Re: [PATCH 3/7] crypto: powerpc/md5 - Remove PowerPC optimized MD5 code

[Christophe Leroy <christophe.leroy@csgroup.eu>]

Le 05/08/2025 à 01:09, Eric Biggers a écrit :
> On Mon, Aug 04, 2025 at 10:59:01PM +0000, Eric Biggers wrote:
>> On Mon, Aug 04, 2025 at 09:02:27PM +0200, Christophe Leroy wrote:
>>>
>>>
>>> Le 04/08/2025 à 20:09, Eric Biggers a écrit :
>>>> On Mon, Aug 04, 2025 at 07:42:15PM +0200, Christophe Leroy wrote:
>>>>>
>>>>>
>>>>> Le 03/08/2025 à 22:44, Eric Biggers a écrit :
>>>>>> MD5 is insecure, is no longer commonly used, and has never been
>>>>>> optimized for the most common architectures in the kernel.  Only mips,
>>>>>> powerpc, and sparc have optimized MD5 code in the kernel.  Of these,
>>>>>> only the powerpc one is actually testable in QEMU.  The mips one works
>>>>>> only on Cavium Octeon SoCs.
>>>>>>
>>>>>> Taken together, it's clear that it's time to retire these additional MD5
>>>>>> implementations, and focus maintenance on the MD5 generic C code.
>>>>>
>>>>> Sorry, for me it is not that clear. Even if MD5 is depracated we still have
>>>>> several applications that use MD5 for various reasons on our boards.
>>>>>
>>>>> I ran the test on kernel v6.16 with following file:
>>>>>
>>>>> # ls -l avion.au
>>>>> -rw-------    1 root     root      12130159 Jan  1  1970 avion.au
>>>>>
>>>>> With CONFIG_CRYPTO_MD5_PPC:
>>>>>
>>>>> # time md5sum avion.au
>>>>> 6513851d6109d42477b20cd56bf57f28  avion.au
>>>>> real    0m 1.02s
>>>>> user    0m 0.01s
>>>>> sys     0m 1.01s
>>>>>
>>>>> Without CONFIG_CRYPTO_MD5_PPC:
>>>>>
>>>>> # time md5sum avion.au
>>>>> 6513851d6109d42477b20cd56bf57f28  avion.au
>>>>> real    0m 1.35s
>>>>> user    0m 0.01s
>>>>> sys     0m 1.34s
>>>>>
>>>>> I think the difference is big enough to consider keeping optimised MD5 code.
>>>>
>>>> But md5sum doesn't use the kernel's MD5 code.  So it's implausible that
>>>> it has any effect on md5sum.  The difference you saw must be due to an
>>>> unrelated reason like I/O caching, CPU frequency, etc.  Try running your
>>>> test multiple times to eliminate other sources of variation.
>>>
>>> md5sum uses the kernel's MD5 code:
>>>
>>> libkcapi.so.1 => /usr/lib/libkcapi.so.1 (0x6ffa0000)    <==
> 
> Oh, I think you used the obscure implementation of md5sum from
> libkcapi-tools, instead of the normal md5sum.  Why?  Did you check how
> the normal md5sum performs too?  Just doing the calculation in userspace
> is much more efficient.

Calculation in userspace is less efficient on my board:

# time md5sum avion.au
6513851d6109d42477b20cd56bf57f28  avion.au
real    0m 1.87s
user    0m 1.51s
sys     0m 0.35s

Christophe