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

From: Toke Høiland-Jørgensen <[email-masked]>
Date: Tue, 08 Mar 2022 15:41:41 +0100

Martin KaFai Lau <[email-masked]> writes:

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

>> +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!

>> +
>> +	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