[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <f0d771d5-ed70-444c-957a-ad4c16f6c115@csgroup.eu>
Date: Tue, 5 Aug 2025 08:21:32 +0200
From: Christophe Leroy <christophe.leroy@...roup.eu>
To: Eric Biggers <ebiggers@...nel.org>
Cc: linux-crypto@...r.kernel.org, linux-kernel@...r.kernel.org,
Ard Biesheuvel <ardb@...nel.org>, "Jason A . Donenfeld" <Jason@...c4.com>,
linux-mips@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
sparclinux@...r.kernel.org
Subject: Re: [PATCH 3/7] crypto: powerpc/md5 - Remove PowerPC optimized MD5
code
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
Powered by blists - more mailing lists