Subject: Re: [PATCH RFC-v5 bpf-next 02/12] net: Add BPF_XDP_EGRESS as a bpf_attach_type

From: Toke Høiland-Jørgensen <[email-masked]>
Date: Thu, 16 Apr 2020 16:01:59 +0200

David Ahern <[email-masked]> writes:

> From: David Ahern <[email-masked]>
>
> Add new bpf_attach_type, BPF_XDP_EGRESS, for BPF programs attached
> at the XDP layer, but the egress path.
>
> Since egress path will not have ingress_ifindex and rx_queue_index
> set, update xdp_is_valid_access to block access to these entries in
> the xdp context when a program is attached to egress path.
>
> Update dev_change_xdp_fd to verify expected_attach_type for a program
> is BPF_XDP_EGRESS if egress argument is set.
>
> The next patch adds support for the egress ifindex.
>
> Signed-off-by: Prashant Bhole <[email-masked]>
> Signed-off-by: David Ahern <[email-masked]>
> ---
>  include/uapi/linux/bpf.h       | 1 +
>  net/core/dev.c                 | 6 ++++++
>  net/core/filter.c              | 8 ++++++++
>  tools/include/uapi/linux/bpf.h | 1 +
>  4 files changed, 16 insertions(+)
>
> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> index 2e29a671d67e..a9d384998e8b 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -215,6 +215,7 @@ enum bpf_attach_type {
>  	BPF_TRACE_FEXIT,
>  	BPF_MODIFY_RETURN,
>  	BPF_LSM_MAC,
> +	BPF_XDP_EGRESS,
>  	__MAX_BPF_ATTACH_TYPE
>  };
>  
> diff --git a/net/core/dev.c b/net/core/dev.c
> index 06e0872ecdae..e763b6cea8ff 100644
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -8731,6 +8731,12 @@ int dev_change_xdp_fd(struct net_device *dev, struct netlink_ext_ack *extack,
>  		if (IS_ERR(prog))
>  			return PTR_ERR(prog);
>  
> +		if (egress && prog->expected_attach_type != BPF_XDP_EGRESS) {
> +			NL_SET_ERR_MSG(extack, "XDP program in Tx path must use BPF_XDP_EGRESS attach type");
> +			bpf_prog_put(prog);
> +			return -EINVAL;
> +		}
> +
>  		if (!offload && bpf_prog_is_dev_bound(prog->aux)) {
>  			NL_SET_ERR_MSG(extack, "using device-bound program without HW_MODE flag is not supported");
>  			bpf_prog_put(prog);
> diff --git a/net/core/filter.c b/net/core/filter.c
> index 7628b947dbc3..c4e0e044722f 100644
> --- a/net/core/filter.c
> +++ b/net/core/filter.c
> @@ -6935,6 +6935,14 @@ static bool xdp_is_valid_access(int off, int size,
>  				const struct bpf_prog *prog,
>  				struct bpf_insn_access_aux *info)
>  {
> +	if (prog->expected_attach_type == BPF_XDP_EGRESS) {
> +		switch (off) {
> +		case offsetof(struct xdp_md, ingress_ifindex):
> +		case offsetof(struct xdp_md, rx_queue_index):
> +			return false;
> +		}
> +	}
> +

How will this be handled for freplace programs - will they also
"inherit" the expected_attach_type of the programs they attach to?

-Toke