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

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Message-ID: <187412bd-3ae0-4fe8-b526-f96af6bea6dc@csgroup.eu>
Date: Mon, 4 Aug 2025 21:02:27 +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 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:

# ldd `which md5sum`
         linux-vdso32.so.1 (0x77b90000)
         libkcapi.so.1 => /usr/lib/libkcapi.so.1 (0x6ffa0000)    <==
         libcrypt.so.1 => /lib/libcrypt.so.1 (0x6ff50000)
         libc.so.6 => /lib/libc.so.6 (0x6fd10000)
         /lib/ld.so.1 => //lib/ld.so.1 (0x77ba0000)

Previous test was on an mpc8xx.

I now did the test on mpc832x and the difference is even bigger:

With CONFIG_CRYPTO_MD5_PPC:

# time md5sum avion.au
6513851d6109d42477b20cd56bf57f28  avion.au
real    0m 0.41s
user    0m 0.00s
sys     0m 0.34s

Without CONFIG_CRYPTO_MD5_PPC:

# time md5sum avion.au
6513851d6109d42477b20cd56bf57f28  avion.au
real    0m 0.58s
user    0m 0.00s
sys     0m 0.47s

Christophe