Re: [PATCH bpf-next v9 5/5] selftests/bpf: Add selftest for XDP_REDIRECT in BPF_PROG_RUN

Martin KaFai Lau [off-list ref] writes:

On Sun, Mar 06, 2022 at 11:34:04PM +0100, Toke Høiland-Jørgensen wrote:

quoted

+#define NUM_PKTS 1000000

It took my qemu 30s to run.
Would it have the same test coverage by lowering it to something
like 10000  ?

Yikes! Sure, that should be fine I think!

quoted

+void test_xdp_do_redirect(void)
+{
+	int err, xdp_prog_fd, tc_prog_fd, ifindex_src, ifindex_dst;
+	char data[sizeof(pkt_udp) + sizeof(__u32)];
+	struct test_xdp_do_redirect *skel = NULL;
+	struct nstoken *nstoken = NULL;
+	struct bpf_link *link;
+
+	struct xdp_md ctx_in = { .data = sizeof(__u32),
+				 .data_end = sizeof(data) };
+	DECLARE_LIBBPF_OPTS(bpf_test_run_opts, opts,
+			    .data_in = &data,
+			    .data_size_in = sizeof(data),
+			    .ctx_in = &ctx_in,
+			    .ctx_size_in = sizeof(ctx_in),
+			    .flags = BPF_F_TEST_XDP_LIVE_FRAMES,
+			    .repeat = NUM_PKTS,
+			    .batch_size = 64,
+		);
+	DECLARE_LIBBPF_OPTS(bpf_tc_hook, tc_hook,
+			    .attach_point = BPF_TC_INGRESS);
+
+	memcpy(&data[sizeof(__u32)], &pkt_udp, sizeof(pkt_udp));
+	*((__u32 *)data) = 0x42; /* metadata test value */
+
+	skel = test_xdp_do_redirect__open();
+	if (!ASSERT_OK_PTR(skel, "skel"))
+		return;
+
+	/* The XDP program we run with bpf_prog_run() will cycle through all
+	 * three xmit (PASS/TX/REDIRECT) return codes starting from above, and
+	 * ending up with PASS, so we should end up with two packets on the dst
+	 * iface and NUM_PKTS-2 in the TC hook. We match the packets on the UDP
+	 * payload.
+	 */
+	SYS("ip netns add testns");
+	nstoken = open_netns("testns");
+	if (!ASSERT_OK_PTR(nstoken, "setns"))
+		goto out;
+
+	SYS("ip link add veth_src type veth peer name veth_dst");
+	SYS("ip link set dev veth_src address 00:11:22:33:44:55");
+	SYS("ip link set dev veth_dst address 66:77:88:99:aa:bb");
+	SYS("ip link set dev veth_src up");
+	SYS("ip link set dev veth_dst up");
+	SYS("ip addr add dev veth_src fc00::1/64");
+	SYS("ip addr add dev veth_dst fc00::2/64");
+	SYS("ip neigh add fc00::2 dev veth_src lladdr 66:77:88:99:aa:bb");
+
+	/* We enable forwarding in the test namespace because that will cause
+	 * the packets that go through the kernel stack (with XDP_PASS) to be
+	 * forwarded back out the same interface (because of the packet dst
+	 * combined with the interface addresses). When this happens, the
+	 * regular forwarding path will end up going through the same
+	 * veth_xdp_xmit() call as the XDP_REDIRECT code, which can cause a
+	 * deadlock if it happens on the same CPU. There's a local_bh_disable()
+	 * in the test_run code to prevent this, but an earlier version of the
+	 * code didn't have this, so we keep the test behaviour to make sure the
+	 * bug doesn't resurface.
+	 */
+	SYS("sysctl -qw net.ipv6.conf.all.forwarding=1");
+
+	ifindex_src = if_nametoindex("veth_src");
+	ifindex_dst = if_nametoindex("veth_dst");
+	if (!ASSERT_NEQ(ifindex_src, 0, "ifindex_src") ||
+	    !ASSERT_NEQ(ifindex_dst, 0, "ifindex_dst"))
+		goto out;
+
+	memcpy(skel->rodata->expect_dst, &pkt_udp.eth.h_dest, ETH_ALEN);
+	skel->rodata->ifindex_out = ifindex_src; /* redirect back to the same iface */
+	skel->rodata->ifindex_in = ifindex_src;
+	ctx_in.ingress_ifindex = ifindex_src;
+	tc_hook.ifindex = ifindex_src;
+
+	if (!ASSERT_OK(test_xdp_do_redirect__load(skel), "load"))
+		goto out;
+
+	link = bpf_program__attach_xdp(skel->progs.xdp_count_pkts, ifindex_dst);
+	if (!ASSERT_OK_PTR(link, "prog_attach"))
+		goto out;
+	skel->links.xdp_count_pkts = link;
+
+	tc_prog_fd = bpf_program__fd(skel->progs.tc_count_pkts);
+	if (attach_tc_prog(&tc_hook, tc_prog_fd))
+		goto out;
+
+	xdp_prog_fd = bpf_program__fd(skel->progs.xdp_redirect);
+	err = bpf_prog_test_run_opts(xdp_prog_fd, &opts);
+	if (!ASSERT_OK(err, "prog_run"))
+		goto out_tc;
+
+	/* wait for the packets to be flushed */
+	kern_sync_rcu();
+
+	/* There will be one packet sent through XDP_REDIRECT and one through
+	 * XDP_TX; these will show up on the XDP counting program, while the
+	 * rest will be counted at the TC ingress hook (and the counting program
+	 * resets the packet payload so they don't get counted twice even though
+	 * they are re-xmited out the veth device
+	 */
+	ASSERT_EQ(skel->bss->pkts_seen_xdp, 2, "pkt_count_xdp");
+	ASSERT_EQ(skel->bss->pkts_seen_tc, NUM_PKTS - 2, "pkt_count_tc");
+
+out_tc:
+	bpf_tc_hook_destroy(&tc_hook);
+out:
+	if (nstoken)
+		close_netns(nstoken);
+	system("ip netns del testns");
+	test_xdp_do_redirect__destroy(skel);
+}

diff --git a/tools/testing/selftests/bpf/progs/test_xdp_do_redirect.c b/tools/testing/selftests/bpf/progs/test_xdp_do_redirect.c
new file mode 100644
index 000000000000..d785f48304ea
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/test_xdp_do_redirect.c

@@ -0,0 +1,92 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <vmlinux.h>
+#include <bpf/bpf_helpers.h>
+
+#define ETH_ALEN 6
+#define HDR_SZ (sizeof(struct ethhdr) + sizeof(struct ipv6hdr) + sizeof(struct udphdr))
+const volatile int ifindex_out;
+const volatile int ifindex_in;
+const volatile __u8 expect_dst[ETH_ALEN];
+volatile int pkts_seen_xdp = 0;
+volatile int pkts_seen_tc = 0;
+volatile int retcode = XDP_REDIRECT;
+
+SEC("xdp")
+int xdp_redirect(struct xdp_md *xdp)
+{
+	__u32 *metadata = (void *)(long)xdp->data_meta;
+	void *data_end = (void *)(long)xdp->data_end;
+	void *data = (void *)(long)xdp->data;
+
+	__u8 *payload = data + HDR_SZ;
+	int ret = retcode;
+
+	if (payload + 1 > data_end)
+		return XDP_ABORTED;
+
+	if (xdp->ingress_ifindex != ifindex_in)
+		return XDP_ABORTED;
+
+	if (metadata + 1 > data)
+		return XDP_ABORTED;
+
+	if (*metadata != 0x42)
+		return XDP_ABORTED;
+
+	*payload = 0x42;

nit. How about also adding a pkts_seen_zero counter here, like
	if (*payload == 0) {
		*payload = 0x42;
		pkts_seen_zero++;
	}

and add ASSERT_EQ(skel->bss->pkts_seen_zero, 2, "pkt_count_zero")
to the prog_tests.  It can better show the recycled page's data
is not re-initialized.

Good idea, will add!

quoted

+
+	if (bpf_xdp_adjust_meta(xdp, 4))
+		return XDP_ABORTED;
+
+	if (retcode > XDP_PASS)
+		retcode--;
+
+	if (ret == XDP_REDIRECT)
+		return bpf_redirect(ifindex_out, 0);
+
+	return ret;
+}
+
+static bool check_pkt(void *data, void *data_end)
+{
+	struct ipv6hdr *iph = data + sizeof(struct ethhdr);
+	__u8 *payload = data + HDR_SZ;
+
+	if (payload + 1 > data_end)
+		return false;
+
+	if (iph->nexthdr != IPPROTO_UDP || *payload != 0x42)
+		return false;
+
+	/* reset the payload so the same packet doesn't get counted twice when
+	 * it cycles back through the kernel path and out the dst veth
+	 */
+	*payload = 0;
+	return true;
+}
+
+SEC("xdp")
+int xdp_count_pkts(struct xdp_md *xdp)
+{
+	void *data = (void *)(long)xdp->data;
+	void *data_end = (void *)(long)xdp->data_end;
+
+	if (check_pkt(data, data_end))
+		pkts_seen_xdp++;
+
+	return XDP_DROP;

nit.  A comment here will be useful to explain XDP_DROP from
the xdp@veth@ingress will put the page back to the recycle
pool, which will be similar to xmit-ing out of a real NIC.

Sure, can do.

-Toke