Simple checker for the format of a Multiboot kernel

mbchk.c

/* mbchk - a simple checker for the format of a Multiboot kernel */
/*
*  Copyright (C) 1999,2001,2002  Free Software Foundation, Inc.
*
*  This program is free software; you can redistribute it and/or modify
*  it under the terms of the GNU General Public License as published by
*  the Free Software Foundation; either version 2 of the License, or
*  (at your option) any later version.
*
*  This program is distributed in the hope that it will be useful,
*  but WITHOUT ANY WARRANTY; without even the implied warranty of
*  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
*  GNU General Public License for more details.
*
*  You should have received a copy of the GNU General Public License
*  along with this program; if not, write to the Free Software
*  Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
*/

#include <stdio.h>
#include <stdlib.h>
#include <getopt.h>
#include <stdint.h>

/* for standalone */
#define GRUB_MAGIC 0x1BADB002
typedef struct multiboot_header
{
  uint32_t magic;
  uint32_t flags;
  uint32_t checksum;
  uint32_t header_addr;
  uint32_t load_addr;
  uint32_t load_end_addr;
  uint32_t bss_end_addr;
  uint32_t entry_addr;
} multiboot_header_t;

static int quiet = 0;
static char *optstring = "hvq";
static struct option longopts[] =
    {
        {"help", no_argument, 0, 'h'},
        {"version", no_argument, 0, 'v'},
        {"quiet", no_argument, 0, 'q'},
        {0}};

static void usage(int status)
{
  if (status)
    fprintf(stderr, "Try ``mbchk --help'' for more information.\n");
  else
    printf("Usage: mbchk [OPTION]... [FILE]...\n"
           "Check if the format of FILE complies with the Multiboot Specification.\n"
           "\n"
           "-q, --quiet                suppress all normal output\n"
           "-h, --help                 display this help and exit\n"
           "-v, --version              output version information and exit.\n"
           "\n"
           "Report bugs to <[email protected]>.\n");

  exit(status);
}

static int check_multiboot(const char *filename, FILE *fp)
{
  multiboot_header_t *mbh = 0;
  int i;
  char buf[8192];

  if (fread(buf, 1, 8192, fp) < 0)
  {
    fprintf(stderr, "%s: Read error.\n", filename);
    return 0;
  }

  for (i = 0; i < 8192 - sizeof(multiboot_header_t); i++)
  {
    unsigned long magic = *((unsigned long *)(buf + i));

    if (magic == GRUB_MAGIC)
    {
      mbh = (multiboot_header_t *)(buf + i);
      break;
    }
  }

  if (!mbh)
  {
    fprintf(stderr, "%s: No Multiboot header.\n", filename);
    return 0;
  }

  if (!quiet)
    printf("%s: The Multiboot header is found at the offset %d.\n",
           filename, i);

  /* Check for the checksum.  */
  if (mbh->magic + mbh->flags + mbh->checksum != 0)
  {
    fprintf(stderr,
            "%s: Bad checksum (0x%x).\n",
            filename, mbh->checksum);
    return 0;
  }

  /* Reserved flags must be zero.  */
  if (mbh->flags & ~0x00010003)
  {
    fprintf(stderr,
            "%s: Non-zero is found in reserved flags (0x%x).\n",
            filename, mbh->flags);
    return 0;
  }

  if (!quiet)
  {
    printf("%s: Page alignment is turned %s.\n",
           filename, (mbh->flags & 0x1) ? "on" : "off");
    printf("%s: Memory information is turned %s.\n",
           filename, (mbh->flags & 0x2) ? "on" : "off");
    printf("%s: Address fields is turned %s.\n",
           filename, (mbh->flags & 0x10000) ? "on" : "off");
  }

  /* Check for the address fields.  */
  if (mbh->flags & 0x10000)
  {
    if (mbh->header_addr < mbh->load_addr)
    {
      fprintf(stderr,
              "%s: header_addr is less than "
              "load_addr (0x%x > 0x%x).\n",
              filename, mbh->header_addr, mbh->load_addr);
      return 0;
    }

    if (mbh->load_end_addr && mbh->load_addr >= mbh->load_end_addr)
    {
      fprintf(stderr,
              "%s: load_addr is not less than load_end_addr"
              " (0x%x >= 0x%x).\n",
              filename, mbh->load_addr, mbh->load_end_addr);
      return 0;
    }

    if (mbh->bss_end_addr && mbh->load_end_addr > mbh->bss_end_addr)
    {
      fprintf(stderr,
              "%s: load_end_addr is greater than bss_end_addr"
              " (0x%x > 0x%x).\n",
              filename, mbh->load_end_addr, mbh->bss_end_addr);
      return 0;
    }

    if (mbh->load_addr > mbh->entry_addr)
    {
      fprintf(stderr,
              "%s: load_addr is greater than entry_addr"
              " (0x%x > 0x%x).\n",
              filename, mbh->load_addr, mbh->entry_addr);
      return 0;
    }

    /* FIXME: It is better to check if the entry address is within the
    file, especially when the load end address is zero.  */
    if (mbh->load_end_addr && mbh->load_end_addr <= mbh->entry_addr)
    {
      fprintf(stderr,
              "%s: load_end_addr is not greater than entry_addr"
              " (0x%x <= 0x%x).\n",
              filename, mbh->load_end_addr, mbh->entry_addr);
      return 0;
    }

    /* This is a GRUB-specific limitation.  */
    if (mbh->load_addr < 0x100000)
    {
      fprintf(stderr,
              "%s: Cannot be loaded at less than 1MB by GRUB"
              " (0x%x).\n",
              filename, mbh->load_addr);
      return 0;
    }
  }

  if (!quiet)
    printf("%s: All checks passed.\n", filename);

  return 1;
}

int main(int argc, char *argv[])
{
  int c;

  do
  {
    c = getopt_long(argc, argv, optstring, longopts, 0);
    switch (c)
    {
    case EOF:
      break;

    case 'h':
      usage(0);
      break;

    case 'v':
      printf("mbchk (Ported standalone from Grub Legacy)\n");
      exit(0);
      break;

    case 'q':
      quiet = 1;
      break;

    default:
      usage(1);
      break;
    }
  } while (c != EOF);

  if (optind < argc)
  {
    while (optind < argc)
    {
      FILE *fp;

      fp = fopen(argv[optind], "r");
      if (!fp)
      {
        fprintf(stderr, "%s: No such file.\n", argv[optind]);
        exit(1);
      }

      if (!check_multiboot(argv[optind], fp))
        exit(1);

      fclose(fp);
      optind++;
    }
  }
  else
  {
    if (!check_multiboot("<stdin>", stdin))
      exit(1);
  }

  return 0;
}

For anyone seeing that: this program doesn't work as expected if compiled for 64bits. unsigned long should be unsigned int.

I'll create a fix soon

Done