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grub/grub-core/loader/i386/pc/chainloader.c
C. Masloch c225298038 chainloader: patch in BPB's sectors_per_track and num_heads 
These fields must reflect the ROM-BIOS's geometry for CHS-based
loaders to correctly load their next stage. Most loaders do not
query the ROM-BIOS (Int13.08), relying on the BPB fields to hold
the correct values already.

Tested with lDebug booted in qemu via grub2's
FreeDOS direct loading support, refer to
https://bitbucket.org/ecm/ldosboot + https://bitbucket.org/ecm/ldebug
(For this test, lDebug's iniload.asm must be assembled with
-D_QUERY_GEOMETRY=0 to leave the BPB values provided by grub.)

Signed-off-by: C. Masloch <pushbx@38.de>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
2018-03-14 13:23:27 +01:00

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/* chainloader.c - boot another boot loader */
/*
* GRUB -- GRand Unified Bootloader
* Copyright (C) 2002,2004,2007,2009,2010 Free Software Foundation, Inc.
*
* GRUB 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 3 of the License, or
* (at your option) any later version.
*
* GRUB 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 GRUB. If not, see <http://www.gnu.org/licenses/>.
*/
#include <grub/loader.h>
#include <grub/machine/chainloader.h>
#include <grub/machine/biosdisk.h>
#include <grub/machine/memory.h>
#include <grub/file.h>
#include <grub/err.h>
#include <grub/device.h>
#include <grub/disk.h>
#include <grub/misc.h>
#include <grub/types.h>
#include <grub/partition.h>
#include <grub/memory.h>
#include <grub/dl.h>
#include <grub/command.h>
#include <grub/msdos_partition.h>
#include <grub/machine/biosnum.h>
#include <grub/cpu/floppy.h>
#include <grub/i18n.h>
#include <grub/video.h>
#include <grub/mm.h>
#include <grub/fat.h>
#include <grub/ntfs.h>
#include <grub/i386/relocator.h>
GRUB_MOD_LICENSE ("GPLv3+");
static grub_dl_t my_mod;
static int boot_drive;
static grub_addr_t boot_part_addr;
static struct grub_relocator *rel;
typedef enum
{
GRUB_CHAINLOADER_FORCE = 0x1,
GRUB_CHAINLOADER_BPB = 0x2,
} grub_chainloader_flags_t;
static grub_err_t
grub_chainloader_boot (void)
{
struct grub_relocator16_state state = {
.edx = boot_drive,
.esi = boot_part_addr,
.ds = 0,
.es = 0,
.fs = 0,
.gs = 0,
.ss = 0,
.cs = 0,
.sp = GRUB_MEMORY_MACHINE_BOOT_LOADER_ADDR,
.ip = GRUB_MEMORY_MACHINE_BOOT_LOADER_ADDR,
.a20 = 0
};
grub_video_set_mode ("text", 0, 0);
return grub_relocator16_boot (rel, state);
}
static grub_err_t
grub_chainloader_unload (void)
{
grub_relocator_unload (rel);
rel = NULL;
grub_dl_unref (my_mod);
return GRUB_ERR_NONE;
}
void
grub_chainloader_patch_bpb (void *bs, grub_device_t dev, grub_uint8_t dl)
{
grub_uint32_t part_start = 0, heads = 0, sectors = 0;
if (dev && dev->disk)
{
part_start = grub_partition_get_start (dev->disk->partition);
if (dev->disk->data)
{
heads = ((struct grub_biosdisk_data *)(dev->disk->data))->heads;
sectors = ((struct grub_biosdisk_data *)(dev->disk->data))->sectors;
}
}
if (grub_memcmp ((char *) &((struct grub_ntfs_bpb *) bs)->oem_name,
"NTFS", 4) == 0)
{
struct grub_ntfs_bpb *bpb = (struct grub_ntfs_bpb *) bs;
bpb->num_hidden_sectors = grub_cpu_to_le32 (part_start);
bpb->bios_drive = dl;
return;
}
do
{
struct grub_fat_bpb *bpb = (struct grub_fat_bpb *) bs;
if (grub_strncmp((const char *) bpb->version_specific.fat12_or_fat16.fstype, "FAT12", 5)
&& grub_strncmp((const char *) bpb->version_specific.fat12_or_fat16.fstype, "FAT16", 5)
&& grub_strncmp((const char *) bpb->version_specific.fat32.fstype, "FAT32", 5))
break;
if (grub_le_to_cpu16 (bpb->bytes_per_sector) < 512
|| (grub_le_to_cpu16 (bpb->bytes_per_sector)
& (grub_le_to_cpu16 (bpb->bytes_per_sector) - 1)))
break;
if (bpb->sectors_per_cluster == 0
|| (bpb->sectors_per_cluster & (bpb->sectors_per_cluster - 1)))
break;
if (bpb->num_reserved_sectors == 0)
break;
if (bpb->num_total_sectors_16 == 0 && bpb->num_total_sectors_32 == 0)
break;
if (bpb->num_fats == 0)
break;
if (bpb->sectors_per_fat_16)
{
bpb->num_hidden_sectors = grub_cpu_to_le32 (part_start);
bpb->version_specific.fat12_or_fat16.num_ph_drive = dl;
if (sectors)
bpb->sectors_per_track = grub_cpu_to_le16 (sectors);
if (heads)
bpb->num_heads = grub_cpu_to_le16 (heads);
return;
}
if (bpb->version_specific.fat32.sectors_per_fat_32)
{
bpb->num_hidden_sectors = grub_cpu_to_le32 (part_start);
bpb->version_specific.fat32.num_ph_drive = dl;
if (sectors)
bpb->sectors_per_track = grub_cpu_to_le16 (sectors);
if (heads)
bpb->num_heads = grub_cpu_to_le16 (heads);
return;
}
break;
}
while (0);
}
static void
grub_chainloader_cmd (const char *filename, grub_chainloader_flags_t flags)
{
grub_file_t file = 0;
grub_uint16_t signature;
grub_device_t dev;
int drive = -1;
grub_addr_t part_addr = 0;
grub_uint8_t *bs, *ptable;
rel = grub_relocator_new ();
if (!rel)
goto fail;
grub_dl_ref (my_mod);
grub_file_filter_disable_compression ();
file = grub_file_open (filename);
if (! file)
goto fail;
{
grub_relocator_chunk_t ch;
grub_err_t err;
err = grub_relocator_alloc_chunk_addr (rel, &ch, 0x7C00,
GRUB_DISK_SECTOR_SIZE);
if (err)
goto fail;
bs = get_virtual_current_address (ch);
err = grub_relocator_alloc_chunk_addr (rel, &ch,
GRUB_MEMORY_MACHINE_PART_TABLE_ADDR,
64);
if (err)
goto fail;
ptable = get_virtual_current_address (ch);
}
/* Read the first block. */
if (grub_file_read (file, bs, GRUB_DISK_SECTOR_SIZE)
!= GRUB_DISK_SECTOR_SIZE)
{
if (!grub_errno)
grub_error (GRUB_ERR_BAD_OS, N_("premature end of file %s"),
filename);
goto fail;
}
/* Check the signature. */
signature = *((grub_uint16_t *) (bs + GRUB_DISK_SECTOR_SIZE - 2));
if (signature != grub_le_to_cpu16 (0xaa55)
&& ! (flags & GRUB_CHAINLOADER_FORCE))
{
grub_error (GRUB_ERR_BAD_OS, "invalid signature");
goto fail;
}
grub_file_close (file);
/* Obtain the partition table from the root device. */
drive = grub_get_root_biosnumber ();
dev = grub_device_open (0);
if (dev && dev->disk && dev->disk->partition)
{
grub_disk_t disk = dev->disk;
if (disk)
{
grub_partition_t p = disk->partition;
if (p && grub_strcmp (p->partmap->name, "msdos") == 0)
{
disk->partition = p->parent;
grub_disk_read (disk, p->offset, 446, 64, ptable);
part_addr = (GRUB_MEMORY_MACHINE_PART_TABLE_ADDR
+ (p->index << 4));
disk->partition = p;
}
}
}
if (flags & GRUB_CHAINLOADER_BPB)
grub_chainloader_patch_bpb ((void *) 0x7C00, dev, drive);
if (dev)
grub_device_close (dev);
/* Ignore errors. Perhaps it's not fatal. */
grub_errno = GRUB_ERR_NONE;
boot_drive = drive;
boot_part_addr = part_addr;
grub_loader_set (grub_chainloader_boot, grub_chainloader_unload, 1);
return;
fail:
if (file)
grub_file_close (file);
grub_dl_unref (my_mod);
}
static grub_err_t
grub_cmd_chainloader (grub_command_t cmd __attribute__ ((unused)),
int argc, char *argv[])
{
grub_chainloader_flags_t flags = 0;
while (argc > 0)
{
if (grub_strcmp (argv[0], "--force") == 0)
{
flags |= GRUB_CHAINLOADER_FORCE;
argc--;
argv++;
continue;
}
if (grub_strcmp (argv[0], "--bpb") == 0)
{
flags |= GRUB_CHAINLOADER_BPB;
argc--;
argv++;
continue;
}
break;
}
if (argc == 0)
return grub_error (GRUB_ERR_BAD_ARGUMENT, N_("filename expected"));
grub_chainloader_cmd (argv[0], flags);
return grub_errno;
}
static grub_command_t cmd;
GRUB_MOD_INIT(chainloader)
{
cmd = grub_register_command ("chainloader", grub_cmd_chainloader,
N_("[--force|--bpb] FILE"),
N_("Load another boot loader."));
my_mod = mod;
}
GRUB_MOD_FINI(chainloader)
{
grub_unregister_command (cmd);
}
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