Re: dm crypt: use unsigned long long instead of sector_t to store iv_offset

[AliOS system security <alios_sys_security@linux.alibaba.com>]

On 2018/11/2 4:06, Mike Snitzer wrote:
> On Thu, Nov 01 2018 at  4:53am -0400,
> AliOS system security <alios_sys_security@linux.alibaba.com> wrote:
>
>> The iv_offset in the mapping table of crypt target is a 64bit number
>> when iv mode is plain64 or plain64be. It will be assigned to iv_offset of
>> struct crypt_config, cc_sector of struct convert_context and iv_sector of
>> struct dm_crypt_request. These structures members are defined as a sector_t.
>> But sector_t is 32bit when CONFIG_LBDAF is not set in 32bit kernel. In this
>> situation sector_t is not big enough to store the 64bit iv_offset.
> I really don't think this is needed.
>
> cc->iv_offset can only address a the address space used to access the
> device.  Which is expressed in terms of sectors.  Therefore if
> CONFIG_LBDAF is not set in 32bit kernel then there is no need to address
> beyond that which 'sector_t' addresses.
>
> Please show proof to the contrary if you still think this change is
> needed.
>
> Mike


Sorry I made a mistake. I read Documentation/device-mapper/dm-crypt.txt 
again and found that the IV
offset is a sector count. So it make sense to store the iv_offset as a 
sector_t.

In addition, I want to describe what problem I met in the beginning. I 
made a crypt.img with the crypt param
"aes-cbc-plain64 0x1234...5678 1311768465173141112 /dev/loop0 0" in a 
32bit kernel with CONFIG_LBDAF=y.
The iv_offset is set to a 64bit number and the iv mode is set to 
plain64. Someday I recompiled my kernel but
CONFIG_LBDAF is not set this time. When I reload the crypt.img with the 
same crypt param in new kernel,
I got ioctl(..., DM_TABLE_LOAD, ...) return 0 but the content of 
/dev/dm-0 is incorrect.

So, is this situation, set the iv mode to plain64 or plain64be in a 
32bit kernel with CONFIG_LBDAF is not set, a problem? Should the 
crypt_ctr() return an error code when this happned? Or we just support 
64bit iv mode
all the time regardless of CONFIG_LBDAF?