_t child) {
  int status = 0;
  sleep(1); // wait until child is set up
  kill(child, SIGSTOP); // pause child
  waitpid(child, &status, 0);

  // unlock zero page
  status = ptrace(PTRACE_PEEKDATA, child, mem, 0);

  // stop tracing so child can continue
  ptrace(PTRACE_DETACH, child, 0, 0);
  kill(child, SIGCONT);
  return status;
}

int main(void) {

  char value = 0xAA;

  mem = (volatile char *)mmap(0, 4096, PROT_READ, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
  mprotect((void *)mem, 4096, PROT_NONE);

  pid_t child = fork();

  if (child == 0) {
    return do_child(value);
  } else {
    do_trace(child);
  }

  int status = 0;
  waitpid(child, &status, 0); // wait for child to exit naturally
  int exit = WEXITSTATUS(status); // get child exit status

  munmap((void *)mem, 4096);

  return exit;
}