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

[Tom Rini]

On Mon, Feb 24, 2014 at 04:56:57PM +0100, Lukasz Majewski wrote:
> Hi Tom,
> 
> > -----BEGIN PGP SIGNED MESSAGE-----
> > Hash: SHA1
> > 
> > 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 at samsung.com>
> > >>> Signed-off-by: Kyungmin Park <kyungmin.park at samsung.com>
> > >>> CC: Tom Rini <trini at ti.com>
> > >>> CC: Albert ARIBAUD <albert.u.boot at 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 at 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.

Yes, which is why I've renewed my effort to correct our behavior with
respect to gcc generating unaligned access faults where we don't need
them, and this shall be resolved for v2014.04-rc2.

-- 
Tom
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