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

From: Anton Protopopov <[email-masked]>
Date: Mon, 25 Mar 2024 12:19:15 +0000

On Sun, Mar 24, 2024 at 11:38:44AM -0600, David Ahern wrote:
> 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 <[email-masked]>
> > Acked-by: Daniel Borkmann <[email-masked]>
> > ---
> >  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.

Thanks, added: https://github.com/aspsk/bpf-next/commit/7cd3685e52d5

> 
> The patch itself looks good to me:
> 
> Reviewed-by: David Ahern <[email-masked]>

Thanks!