/* Linux kernel image support for libdwfl.

   Copyright (C) 2009-2011 Red Hat, Inc.

   Copyright (C) 2022, 2024 Mark J. Wielaard <mark@klomp.org>

   This file is part of elfutils.

   This file is free software; you can redistribute it and/or modify

   it under the terms of either

     * the GNU Lesser General Public License as published by the Free

       Software Foundation; either version 3 of the License, or (at

       your option) any later version

   or

     * 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

   or both in parallel, as here.

   elfutils 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 copies of the GNU General Public License and

   the GNU Lesser General Public License along with this program.  If

   not, see <http://www.gnu.org/licenses/>.  */

#ifdef HAVE_CONFIG_H

# include <config.h>

#endif

#include "libdwflP.h"

#if BYTE_ORDER == LITTLE_ENDIAN

# define LE16(x)  (x)

#else

# define LE16(x)  bswap_16 (x)

#endif

/* See Documentation/x86/boot.txt in Linux kernel sources

   for an explanation of these format details.  */

#define MAGIC1      0xaa55

#define MAGIC2      0x53726448 /* "HdrS" little-endian */

#define MIN_VERSION   0x0208

#define H_START     (H_SETUP_SECTS & -4)

#define H_SETUP_SECTS   0x1f1

#define H_MAGIC1    0x1fe

#define H_MAGIC2    0x202

#define H_VERSION   0x206

#define H_PAYLOAD_OFFSET  0x248

#define H_PAYLOAD_LENGTH  0x24c

#define H_END     0x250

#define H_READ_SIZE   (H_END - H_START)

Dwfl_Error

internal_function

__libdw_image_header (int fd, off_t *start_offset,

          void *mapped, size_t mapped_size)

{

  if (likely (mapped_size > H_END))

    {

      const void *header = mapped;

      char header_buffer[H_READ_SIZE + H_START];

      if (header == NULL)

  {

    ssize_t n = pread_retry (fd, header_buffer + H_START, H_READ_SIZE,

           *start_offset + H_START);

    if (n < 0)

      return DWFL_E_ERRNO;

    if (n < H_READ_SIZE)

      return DWFL_E_BADELF;

    header = header_buffer;

  }

      uint16_t magic1;

      uint32_t magic2;

      uint16_t version;

      memcpy (&magic1, header + H_MAGIC1, sizeof (uint16_t));

      memcpy (&magic2, header + H_MAGIC2, sizeof (uint32_t));

      memcpy (&version, header + H_VERSION, sizeof (uint16_t));

      if (magic1 == LE16 (MAGIC1) && magic2 == LE32 (MAGIC2)

    && LE16 (version) >= MIN_VERSION)

  {

    /* The magic numbers match and the version field is sufficient.

       Extract the payload bounds.  */

    uint32_t offset;

    uint32_t length;

    uint8_t sects;

    memcpy (&offset, header + H_PAYLOAD_OFFSET, sizeof (uint32_t));

    memcpy (&length, header + H_PAYLOAD_LENGTH, sizeof (uint32_t));

    memcpy (&sects, header + H_SETUP_SECTS, sizeof (uint8_t));

    offset = LE32 (offset);

    length = LE32 (length);

    offset += ((sects ?: 4) + 1) * 512;

    if (offset > H_END && offset < mapped_size

        && mapped_size - offset >= length)

      {

        /* It looks kosher.  Use it!  */

        *start_offset += offset;

        return DWFL_E_NOERROR;

      }

  }

    }

  return DWFL_E_BADELF;

}