selftests/bpf: add XDP selftests for modifying and popping VLAN headers

This XDP selftest also contain a small TC-bpf component. It provoke
the generic-XDP bug fixed in previous commit.

The selftest itself shows how to do VLAN manipulation from XDP and TC.
The test demonstrate how XDP ingress can remove a VLAN tag, and how TC
egress can add back a VLAN tag.

This use-case originates from a production need by ISP (kviknet.dk),
who gets DSL-lines terminated as VLAN Q-in-Q tagged packets, and want
to avoid having an net_device for every end-customer on the box doing
the L2 to L3 termination.
  The test-setup is done via a veth-pair and creating two network
namespaces (ns1 and ns2).  The 'ns1' simulate the ISP network that are
loading the BPF-progs stripping and adding VLAN IDs.  The 'ns2'
simulate the DSL-customer that are using VLAN tagged packets.

Running the script with --interactive, will simply not call the
cleanup function.  This gives the effect of creating a testlab, that
the users can inspect and play with.  The --verbose option will simply
request that the shell will print input lines as they are read, this
include comments, which in effect make the comments visible docs.

Reported-by: Yoel Caspersen <yoel@kviknet.dk>
Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

tools/testing/selftests/bpf/Makefile

@@ -36,7 +36,8 @@ TEST_GEN_FILES = test_pkt_access.o test_xdp.o test_l4lb.o test_tcp_estats.o test
 	test_get_stack_rawtp.o test_sockmap_kern.o test_sockhash_kern.o \
 	test_lwt_seg6local.o sendmsg4_prog.o sendmsg6_prog.o test_lirc_mode2_kern.o \
 	get_cgroup_id_kern.o socket_cookie_prog.o test_select_reuseport_kern.o \
-	test_skb_cgroup_id_kern.o bpf_flow.o netcnt_prog.o test_sk_lookup_kern.o
+	test_skb_cgroup_id_kern.o bpf_flow.o netcnt_prog.o \
+	test_sk_lookup_kern.o test_xdp_vlan.o
 
 # Order correspond to 'make run_tests' order
 TEST_PROGS := test_kmod.sh \
@@ -49,7 +50,8 @@ TEST_PROGS := test_kmod.sh \
 	test_lwt_seg6local.sh \
 	test_lirc_mode2.sh \
 	test_skb_cgroup_id.sh \
-	test_flow_dissector.sh
+	test_flow_dissector.sh \
+	test_xdp_vlan.sh
 
 # Compile but not part of 'make run_tests'
 TEST_GEN_PROGS_EXTENDED = test_libbpf_open test_sock_addr test_skb_cgroup_id_user \

tools/testing/selftests/bpf/test_xdp_vlan.c

@@ -0,0 +1,292 @@
+/* SPDX-License-Identifier: GPL-2.0
+ *  Copyright(c) 2018 Jesper Dangaard Brouer.
+ *
+ * XDP/TC VLAN manipulation example
+ *
+ * GOTCHA: Remember to disable NIC hardware offloading of VLANs,
+ * else the VLAN tags are NOT inlined in the packet payload:
+ *
+ *  # ethtool -K ixgbe2 rxvlan off
+ *
+ * Verify setting:
+ *  # ethtool -k ixgbe2 | grep rx-vlan-offload
+ *  rx-vlan-offload: off
+ *
+ */
+#include <stddef.h>
+#include <stdbool.h>
+#include <string.h>
+#include <linux/bpf.h>
+#include <linux/if_ether.h>
+#include <linux/if_vlan.h>
+#include <linux/in.h>
+#include <linux/pkt_cls.h>
+
+#include "bpf_helpers.h"
+#include "bpf_endian.h"
+
+/* linux/if_vlan.h have not exposed this as UAPI, thus mirror some here
+ *
+ *	struct vlan_hdr - vlan header
+ *	@h_vlan_TCI: priority and VLAN ID
+ *	@h_vlan_encapsulated_proto: packet type ID or len
+ */
+struct _vlan_hdr {
+	__be16 h_vlan_TCI;
+	__be16 h_vlan_encapsulated_proto;
+};
+#define VLAN_PRIO_MASK		0xe000 /* Priority Code Point */
+#define VLAN_PRIO_SHIFT		13
+#define VLAN_CFI_MASK		0x1000 /* Canonical Format Indicator */
+#define VLAN_TAG_PRESENT	VLAN_CFI_MASK
+#define VLAN_VID_MASK		0x0fff /* VLAN Identifier */
+#define VLAN_N_VID		4096
+
+struct parse_pkt {
+	__u16 l3_proto;
+	__u16 l3_offset;
+	__u16 vlan_outer;
+	__u16 vlan_inner;
+	__u8  vlan_outer_offset;
+	__u8  vlan_inner_offset;
+};
+
+char _license[] SEC("license") = "GPL";
+
+static __always_inline
+bool parse_eth_frame(struct ethhdr *eth, void *data_end, struct parse_pkt *pkt)
+{
+	__u16 eth_type;
+	__u8 offset;
+
+	offset = sizeof(*eth);
+	/* Make sure packet is large enough for parsing eth + 2 VLAN headers */
+	if ((void *)eth + offset + (2*sizeof(struct _vlan_hdr)) > data_end)
+		return false;
+
+	eth_type = eth->h_proto;
+
+	/* Handle outer VLAN tag */
+	if (eth_type == bpf_htons(ETH_P_8021Q)
+	    || eth_type == bpf_htons(ETH_P_8021AD)) {
+		struct _vlan_hdr *vlan_hdr;
+
+		vlan_hdr = (void *)eth + offset;
+		pkt->vlan_outer_offset = offset;
+		pkt->vlan_outer = bpf_ntohs(vlan_hdr->h_vlan_TCI)
+				& VLAN_VID_MASK;
+		eth_type        = vlan_hdr->h_vlan_encapsulated_proto;
+		offset += sizeof(*vlan_hdr);
+	}
+
+	/* Handle inner (double) VLAN tag */
+	if (eth_type == bpf_htons(ETH_P_8021Q)
+	    || eth_type == bpf_htons(ETH_P_8021AD)) {
+		struct _vlan_hdr *vlan_hdr;
+
+		vlan_hdr = (void *)eth + offset;
+		pkt->vlan_inner_offset = offset;
+		pkt->vlan_inner = bpf_ntohs(vlan_hdr->h_vlan_TCI)
+				& VLAN_VID_MASK;
+		eth_type        = vlan_hdr->h_vlan_encapsulated_proto;
+		offset += sizeof(*vlan_hdr);
+	}
+
+	pkt->l3_proto = bpf_ntohs(eth_type); /* Convert to host-byte-order */
+	pkt->l3_offset = offset;
+
+	return true;
+}
+
+/* Hint, VLANs are choosen to hit network-byte-order issues */
+#define TESTVLAN 4011 /* 0xFAB */
+// #define TO_VLAN  4000 /* 0xFA0 (hint 0xOA0 = 160) */
+
+SEC("xdp_drop_vlan_4011")
+int  xdp_prognum0(struct xdp_md *ctx)
+{
+	void *data_end = (void *)(long)ctx->data_end;
+	void *data     = (void *)(long)ctx->data;
+	struct parse_pkt pkt = { 0 };
+
+	if (!parse_eth_frame(data, data_end, &pkt))
+		return XDP_ABORTED;
+
+	/* Drop specific VLAN ID example */
+	if (pkt.vlan_outer == TESTVLAN)
+		return XDP_ABORTED;
+	/*
+	 * Using XDP_ABORTED makes it possible to record this event,
+	 * via tracepoint xdp:xdp_exception like:
+	 *  # perf record -a -e xdp:xdp_exception
+	 *  # perf script
+	 */
+	return XDP_PASS;
+}
+/*
+Commands to setup VLAN on Linux to test packets gets dropped:
+
+ export ROOTDEV=ixgbe2
+ export VLANID=4011
+ ip link add link $ROOTDEV name $ROOTDEV.$VLANID type vlan id $VLANID
+ ip link set dev  $ROOTDEV.$VLANID up
+
+ ip link set dev $ROOTDEV mtu 1508
+ ip addr add 100.64.40.11/24 dev $ROOTDEV.$VLANID
+
+Load prog with ip tool:
+
+ ip link set $ROOTDEV xdp off
+ ip link set $ROOTDEV xdp object xdp_vlan01_kern.o section xdp_drop_vlan_4011
+
+*/
+
+/* Changing VLAN to zero, have same practical effect as removing the VLAN. */
+#define TO_VLAN	0
+
+SEC("xdp_vlan_change")
+int  xdp_prognum1(struct xdp_md *ctx)
+{
+	void *data_end = (void *)(long)ctx->data_end;
+	void *data     = (void *)(long)ctx->data;
+	struct parse_pkt pkt = { 0 };
+
+	if (!parse_eth_frame(data, data_end, &pkt))
+		return XDP_ABORTED;
+
+	/* Change specific VLAN ID */
+	if (pkt.vlan_outer == TESTVLAN) {
+		struct _vlan_hdr *vlan_hdr = data + pkt.vlan_outer_offset;
+
+		/* Modifying VLAN, preserve top 4 bits */
+		vlan_hdr->h_vlan_TCI =
+			bpf_htons((bpf_ntohs(vlan_hdr->h_vlan_TCI) & 0xf000)
+				  | TO_VLAN);
+	}
+
+	return XDP_PASS;
+}
+
+/*
+ * Show XDP+TC can cooperate, on creating a VLAN rewriter.
+ * 1. Create a XDP prog that can "pop"/remove a VLAN header.
+ * 2. Create a TC-bpf prog that egress can add a VLAN header.
+ */
+
+#ifndef ETH_ALEN /* Ethernet MAC address length */
+#define ETH_ALEN	6	/* bytes */
+#endif
+#define VLAN_HDR_SZ	4	/* bytes */
+
+SEC("xdp_vlan_remove_outer")
+int  xdp_prognum2(struct xdp_md *ctx)
+{
+	void *data_end = (void *)(long)ctx->data_end;
+	void *data     = (void *)(long)ctx->data;
+	struct parse_pkt pkt = { 0 };
+	char *dest;
+
+	if (!parse_eth_frame(data, data_end, &pkt))
+		return XDP_ABORTED;
+
+	/* Skip packet if no outer VLAN was detected */
+	if (pkt.vlan_outer_offset == 0)
+		return XDP_PASS;
+
+	/* Moving Ethernet header, dest overlap with src, memmove handle this */
+	dest = data;
+	dest+= VLAN_HDR_SZ;
+	/*
+	 * Notice: Taking over vlan_hdr->h_vlan_encapsulated_proto, by
+	 * only moving two MAC addrs (12 bytes), not overwriting last 2 bytes
+	 */
+	__builtin_memmove(dest, data, ETH_ALEN * 2);
+	/* Note: LLVM built-in memmove inlining require size to be constant */
+
+	/* Move start of packet header seen by Linux kernel stack */
+	bpf_xdp_adjust_head(ctx, VLAN_HDR_SZ);
+
+	return XDP_PASS;
+}
+
+static __always_inline
+void shift_mac_4bytes_16bit(void *data)
+{
+	__u16 *p = data;
+
+	p[7] = p[5]; /* delete p[7] was vlan_hdr->h_vlan_TCI */
+	p[6] = p[4]; /* delete p[6] was ethhdr->h_proto */
+	p[5] = p[3];
+	p[4] = p[2];
+	p[3] = p[1];
+	p[2] = p[0];
+}
+
+static __always_inline
+void shift_mac_4bytes_32bit(void *data)
+{
+	__u32 *p = data;
+
+	/* Assuming VLAN hdr present. The 4 bytes in p[3] that gets
+	 * overwritten, is ethhdr->h_proto and vlan_hdr->h_vlan_TCI.
+	 * The vlan_hdr->h_vlan_encapsulated_proto take over role as
+	 * ethhdr->h_proto.
+	 */
+	p[3] = p[2];
+	p[2] = p[1];
+	p[1] = p[0];
+}
+
+SEC("xdp_vlan_remove_outer2")
+int  xdp_prognum3(struct xdp_md *ctx)
+{
+	void *data_end = (void *)(long)ctx->data_end;
+	void *data     = (void *)(long)ctx->data;
+	struct ethhdr *orig_eth = data;
+	struct parse_pkt pkt = { 0 };
+
+	if (!parse_eth_frame(orig_eth, data_end, &pkt))
+		return XDP_ABORTED;
+
+	/* Skip packet if no outer VLAN was detected */
+	if (pkt.vlan_outer_offset == 0)
+		return XDP_PASS;
+
+	/* Simply shift down MAC addrs 4 bytes, overwrite h_proto + TCI */
+	shift_mac_4bytes_32bit(data);
+
+	/* Move start of packet header seen by Linux kernel stack */
+	bpf_xdp_adjust_head(ctx, VLAN_HDR_SZ);
+
+	return XDP_PASS;
+}
+
+/*=====================================
+ *  BELOW: TC-hook based ebpf programs
+ * ====================================
+ * The TC-clsact eBPF programs (currently) need to be attach via TC commands
+ */
+
+SEC("tc_vlan_push")
+int _tc_progA(struct __sk_buff *ctx)
+{
+	bpf_skb_vlan_push(ctx, bpf_htons(ETH_P_8021Q), TESTVLAN);
+
+	return TC_ACT_OK;
+}
+/*
+Commands to setup TC to use above bpf prog:
+
+export ROOTDEV=ixgbe2
+export FILE=xdp_vlan01_kern.o
+
+# Re-attach clsact to clear/flush existing role
+tc qdisc del dev $ROOTDEV clsact 2> /dev/null ;\
+tc qdisc add dev $ROOTDEV clsact
+
+# Attach BPF prog EGRESS
+tc filter add dev $ROOTDEV egress \
+  prio 1 handle 1 bpf da obj $FILE sec tc_vlan_push
+
+tc filter show dev $ROOTDEV egress
+*/