Re: [PATCH v2 0/7] dm-integrity: asynchronous hash support

Harald Freudenberger
2025-09-15T09:26:32Z

On 2025-09-12 10:08, Ingo Franzki wrote:
> On 11.09.2025 17:58, Mikulas Patocka wrote:
>>
>>
>> On Thu, 11 Sep 2025, Ingo Franzki wrote:
>>
>>>>> So, it looks like a dm-crypt bug.
>>>>>
>>>>> Please, revert my patches and run the same test on a clean
>>>>> 6.17.0-rc5 just
>>>>> to verify that the patches do not introduce the bug.
>>>>
>>>> With your patches reverted the combined mode fails the same way as
>>>> with your patches.
>>>> So they did not introduce the bug.
>>>
>>> Mikulas, do you have any idea what could be causing this errors?
>>> Is it that dm-crypt is not properly dealing with async-only HMAC
>>> ciphers?
>>> Async-only encryption ciphers seem to work fine in dm-crypt, since
>>> LUKS with PAES (but no integrity) works fine, and PAES is an
>>> async-onky cipher.
>>> LUKS with sync-HMAC ciphers (e.g. clear key HMAC) also works fine,
>>> even in combination with PAES.
>>
>> Yes, I think that it's a problem with async HMAC. The bug is probably
>> either in dm-crypt or in the crypto library.
>>
>> Do you have some other (non-dm-crypt-related) workload that uses the
>> async authentication, so that we can determine whether the bug is in
>> dm-crypt or crypto?
>
> Well, dm-integrity can use PHMAC and this works (with you patches) as
> confirmed in this mail thread.
> I don't think we have other non-dm-crypt or non-dm-integrity related
> workload.
> We could probably come up with a test program using AF_ALG that uses
> PHMAC.
> @Harald: Do you possibly have such already?
>

I do have. But still it only runs on a s390 platform. And for the qemu
s390
emulation - all the cpacf stuff is not covered. I think the better
approach
is really some kind of a pseudo module which offers some pseudo phmac
for
x64. Let me see how this can be done.

>>
>> Otherwise, would it be possible to give us a virtual machine on the
>> mainframe to debug this issue?
>
> @Harald: What do you think, could this be possible?

Hm - I have my doubts that this is possible.

>
>>
>> Mikulas
>>