Re: [PATCH v1 bpf-next 1/2] bpf: add support for passing mark with bpf_fib_lookup

[David Ahern <dsahern@kernel.org>]

On 3/22/24 8:02 AM, Anton Protopopov wrote:
> Extend the bpf_fib_lookup() helper by making it to utilize mark if
> the BPF_FIB_LOOKUP_MARK flag is set. In order to pass the mark the
> four bytes of struct bpf_fib_lookup are used, shared with the
> output-only smac/dmac fields.
> 
> Signed-off-by: Anton Protopopov <aspsk@isovalent.com>
> Acked-by: Daniel Borkmann <daniel@iogearbox.net>
> ---
>  include/uapi/linux/bpf.h       | 20 ++++++++++++++++++--
>  net/core/filter.c              | 12 +++++++++---
>  tools/include/uapi/linux/bpf.h | 20 ++++++++++++++++++--
>  3 files changed, 45 insertions(+), 7 deletions(-)
> 
> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> index 9585f5345353..96d57e483133 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -3394,6 +3394,10 @@ union bpf_attr {
>   *			for the nexthop. If the src addr cannot be derived,
>   *			**BPF_FIB_LKUP_RET_NO_SRC_ADDR** is returned. In this
>   *			case, *params*->dmac and *params*->smac are not set either.
> + *		**BPF_FIB_LOOKUP_MARK**
> + *			Use the mark present in *params*->mark for the fib lookup.
> + *			This option should not be used with BPF_FIB_LOOKUP_DIRECT,
> + *			as it only has meaning for full lookups.
>   *
>   *		*ctx* is either **struct xdp_md** for XDP programs or
>   *		**struct sk_buff** tc cls_act programs.
> @@ -7120,6 +7124,7 @@ enum {
>  	BPF_FIB_LOOKUP_SKIP_NEIGH = (1U << 2),
>  	BPF_FIB_LOOKUP_TBID    = (1U << 3),
>  	BPF_FIB_LOOKUP_SRC     = (1U << 4),
> +	BPF_FIB_LOOKUP_MARK    = (1U << 5),
>  };
>  
>  enum {
> @@ -7197,8 +7202,19 @@ struct bpf_fib_lookup {
>  		__u32	tbid;
>  	};
>  
> -	__u8	smac[6];     /* ETH_ALEN */
> -	__u8	dmac[6];     /* ETH_ALEN */
> +	union {
> +		/* input */
> +		struct {
> +			__u32	mark;   /* policy routing */
> +			/* 2 4-byte holes for input */
> +		};
> +
> +		/* output: source and dest mac */
> +		struct {
> +			__u8	smac[6];	/* ETH_ALEN */
> +			__u8	dmac[6];	/* ETH_ALEN */
> +		};
> +	};
>  };
>  
>  struct bpf_redir_neigh {
> diff --git a/net/core/filter.c b/net/core/filter.c
> index 0c66e4a3fc5b..1205dd777dc2 100644
> --- a/net/core/filter.c
> +++ b/net/core/filter.c
> @@ -5884,7 +5884,10 @@ static int bpf_ipv4_fib_lookup(struct net *net, struct bpf_fib_lookup *params,
>  
>  		err = fib_table_lookup(tb, &fl4, &res, FIB_LOOKUP_NOREF);
>  	} else {
> -		fl4.flowi4_mark = 0;
> +		if (flags & BPF_FIB_LOOKUP_MARK)
> +			fl4.flowi4_mark = params->mark;
> +		else
> +			fl4.flowi4_mark = 0;
>  		fl4.flowi4_secid = 0;
>  		fl4.flowi4_tun_key.tun_id = 0;
>  		fl4.flowi4_uid = sock_net_uid(net, NULL);
> @@ -6027,7 +6030,10 @@ static int bpf_ipv6_fib_lookup(struct net *net, struct bpf_fib_lookup *params,
>  		err = ipv6_stub->fib6_table_lookup(net, tb, oif, &fl6, &res,
>  						   strict);
>  	} else {
> -		fl6.flowi6_mark = 0;
> +		if (flags & BPF_FIB_LOOKUP_MARK)
> +			fl6.flowi6_mark = params->mark;
> +		else
> +			fl6.flowi6_mark = 0;
>  		fl6.flowi6_secid = 0;
>  		fl6.flowi6_tun_key.tun_id = 0;
>  		fl6.flowi6_uid = sock_net_uid(net, NULL);
> @@ -6105,7 +6111,7 @@ static int bpf_ipv6_fib_lookup(struct net *net, struct bpf_fib_lookup *params,
>  
>  #define BPF_FIB_LOOKUP_MASK (BPF_FIB_LOOKUP_DIRECT | BPF_FIB_LOOKUP_OUTPUT | \
>  			     BPF_FIB_LOOKUP_SKIP_NEIGH | BPF_FIB_LOOKUP_TBID | \
> -			     BPF_FIB_LOOKUP_SRC)
> +			     BPF_FIB_LOOKUP_SRC | BPF_FIB_LOOKUP_MARK)
>  
>  BPF_CALL_4(bpf_xdp_fib_lookup, struct xdp_buff *, ctx,
>  	   struct bpf_fib_lookup *, params, int, plen, u32, flags)
> diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
> index bf80b614c4db..4c9b5bfbd9c6 100644
> --- a/tools/include/uapi/linux/bpf.h
> +++ b/tools/include/uapi/linux/bpf.h
> @@ -3393,6 +3393,10 @@ union bpf_attr {
>   *			for the nexthop. If the src addr cannot be derived,
>   *			**BPF_FIB_LKUP_RET_NO_SRC_ADDR** is returned. In this
>   *			case, *params*->dmac and *params*->smac are not set either.
> + *		**BPF_FIB_LOOKUP_MARK**
> + *			Use the mark present in *params*->mark for the fib lookup.
> + *			This option should not be used with BPF_FIB_LOOKUP_DIRECT,
> + *			as it only has meaning for full lookups.
>   *
>   *		*ctx* is either **struct xdp_md** for XDP programs or
>   *		**struct sk_buff** tc cls_act programs.
> @@ -7119,6 +7123,7 @@ enum {
>  	BPF_FIB_LOOKUP_SKIP_NEIGH = (1U << 2),
>  	BPF_FIB_LOOKUP_TBID    = (1U << 3),
>  	BPF_FIB_LOOKUP_SRC     = (1U << 4),
> +	BPF_FIB_LOOKUP_MARK    = (1U << 5),
>  };
>  
>  enum {
> @@ -7196,8 +7201,19 @@ struct bpf_fib_lookup {
>  		__u32	tbid;
>  	};
>  
> -	__u8	smac[6];     /* ETH_ALEN */
> -	__u8	dmac[6];     /* ETH_ALEN */
> +	union {
> +		/* input */
> +		struct {
> +			__u32	mark;   /* policy routing */
> +			/* 2 4-byte holes for input */
> +		};
> +
> +		/* output: source and dest mac */
> +		struct {
> +			__u8	smac[6];	/* ETH_ALEN */
> +			__u8	dmac[6];	/* ETH_ALEN */
> +		};
> +	};
>  };
>  
>  struct bpf_redir_neigh {

It would be good to add

static_assert(sizeof(struct bpf_fib_lookup) == 64, "bpf_fib_lookup size
check");

to ensure this struct never exceeds a cacheline.

The patch itself looks good to me:

Reviewed-by: David Ahern <dsahern@kernel.org>