Subject: Re: [PATCH bpf-next 1/2] bpf, xdp: per-map bpf_redirect_map functions for XDP

From: Toke Høiland-Jørgensen <[email-masked]>
Date: Fri, 19 Feb 2021 18:05:15 +0100

Björn Töpel <[email-masked]> writes:

> From: Björn Töpel <[email-masked]>
>
> Currently the bpf_redirect_map() implementation dispatches to the
> correct map-lookup function via a switch-statement. To avoid the
> dispatching, this change adds one bpf_redirect_map() implementation per
> map. Correct function is automatically selected by the BPF verifier.
>
> rfc->v1: Get rid of the macro and use __always_inline. (Jesper)
>
> Signed-off-by: Björn Töpel <[email-masked]>

Nice! Way better with the __always_inline. One small nit below, but
otherwise:

Acked-by: Toke Høiland-Jørgensen <[email-masked]>

> ---
>  include/linux/bpf.h    | 20 +++++++------
>  include/linux/filter.h |  2 ++
>  include/net/xdp_sock.h |  6 ++--
>  kernel/bpf/cpumap.c    |  2 +-
>  kernel/bpf/devmap.c    |  4 +--
>  kernel/bpf/verifier.c  | 28 +++++++++++-------
>  net/core/filter.c      | 67 ++++++++++++++++++++++++++----------------
>  7 files changed, 76 insertions(+), 53 deletions(-)
>
> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> index cccaef1088ea..3dd186eeaf98 100644
> --- a/include/linux/bpf.h
> +++ b/include/linux/bpf.h
> @@ -314,12 +314,14 @@ enum bpf_return_type {
>  	RET_PTR_TO_BTF_ID,		/* returns a pointer to a btf_id */
>  };
>  
> +typedef u64 (*bpf_func_proto_func)(u64 r1, u64 r2, u64 r3, u64 r4, u64 r5);
> +
>  /* eBPF function prototype used by verifier to allow BPF_CALLs from eBPF programs
>   * to in-kernel helper functions and for adjusting imm32 field in BPF_CALL
>   * instructions after verifying
>   */
>  struct bpf_func_proto {
> -	u64 (*func)(u64 r1, u64 r2, u64 r3, u64 r4, u64 r5);
> +	bpf_func_proto_func func;
>  	bool gpl_only;
>  	bool pkt_access;
>  	enum bpf_return_type ret_type;
> @@ -1429,9 +1431,11 @@ struct btf *bpf_get_btf_vmlinux(void);
>  /* Map specifics */
>  struct xdp_buff;
>  struct sk_buff;
> +struct bpf_dtab_netdev;
> +struct bpf_cpu_map_entry;
>  
> -struct bpf_dtab_netdev *__dev_map_lookup_elem(struct bpf_map *map, u32 key);
> -struct bpf_dtab_netdev *__dev_map_hash_lookup_elem(struct bpf_map *map, u32 key);
> +void *__dev_map_lookup_elem(struct bpf_map *map, u32 key);
> +void *__dev_map_hash_lookup_elem(struct bpf_map *map, u32 key);
>  void __dev_flush(void);
>  int dev_xdp_enqueue(struct net_device *dev, struct xdp_buff *xdp,
>  		    struct net_device *dev_rx);
> @@ -1441,7 +1445,7 @@ int dev_map_generic_redirect(struct bpf_dtab_netdev *dst, struct sk_buff *skb,
>  			     struct bpf_prog *xdp_prog);
>  bool dev_map_can_have_prog(struct bpf_map *map);
>  
> -struct bpf_cpu_map_entry *__cpu_map_lookup_elem(struct bpf_map *map, u32 key);
> +void *__cpu_map_lookup_elem(struct bpf_map *map, u32 key);
>  void __cpu_map_flush(void);
>  int cpu_map_enqueue(struct bpf_cpu_map_entry *rcpu, struct xdp_buff *xdp,
>  		    struct net_device *dev_rx);
> @@ -1568,14 +1572,12 @@ static inline int bpf_obj_get_user(const char __user *pathname, int flags)
>  	return -EOPNOTSUPP;
>  }
>  
> -static inline struct net_device  *__dev_map_lookup_elem(struct bpf_map *map,
> -						       u32 key)
> +static inline void  *__dev_map_lookup_elem(struct bpf_map *map, u32 key)
>  {
>  	return NULL;
>  }
>  
> -static inline struct net_device  *__dev_map_hash_lookup_elem(struct bpf_map *map,
> -							     u32 key)
> +static inline void  *__dev_map_hash_lookup_elem(struct bpf_map *map, u32 key)
>  {
>  	return NULL;
>  }
> @@ -1615,7 +1617,7 @@ static inline int dev_map_generic_redirect(struct bpf_dtab_netdev *dst,
>  }
>  
>  static inline
> -struct bpf_cpu_map_entry *__cpu_map_lookup_elem(struct bpf_map *map, u32 key)
> +void *__cpu_map_lookup_elem(struct bpf_map *map, u32 key)
>  {
>  	return NULL;
>  }
> diff --git a/include/linux/filter.h b/include/linux/filter.h
> index 3b00fc906ccd..1dedcf66b694 100644
> --- a/include/linux/filter.h
> +++ b/include/linux/filter.h
> @@ -1472,4 +1472,6 @@ static inline bool bpf_sk_lookup_run_v6(struct net *net, int protocol,
>  }
>  #endif /* IS_ENABLED(CONFIG_IPV6) */
>  
> +bpf_func_proto_func get_xdp_redirect_func(enum bpf_map_type map_type);
> +
>  #endif /* __LINUX_FILTER_H__ */
> diff --git a/include/net/xdp_sock.h b/include/net/xdp_sock.h
> index cc17bc957548..da4139a58630 100644
> --- a/include/net/xdp_sock.h
> +++ b/include/net/xdp_sock.h
> @@ -80,8 +80,7 @@ int xsk_generic_rcv(struct xdp_sock *xs, struct xdp_buff *xdp);
>  int __xsk_map_redirect(struct xdp_sock *xs, struct xdp_buff *xdp);
>  void __xsk_map_flush(void);
>  
> -static inline struct xdp_sock *__xsk_map_lookup_elem(struct bpf_map *map,
> -						     u32 key)
> +static inline void *__xsk_map_lookup_elem(struct bpf_map *map, u32 key)
>  {
>  	struct xsk_map *m = container_of(map, struct xsk_map, map);
>  	struct xdp_sock *xs;
> @@ -109,8 +108,7 @@ static inline void __xsk_map_flush(void)
>  {
>  }
>  
> -static inline struct xdp_sock *__xsk_map_lookup_elem(struct bpf_map *map,
> -						     u32 key)
> +static inline void *__xsk_map_lookup_elem(struct bpf_map *map, u32 key)
>  {
>  	return NULL;
>  }
> diff --git a/kernel/bpf/cpumap.c b/kernel/bpf/cpumap.c
> index 5d1469de6921..a4d2cb93cd69 100644
> --- a/kernel/bpf/cpumap.c
> +++ b/kernel/bpf/cpumap.c
> @@ -563,7 +563,7 @@ static void cpu_map_free(struct bpf_map *map)
>  	kfree(cmap);
>  }
>  
> -struct bpf_cpu_map_entry *__cpu_map_lookup_elem(struct bpf_map *map, u32 key)
> +void *__cpu_map_lookup_elem(struct bpf_map *map, u32 key)
>  {
>  	struct bpf_cpu_map *cmap = container_of(map, struct bpf_cpu_map, map);
>  	struct bpf_cpu_map_entry *rcpu;
> diff --git a/kernel/bpf/devmap.c b/kernel/bpf/devmap.c
> index 85d9d1b72a33..37ac4cde9713 100644
> --- a/kernel/bpf/devmap.c
> +++ b/kernel/bpf/devmap.c
> @@ -258,7 +258,7 @@ static int dev_map_get_next_key(struct bpf_map *map, void *key, void *next_key)
>  	return 0;
>  }
>  
> -struct bpf_dtab_netdev *__dev_map_hash_lookup_elem(struct bpf_map *map, u32 key)
> +void *__dev_map_hash_lookup_elem(struct bpf_map *map, u32 key)
>  {
>  	struct bpf_dtab *dtab = container_of(map, struct bpf_dtab, map);
>  	struct hlist_head *head = dev_map_index_hash(dtab, key);
> @@ -392,7 +392,7 @@ void __dev_flush(void)
>   * update happens in parallel here a dev_put wont happen until after reading the
>   * ifindex.
>   */
> -struct bpf_dtab_netdev *__dev_map_lookup_elem(struct bpf_map *map, u32 key)
> +void *__dev_map_lookup_elem(struct bpf_map *map, u32 key)
>  {
>  	struct bpf_dtab *dtab = container_of(map, struct bpf_dtab, map);
>  	struct bpf_dtab_netdev *obj;
> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index 3d34ba492d46..b5fb0c4e911a 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -5409,7 +5409,8 @@ record_func_map(struct bpf_verifier_env *env, struct bpf_call_arg_meta *meta,
>  	    func_id != BPF_FUNC_map_delete_elem &&
>  	    func_id != BPF_FUNC_map_push_elem &&
>  	    func_id != BPF_FUNC_map_pop_elem &&
> -	    func_id != BPF_FUNC_map_peek_elem)
> +	    func_id != BPF_FUNC_map_peek_elem &&
> +	    func_id != BPF_FUNC_redirect_map)
>  		return 0;
>  
>  	if (map == NULL) {
> @@ -11860,17 +11861,22 @@ static int fixup_bpf_calls(struct bpf_verifier_env *env)
>  		}
>  
>  patch_call_imm:
> -		fn = env->ops->get_func_proto(insn->imm, env->prog);
> -		/* all functions that have prototype and verifier allowed
> -		 * programs to call them, must be real in-kernel functions
> -		 */
> -		if (!fn->func) {
> -			verbose(env,
> -				"kernel subsystem misconfigured func %s#%d\n",
> -				func_id_name(insn->imm), insn->imm);
> -			return -EFAULT;
> +		if (insn->imm == BPF_FUNC_redirect_map) {
> +			aux = &env->insn_aux_data[i];
> +			map_ptr = BPF_MAP_PTR(aux->map_ptr_state);
> +			insn->imm = get_xdp_redirect_func(map_ptr->map_type) - __bpf_call_base;
> +		} else {
> +			fn = env->ops->get_func_proto(insn->imm, env->prog);
> +			/* all functions that have prototype and verifier allowed
> +			 * programs to call them, must be real in-kernel functions
> +			 */
> +			if (!fn->func) {
> +				verbose(env, "kernel subsystem misconfigured func %s#%d\n",
> +					func_id_name(insn->imm), insn->imm);
> +				return -EFAULT;
> +			}
> +			insn->imm = fn->func - __bpf_call_base;
>  		}
> -		insn->imm = fn->func - __bpf_call_base;
>  	}
>  
>  	/* Since poke tab is now finalized, publish aux to tracker. */
> diff --git a/net/core/filter.c b/net/core/filter.c
> index adfdad234674..fd64d768e16a 100644
> --- a/net/core/filter.c
> +++ b/net/core/filter.c
> @@ -3944,22 +3944,6 @@ void xdp_do_flush(void)
>  }
>  EXPORT_SYMBOL_GPL(xdp_do_flush);
>  
> -static inline void *__xdp_map_lookup_elem(struct bpf_map *map, u32 index)
> -{
> -	switch (map->map_type) {
> -	case BPF_MAP_TYPE_DEVMAP:
> -		return __dev_map_lookup_elem(map, index);
> -	case BPF_MAP_TYPE_DEVMAP_HASH:
> -		return __dev_map_hash_lookup_elem(map, index);
> -	case BPF_MAP_TYPE_CPUMAP:
> -		return __cpu_map_lookup_elem(map, index);
> -	case BPF_MAP_TYPE_XSKMAP:
> -		return __xsk_map_lookup_elem(map, index);
> -	default:
> -		return NULL;
> -	}
> -}
> -
>  void bpf_clear_redirect_map(struct bpf_map *map)
>  {
>  	struct bpf_redirect_info *ri;
> @@ -4110,22 +4094,17 @@ static const struct bpf_func_proto bpf_xdp_redirect_proto = {
>  	.arg2_type      = ARG_ANYTHING,
>  };
>  
> -BPF_CALL_3(bpf_xdp_redirect_map, struct bpf_map *, map, u32, ifindex,
> -	   u64, flags)
> +static __always_inline s64 __bpf_xdp_redirect_map(struct bpf_map *map, u32 ifindex, u64 flags,
> +						  void *lookup_elem(struct bpf_map *map,
> +								    u32 key))
>  {
>  	struct bpf_redirect_info *ri = this_cpu_ptr(&bpf_redirect_info);
>  
> -	/* Lower bits of the flags are used as return code on lookup failure */
>  	if (unlikely(flags > XDP_TX))
>  		return XDP_ABORTED;
>  
> -	ri->tgt_value = __xdp_map_lookup_elem(map, ifindex);
> +	ri->tgt_value = lookup_elem(map, ifindex);
>  	if (unlikely(!ri->tgt_value)) {
> -		/* If the lookup fails we want to clear out the state in the
> -		 * redirect_info struct completely, so that if an eBPF program
> -		 * performs multiple lookups, the last one always takes
> -		 * precedence.
> -		 */

Why remove the comments?

>  		WRITE_ONCE(ri->map, NULL);
>  		return flags;
>  	}
> @@ -4137,8 +4116,44 @@ BPF_CALL_3(bpf_xdp_redirect_map, struct bpf_map *, map, u32, ifindex,
>  	return XDP_REDIRECT;
>  }
>  
> +BPF_CALL_3(bpf_xdp_redirect_devmap, struct bpf_map *, map, u32, ifindex, u64, flags)
> +{
> +	return __bpf_xdp_redirect_map(map, ifindex, flags, __dev_map_lookup_elem);
> +}
> +
> +BPF_CALL_3(bpf_xdp_redirect_devmap_hash, struct bpf_map *, map, u32, ifindex, u64, flags)
> +{
> +	return __bpf_xdp_redirect_map(map, ifindex, flags, __dev_map_hash_lookup_elem);
> +}
> +
> +BPF_CALL_3(bpf_xdp_redirect_cpumap, struct bpf_map *, map, u32, ifindex, u64, flags)
> +{
> +	return __bpf_xdp_redirect_map(map, ifindex, flags, __cpu_map_lookup_elem);
> +}
> +
> +BPF_CALL_3(bpf_xdp_redirect_xskmap, struct bpf_map *, map, u32, ifindex, u64, flags)
> +{
> +	return __bpf_xdp_redirect_map(map, ifindex, flags, __xsk_map_lookup_elem);
> +}
> +
> +bpf_func_proto_func get_xdp_redirect_func(enum bpf_map_type map_type)
> +{
> +	switch (map_type) {
> +	case BPF_MAP_TYPE_DEVMAP:
> +		return bpf_xdp_redirect_devmap;
> +	case BPF_MAP_TYPE_DEVMAP_HASH:
> +		return bpf_xdp_redirect_devmap_hash;
> +	case BPF_MAP_TYPE_CPUMAP:
> +		return bpf_xdp_redirect_cpumap;
> +	case BPF_MAP_TYPE_XSKMAP:
> +		return bpf_xdp_redirect_xskmap;
> +	default:
> +		return NULL;
> +	}
> +}
> +
> +/* NB! .func is NULL! get_xdp_redirect_func() is used instead! */
>  static const struct bpf_func_proto bpf_xdp_redirect_map_proto = {
> -	.func           = bpf_xdp_redirect_map,
>  	.gpl_only       = false,
>  	.ret_type       = RET_INTEGER,
>  	.arg1_type      = ARG_CONST_MAP_PTR,
> -- 
> 2.27.0