linux-kernel - Re: [PATCH v3] partitions/efi: Fix partition name parsing in GUID partition entry

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Message-ID: <20200218185336.GA14242@infradead.org>
Date:   Tue, 18 Feb 2020 10:53:36 -0800
From:   Christoph Hellwig <hch@...radead.org>
To:     Nikolai Merinov <n.merinov@...ngo-systems.com>
Cc:     hch@...radead.org, Davidlohr Bueso <dave@...olabs.net>,
        Jens Axboe <axboe@...nel.dk>, Ard Biesheuvel <ardb@...nel.org>,
        linux-efi@...r.kernel.org, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] partitions/efi: Fix partition name parsing in GUID
 partition entry

On Mon, Jan 13, 2020 at 03:27:23PM +0500, Nikolai Merinov wrote:
> GUID partition entry defined to have a partition name as 36 UTF-16LE
> code units. This means that on big-endian platforms ASCII symbols
> would be read with 0xXX00 efi_char16_t character code. In order to
> correctly extract ASCII characters from a partition name field we
> should be converted from 16LE to CPU architecture.
> 
> The problem exists on all big endian platforms.
> 
> Signed-off-by: Nikolai Merinov <n.merinov@...ngo-systems.com>
> ---
>  block/partitions/efi.c | 3 ++-
>  block/partitions/efi.h | 2 +-
>  include/linux/efi.h    | 5 +++++
>  3 files changed, 8 insertions(+), 2 deletions(-)
> 
> diff --git a/block/partitions/efi.c b/block/partitions/efi.c
> index db2fef7dfc47..f1d0820de844 100644
> --- a/block/partitions/efi.c
> +++ b/block/partitions/efi.c
> @@ -715,7 +715,8 @@ int efi_partition(struct parsed_partitions *state)
>  				ARRAY_SIZE(ptes[i].partition_name));
>  		info->volname[label_max] = 0;
>  		while (label_count < label_max) {
> -			u8 c = ptes[i].partition_name[label_count] & 0xff;
> +			u8 c = 0xff & efi_char16le_to_cpu(
> +					ptes[i].partition_name[label_count]);

Why are you swapping the order of the comparism to an unusual one here?

> -	efi_char16_t partition_name[72 / sizeof (efi_char16_t)];
> +	efi_char16le_t partition_name[72 / sizeof(efi_char16le_t)];
>  } __packed gpt_entry;
>  
>  typedef struct _gpt_mbr_record {
> diff --git a/include/linux/efi.h b/include/linux/efi.h
> index aa54586db7a5..47882f2d45db 100644
> --- a/include/linux/efi.h
> +++ b/include/linux/efi.h
> @@ -45,9 +45,14 @@
>  typedef unsigned long efi_status_t;
>  typedef u8 efi_bool_t;
>  typedef u16 efi_char16_t;		/* UNICODE character */
> +typedef __le16 efi_char16le_t;		/* UTF16-LE */
> +typedef __be16 efi_char16be_t;		/* UTF16-BE */
>  typedef u64 efi_physical_addr_t;
>  typedef void *efi_handle_t;
>  
> +#define efi_char16le_to_cpu le16_to_cpu
> +#define efi_char16be_to_cpu be16_to_cpu

I'd rather use plain __le16 and le16_to_cpu here.  Also the be
variants seems to be entirely unused.