Re: [PATCH] net: tls: fix tls with sk_redirect using a BPF verdict.
From: Jakub Kicinski <kuba@kernel.org>
Date: 2022-06-28 17:34:34
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bpf
On Tue, 28 Jun 2022 17:25:05 +0200 Julien Salleyron wrote:
This patch allows to use KTLS on a socket where we apply sk_redirect using a BPF verdict program. Without this patch, we see that the data received after the redirection are decrypted but with an incorrect offset and length. It seems to us that the offset and length are correct in the stream-parser data, but finally not applied in the skb. We have simply applied those values to the skb. In the case of regular sockets, we saw a big performance improvement from applying redirect. This is not the case now with KTLS, may be related to the following point.
It's because kTLS does a very expensive reallocation and copy for the non-zerocopy case (which currently means all of TLS 1.3). I have code almost ready to fix that (just needs to be reshuffled into upstreamable patches). Brings us up from 5.9 Gbps to 8.4 Gbps per CPU on my test box with 16k records. Probably much more than that with smaller records.
quoted hunk ↗ jump to hunk
It is still necessary to perform a read operation (never triggered) from user space despite the redirection. It makes no sense, since this read operation is not necessary on regular sockets without KTLS. We do not see how to fix this problem without a change of architecture, for example by performing TLS decrypt directly inside the BPF verdict program. An example program can be found at https://github.com/juliens/ktls-bpf_redirect-example/ Co-authored-by: Marc Vertes [off-list ref] --- net/tls/tls_sw.c | 6 ++++++ tools/testing/selftests/bpf/test_sockmap.c | 8 +++----- 2 files changed, 9 insertions(+), 5 deletions(-)diff --git a/net/tls/tls_sw.c b/net/tls/tls_sw.c index 0513f82b8537..a409f8a251db 100644 --- a/net/tls/tls_sw.c +++ b/net/tls/tls_sw.c@@ -1839,8 +1839,14 @@ int tls_sw_recvmsg(struct sock *sk, if (bpf_strp_enabled) { /* BPF may try to queue the skb */ __skb_unlink(skb, &ctx->rx_list); + err = sk_psock_tls_strp_read(psock, skb); + if (err != __SK_PASS) { + if (err == __SK_REDIRECT) { + skb->data += rxm->offset; + skb->len = rxm->full_len; + }
IDK what this is trying to do but I certainly depends on the fact we run skb_cow_data() and is not "generally correct" :S