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gpt: prefer disk size from header over firmware

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The firmware and the OS may disagree on the disk configuration and size.
Although such a setup should be avoided users are unlikely to know about
the problem, assuming everything behaves like the OS. Tolerate this as
best we can and trust the reported on-disk location over the firmware
when looking for the backup GPT. If the location is inaccessible report
the error as best we can and move on.
This commit is contained in:
Michael Marineau 2016-08-23 13:09:14 -07:00
parent d5ba259c89
commit e4d25afd18
2 changed files with 55 additions and 5 deletions
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18
grub-core/lib/gpt.c
View file

@ -425,13 +425,21 @@ grub_gpt_read_backup (grub_disk_t disk, grub_gpt_t gpt)
grub_disk_addr_t addr;
/* Assumes gpt->log_sector_size == disk->log_sector_size */
if (grub_gpt_disk_size_valid(disk))
if (gpt->status & GRUB_GPT_PRIMARY_HEADER_VALID)
{
sector = grub_le_to_cpu64 (gpt->primary.alternate_lba);
if (grub_gpt_disk_size_valid (disk) && sector >= disk->total_sectors)
return grub_error (GRUB_ERR_OUT_OF_RANGE,
"backup GPT located at 0x%llx, "
"beyond last disk sector at 0x%llx",
(unsigned long long) sector,
(unsigned long long) disk->total_sectors - 1);
}
else if (grub_gpt_disk_size_valid (disk))
sector = disk->total_sectors - 1;
else if (gpt->status & GRUB_GPT_PRIMARY_HEADER_VALID)
sector = grub_le_to_cpu64 (gpt->primary.alternate_lba);
else
return grub_error (GRUB_ERR_NOT_IMPLEMENTED_YET,
"Unable to locate backup GPT");
return grub_error (GRUB_ERR_OUT_OF_RANGE,
"size of disk unknown, cannot locate backup GPT");
grub_dprintf ("gpt", "reading backup GPT from sector 0x%llx\n",
(unsigned long long) sector);

42
tests/gpt_unit_test.c
View file

@ -544,6 +544,46 @@ repair_test (void)
close_disk (&data);
}
/* Finding/reading/writing the backup GPT may be difficult if the OS and
* BIOS report different sizes for the same disk. We need to gracefully
* recognize this and avoid causing trouble for the OS. */
static void
weird_disk_size_test (void)
{
struct test_data data;
grub_gpt_t gpt;
open_disk (&data);
/* Chop off 65536 bytes (128 512B sectors) which may happen when the
* BIOS thinks you are using a software RAID system that reserves that
* area for metadata when in fact you are not and using the bare disk. */
grub_test_assert(data.dev->disk->total_sectors == DISK_SECTORS,
"unexpected disk size: 0x%llx",
(unsigned long long) data.dev->disk->total_sectors);
data.dev->disk->total_sectors -= 128;
gpt = read_disk (&data);
assert_error_stack_empty ();
/* Reading the alternate_lba should have been blocked and reading
* the (new) end of disk should have found no useful data. */
grub_test_assert ((gpt->status & GRUB_GPT_BACKUP_HEADER_VALID) == 0,
"unreported missing backup header");
/* We should be able to reconstruct the backup header and the location
* of the backup should remain unchanged, trusting the GPT data over
* what the BIOS is telling us. Further changes are left to the OS. */
grub_gpt_repair (data.dev->disk, gpt);
grub_test_assert (grub_errno == GRUB_ERR_NONE,
"repair failed: %s", grub_errmsg);
grub_test_assert (memcmp (&gpt->primary, &example_primary,
sizeof (gpt->primary)) == 0,
"repair corrupted primary header");
grub_gpt_free (gpt);
close_disk (&data);
}
static void
iterate_partitions_test (void)
{
@ -774,6 +814,7 @@ grub_unit_test_init (void)
grub_test_register ("gpt_iterate_partitions_test", iterate_partitions_test);
grub_test_register ("gpt_large_partitions_test", large_partitions_test);
grub_test_register ("gpt_invalid_partsize_test", invalid_partsize_test);
grub_test_register ("gpt_weird_disk_size_test", weird_disk_size_test);
grub_test_register ("gpt_search_part_label_test", search_part_label_test);
grub_test_register ("gpt_search_uuid_test", search_part_uuid_test);
grub_test_register ("gpt_search_disk_uuid_test", search_disk_uuid_test);
@ -791,6 +832,7 @@ grub_unit_test_fini (void)
grub_test_unregister ("gpt_iterate_partitions_test");
grub_test_unregister ("gpt_large_partitions_test");
grub_test_unregister ("gpt_invalid_partsize_test");
grub_test_unregister ("gpt_weird_disk_size_test");
grub_test_unregister ("gpt_search_part_label_test");
grub_test_unregister ("gpt_search_part_uuid_test");
grub_test_unregister ("gpt_search_disk_uuid_test");