netdev - Re: [PATCH net-next v4 02/11] net-timestamp: prepare for bpf prog use

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Message-ID: <f8e9ab4a-38b9-43a5-aaf4-15f95a3463d0@linux.dev>
Date: Tue, 10 Dec 2024 18:02:31 -0800
From: Martin KaFai Lau <martin.lau@...ux.dev>
To: Jason Xing <kerneljasonxing@...il.com>
Cc: davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org,
 pabeni@...hat.com, dsahern@...nel.org, willemdebruijn.kernel@...il.com,
 willemb@...gle.com, ast@...nel.org, daniel@...earbox.net, andrii@...nel.org,
 eddyz87@...il.com, song@...nel.org, yonghong.song@...ux.dev,
 john.fastabend@...il.com, kpsingh@...nel.org, sdf@...ichev.me,
 haoluo@...gle.com, jolsa@...nel.org, bpf@...r.kernel.org,
 netdev@...r.kernel.org, Jason Xing <kernelxing@...cent.com>
Subject: Re: [PATCH net-next v4 02/11] net-timestamp: prepare for bpf prog use

On 12/7/24 9:37 AM, Jason Xing wrote:
> From: Jason Xing <kernelxing@...cent.com>
> 
> Later, I would introduce three points to report some information
> to user space based on this.
> 
> Signed-off-by: Jason Xing <kernelxing@...cent.com>
> ---
>   include/net/sock.h |  7 +++++++
>   net/core/sock.c    | 15 +++++++++++++++
>   2 files changed, 22 insertions(+)
> 
> diff --git a/include/net/sock.h b/include/net/sock.h
> index 0dd464ba9e46..f88a00108a2f 100644
> --- a/include/net/sock.h
> +++ b/include/net/sock.h
> @@ -2920,6 +2920,13 @@ int sock_set_timestamping(struct sock *sk, int optname,
>   			  struct so_timestamping timestamping);
>   
>   void sock_enable_timestamps(struct sock *sk);
> +#if defined(CONFIG_CGROUP_BPF) && defined(CONFIG_BPF_SYSCALL)
> +void bpf_skops_tx_timestamping(struct sock *sk, struct sk_buff *skb, int op);
> +#else
> +static inline void bpf_skops_tx_timestamping(struct sock *sk, struct sk_buff *skb, int op)
> +{
> +}
> +#endif
>   void sock_no_linger(struct sock *sk);
>   void sock_set_keepalive(struct sock *sk);
>   void sock_set_priority(struct sock *sk, u32 priority);
> diff --git a/net/core/sock.c b/net/core/sock.c
> index 74729d20cd00..79cb5c74c76c 100644
> --- a/net/core/sock.c
> +++ b/net/core/sock.c
> @@ -941,6 +941,21 @@ int sock_set_timestamping(struct sock *sk, int optname,
>   	return 0;
>   }
>   
> +#if defined(CONFIG_CGROUP_BPF) && defined(CONFIG_BPF_SYSCALL)
> +void bpf_skops_tx_timestamping(struct sock *sk, struct sk_buff *skb, int op)
> +{
> +	struct bpf_sock_ops_kern sock_ops;
> +
> +	sock_owned_by_me(sk);

I don't think this can be assumed in the time stamping callback.

To remove this assumption for sockops, I believe it needs to stop the bpf prog 
from calling a few bpf helpers. In particular, the bpf_sock_ops_cb_flags_set and 
bpf_sock_ops_setsockopt. This should be easy by asking the helpers to check the 
"u8 op" in "struct bpf_sock_ops_kern *".

I just noticed a trickier one, sockops bpf prog can write to sk->sk_txhash. The 
same should go for reading from sk. Also, sockops prog assumes a fullsock sk is 
a tcp_sock which also won't work for the udp case. A quick thought is to do 
something similar to is_fullsock. May be repurpose the is_fullsock somehow or a 
new u8 is needed. Take a look at SOCK_OPS_{GET,SET}_FIELD. It avoids 
writing/reading the sk when is_fullsock is false.

This is a signal that the existing sockops interface has already seen better 
days. I hope not too many fixes like these are needed to get tcp/udp 
timestamping to work.

> +
> +	memset(&sock_ops, 0, offsetof(struct bpf_sock_ops_kern, temp));
> +	sock_ops.op = op;
> +	sock_ops.is_fullsock = 1;

I don't think we can assume it is always is_fullsock either.

> +	sock_ops.sk = sk;
> +	__cgroup_bpf_run_filter_sock_ops(sk, &sock_ops, CGROUP_SOCK_OPS);

Same here. sk may not be fullsock. BPF_CGROUP_RUN_PROG_SOCK_OPS(&sock_ops) is 
needed.

[ I will continue the rest of the set later. ]

> +}
> +#endif
> +
>   void sock_set_keepalive(struct sock *sk)
>   {
>   	lock_sock(sk);