selftests/bpf: Tests using bpf_check_mtu BPF-helper

Adding selftest for BPF-helper bpf_check_mtu(). Making sure
it can be used from both XDP and TC.

V16:
 - Fix 'void' function definition

V11:
 - Addresse nitpicks from Andrii Nakryiko

V10:
 - Remove errno non-zero test in CHECK_ATTR()
 - Addresse comments from Andrii Nakryiko

Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/161287791989.790810.13612620012522164562.stgit@firesoul

2 files changed, 414 insertions, 0 deletions

diff --git a/tools/testing/selftests/bpf/prog_tests/check_mtu.c b/tools/testing/selftests/bpf/prog_tests/check_mtu.c
new file mode 100644
index 000000000000..36af1c138faf
--- /dev/null
+++ b/tools/testing/selftests/bpf/prog_tests/check_mtu.c
@@ -0,0 +1,216 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2020 Jesper Dangaard Brouer */
+
+#include <linux/if_link.h> /* before test_progs.h, avoid bpf_util.h redefines */
+#include <test_progs.h>
+#include "test_check_mtu.skel.h"
+#include "network_helpers.h"
+
+#include <stdlib.h>
+#include <inttypes.h>
+
+#define IFINDEX_LO 1
+
+static __u32 duration; /* Hint: needed for CHECK macro */
+
+static int read_mtu_device_lo(void)
+{
+	const char *filename = "/sys/class/net/lo/mtu";
+	char buf[11] = {};
+	int value, n, fd;
+
+	fd = open(filename, 0, O_RDONLY);
+	if (fd == -1)
+		return -1;
+
+	n = read(fd, buf, sizeof(buf));
+	close(fd);
+
+	if (n == -1)
+		return -2;
+
+	value = strtoimax(buf, NULL, 10);
+	if (errno == ERANGE)
+		return -3;
+
+	return value;
+}
+
+static void test_check_mtu_xdp_attach(void)
+{
+	struct bpf_link_info link_info;
+	__u32 link_info_len = sizeof(link_info);
+	struct test_check_mtu *skel;
+	struct bpf_program *prog;
+	struct bpf_link *link;
+	int err = 0;
+	int fd;
+
+	skel = test_check_mtu__open_and_load();
+	if (CHECK(!skel, "open and load skel", "failed"))
+		return; /* Exit if e.g. helper unknown to kernel */
+
+	prog = skel->progs.xdp_use_helper_basic;
+
+	link = bpf_program__attach_xdp(prog, IFINDEX_LO);
+	if (CHECK(IS_ERR(link), "link_attach", "failed: %ld\n", PTR_ERR(link)))
+		goto out;
+	skel->links.xdp_use_helper_basic = link;
+
+	memset(&link_info, 0, sizeof(link_info));
+	fd = bpf_link__fd(link);
+	err = bpf_obj_get_info_by_fd(fd, &link_info, &link_info_len);
+	if (CHECK(err, "link_info", "failed: %d\n", err))
+		goto out;
+
+	CHECK(link_info.type != BPF_LINK_TYPE_XDP, "link_type",
+	      "got %u != exp %u\n", link_info.type, BPF_LINK_TYPE_XDP);
+	CHECK(link_info.xdp.ifindex != IFINDEX_LO, "link_ifindex",
+	      "got %u != exp %u\n", link_info.xdp.ifindex, IFINDEX_LO);
+
+	err = bpf_link__detach(link);
+	CHECK(err, "link_detach", "failed %d\n", err);
+
+out:
+	test_check_mtu__destroy(skel);
+}
+
+static void test_check_mtu_run_xdp(struct test_check_mtu *skel,
+				   struct bpf_program *prog,
+				   __u32 mtu_expect)
+{
+	const char *prog_name = bpf_program__name(prog);
+	int retval_expect = XDP_PASS;
+	__u32 mtu_result = 0;
+	char buf[256] = {};
+	int err;
+	struct bpf_prog_test_run_attr tattr = {
+		.repeat = 1,
+		.data_in = &pkt_v4,
+		.data_size_in = sizeof(pkt_v4),
+		.data_out = buf,
+		.data_size_out = sizeof(buf),
+		.prog_fd = bpf_program__fd(prog),
+	};
+
+	err = bpf_prog_test_run_xattr(&tattr);
+	CHECK_ATTR(err != 0, "bpf_prog_test_run",
+		   "prog_name:%s (err %d errno %d retval %d)\n",
+		   prog_name, err, errno, tattr.retval);
+
+	CHECK(tattr.retval != retval_expect, "retval",
+	      "progname:%s unexpected retval=%d expected=%d\n",
+	      prog_name, tattr.retval, retval_expect);
+
+	/* Extract MTU that BPF-prog got */
+	mtu_result = skel->bss->global_bpf_mtu_xdp;
+	ASSERT_EQ(mtu_result, mtu_expect, "MTU-compare-user");
+}
+
+
+static void test_check_mtu_xdp(__u32 mtu, __u32 ifindex)
+{
+	struct test_check_mtu *skel;
+	int err;
+
+	skel = test_check_mtu__open();
+	if (CHECK(!skel, "skel_open", "failed"))
+		return;
+
+	/* Update "constants" in BPF-prog *BEFORE* libbpf load */
+	skel->rodata->GLOBAL_USER_MTU = mtu;
+	skel->rodata->GLOBAL_USER_IFINDEX = ifindex;
+
+	err = test_check_mtu__load(skel);
+	if (CHECK(err, "skel_load", "failed: %d\n", err))
+		goto cleanup;
+
+	test_check_mtu_run_xdp(skel, skel->progs.xdp_use_helper, mtu);
+	test_check_mtu_run_xdp(skel, skel->progs.xdp_exceed_mtu, mtu);
+	test_check_mtu_run_xdp(skel, skel->progs.xdp_minus_delta, mtu);
+
+cleanup:
+	test_check_mtu__destroy(skel);
+}
+
+static void test_check_mtu_run_tc(struct test_check_mtu *skel,
+				  struct bpf_program *prog,
+				  __u32 mtu_expect)
+{
+	const char *prog_name = bpf_program__name(prog);
+	int retval_expect = BPF_OK;
+	__u32 mtu_result = 0;
+	char buf[256] = {};
+	int err;
+	struct bpf_prog_test_run_attr tattr = {
+		.repeat = 1,
+		.data_in = &pkt_v4,
+		.data_size_in = sizeof(pkt_v4),
+		.data_out = buf,
+		.data_size_out = sizeof(buf),
+		.prog_fd = bpf_program__fd(prog),
+	};
+
+	err = bpf_prog_test_run_xattr(&tattr);
+	CHECK_ATTR(err != 0, "bpf_prog_test_run",
+		   "prog_name:%s (err %d errno %d retval %d)\n",
+		   prog_name, err, errno, tattr.retval);
+
+	CHECK(tattr.retval != retval_expect, "retval",
+	      "progname:%s unexpected retval=%d expected=%d\n",
+	      prog_name, tattr.retval, retval_expect);
+
+	/* Extract MTU that BPF-prog got */
+	mtu_result = skel->bss->global_bpf_mtu_tc;
+	ASSERT_EQ(mtu_result, mtu_expect, "MTU-compare-user");
+}
+
+
+static void test_check_mtu_tc(__u32 mtu, __u32 ifindex)
+{
+	struct test_check_mtu *skel;
+	int err;
+
+	skel = test_check_mtu__open();
+	if (CHECK(!skel, "skel_open", "failed"))
+		return;
+
+	/* Update "constants" in BPF-prog *BEFORE* libbpf load */
+	skel->rodata->GLOBAL_USER_MTU = mtu;
+	skel->rodata->GLOBAL_USER_IFINDEX = ifindex;
+
+	err = test_check_mtu__load(skel);
+	if (CHECK(err, "skel_load", "failed: %d\n", err))
+		goto cleanup;
+
+	test_check_mtu_run_tc(skel, skel->progs.tc_use_helper, mtu);
+	test_check_mtu_run_tc(skel, skel->progs.tc_exceed_mtu, mtu);
+	test_check_mtu_run_tc(skel, skel->progs.tc_exceed_mtu_da, mtu);
+	test_check_mtu_run_tc(skel, skel->progs.tc_minus_delta, mtu);
+cleanup:
+	test_check_mtu__destroy(skel);
+}
+
+void test_check_mtu(void)
+{
+	__u32 mtu_lo;
+
+	if (test__start_subtest("bpf_check_mtu XDP-attach"))
+		test_check_mtu_xdp_attach();
+
+	mtu_lo = read_mtu_device_lo();
+	if (CHECK(mtu_lo < 0, "reading MTU value", "failed (err:%d)", mtu_lo))
+		return;
+
+	if (test__start_subtest("bpf_check_mtu XDP-run"))
+		test_check_mtu_xdp(mtu_lo, 0);
+
+	if (test__start_subtest("bpf_check_mtu XDP-run ifindex-lookup"))
+		test_check_mtu_xdp(mtu_lo, IFINDEX_LO);
+
+	if (test__start_subtest("bpf_check_mtu TC-run"))
+		test_check_mtu_tc(mtu_lo, 0);
+
+	if (test__start_subtest("bpf_check_mtu TC-run ifindex-lookup"))
+		test_check_mtu_tc(mtu_lo, IFINDEX_LO);
+}
diff --git a/tools/testing/selftests/bpf/progs/test_check_mtu.c b/tools/testing/selftests/bpf/progs/test_check_mtu.c
new file mode 100644
index 000000000000..b7787b43f9db
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/test_check_mtu.c
@@ -0,0 +1,198 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2020 Jesper Dangaard Brouer */
+
+#include <linux/bpf.h>
+#include <bpf/bpf_helpers.h>
+#include <linux/if_ether.h>
+
+#include <stddef.h>
+#include <stdint.h>
+
+char _license[] SEC("license") = "GPL";
+
+/* Userspace will update with MTU it can see on device */
+static volatile const int GLOBAL_USER_MTU;
+static volatile const __u32 GLOBAL_USER_IFINDEX;
+
+/* BPF-prog will update these with MTU values it can see */
+__u32 global_bpf_mtu_xdp = 0;
+__u32 global_bpf_mtu_tc  = 0;
+
+SEC("xdp")
+int xdp_use_helper_basic(struct xdp_md *ctx)
+{
+	__u32 mtu_len = 0;
+
+	if (bpf_check_mtu(ctx, 0, &mtu_len, 0, 0))
+		return XDP_ABORTED;
+
+	return XDP_PASS;
+}
+
+SEC("xdp")
+int xdp_use_helper(struct xdp_md *ctx)
+{
+	int retval = XDP_PASS; /* Expected retval on successful test */
+	__u32 mtu_len = 0;
+	__u32 ifindex = 0;
+	int delta = 0;
+
+	/* When ifindex is zero, save net_device lookup and use ctx netdev */
+	if (GLOBAL_USER_IFINDEX > 0)
+		ifindex = GLOBAL_USER_IFINDEX;
+
+	if (bpf_check_mtu(ctx, ifindex, &mtu_len, delta, 0)) {
+		/* mtu_len is also valid when check fail */
+		retval = XDP_ABORTED;
+		goto out;
+	}
+
+	if (mtu_len != GLOBAL_USER_MTU)
+		retval = XDP_DROP;
+
+out:
+	global_bpf_mtu_xdp = mtu_len;
+	return retval;
+}
+
+SEC("xdp")
+int xdp_exceed_mtu(struct xdp_md *ctx)
+{
+	void *data_end = (void *)(long)ctx->data_end;
+	void *data = (void *)(long)ctx->data;
+	__u32 ifindex = GLOBAL_USER_IFINDEX;
+	__u32 data_len = data_end - data;
+	int retval = XDP_ABORTED; /* Fail */
+	__u32 mtu_len = 0;
+	int delta;
+	int err;
+
+	/* Exceed MTU with 1 via delta adjust */
+	delta = GLOBAL_USER_MTU - (data_len - ETH_HLEN) + 1;
+
+	err = bpf_check_mtu(ctx, ifindex, &mtu_len, delta, 0);
+	if (err) {
+		retval = XDP_PASS; /* Success in exceeding MTU check */
+		if (err != BPF_MTU_CHK_RET_FRAG_NEEDED)
+			retval = XDP_DROP;
+	}
+
+	global_bpf_mtu_xdp = mtu_len;
+	return retval;
+}
+
+SEC("xdp")
+int xdp_minus_delta(struct xdp_md *ctx)
+{
+	int retval = XDP_PASS; /* Expected retval on successful test */
+	void *data_end = (void *)(long)ctx->data_end;
+	void *data = (void *)(long)ctx->data;
+	__u32 ifindex = GLOBAL_USER_IFINDEX;
+	__u32 data_len = data_end - data;
+	__u32 mtu_len = 0;
+	int delta;
+
+	/* Borderline test case: Minus delta exceeding packet length allowed */
+	delta = -((data_len - ETH_HLEN) + 1);
+
+	/* Minus length (adjusted via delta) still pass MTU check, other helpers
+	 * are responsible for catching this, when doing actual size adjust
+	 */
+	if (bpf_check_mtu(ctx, ifindex, &mtu_len, delta, 0))
+		retval = XDP_ABORTED;
+
+	global_bpf_mtu_xdp = mtu_len;
+	return retval;
+}
+
+SEC("classifier")
+int tc_use_helper(struct __sk_buff *ctx)
+{
+	int retval = BPF_OK; /* Expected retval on successful test */
+	__u32 mtu_len = 0;
+	int delta = 0;
+
+	if (bpf_check_mtu(ctx, 0, &mtu_len, delta, 0)) {
+		retval = BPF_DROP;
+		goto out;
+	}
+
+	if (mtu_len != GLOBAL_USER_MTU)
+		retval = BPF_REDIRECT;
+out:
+	global_bpf_mtu_tc = mtu_len;
+	return retval;
+}
+
+SEC("classifier")
+int tc_exceed_mtu(struct __sk_buff *ctx)
+{
+	__u32 ifindex = GLOBAL_USER_IFINDEX;
+	int retval = BPF_DROP; /* Fail */
+	__u32 skb_len = ctx->len;
+	__u32 mtu_len = 0;
+	int delta;
+	int err;
+
+	/* Exceed MTU with 1 via delta adjust */
+	delta = GLOBAL_USER_MTU - (skb_len - ETH_HLEN) + 1;
+
+	err = bpf_check_mtu(ctx, ifindex, &mtu_len, delta, 0);
+	if (err) {
+		retval = BPF_OK; /* Success in exceeding MTU check */
+		if (err != BPF_MTU_CHK_RET_FRAG_NEEDED)
+			retval = BPF_DROP;
+	}
+
+	global_bpf_mtu_tc = mtu_len;
+	return retval;
+}
+
+SEC("classifier")
+int tc_exceed_mtu_da(struct __sk_buff *ctx)
+{
+	/* SKB Direct-Access variant */
+	void *data_end = (void *)(long)ctx->data_end;
+	void *data = (void *)(long)ctx->data;
+	__u32 ifindex = GLOBAL_USER_IFINDEX;
+	__u32 data_len = data_end - data;
+	int retval = BPF_DROP; /* Fail */
+	__u32 mtu_len = 0;
+	int delta;
+	int err;
+
+	/* Exceed MTU with 1 via delta adjust */
+	delta = GLOBAL_USER_MTU - (data_len - ETH_HLEN) + 1;
+
+	err = bpf_check_mtu(ctx, ifindex, &mtu_len, delta, 0);
+	if (err) {
+		retval = BPF_OK; /* Success in exceeding MTU check */
+		if (err != BPF_MTU_CHK_RET_FRAG_NEEDED)
+			retval = BPF_DROP;
+	}
+
+	global_bpf_mtu_tc = mtu_len;
+	return retval;
+}
+
+SEC("classifier")
+int tc_minus_delta(struct __sk_buff *ctx)
+{
+	int retval = BPF_OK; /* Expected retval on successful test */
+	__u32 ifindex = GLOBAL_USER_IFINDEX;
+	__u32 skb_len = ctx->len;
+	__u32 mtu_len = 0;
+	int delta;
+
+	/* Borderline test case: Minus delta exceeding packet length allowed */
+	delta = -((skb_len - ETH_HLEN) + 1);
+
+	/* Minus length (adjusted via delta) still pass MTU check, other helpers
+	 * are responsible for catching this, when doing actual size adjust
+	 */
+	if (bpf_check_mtu(ctx, ifindex, &mtu_len, delta, 0))
+		retval = BPF_DROP;
+
+	global_bpf_mtu_xdp = mtu_len;
+	return retval;
+}