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partitions/efi: loosen check fot pmbr size in lba

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Matt found that commit 27a7c64217 ("partitions/efi: account for pmbr
size in lba") caused his GPT formatted eMMC device not to boot.  The
reason is that this commit enforced Linux to always check the lesser of
the whole disk or 2Tib for the pMBR size in LBA.  While most disk
partitioning tools out there create a pMBR with these characteristics,
Microsoft does not, as it always sets the entry to the maximum 32-bit
limitation - even though a drive may be smaller than that[1].

Loosen this check and only verify that the size is either the whole disk
or 0xFFFFFFFF.  No tool in its right mind would set it to any value
other than these.

[1] http://thestarman.pcministry.com/asm/mbr/GPT.htm#GPTPT

Reported-and-tested-by: Matt Porter <matt.porter@linaro.org>
Signed-off-by: Davidlohr Bueso <davidlohr@hp.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Davidlohr Bueso 2013-09-13 15:02:22 -07:00 committed by Linus Torvalds
parent 3711d86a2d
commit 6b02fa59a7
1 changed files with 6 additions and 2 deletions
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8
block/partitions/efi.c
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@ -186,6 +186,7 @@ static inline int pmbr_part_valid(gpt_mbr_record *part)
*/
static int is_pmbr_valid(legacy_mbr *mbr, sector_t total_sectors)
{
uint32_t sz = 0;
int i, part = 0, ret = 0; /* invalid by default */
if (!mbr || le16_to_cpu(mbr->signature) != MSDOS_MBR_SIGNATURE)
@ -216,12 +217,15 @@ static int is_pmbr_valid(legacy_mbr *mbr, sector_t total_sectors)
/*
* Protective MBRs take up the lesser of the whole disk
* or 2 TiB (32bit LBA), ignoring the rest of the disk.
* Some partitioning programs, nonetheless, choose to set
* the size to the maximum 32-bit limitation, disregarding
* the disk size.
*
* Hybrid MBRs do not necessarily comply with this.
*/
if (ret == GPT_MBR_PROTECTIVE) {
if (le32_to_cpu(mbr->partition_record[part].size_in_lba) !=
min((uint32_t) total_sectors - 1, 0xFFFFFFFF))
sz = le32_to_cpu(mbr->partition_record[part].size_in_lba);
if (sz != (uint32_t) total_sectors - 1 && sz != 0xFFFFFFFF)
ret = 0;
}
done: