source: bootcd/isolinux/syslinux-6.03/gpxe/src/arch/i386/image/eltorito.c

/*
 * Copyright (C) 2007 Michael Brown <mbrown@fensystems.co.uk>.
 *
 * 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 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.
 */

FILE_LICENCE ( GPL2_OR_LATER );

/**
 * @file
 *
 * El Torito bootable ISO image format
 *
 */

#include <stdint.h>
#include <errno.h>
#include <assert.h>
#include <realmode.h>
#include <bootsector.h>
#include <int13.h>
#include <gpxe/uaccess.h>
#include <gpxe/image.h>
#include <gpxe/segment.h>
#include <gpxe/ramdisk.h>
#include <gpxe/init.h>

#define ISO9660_BLKSIZE 2048
#define ELTORITO_VOL_DESC_OFFSET ( 17 * ISO9660_BLKSIZE )

/** An El Torito Boot Record Volume Descriptor */
struct eltorito_vol_desc {
        /** Boot record indicator; must be 0 */
        uint8_t record_indicator;
        /** ISO-9660 identifier; must be "CD001" */
        uint8_t iso9660_id[5];
        /** Version, must be 1 */
        uint8_t version;
        /** Boot system indicator; must be "EL TORITO SPECIFICATION" */
        uint8_t system_indicator[32];
        /** Unused */
        uint8_t unused[32];
        /** Boot catalog sector */
        uint32_t sector;
} __attribute__ (( packed ));

/** An El Torito Boot Catalog Validation Entry */
struct eltorito_validation_entry {
        /** Header ID; must be 1 */
        uint8_t header_id;
        /** Platform ID
         *
         * 0 = 80x86
         * 1 = PowerPC
         * 2 = Mac
         */
        uint8_t platform_id;
        /** Reserved */
        uint16_t reserved;
        /** ID string */
        uint8_t id_string[24];
        /** Checksum word */
        uint16_t checksum;
        /** Signature; must be 0xaa55 */
        uint16_t signature;
} __attribute__ (( packed ));

/** A bootable entry in the El Torito Boot Catalog */
struct eltorito_boot_entry {
        /** Boot indicator
         *
         * Must be @c ELTORITO_BOOTABLE for a bootable ISO image
         */
        uint8_t indicator;
        /** Media type
         *
         */
        uint8_t media_type;
        /** Load segment */
        uint16_t load_segment;
        /** System type */
        uint8_t filesystem;
        /** Unused */
        uint8_t reserved_a;
        /** Sector count */
        uint16_t length;
        /** Starting sector */
        uint32_t start;
        /** Unused */
        uint8_t reserved_b[20];
} __attribute__ (( packed ));

/** Boot indicator for a bootable ISO image */
#define ELTORITO_BOOTABLE 0x88

/** El Torito media types */
enum eltorito_media_type {
        /** No emulation */
        ELTORITO_NO_EMULATION = 0,
};

struct image_type eltorito_image_type __image_type ( PROBE_NORMAL );

/**
 * Calculate 16-bit word checksum
 *
 * @v data              Data to checksum
 * @v len               Length (in bytes, must be even)
 * @ret sum             Checksum
 */
static unsigned int word_checksum ( void *data, size_t len ) {
        uint16_t *words;
        uint16_t sum = 0;

        for ( words = data ; len ; words++, len -= 2 ) {
                sum += *words;
        }
        return sum;
}

/**
 * Execute El Torito image
 *
 * @v image             El Torito image
 * @ret rc              Return status code
 */
static int eltorito_exec ( struct image *image ) {
        struct ramdisk ramdisk;
        struct int13_drive int13_drive;
        unsigned int load_segment = image->priv.ul;
        unsigned int load_offset = ( load_segment ? 0 : 0x7c00 );
        int rc;

        memset ( &ramdisk, 0, sizeof ( ramdisk ) );
        init_ramdisk ( &ramdisk, image->data, image->len, ISO9660_BLKSIZE );
        
        memset ( &int13_drive, 0, sizeof ( int13_drive ) );
        int13_drive.blockdev = &ramdisk.blockdev;
        register_int13_drive ( &int13_drive );

        if ( ( rc = call_bootsector ( load_segment, load_offset, 
                                      int13_drive.drive ) ) != 0 ) {
                DBGC ( image, "ElTorito %p boot failed: %s\n",
                       image, strerror ( rc ) );
                goto err;
        }
        
        rc = -ECANCELED; /* -EIMPOSSIBLE */
 err:
        unregister_int13_drive ( &int13_drive );
        return rc;
}

/**
 * Read and verify El Torito Boot Record Volume Descriptor
 *
 * @v image             El Torito file
 * @ret catalog_offset  Offset of Boot Catalog
 * @ret rc              Return status code
 */
static int eltorito_read_voldesc ( struct image *image,
                                   unsigned long *catalog_offset ) {
        static const struct eltorito_vol_desc vol_desc_signature = {
                .record_indicator = 0,
                .iso9660_id = "CD001",
                .version = 1,
                .system_indicator = "EL TORITO SPECIFICATION",
        };
        struct eltorito_vol_desc vol_desc;

        /* Sanity check */
        if ( image->len < ( ELTORITO_VOL_DESC_OFFSET + ISO9660_BLKSIZE ) ) {
                DBGC ( image, "ElTorito %p too short\n", image );
                return -ENOEXEC;
        }

        /* Read and verify Boot Record Volume Descriptor */
        copy_from_user ( &vol_desc, image->data, ELTORITO_VOL_DESC_OFFSET,
                         sizeof ( vol_desc ) );
        if ( memcmp ( &vol_desc, &vol_desc_signature,
                      offsetof ( typeof ( vol_desc ), sector ) ) != 0 ) {
                DBGC ( image, "ElTorito %p invalid Boot Record Volume "
                       "Descriptor\n", image );
                return -ENOEXEC;
        }
        *catalog_offset = ( vol_desc.sector * ISO9660_BLKSIZE );

        DBGC ( image, "ElTorito %p boot catalog at offset %#lx\n",
               image, *catalog_offset );

        return 0;
}

/**
 * Read and verify El Torito Boot Catalog
 *
 * @v image             El Torito file
 * @v catalog_offset    Offset of Boot Catalog
 * @ret boot_entry      El Torito boot entry
 * @ret rc              Return status code
 */
static int eltorito_read_catalog ( struct image *image,
                                   unsigned long catalog_offset,
                                   struct eltorito_boot_entry *boot_entry ) {
        struct eltorito_validation_entry validation_entry;

        /* Sanity check */
        if ( image->len < ( catalog_offset + ISO9660_BLKSIZE ) ) {
                DBGC ( image, "ElTorito %p bad boot catalog offset %#lx\n",
                       image, catalog_offset );
                return -ENOEXEC;
        }

        /* Read and verify the Validation Entry of the Boot Catalog */
        copy_from_user ( &validation_entry, image->data, catalog_offset,
                         sizeof ( validation_entry ) );
        if ( word_checksum ( &validation_entry,
                             sizeof ( validation_entry ) ) != 0 ) {
                DBGC ( image, "ElTorito %p bad Validation Entry checksum\n",
                       image );
                return -ENOEXEC;
        }

        /* Read and verify the Initial/Default entry */
        copy_from_user ( boot_entry, image->data,
                         ( catalog_offset + sizeof ( validation_entry ) ),
                         sizeof ( *boot_entry ) );
        if ( boot_entry->indicator != ELTORITO_BOOTABLE ) {
                DBGC ( image, "ElTorito %p not bootable\n", image );
                return -ENOEXEC;
        }
        if ( boot_entry->media_type != ELTORITO_NO_EMULATION ) {
                DBGC ( image, "ElTorito %p cannot support media type %d\n",
                       image, boot_entry->media_type );
                return -ENOTSUP;
        }

        DBGC ( image, "ElTorito %p media type %d segment %04x\n",
               image, boot_entry->media_type, boot_entry->load_segment );

        return 0;
}

/**
 * Load El Torito virtual disk image into memory
 *
 * @v image             El Torito file
 * @v boot_entry        El Torito boot entry
 * @ret rc              Return status code
 */
static int eltorito_load_disk ( struct image *image,
                                struct eltorito_boot_entry *boot_entry ) {
        unsigned long start = ( boot_entry->start * ISO9660_BLKSIZE );
        unsigned long length = ( boot_entry->length * ISO9660_BLKSIZE );
        unsigned int load_segment;
        userptr_t buffer;
        int rc;

        /* Sanity check */
        if ( image->len < ( start + length ) ) {
                DBGC ( image, "ElTorito %p virtual disk lies outside image\n",
                       image );
                return -ENOEXEC;
        }
        DBGC ( image, "ElTorito %p virtual disk at %#lx+%#lx\n",
               image, start, length );

        /* Calculate load address */
        load_segment = boot_entry->load_segment;
        buffer = real_to_user ( load_segment, ( load_segment ? 0 : 0x7c00 ) );

        /* Verify and prepare segment */
        if ( ( rc = prep_segment ( buffer, length, length ) ) != 0 ) {
                DBGC ( image, "ElTorito %p could not prepare segment: %s\n",
                       image, strerror ( rc ) );
                return rc;
        }

        /* Copy image to segment */
        memcpy_user ( buffer, 0, image->data, start, length );

        return 0;
}

/**
 * Load El Torito image into memory
 *
 * @v image             El Torito file
 * @ret rc              Return status code
 */
static int eltorito_load ( struct image *image ) {
        struct eltorito_boot_entry boot_entry;
        unsigned long bootcat_offset;
        int rc;

        /* Read Boot Record Volume Descriptor, if present */
        if ( ( rc = eltorito_read_voldesc ( image, &bootcat_offset ) ) != 0 )
                return rc;

        /* This is an El Torito image, valid or otherwise */
        if ( ! image->type )
                image->type = &eltorito_image_type;

        /* Read Boot Catalog */
        if ( ( rc = eltorito_read_catalog ( image, bootcat_offset,
                                            &boot_entry ) ) != 0 )
                return rc;

        /* Load Virtual Disk image */
        if ( ( rc = eltorito_load_disk ( image, &boot_entry ) ) != 0 )
                return rc;

        /* Record load segment in image private data field */
        image->priv.ul = boot_entry.load_segment;

        return 0;
}

/** El Torito image type */
struct image_type eltorito_image_type __image_type ( PROBE_NORMAL ) = {
        .name = "El Torito",
        .load = eltorito_load,
        .exec = eltorito_exec,
};