[U-Boot] [PATCH V2] disk:efi: avoid unaligned access on efi partition

Lukasz Majewski
2014-02-24T15:56:57Z

Hi Tom,

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> On 02/19/2014 10:03 AM, Tom Rini wrote:
> > On 02/19/2014 09:56 AM, Hector Palacios wrote:
> >> On 01/28/2014 01:46 PM, Piotr Wilczek wrote:
> >>> This patch fixes part_efi code to avoid unaligned access exception
> >>> on some ARM platforms.
> >>>
> >>> Signed-off-by: Piotr Wilczek <p.wilczek@samsung.com>
> >>> Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
> >>> CC: Tom Rini <trini@ti.com>
> >>> CC: Albert ARIBAUD <albert.u.boot@aribaud.net>
> >>> ---
> >>> Chnages for V2:
> >>> - used put_unaligned to copy value;
> >>> - use __aligned to align local array;
> >>>
> >>> disk/part_efi.c | 7 ++++---
> >>> 1 file changed, 4 insertions(+), 3 deletions(-)
> >>>
> >>> diff --git a/disk/part_efi.c b/disk/part_efi.c
> >>> index 9c33ae7..eb2cd57 100644
> >>> --- a/disk/part_efi.c
> >>> +++ b/disk/part_efi.c
> >>> @@ -225,7 +225,7 @@ static int set_protective_mbr(block_dev_desc_t
> >>> *dev_desc)
> >>> p_mbr->signature = MSDOS_MBR_SIGNATURE;
> >>> p_mbr->partition_record[0].sys_ind =
> >>> EFI_PMBR_OSTYPE_EFI_GPT; p_mbr->partition_record[0].start_sect =
> >>> 1;
> >>> - p_mbr->partition_record[0].nr_sects = (u32) dev_desc->lba;
> >>> + put_unaligned(dev_desc->lba,
> >>> &p_mbr->partition_record[0].nr_sects);
> >>>
> >>> /* Write MBR sector to the MMC device */
> >>> if (dev_desc->block_write(dev_desc->dev, 0, 1, p_mbr) != 1)
> >>> { @@ -361,6 +361,8 @@ int gpt_fill_pte(gpt_header *gpt_h,
> >>> gpt_entry *gpt_e, #ifdef CONFIG_PARTITION_UUIDS
> >>> char *str_uuid;
> >>> #endif
> >>> + static efi_guid_t basic_guid __aligned(0x04) =
> >>> + PARTITION_BASIC_DATA_GUID;
> >>>
> >>> for (i = 0; i < parts; i++) {
> >>> /* partition starting lba */
> >>> @@ -388,8 +390,7 @@ int gpt_fill_pte(gpt_header *gpt_h, gpt_entry
> >>> *gpt_e, gpt_e[i].ending_lba = cpu_to_le64(offset - 1);
> >>>
> >>> /* partition type GUID */
> >>> - memcpy(gpt_e[i].partition_type_guid.b,
> >>> - &PARTITION_BASIC_DATA_GUID, 16);
> >>> + gpt_e[i].partition_type_guid = basic_guid;
> >>>
> >>> #ifdef CONFIG_PARTITION_UUIDS
> >>> str_uuid = partitions[i].uuid;
> >>>
> >
> >> Sorry, I sent my tested-by on a different thread:
> >> http://patchwork.ozlabs.org/patch/319649/
> >
> >> Tested on i.MX6 (armv7) custom board and it is working fine without
> >> the -mno-unaligned-access flag.
> >
> >> Tested-by: Hector Palacios <hector.palacios@digi.com>
> >
> >> Replying to Tom's question in that other thread, regarding the
> >> issue:
> >
> >>> Can you give me some steps on how to hit this bug? I believe
> >>> it's a bug and I believe we need to fix it, I just want to
> >>> investigate a few things while we've got a trigger case right
> >>> now. Thanks!
> >
> >> GPT partition table needs to write a protective MBR to sector 0.
> >> The MBR structure has four partition entries (each occupying 16
> >> bytes) at unaligned offsets +1BEh, +1CEh, +1DEh, +1EEh (see [1]).
> >> The structure of each partition entry is defined at
> >> include/part_efi.h
> >
> >> struct partition {
> >> u8 boot_ind; /* 0x80 - active */
> >> u8 head; /* starting head */
> >> u8 sector; /* starting sector */
> >> u8 cyl; /* starting cylinder */
> >> u8 sys_ind; /* What partition type */
> >> u8 end_head; /* end head */
> >> u8 end_sector; /* end sector */
> >> u8 end_cyl; /* end cylinder */
> >> __le32 start_sect; /* starting sector counting from 0 */
> >> __le32 nr_sects; /* nr of sectors in partition */
> >> } __packed;
> >
> >> showing eight 1-byte fields and two 4-byte fields. Since the
> >> offsets for each partition entry are unaligned, the last two
> >> fields (which are 32bit) are unaligned as well. But it's not an
> >> error, it's just the specification of the MBR requires these
> >> fields to be at those exact offsets. So the usage of unaligned
> >> macros for accessing those fields is justified.
> >
> > Right. I would have sworn I used the GPT commands since we've
> > dropped -mno-unaligned-access but I'll just go re-test locally now
> > then, thanks.
>
> Indeed I hadn't re-tested recently enough, thanks.

Have you managed to reproduce the problem on your setup?

I've reproduced it on Trats/Trats2 with ELDK 5.4 (gcc 4.7.2 armv7a
toolchain).

This patch fixes the problem.

>
> - --
> Tom
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--
Best regards,

Lukasz Majewski

Samsung R&D Institute Poland (SRPOL) | Linux Platform Group