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Re: [PATCH] disk: Move hardcoded max disk size literal to a GRUB_DISK_MA


From: Daniel Kiper
Subject: Re: [PATCH] disk: Move hardcoded max disk size literal to a GRUB_DISK_MAX_SECTORS in disk.h
Date: Mon, 30 Nov 2020 15:42:14 +0100
User-agent: NeoMutt/20170113 (1.7.2)

On Fri, Nov 27, 2020 at 02:36:23AM -0600, Glenn Washburn wrote:
> There is a hardcoded maximum disk size that can be read or written from,
> currently set at 1EiB in grub_disk_adjust_range. Move the literal into a
> macro in disk.h, so our assumptions are more visible. This hard coded limit
> does not prevent using larger disks, just grub won't read/write past the
> limit. The comment accompanying this restriction didn't quite make sense to
> me, so its been modified.
>
> Signed-off-by: Glenn Washburn <development@efficientek.com>
> ---
>  grub-core/kern/disk_common.c | 13 +++++++------
>  include/grub/disk.h          |  6 ++++++
>  2 files changed, 13 insertions(+), 6 deletions(-)
>
> diff --git a/grub-core/kern/disk_common.c b/grub-core/kern/disk_common.c
> index 5b92f670b..d20ed20d2 100644
> --- a/grub-core/kern/disk_common.c
> +++ b/grub-core/kern/disk_common.c
> @@ -32,13 +32,14 @@ grub_disk_adjust_range (grub_disk_t disk, 
> grub_disk_addr_t *sector,
>    /* Transform total_sectors to number of 512B blocks.  */
>    total_sectors = grub_disk_from_native_sector (disk, disk->total_sectors);
>
> -  /* Some drivers have problems with disks above reasonable.
> -     Treat unknown as 1EiB disk. While on it, clamp the size to 1EiB.
> -     Just one condition is enough since GRUB_DISK_UNKNOWN_SIZE << ls is 
> always
> -     above 9EiB.
> +  /*
> +     Some drivers have problems with disks above reasonable sizes.
> +     Clamp the size to GRUB_DISK_MAX_SECTORS. Just one condition is enough
> +     since GRUB_DISK_UNKNOWN_SIZE is always above GRUB_DISK_MAX_SECTORS,
> +     assuming a maximum 4KiB sector size.
>    */
> -  if (total_sectors > (1ULL << 51))
> -    total_sectors = (1ULL << 51);
> +  if (total_sectors > GRUB_DISK_MAX_SECTORS)
> +    total_sectors = GRUB_DISK_MAX_SECTORS;
>
>    if ((total_sectors <= *sector
>         || ((*offset + size + GRUB_DISK_SECTOR_SIZE - 1)
> diff --git a/include/grub/disk.h b/include/grub/disk.h
> index 1a9e8fcf4..0bf08091f 100644
> --- a/include/grub/disk.h
> +++ b/include/grub/disk.h
> @@ -157,6 +157,12 @@ struct grub_disk_memberlist
>  typedef struct grub_disk_memberlist *grub_disk_memberlist_t;
>  #endif
>
> +/*
> +   Some drivers have problems with disks above reasonable sizes.
> +   Set max disk size at 1EiB.

The comment is formatted incorrectly [1].

> +*/
> +#define GRUB_DISK_MAX_SECTORS        (1ULL << (60 - 9))
> +
>  /* The sector size.  */
>  #define GRUB_DISK_SECTOR_SIZE        0x200
>  #define GRUB_DISK_SECTOR_BITS        9

Please move the constant below these definitions and do this:
  #define GRUB_DISK_MAX_SECTORS         (1ULL << (60 - GRUB_DISK_SECTOR_BITS))

[1] https://www.gnu.org/software/grub/manual/grub-dev/grub-dev.html#Comments



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