netdev - [PATCH net-next v4 4/6] docs: tls: document TLS1.3 key updates

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Message-ID: <6baaaaf467845c56d7ec47250aaa2138de948003.1731597571.git.sd@queasysnail.net>
Date: Thu, 14 Nov 2024 16:50:51 +0100
From: Sabrina Dubroca <sd@...asysnail.net>
To: netdev@...r.kernel.org
Cc: Sabrina Dubroca <sd@...asysnail.net>,
	Vadim Fedorenko <vfedorenko@...ek.ru>,
	Frantisek Krenzelok <fkrenzel@...hat.com>,
	Jakub Kicinski <kuba@...nel.org>,
	Kuniyuki Iwashima <kuniyu@...zon.com>,
	Apoorv Kothari <apoorvko@...zon.com>,
	Boris Pismenny <borisp@...dia.com>,
	John Fastabend <john.fastabend@...il.com>,
	Shuah Khan <shuah@...nel.org>,
	linux-kselftest@...r.kernel.org,
	Gal Pressman <gal@...dia.com>,
	Marcel Holtmann <marcel@...tmann.org>,
	Simon Horman <horms@...nel.org>
Subject: [PATCH net-next v4 4/6] docs: tls: document TLS1.3 key updates

v3: added following Jakub's comment on the cover letter
v4: add the new counters

Signed-off-by: Sabrina Dubroca <sd@...asysnail.net>
---
 Documentation/networking/tls.rst | 31 +++++++++++++++++++++++++++++++
 1 file changed, 31 insertions(+)

diff --git a/Documentation/networking/tls.rst b/Documentation/networking/tls.rst
index 658ed3a71e1b..dfce109fe2ca 100644
--- a/Documentation/networking/tls.rst
+++ b/Documentation/networking/tls.rst
@@ -200,6 +200,31 @@ received without a cmsg buffer set.
 
 recv will never return data from mixed types of TLS records.
 
+TLS 1.3 Key Updates
+-------------------
+
+In TLS 1.3, KeyUpdate handshake messages signal that the sender is
+updating its TX key. Any message sent after a KeyUpdate will be
+encrypted using the new key. The userspace library can pass the new
+key to the kernel using the TLS_TX and TLS_RX socket options, as for
+the initial keys. TLS version and cipher cannot be changed.
+
+To prevent attempting to decrypt incoming records using the wrong key,
+decryption will be paused when a KeyUpdate message is received by the
+kernel, until the new key has been provided using the TLS_RX socket
+option. Any read occurring after the KeyUpdate has been read and
+before the new key is provided will fail with EKEYEXPIRED. Poll()'ing
+the socket will also sleep until the new key is provided. There is no
+pausing on the transmit side.
+
+Userspace should make sure that the crypto_info provided has been set
+properly. In particular, the kernel will not check for key/nonce
+reuse.
+
+The number of successful and failed key updates is tracked in the
+``TlsTxRekeyOk``, ``TlsRxRekeyOk``, ``TlsTxRekeyError``,
+``TlsRxRekeyError`` statistics.
+
 Integrating in to userspace TLS library
 ---------------------------------------
 
@@ -286,3 +311,9 @@ TLS implementation exposes the following per-namespace statistics
 - ``TlsRxNoPadViolation`` -
   number of data RX records which had to be re-decrypted due to
   ``TLS_RX_EXPECT_NO_PAD`` mis-prediction.
+
+- ``TlsTxRekeyOk``, ``TlsRxRekeyOk`` -
+  number of successful rekeys on existing sessions for TX and RX
+
+- ``TlsTxRekeyError``, ``TlsRxRekeyError`` -
+  number of failed rekeys on existing sessions for TX and RX
-- 
2.47.0