[PATCH v6 bpf-next 2/3] netfilter: add bpf_xdp_flow_lookup kfunc

Lorenzo Bianconi
2024-06-29T22:27:51Z

Introduce bpf_xdp_flow_lookup kfunc in order to perform the lookup
of a given flowtable entry based on a fib tuple of incoming traffic.
bpf_xdp_flow_lookup can be used as building block to offload in xdp
the processing of sw flowtable when hw flowtable is not available.

Acked-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
---
include/net/netfilter/nf_flow_table.h | 10 +++
net/netfilter/Makefile | 5 ++
net/netfilter/nf_flow_table_bpf.c | 121 ++++++++++++++++++++++++++
net/netfilter/nf_flow_table_inet.c | 2 +-
4 files changed, 137 insertions(+), 1 deletion(-)
create mode 100644 net/netfilter/nf_flow_table_bpf.c

diff --git a/include/net/netfilter/nf_flow_table.h b/include/net/netfilter/nf_flow_table.h
index d845745207d2d..b63d53bb9dd6d 100644
--- a/include/net/netfilter/nf_flow_table.h
+++ b/include/net/netfilter/nf_flow_table.h
@@ -315,6 +315,16 @@ unsigned int nf_flow_offload_ip_hook(void *priv, struct sk_buff *skb,
unsigned int nf_flow_offload_ipv6_hook(void *priv, struct sk_buff *skb,
const struct nf_hook_state *state);

+#if (IS_BUILTIN(CONFIG_NF_FLOW_TABLE) && IS_ENABLED(CONFIG_DEBUG_INFO_BTF)) || \
+ (IS_MODULE(CONFIG_NF_FLOW_TABLE) && IS_ENABLED(CONFIG_DEBUG_INFO_BTF_MODULES))
+extern int nf_flow_register_bpf(void);
+#else
+static inline int nf_flow_register_bpf(void)
+{
+ return 0;
+}
+#endif
+
#define MODULE_ALIAS_NF_FLOWTABLE(family) \
MODULE_ALIAS("nf-flowtable-" __stringify(family))

diff --git a/net/netfilter/Makefile b/net/netfilter/Makefile
index 18046872a38aa..f0aa4d7ef4998 100644
--- a/net/netfilter/Makefile
+++ b/net/netfilter/Makefile
@@ -144,6 +144,11 @@ obj-$(CONFIG_NF_FLOW_TABLE) += nf_flow_table.o
nf_flow_table-objs := nf_flow_table_core.o nf_flow_table_ip.o \
nf_flow_table_offload.o nf_flow_table_xdp.o
nf_flow_table-$(CONFIG_NF_FLOW_TABLE_PROCFS) += nf_flow_table_procfs.o
+ifeq ($(CONFIG_NF_FLOW_TABLE),m)
+nf_flow_table-$(CONFIG_DEBUG_INFO_BTF_MODULES) += nf_flow_table_bpf.o
+else ifeq ($(CONFIG_NF_FLOW_TABLE),y)
+nf_flow_table-$(CONFIG_DEBUG_INFO_BTF) += nf_flow_table_bpf.o
+endif

obj-$(CONFIG_NF_FLOW_TABLE_INET) += nf_flow_table_inet.o

diff --git a/net/netfilter/nf_flow_table_bpf.c b/net/netfilter/nf_flow_table_bpf.c
new file mode 100644
index 0000000000000..4a5f5195f2d27
--- /dev/null
+++ b/net/netfilter/nf_flow_table_bpf.c
@@ -0,0 +1,121 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/* Unstable Flow Table Helpers for XDP hook
+ *
+ * These are called from the XDP programs.
+ * Note that it is allowed to break compatibility for these functions since
+ * the interface they are exposed through to BPF programs is explicitly
+ * unstable.
+ */
+
+#include <linux/kernel.h>
+#include <linux/init.h>
+#include <linux/module.h>
+#include <net/netfilter/nf_flow_table.h>
+#include <linux/bpf.h>
+#include <linux/btf.h>
+#include <net/xdp.h>
+
+/* bpf_flowtable_opts - options for bpf flowtable helpers
+ * @error: out parameter, set for any encountered error
+ */
+struct bpf_flowtable_opts {
+ s32 error;
+};
+
+enum {
+ NF_BPF_FLOWTABLE_OPTS_SZ = 4,
+};
+
+__diag_push();
+__diag_ignore_all("-Wmissing-prototypes",
+ "Global functions as their definitions will be in nf_flow_table BTF");
+
+__bpf_kfunc_start_defs();
+
+static struct flow_offload_tuple_rhash *
+bpf_xdp_flow_tuple_lookup(struct net_device *dev,
+ struct flow_offload_tuple *tuple, __be16 proto)
+{
+ struct flow_offload_tuple_rhash *tuplehash;
+ struct nf_flowtable *nf_flow_table;
+ struct flow_offload *nf_flow;
+
+ nf_flow_table = nf_flowtable_by_dev(dev);
+ if (!nf_flow_table)
+ return ERR_PTR(-ENOENT);
+
+ tuplehash = flow_offload_lookup(nf_flow_table, tuple);
+ if (!tuplehash)
+ return ERR_PTR(-ENOENT);
+
+ nf_flow = container_of(tuplehash, struct flow_offload,
+ tuplehash[tuplehash->tuple.dir]);
+ flow_offload_refresh(nf_flow_table, nf_flow, false);
+
+ return tuplehash;
+}
+
+__bpf_kfunc struct flow_offload_tuple_rhash *
+bpf_xdp_flow_lookup(struct xdp_md *ctx, struct bpf_fib_lookup *fib_tuple,
+ struct bpf_flowtable_opts *opts, u32 opts_len)
+{
+ struct xdp_buff *xdp = (struct xdp_buff *)ctx;
+ struct flow_offload_tuple tuple = {
+ .iifidx = fib_tuple->ifindex,
+ .l3proto = fib_tuple->family,
+ .l4proto = fib_tuple->l4_protocol,
+ .src_port = fib_tuple->sport,
+ .dst_port = fib_tuple->dport,
+ };
+ struct flow_offload_tuple_rhash *tuplehash;
+ __be16 proto;
+
+ if (opts_len != NF_BPF_FLOWTABLE_OPTS_SZ) {
+ opts->error = -EINVAL;
+ return NULL;
+ }
+
+ switch (fib_tuple->family) {
+ case AF_INET:
+ tuple.src_v4.s_addr = fib_tuple->ipv4_src;
+ tuple.dst_v4.s_addr = fib_tuple->ipv4_dst;
+ proto = htons(ETH_P_IP);
+ break;
+ case AF_INET6:
+ tuple.src_v6 = *(struct in6_addr *)&fib_tuple->ipv6_src;
+ tuple.dst_v6 = *(struct in6_addr *)&fib_tuple->ipv6_dst;
+ proto = htons(ETH_P_IPV6);
+ break;
+ default:
+ opts->error = -EAFNOSUPPORT;
+ return NULL;
+ }
+
+ tuplehash = bpf_xdp_flow_tuple_lookup(xdp->rxq->dev, &tuple, proto);
+ if (IS_ERR(tuplehash)) {
+ opts->error = PTR_ERR(tuplehash);
+ return NULL;
+ }
+
+ return tuplehash;
+}
+
+__diag_pop()
+
+__bpf_kfunc_end_defs();
+
+BTF_KFUNCS_START(nf_ft_kfunc_set)
+BTF_ID_FLAGS(func, bpf_xdp_flow_lookup, KF_TRUSTED_ARGS | KF_RET_NULL)
+BTF_KFUNCS_END(nf_ft_kfunc_set)
+
+static const struct btf_kfunc_id_set nf_flow_kfunc_set = {
+ .owner = THIS_MODULE,
+ .set = &nf_ft_kfunc_set,
+};
+
+int nf_flow_register_bpf(void)
+{
+ return register_btf_kfunc_id_set(BPF_PROG_TYPE_XDP,
+ &nf_flow_kfunc_set);
+}
+EXPORT_SYMBOL_GPL(nf_flow_register_bpf);
diff --git a/net/netfilter/nf_flow_table_inet.c b/net/netfilter/nf_flow_table_inet.c
index 6eef15648b7b0..88787b45e30d6 100644
--- a/net/netfilter/nf_flow_table_inet.c
+++ b/net/netfilter/nf_flow_table_inet.c
@@ -98,7 +98,7 @@ static int __init nf_flow_inet_module_init(void)
nft_register_flowtable_type(&flowtable_ipv6);
nft_register_flowtable_type(&flowtable_inet);

- return 0;
+ return nf_flow_register_bpf();
}

static void __exit nf_flow_inet_module_exit(void)
--
2.45.2