On 22.08.2024 18:21, Mikulas Patocka wrote: > > > On Wed, 21 Aug 2024, Ingo Franzki wrote: > >> On 20.08.2024 17:56, Mikulas Patocka wrote: >>> >>> >>> On Fri, 16 Aug 2024, Ingo Franzki wrote: >>> >>>> For the MAC based integrity operation, the integrity key size (i.e. >>>> key_mac_size) is currently set to the digest size of the used digest. >>>> >>>> For wrapped key HMAC algorithms, the key size is independent of the >>>> cryptographic key size. So there is no known size of the mac key in >>>> such cases. The desired key size can optionally be specified as argument >>>> when the dm-crypt device is configured via 'integrity_key_size:%u'. >>>> If no integrity_key_size argument is specified, the mac key size >>>> is still set to the digest size, as before. >>>> >>>> Increase version number to 1.28.0 so that support for the new >>>> argument can be detected by user space (i.e. cryptsetup). >>> >>> Hi >>> >>> I know you already discussed it with Milan. I'd like to ask, what's the >>> reason for this patch? Milan said that you need it for mainframes - >>> please, describe the specific configuration when this patch is needed. >>> >>> Mikulas >> >> Hi Mikulas, >> >> thanks for looking into this. >> >> In short: Yes, we need it for a new function on Linux on IBM Z platform >> (aka s390x), but the general concept of using wrapped keys is not >> limited to that platform but can be used by other platforms as well. >> Furthermore, the proposed change can also be beneficial for clear key >> HMAC integrity protection, to allow choosing the size of the integrity >> key. > > Hi > > Thanks for the explanation. I discussed it with Milan and we concluded > that the patch is OK and that we can stage it for the kernel 6.12. > > I added the patch to the device mapper repository. You can get it from > "git://git.kernel.org/pub/scm/linux/kernel/git/device-mapper/linux-dm.git", > checkout branch "remotes/origin/dm-6.12". > > I fixed two bugs in the patch: > 1. crypt_status must report the new argument in its table line > 2. sscanf(opt_string, "integrity_key_size:%u"...) should really be > sscanf(opt_string, "integrity_key_size:%u%c"...), so that we report > syntax error if there are trailing characters after the number. > > Please, download the updated patch from the "linux-dm.git" repository and > test it. Thanks for fixing these bugs. They all make very much sense. I have downloaded the patch from https://git.kernel.org/pub/scm/linux/kernel/git/device-mapper/linux-dm.git/commit/?h=dm-6.12&id=4441686b24a1d7acf9834ca95864d67e3f97666a and tested it successfully on my system. Works great. 'dmsetup table' now also shows the 'integrity_key_size' option. @Milan: I noticed that now that dm-crypt also reports the integrity_key_size param in the status query, I need to also support that in my cryptsetup changes (i.e. in function _dm_target_query_crypt() in lib/libdevmapper.c). With this additional change, luksFormat and friends work fine with the updated dm-crypt module. > > Mikulas > -- Ingo Franzki eMail: ifranzki@xxxxxxxxxxxxx Tel: ++49 (0)7031-16-4648 Linux on IBM Z Development, Schoenaicher Str. 220, 71032 Boeblingen, Germany IBM Deutschland Research & Development GmbH Vorsitzender des Aufsichtsrats: Gregor Pillen Geschäftsführung: David Faller Sitz der Gesellschaft: Böblingen / Registergericht: Amtsgericht Stuttgart, HRB 243294 IBM DATA Privacy Statement: https://www.ibm.com/privacy/us/en/
