On Tue, Oct 21, 2025 at 3:46 AM Hannes Reinecke [off-list ref] wrote:

On 10/17/25 06:23, alistair23@gmail.com wrote:

quoted

From: Alistair Francis <redacted>

The TLS 1.3 specification allows the TLS client or server to send a
KeyUpdate. This is generally used when the sequence is about to
overflow or after a certain amount of bytes have been encrypted.

The TLS spec doesn't mandate the conditions though, so a KeyUpdate
can be sent by the TLS client or server at any time. This includes
when running NVMe-OF over a TLS 1.3 connection.

As such Linux should be able to handle a KeyUpdate event, as the
other NVMe side could initiate a KeyUpdate.

Upcoming WD NVMe-TCP hardware controllers implement TLS support
and send KeyUpdate requests.

This series builds on top of the existing TLS EKEYEXPIRED work,
which already detects a KeyUpdate request. We can now pass that
information up to the NVMe layer (target and host) and then pass
it up to userspace.

Userspace (ktls-utils) will need to save the connection state
in the keyring during the initial handshake. The kernel then
provides the key serial back to userspace when handling a
KeyUpdate. Userspace can use this to restore the connection
information and then update the keys, this final process
is similar to the initial handshake.

I am rather sceptical at the current tlshd implementation.
At which place do you update the sending keys?

The sending keys are updated as part of gnutls_session_key_update().

gnutls_session_key_update() calls update_sending_key() which updates
the sending keys.

The idea is that when the sequence number is about to overflow the
kernel will request userspace to update the sending keys via the
HANDSHAKE_KEY_UPDATE_TYPE_SEND key_update_type. Userspace updates the
keys and initiates a KeyUpdate.

I'm only seeing a call to 'gnutls_handhake_update_receiving_key()'.

But I haven't found the matching function
'gnutls_handshake_update_sending_key()' in current gnutls.
So how does updating of the sending keys work?

gnutls_session_key_update() calls update_sending_key() which updates
the sending keys.

When updating the sending keys we want to send a KeyUpdate request,
which is why it's a different flow.

Alistair

Cheers,

Hannes
--
Dr. Hannes Reinecke                  Kernel Storage Architect
hare@suse.de                                +49 911 74053 688
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