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

[Christoph Hellwig]

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.

It sounds like xxhash should be removed the crypto API entirely.
There's no user of it, it's not crypto, and doing xxhash through
the userspace crypto API socket is so stupid that I doubt anyone
attempted it.