Re: [PATCH bpf-next v8 01/12] bpf: add support for bpf_setsockopt()

[Willem de Bruijn <willemdebruijn.kernel@gmail.com>]

Jason Xing wrote:
> Users can write the following code to enable the bpf extension:
> int flags = SK_BPF_CB_TX_TIMESTAMPING;
> int opts = SK_BPF_CB_FLAGS;
> bpf_setsockopt(skops, SOL_SOCKET, opts, &flags, sizeof(flags));
> 
> Signed-off-by: Jason Xing <kerneljasonxing@gmail.com>
> ---
>  include/net/sock.h             |  3 +++
>  include/uapi/linux/bpf.h       |  8 ++++++++
>  net/core/filter.c              | 23 +++++++++++++++++++++++
>  tools/include/uapi/linux/bpf.h |  1 +
>  4 files changed, 35 insertions(+)
> 
> diff --git a/include/net/sock.h b/include/net/sock.h
> index 8036b3b79cd8..7916982343c6 100644
> --- a/include/net/sock.h
> +++ b/include/net/sock.h
> @@ -303,6 +303,7 @@ struct sk_filter;
>    *	@sk_stamp: time stamp of last packet received
>    *	@sk_stamp_seq: lock for accessing sk_stamp on 32 bit architectures only
>    *	@sk_tsflags: SO_TIMESTAMPING flags
> +  *	@sk_bpf_cb_flags: used in bpf_setsockopt()
>    *	@sk_use_task_frag: allow sk_page_frag() to use current->task_frag.
>    *			   Sockets that can be used under memory reclaim should
>    *			   set this to false.
> @@ -445,6 +446,8 @@ struct sock {
>  	u32			sk_reserved_mem;
>  	int			sk_forward_alloc;
>  	u32			sk_tsflags;
> +#define SK_BPF_CB_FLAG_TEST(SK, FLAG) ((SK)->sk_bpf_cb_flags & (FLAG))
> +	u32			sk_bpf_cb_flags;
>  	__cacheline_group_end(sock_write_rxtx);
>  
>  	__cacheline_group_begin(sock_write_tx);
> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> index 2acf9b336371..6116eb3d1515 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -6913,6 +6913,13 @@ enum {
>  	BPF_SOCK_OPS_ALL_CB_FLAGS       = 0x7F,
>  };
>  
> +/* Definitions for bpf_sk_cb_flags */
> +enum {
> +	SK_BPF_CB_TX_TIMESTAMPING	= 1<<0,
> +	SK_BPF_CB_MASK			= (SK_BPF_CB_TX_TIMESTAMPING - 1) |
> +					   SK_BPF_CB_TX_TIMESTAMPING
> +};
> +
>  /* List of known BPF sock_ops operators.
>   * New entries can only be added at the end
>   */
> @@ -7091,6 +7098,7 @@ enum {
>  	TCP_BPF_SYN_IP		= 1006, /* Copy the IP[46] and TCP header */
>  	TCP_BPF_SYN_MAC         = 1007, /* Copy the MAC, IP[46], and TCP header */
>  	TCP_BPF_SOCK_OPS_CB_FLAGS = 1008, /* Get or Set TCP sock ops flags */
> +	SK_BPF_CB_FLAGS		= 1009, /* Used to set socket bpf flags */
>  };
>  
>  enum {
> diff --git a/net/core/filter.c b/net/core/filter.c
> index 2ec162dd83c4..1c6c07507a78 100644
> --- a/net/core/filter.c
> +++ b/net/core/filter.c
> @@ -5222,6 +5222,25 @@ static const struct bpf_func_proto bpf_get_socket_uid_proto = {
>  	.arg1_type      = ARG_PTR_TO_CTX,
>  };
>  
> +static int sk_bpf_set_get_cb_flags(struct sock *sk, char *optval, bool getopt)
> +{
> +	u32 sk_bpf_cb_flags;
> +
> +	if (getopt) {
> +		*(u32 *)optval = sk->sk_bpf_cb_flags;
> +		return 0;
> +	}
> +
> +	sk_bpf_cb_flags = *(u32 *)optval;
> +
> +	if (sk_bpf_cb_flags & ~SK_BPF_CB_MASK)
> +		return -EINVAL;
> +
> +	sk->sk_bpf_cb_flags = sk_bpf_cb_flags;

I don't know BPF internals that well:

Is there mutual exclusion between these sol_socket_sockopt calls?
Or do these sk field accesses need WRITE_ONCE/READ_ONCE.

> +
> +	return 0;
> +}
> +
>  static int sol_socket_sockopt(struct sock *sk, int optname,
>  			      char *optval, int *optlen,
>  			      bool getopt)
> @@ -5238,6 +5257,7 @@ static int sol_socket_sockopt(struct sock *sk, int optname,
>  	case SO_MAX_PACING_RATE:
>  	case SO_BINDTOIFINDEX:
>  	case SO_TXREHASH:
> +	case SK_BPF_CB_FLAGS:
>  		if (*optlen != sizeof(int))
>  			return -EINVAL;
>  		break;
> @@ -5247,6 +5267,9 @@ static int sol_socket_sockopt(struct sock *sk, int optname,
>  		return -EINVAL;
>  	}
>  
> +	if (optname == SK_BPF_CB_FLAGS)
> +		return sk_bpf_set_get_cb_flags(sk, optval, getopt);
> +
>  	if (getopt) {
>  		if (optname == SO_BINDTODEVICE)
>  			return -EINVAL;
> diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
> index 2acf9b336371..70366f74ef4e 100644
> --- a/tools/include/uapi/linux/bpf.h
> +++ b/tools/include/uapi/linux/bpf.h
> @@ -7091,6 +7091,7 @@ enum {
>  	TCP_BPF_SYN_IP		= 1006, /* Copy the IP[46] and TCP header */
>  	TCP_BPF_SYN_MAC         = 1007, /* Copy the MAC, IP[46], and TCP header */
>  	TCP_BPF_SOCK_OPS_CB_FLAGS = 1008, /* Get or Set TCP sock ops flags */
> +	SK_BPF_CB_FLAGS		= 1009, /* Used to set socket bpf flags */
>  };
>  
>  enum {
> -- 
> 2.43.5
>