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Date:   Wed, 5 Aug 2020 13:45:44 +0900
From:   Yoshiki Komachi <komachi.yoshiki@...il.com>
To:     Daniel Borkmann <daniel@...earbox.net>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Alexei Starovoitov <ast@...nel.org>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        John Fastabend <john.fastabend@...il.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        Andrii Nakryiko <andriin@...com>,
        KP Singh <kpsingh@...omium.org>,
        Roopa Prabhu <roopa@...ulusnetworks.com>,
        Nikolay Aleksandrov <nikolay@...ulusnetworks.com>,
        David Ahern <dsahern@...nel.org>, netdev@...r.kernel.org,
        bridge@...ts.linux-foundation.org, bpf@...r.kernel.org
Subject: Re: [RFC PATCH bpf-next 2/3] bpf: Add helper to do forwarding lookups
 in kernel FDB table


> 2020/08/01 6:12、Daniel Borkmann <daniel@...earbox.net>のメール:
> 
> On 7/31/20 6:44 AM, Yoshiki Komachi wrote:
>> This patch adds a new bpf helper to access FDB in the kernel tables
>> from XDP programs. The helper enables us to find the destination port
>> of master bridge in XDP layer with high speed. If an entry in the
>> tables is successfully found, egress device index will be returned.
>> In cases of failure, packets will be dropped or forwarded to upper
>> networking stack in the kernel by XDP programs. Multicast and broadcast
>> packets are currently not supported. Thus, these will need to be
>> passed to upper layer on the basis of XDP_PASS action.
>> The API uses destination MAC and VLAN ID as keys, so XDP programs
>> need to extract these from forwarded packets.
>> Signed-off-by: Yoshiki Komachi <komachi.yoshiki@...il.com>
> 
> Few initial comments below:
> 
>> ---
>>  include/uapi/linux/bpf.h       | 28 +++++++++++++++++++++
>>  net/core/filter.c              | 45 ++++++++++++++++++++++++++++++++++
>>  scripts/bpf_helpers_doc.py     |  1 +
>>  tools/include/uapi/linux/bpf.h | 28 +++++++++++++++++++++
>>  4 files changed, 102 insertions(+)
>> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
>> index 54d0c886e3ba..f2e729dd1721 100644
>> --- a/include/uapi/linux/bpf.h
>> +++ b/include/uapi/linux/bpf.h
>> @@ -2149,6 +2149,22 @@ union bpf_attr {
>>   *		* > 0 one of **BPF_FIB_LKUP_RET_** codes explaining why the
>>   *		  packet is not forwarded or needs assist from full stack
>>   *
>> + * long bpf_fdb_lookup(void *ctx, struct bpf_fdb_lookup *params, int plen, u32 flags)
>> + *	Description
>> + *		Do FDB lookup in kernel tables using parameters in *params*.
>> + *		If lookup is successful (ie., FDB lookup finds a destination entry),
>> + *		ifindex is set to the egress device index from the FDB lookup.
>> + *		Both multicast and broadcast packets are currently unsupported
>> + *		in XDP layer.
>> + *
>> + *		*plen* argument is the size of the passed **struct bpf_fdb_lookup**.
>> + *		*ctx* is only **struct xdp_md** for XDP programs.
>> + *
>> + *     Return
>> + *		* < 0 if any input argument is invalid
>> + *		*   0 on success (destination port is found)
>> + *		* > 0 on failure (there is no entry)
>> + *
>>   * long bpf_sock_hash_update(struct bpf_sock_ops *skops, struct bpf_map *map, void *key, u64 flags)
>>   *	Description
>>   *		Add an entry to, or update a sockhash *map* referencing sockets.
>> @@ -3449,6 +3465,7 @@ union bpf_attr {
>>  	FN(get_stack),			\
>>  	FN(skb_load_bytes_relative),	\
>>  	FN(fib_lookup),			\
>> +	FN(fdb_lookup),			\
> 
> This breaks UAPI. Needs to be added to the very end of the list.

I figured it out and will move it to the very end of the list. Thanks!

>>  	FN(sock_hash_update),		\
>>  	FN(msg_redirect_hash),		\
>>  	FN(sk_redirect_hash),		\
>> @@ -4328,6 +4345,17 @@ struct bpf_fib_lookup {
>>  	__u8	dmac[6];     /* ETH_ALEN */
>>  };
>>  +enum {
>> +	BPF_FDB_LKUP_RET_SUCCESS,      /* lookup successful */
>> +	BPF_FDB_LKUP_RET_NOENT,        /* entry is not found */
>> +};
>> +
>> +struct bpf_fdb_lookup {
>> +	unsigned char addr[6];     /* ETH_ALEN */
>> +	__u16 vlan_id;
>> +	__u32 ifindex;
>> +};
>> +
>>  enum bpf_task_fd_type {
>>  	BPF_FD_TYPE_RAW_TRACEPOINT,	/* tp name */
>>  	BPF_FD_TYPE_TRACEPOINT,		/* tp name */
>> diff --git a/net/core/filter.c b/net/core/filter.c
>> index 654c346b7d91..68800d1b8cd5 100644
>> --- a/net/core/filter.c
>> +++ b/net/core/filter.c
>> @@ -45,6 +45,7 @@
>>  #include <linux/filter.h>
>>  #include <linux/ratelimit.h>
>>  #include <linux/seccomp.h>
>> +#include <linux/if_bridge.h>
>>  #include <linux/if_vlan.h>
>>  #include <linux/bpf.h>
>>  #include <linux/btf.h>
>> @@ -5084,6 +5085,46 @@ static const struct bpf_func_proto bpf_skb_fib_lookup_proto = {
>>  	.arg4_type	= ARG_ANYTHING,
>>  };
>>  +#if IS_ENABLED(CONFIG_BRIDGE)
>> +BPF_CALL_4(bpf_xdp_fdb_lookup, struct xdp_buff *, ctx,
>> +	   struct bpf_fdb_lookup *, params, int, plen, u32, flags)
>> +{
>> +	struct net_device *src, *dst;
>> +	struct net *net;
>> +
>> +	if (plen < sizeof(*params))
>> +		return -EINVAL;
> 
> Given flags are not used, this needs to reject anything invalid otherwise
> you're not able to extend it in future.

I added this flags based on the bpf_fib_lookup() helper, but these are not
used at this point.

I will make sure whether this flags are required or not.

>> +	net = dev_net(ctx->rxq->dev);
>> +
>> +	if (is_multicast_ether_addr(params->addr) ||
>> +	    is_broadcast_ether_addr(params->addr))
>> +		return BPF_FDB_LKUP_RET_NOENT;
>> +
>> +	src = dev_get_by_index_rcu(net, params->ifindex);
>> +	if (unlikely(!src))
>> +		return -ENODEV;
>> +
>> +	dst = br_fdb_find_port_xdp(src, params->addr, params->vlan_id);
>> +	if (dst) {
>> +		params->ifindex = dst->ifindex;
>> +		return BPF_FDB_LKUP_RET_SUCCESS;
>> +	}
> 
> Currently the helper description says nothing that this is /only/ limited to
> bridges. I think it would be better to also name the helper bpf_br_fdb_lookup()
> as well if so to avoid any confusion.

For now, the helper enables only bridges to access FDB table in the kernel
as you understand, so I will try to rename the helper in the next version.

>> +	return BPF_FDB_LKUP_RET_NOENT;
>> +}
>> +
>> +static const struct bpf_func_proto bpf_xdp_fdb_lookup_proto = {
>> +	.func		= bpf_xdp_fdb_lookup,
>> +	.gpl_only	= true,
>> +	.ret_type	= RET_INTEGER,
>> +	.arg1_type      = ARG_PTR_TO_CTX,
>> +	.arg2_type      = ARG_PTR_TO_MEM,
>> +	.arg3_type      = ARG_CONST_SIZE,
>> +	.arg4_type	= ARG_ANYTHING,
>> +};
>> +#endif
> 
> This should also have a tc pendant (similar as done in routing lookup helper)
> in case native XDP is not available. This will be useful for those that have
> the same code compilable for both tc/XDP.

Thanks, I agree with your idea. On the basis of the bpf_fib_lookup() helper,
I will try to add the feature so that the helper can also be used in the TC hook.

Best regards,

>>  #if IS_ENABLED(CONFIG_IPV6_SEG6_BPF)
>>  static int bpf_push_seg6_encap(struct sk_buff *skb, u32 type, void *hdr, u32 len)
>>  {
>> @@ -6477,6 +6518,10 @@ xdp_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
>>  		return &bpf_xdp_adjust_tail_proto;
>>  	case BPF_FUNC_fib_lookup:
>>  		return &bpf_xdp_fib_lookup_proto;
>> +#if IS_ENABLED(CONFIG_BRIDGE)
>> +	case BPF_FUNC_fdb_lookup:
>> +		return &bpf_xdp_fdb_lookup_proto;
>> +#endif
>>  #ifdef CONFIG_INET
>>  	case BPF_FUNC_sk_lookup_udp:
>>  		return &bpf_xdp_sk_lookup_udp_proto;

—
Yoshiki Komachi
komachi.yoshiki@...il.com

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