Re: [PATCH] crypto: testmgr - block Crypto API xxhash64 in FIPS mode

[Thomas Huth <thuth@redhat.com>]

On 15/03/2026 01.43, Joachim Vandersmissen wrote:
> Hi Herbert,
> 
> I don't think this one can be applied yet since dm-integrity still uses 
> xxhash64 through the crypto API. This would break fips=1 systems that use it.

Out of curiosity: Wouldn't such a system be FIPS-incompliant anyway? If 
xxhash64 isn't FIPS-compliant, nobody should use it for dm-integrity there, 
right? So I doubt that there are any systems out there that use fips=1 and 
use xxhash64 at the same time?

  Thomas

> 
> On 3/14/26 12:11 AM, Herbert Xu wrote:
>> On Tue, Mar 03, 2026 at 12:05:09AM -0600, Joachim Vandersmissen wrote:
>>> xxhash64 is not a cryptographic hash algorithm, but is offered in the
>>> same API (shash) as actual cryptographic hash algorithms such as
>>> SHA-256. The Cryptographic Module Validation Program (CMVP), managing
>>> FIPS certification, believes that this could cause confusion. xxhash64
>>> must therefore be blocked in FIPS mode.
>>>
>>> The only usage of xxhash64 in the kernel is btrfs. Commit fe11ac191ce0
>>> ("btrfs: switch to library APIs for checksums") recently modified the
>>> btrfs code to use the lib/crypto API, avoiding the Kernel Cryptographic
>>> API. Consequently, the removal of xxhash64 from the Crypto API in FIPS
>>> mode should now have no impact on btrfs usage.
>>>
>>> Signed-off-by: Joachim Vandersmissen <git@jvdsn.com>
>>> ---
>>>   crypto/testmgr.c | 1 -
>>>   1 file changed, 1 deletion(-)
>> Patch applied.  Thanks.
>