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

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Message-ID: <CAL+tcoDGq8Jih9vwsz=-O8byC1S0R1uojShMvUiTZKQvMDnfTQ@mail.gmail.com>
Date: Wed, 11 Dec 2024 17:17:55 +0800
From: Jason Xing <kerneljasonxing@...il.com>
To: Martin KaFai Lau <martin.lau@...ux.dev>
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 Wed, Dec 11, 2024 at 10:02 AM Martin KaFai Lau <martin.lau@...ux.dev> wrote:
>
> 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.

I'll remove this.

>
> 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 *".

Sorry, I don't follow. Could you rephrase your thoughts? Thanks.

>
> 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.

Do you mean that if we introduce a new field, then bpf prog can
read/write the socket?

Reading the socket could be very helpful in the long run.

>
> 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.

Right, but for now, TCP seems to need this. I can remove this also.

>
> > +     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.

If we use this helper, we will change when the udp bpf extension needs
to be supported.

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

Thanks a lot :)

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