[dm-devel] [PATCH v2 0/2] Introduce the bulk IV mode for improving the crypto engine efficiency

[Baolin Wang]

Hi Milan,

On 3 January 2016 at 06:46, Milan Broz <gmazyland at gmail.com> wrote:
>
> Sorry for delay, I tried to compile it.
> It doesn't crash now, but it also does not work.
>
> You usage of IV in XTS mode is not correct - it cannot just work this way,
> you have to initialize IV after each block. And just one write not aligned
> to your large XTS block will corrupt it.
>
> Did you tried to _read_ data you write to the device?
>
> See this test :
>
> # create  device with your patch
> $ echo "test"|cryptsetup create -s 512 -c aes-xts-bulk tst /dev/sdg
>
> # prepare random test file
> $ dd if=/dev/urandom of=/src.img bs=1M count=16
>
> # now copy the file to the plaintext device and drop caches
> $ dd if=/src.img of=/dev/mapper/tst bs=1M count=16
>
> $ echo 3 > /proc/sys/vm/drop_caches
>
> # and verify that we are (not) reading the same data ...
>
> $ dd if=/dev/mapper/tst of=/dst1.img bs=1M count=16
>
> $ sha256sum /src.img /dst1.img
> 5401119fa9975bbeebac58e0b2598bc87247a29e62417f9f58fe200b531602ad  /src.img
> e9bf5efa95031fdb5adf618db141f48ed23f71b12c017b8a0cbe0a694f18b979  /dst1.img
>
> (I think only first page-sized block is correct, because without direct-io
> it writes in page-sized IOs.)
>
>
> ... or just try to mkfs and mount it
> $ mkfs -t ext4  /dev/mapper/tst
>
> mke2fs 1.42.13 (17-May-2015)
> Creating filesystem with 262144 4k blocks and 65536 inodes
> ...
>
> $ mount /dev/mapper/tst /mnt/tst
> mount: wrong fs type, bad option, bad superblock on /dev/mapper/tst,
>        missing codepage or helper program, or other error
>
>
> You approach simply does not work. (It will probably work for ECB mode but it is
> unusable in real world.)
>
>
> Anyway, I think that you should optimize driver, not add strange hw-dependent
> crypto modes to dmcrypt. This is not the first crypto accelerator that is just not
> suited for this kind of use.

Very grateful for your feedback. I'm sorry I didn't check much data
correctness, mostly focus on the encryption speed. It looks like there
are something wrong when I follow your test procedure. I will optimize
the driver and need to be known much about XTS mode to check why it
can not work. Thanks.

>
> (If it can process batch of chunks of data each with own IV, then it can work
> with dmcrypt, but I think such optimized code should be inside crypto API,
> not in dmcrypt.)
>
> Milan



-- 
Baolin.wang
Best Regards