handshake: support extracting record size limit value

[twilfredo]

RFC 8449 [1] Section 4 defines the record_size_limit TLS extension, which allows peers to negotiate a maximum plaintext record size during the TLS handshake. The value must be between 64 bytes and 16,384 bytes (2^14). If a TLS endpoint receives a record larger than its advertised limit, it must send a fatal record_overflow alert.

This patch adds support for extracting the record size limit value from the gnutls session and passing it to the kernel. This is to be used by the kernel at the tls layer limit outgoing records to the maximum record size limit as specified by the endpoint.

Based on GnuTLS [2] and Kernel Integration [3].

[1] https://www.rfc-editor.org/rfc/rfc8449#section-4
[2] https://gitlab.com/gnutls/gnutls/-/merge_requests/1989
[3] https://github.com/twilfredo/spdm-linux/commits/wilfred/record-size-tls-test/

[chucklever]

This patch adds support for extracting the record size limit value from the gnutls session and passing it to the kernel. This is to be used by the kernel at the tls layer limit outgoing records to the maximum record size limit as specified by the endpoint.

Based on GnuTLS [2] and Kernel Integration [3].

[1] https://www.rfc-editor.org/rfc/rfc8449#section-4
[2] https://gitlab.com/gnutls/gnutls/-/merge_requests/1989
[3] https://github.com/twilfredo/spdm-linux/commits/wilfred/record-size-tls-test/

Two questions:

• Has [3] been reviewed by netdev@ ?
• gnutls_record_get_record_size_limit(3) does not appear to exist in some versions of gnuTLS, so an autoconf strategy will be necessary to allow ktls-utils to build on such platforms

[twilfredo]

This patch adds support for extracting the record size limit value from the gnutls session and passing it to the kernel. This is to be used by the kernel at the tls layer limit outgoing records to the maximum record size limit as specified by the endpoint.
Based on GnuTLS [2] and Kernel Integration [3].
[1] https://www.rfc-editor.org/rfc/rfc8449#section-4
[2] https://gitlab.com/gnutls/gnutls/-/merge_requests/1989
[3] https://github.com/twilfredo/spdm-linux/commits/wilfred/record-size-tls-test/

Two questions:

* Has [3] been reviewed by netdev@ ?

I have not sent out the kernel patches yet, I was waiting to see if the GnuTLS patches can be approved beforehand. Since all of this depends on that.

* gnutls_record_get_record_size_limit(3) does not appear to exist in some versions of gnuTLS, so an autoconf strategy will be necessary to allow ktls-utils to build on such platforms

Ah I see, I will add that. Thanks!