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

[Martin Lau <kafai@fb.com>]

On Wed, Jan 22, 2020 at 06:42:00PM -0700, David Ahern wrote:
> From: Prashant Bhole <prashantbhole.linux@gmail.com>
> 
> Add new bpf_attach_type, BPF_XDP_EGRESS, for BPF programs attached
> at the XDP layer, but the egress path.
> 
> Since egress path does not have rx_queue_index and ingress_ifindex set,
> update xdp_is_valid_access to block access to these entries in the xdp
> context when a program is attached to egress path.
> 
> Signed-off-by: Prashant Bhole <prashantbhole.linux@gmail.com>
> Signed-off-by: David Ahern <dahern@digitalocean.com>
> ---
>  include/uapi/linux/bpf.h       | 1 +
>  net/core/filter.c              | 8 ++++++++
>  tools/include/uapi/linux/bpf.h | 1 +
>  3 files changed, 10 insertions(+)
> 
> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> index 033d90a2282d..72f2a9a4621e 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -209,6 +209,7 @@ enum bpf_attach_type {
>  	BPF_TRACE_RAW_TP,
>  	BPF_TRACE_FENTRY,
>  	BPF_TRACE_FEXIT,
> +	BPF_XDP_EGRESS,
>  	__MAX_BPF_ATTACH_TYPE
>  };
>  
> diff --git a/net/core/filter.c b/net/core/filter.c
> index 17de6747d9e3..a903f3a15d74 100644
> --- a/net/core/filter.c
> +++ b/net/core/filter.c
> @@ -6803,6 +6803,14 @@ static bool xdp_is_valid_access(int off, int size,
>  		return false;
>  	}
>  
> +	if (prog->expected_attach_type == BPF_XDP_EGRESS) {
For BPF_PROG_TYPE_XDP, the expected_attach_type is currently not
enforced to be 0 in bpf_prog_load_check_attach().  Not sure if it
is ok to test it here and also return false in some of the
following switch cases.

> +		switch (off) {
> +		case offsetof(struct xdp_md, rx_queue_index):
> +		case offsetof(struct xdp_md, ingress_ifindex):
> +			return false;
> +		}
> +	}
> +
>  	switch (off) {
>  	case offsetof(struct xdp_md, data):
>  		info->reg_type = PTR_TO_PACKET;