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Re: [PATCH] efidisk: Respect block_io_protocol buffer alignment


From: Andrei Borzenkov
Subject: Re: [PATCH] efidisk: Respect block_io_protocol buffer alignment
Date: Thu, 18 Feb 2016 06:36:06 +0300
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.5.1

17.02.2016 22:44, Leif Lindholm пишет:
> Returned from the OpenProtocol operation, the grub_efi_block_io_media
> structure contains the io_align field, specifying the minimum alignment
> required for buffers used in any data transfers with the device.
> 
> Make grub_efidisk_readwrite() allocate a temporary buffer, aligned to
> this boundary, if the buffer passed to it does not already meet the
> requirements.
> 
> Reported-by: Jeremy Linton <address@hidden>
> ---
> 
> This modified version is contained entirely within the efidisk driver.
> There is some excessive copying going on, but it removes the risk of
> the changes interfering with other disk drivers.
> 
>  grub-core/disk/efi/efidisk.c | 37 ++++++++++++++++++++++++++++++++-----
>  1 file changed, 32 insertions(+), 5 deletions(-)
> 
> diff --git a/grub-core/disk/efi/efidisk.c b/grub-core/disk/efi/efidisk.c
> index 1c00e3e..901133f 100644
> --- a/grub-core/disk/efi/efidisk.c
> +++ b/grub-core/disk/efi/efidisk.c
> @@ -524,15 +524,42 @@ grub_efidisk_readwrite (struct grub_disk *disk, 
> grub_disk_addr_t sector,
>  {
>    struct grub_efidisk_data *d;
>    grub_efi_block_io_t *bio;
> +  grub_efi_status_t status;
> +  grub_size_t io_align, num_bytes;
> +  char *aligned_buf;
>  
>    d = disk->data;
>    bio = d->block_io;
>  
> -  return efi_call_5 ((wr ? bio->write_blocks : bio->read_blocks), bio,
> -                  bio->media->media_id,
> -                  (grub_efi_uint64_t) sector,
> -                  (grub_efi_uintn_t) size << disk->log_sector_size,
> -                  buf);
> +  /* Set alignment to 1 if 0 specified */
> +  io_align = bio->media->io_align ? bio->media->io_align : 1;

We probably should sanity check that it is power of two in
grub_efidisk_open.

> +  num_bytes = size << disk->log_sector_size;
> +
> +  if ((unsigned long) buf & (io_align - 1))

grub_addr_t?

> +    {
> +      aligned_buf = grub_memalign (io_align, num_bytes);
> +      if (! aligned_buf)
> +     return GRUB_EFI_OUT_OF_RESOURCES;
> +      if (wr)
> +     grub_memcpy (aligned_buf, buf, num_bytes);
> +    }
> +  else
> +    {
> +      aligned_buf = buf;
> +    }
> +
> +  status =  efi_call_5 ((wr ? bio->write_blocks : bio->read_blocks), bio,
> +                     bio->media->media_id, (grub_efi_uint64_t) sector,
> +                     (grub_efi_uintn_t) num_bytes, aligned_buf);
> +
> +  if ((unsigned long) buf & (io_align - 1))
> +    {
> +      if (!wr)
> +     grub_memcpy (buf, aligned_buf, num_bytes);
> +      grub_free (aligned_buf);
> +    }
> +
> +  return status;
>  }
>  
>  static grub_err_t
> 




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