From e4d25afd1857b0ec1a00bb05374dc49a2f62a5d4 Mon Sep 17 00:00:00 2001 From: Michael Marineau Date: Tue, 23 Aug 2016 13:09:14 -0700 Subject: [PATCH] gpt: prefer disk size from header over firmware 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. --- grub-core/lib/gpt.c | 18 +++++++++++++----- tests/gpt_unit_test.c | 42 ++++++++++++++++++++++++++++++++++++++++++ 2 files changed, 55 insertions(+), 5 deletions(-) diff --git a/grub-core/lib/gpt.c b/grub-core/lib/gpt.c index 2fcb22715..519e05d89 100644 --- a/grub-core/lib/gpt.c +++ b/grub-core/lib/gpt.c @@ -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); diff --git a/tests/gpt_unit_test.c b/tests/gpt_unit_test.c index 9cf3414c2..218b18697 100644 --- a/tests/gpt_unit_test.c +++ b/tests/gpt_unit_test.c @@ -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");