selftests/bpf: Verify skb metadata in BPF instead of userspace

Move metadata verification into the BPF TC programs. Previously,
userspace read metadata from a map and verified it once at test end.

Now TC programs compare metadata directly using __builtin_memcmp() and
set a test_pass flag. This enables verification at multiple points during
test execution rather than a single final check.

Signed-off-by: Jakub Sitnicki <[email protected]>

Author: jsitnicki

tools/testing/selftests/bpf/prog_tests/xdp_context_test_run.c

@@ -171,33 +171,6 @@ static int write_test_packet(int tap_fd)
 	return 0;
 }
 
-static void assert_test_result(const struct bpf_map *result_map)
-{
-	int err;
-	__u32 map_key = 0;
-	__u8 map_value[TEST_PAYLOAD_LEN];
-
-	err = bpf_map__lookup_elem(result_map, &map_key, sizeof(map_key),
-				   &map_value, TEST_PAYLOAD_LEN, BPF_ANY);
-	if (!ASSERT_OK(err, "lookup test_result"))
-		return;
-
-	ASSERT_MEMEQ(&map_value, &test_payload, TEST_PAYLOAD_LEN,
-		     "test_result map contains test payload");
-}
-
-static bool clear_test_result(struct bpf_map *result_map)
-{
-	const __u8 v[sizeof(test_payload)] = {};
-	const __u32 k = 0;
-	int err;
-
-	err = bpf_map__update_elem(result_map, &k, sizeof(k), v, sizeof(v), BPF_ANY);
-	ASSERT_OK(err, "update test_result");
-
-	return err == 0;
-}
-
 void test_xdp_context_veth(void)
 {
 	LIBBPF_OPTS(bpf_tc_hook, tc_hook, .attach_point = BPF_TC_INGRESS);
@@ -270,11 +243,13 @@ void test_xdp_context_veth(void)
 	if (!ASSERT_GE(tx_ifindex, 0, "if_nametoindex tx"))
 		goto close;
 
+	skel->bss->test_pass = false;
+
 	ret = send_test_packet(tx_ifindex);
 	if (!ASSERT_OK(ret, "send_test_packet"))
 		goto close;
 
-	assert_test_result(skel->maps.test_result);
+	ASSERT_TRUE(skel->bss->test_pass, "test_pass");
 
 close:
 	close_netns(nstoken);
@@ -286,7 +261,7 @@ void test_xdp_context_veth(void)
 static void test_tuntap(struct bpf_program *xdp_prog,
 			struct bpf_program *tc_prio_1_prog,
 			struct bpf_program *tc_prio_2_prog,
-			struct bpf_map *result_map)
+			bool *test_pass)
 {
 	LIBBPF_OPTS(bpf_tc_hook, tc_hook, .attach_point = BPF_TC_INGRESS);
 	LIBBPF_OPTS(bpf_tc_opts, tc_opts, .handle = 1, .priority = 1);
@@ -295,8 +270,7 @@ static void test_tuntap(struct bpf_program *xdp_prog,
 	int tap_ifindex;
 	int ret;
 
-	if (!clear_test_result(result_map))
-		return;
+	*test_pass = false;
 
 	ns = netns_new(TAP_NETNS, true);
 	if (!ASSERT_OK_PTR(ns, "create and open ns"))
@@ -340,7 +314,7 @@ static void test_tuntap(struct bpf_program *xdp_prog,
 	if (!ASSERT_OK(ret, "write_test_packet"))
 		goto close;
 
-	assert_test_result(result_map);
+	ASSERT_TRUE(*test_pass, "test_pass");
 
 close:
 	if (tap_fd >= 0)
@@ -431,37 +405,37 @@ void test_xdp_context_tuntap(void)
 		test_tuntap(skel->progs.ing_xdp,
 			    skel->progs.ing_cls,
 			    NULL, /* tc prio 2 */
-			    skel->maps.test_result);
+			    &skel->bss->test_pass);
 	if (test__start_subtest("dynptr_read"))
 		test_tuntap(skel->progs.ing_xdp,
 			    skel->progs.ing_cls_dynptr_read,
 			    NULL, /* tc prio 2 */
-			    skel->maps.test_result);
+			    &skel->bss->test_pass);
 	if (test__start_subtest("dynptr_slice"))
 		test_tuntap(skel->progs.ing_xdp,
 			    skel->progs.ing_cls_dynptr_slice,
 			    NULL, /* tc prio 2 */
-			    skel->maps.test_result);
+			    &skel->bss->test_pass);
 	if (test__start_subtest("dynptr_write"))
 		test_tuntap(skel->progs.ing_xdp_zalloc_meta,
 			    skel->progs.ing_cls_dynptr_write,
 			    skel->progs.ing_cls_dynptr_read,
-			    skel->maps.test_result);
+			    &skel->bss->test_pass);
 	if (test__start_subtest("dynptr_slice_rdwr"))
 		test_tuntap(skel->progs.ing_xdp_zalloc_meta,
 			    skel->progs.ing_cls_dynptr_slice_rdwr,
 			    skel->progs.ing_cls_dynptr_slice,
-			    skel->maps.test_result);
+			    &skel->bss->test_pass);
 	if (test__start_subtest("dynptr_offset"))
 		test_tuntap(skel->progs.ing_xdp_zalloc_meta,
 			    skel->progs.ing_cls_dynptr_offset_wr,
 			    skel->progs.ing_cls_dynptr_offset_rd,
-			    skel->maps.test_result);
+			    &skel->bss->test_pass);
 	if (test__start_subtest("dynptr_offset_oob"))
 		test_tuntap(skel->progs.ing_xdp,
 			    skel->progs.ing_cls_dynptr_offset_oob,
 			    skel->progs.ing_cls,
-			    skel->maps.test_result);
+			    &skel->bss->test_pass);
 	if (test__start_subtest("clone_data_meta_empty_on_data_write"))
 		test_tuntap_mirred(skel->progs.ing_xdp,
 				   skel->progs.clone_data_meta_empty_on_data_write,

tools/testing/selftests/bpf/progs/test_xdp_meta.c

@@ -11,55 +11,54 @@
 
 #define ctx_ptr(ctx, mem) (void *)(unsigned long)ctx->mem
 
-/* Demonstrates how metadata can be passed from an XDP program to a TC program
- * using bpf_xdp_adjust_meta.
- * For the sake of testing the metadata support in drivers, the XDP program uses
- * a fixed-size payload after the Ethernet header as metadata. The TC program
- * copies the metadata it receives into a map so it can be checked from
- * userspace.
+/* Demonstrate passing metadata from XDP to TC using bpf_xdp_adjust_meta.
+ *
+ * The XDP program extracts a fixed-size payload following the Ethernet header
+ * and stores it as packet metadata to test the driver's metadata support. The
+ * TC program then verifies if the passed metadata is correct.
  */
 
-struct {
-	__uint(type, BPF_MAP_TYPE_ARRAY);
-	__uint(max_entries, 1);
-	__type(key, __u32);
-	__uint(value_size, META_SIZE);
-} test_result SEC(".maps");
-
 bool test_pass;
 
+static const __u8 meta_want[META_SIZE] = {
+	0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08,
+	0x11, 0x12, 0x13, 0x14, 0x15, 0x16, 0x17, 0x18,
+	0x21, 0x22, 0x23, 0x24, 0x25, 0x26, 0x27, 0x28,
+	0x31, 0x32, 0x33, 0x34, 0x35, 0x36, 0x37, 0x38,
+};
+
 SEC("tc")
 int ing_cls(struct __sk_buff *ctx)
 {
-	__u8 *data, *data_meta;
-	__u32 key = 0;
-
-	data_meta = ctx_ptr(ctx, data_meta);
-	data      = ctx_ptr(ctx, data);
+	__u8 *meta_have = ctx_ptr(ctx, data_meta);
+	__u8 *data = ctx_ptr(ctx, data);
 
-	if (data_meta + META_SIZE > data)
-		return TC_ACT_SHOT;
+	if (meta_have + META_SIZE > data)
+		goto out;
 
-	bpf_map_update_elem(&test_result, &key, data_meta, BPF_ANY);
+	if (__builtin_memcmp(meta_want, meta_have, META_SIZE))
+		goto out;
 
+	test_pass = true;
+out:
 	return TC_ACT_SHOT;
 }
 
 /* Read from metadata using bpf_dynptr_read helper */
 SEC("tc")
 int ing_cls_dynptr_read(struct __sk_buff *ctx)
 {
+	__u8 meta_have[META_SIZE];
 	struct bpf_dynptr meta;
-	const __u32 zero = 0;
-	__u8 *dst;
-
-	dst = bpf_map_lookup_elem(&test_result, &zero);
-	if (!dst)
-		return TC_ACT_SHOT;
 
 	bpf_dynptr_from_skb_meta(ctx, 0, &meta);
-	bpf_dynptr_read(dst, META_SIZE, &meta, 0, 0);
+	bpf_dynptr_read(meta_have, META_SIZE, &meta, 0, 0);
+
+	if (__builtin_memcmp(meta_want, meta_have, META_SIZE))
+		goto out;
 
+	test_pass = true;
+out:
 	return TC_ACT_SHOT;
 }
 
@@ -86,20 +85,18 @@ SEC("tc")
 int ing_cls_dynptr_slice(struct __sk_buff *ctx)
 {
 	struct bpf_dynptr meta;
-	const __u32 zero = 0;
-	__u8 *dst, *src;
-
-	dst = bpf_map_lookup_elem(&test_result, &zero);
-	if (!dst)
-		return TC_ACT_SHOT;
+	__u8 *meta_have;
 
 	bpf_dynptr_from_skb_meta(ctx, 0, &meta);
-	src = bpf_dynptr_slice(&meta, 0, NULL, META_SIZE);
-	if (!src)
-		return TC_ACT_SHOT;
+	meta_have = bpf_dynptr_slice(&meta, 0, NULL, META_SIZE);
+	if (!meta_have)
+		goto out;
 
-	__builtin_memcpy(dst, src, META_SIZE);
+	if (__builtin_memcmp(meta_want, meta_have, META_SIZE))
+		goto out;
 
+	test_pass = true;
+out:
 	return TC_ACT_SHOT;
 }
 
@@ -129,14 +126,12 @@ int ing_cls_dynptr_slice_rdwr(struct __sk_buff *ctx)
 SEC("tc")
 int ing_cls_dynptr_offset_rd(struct __sk_buff *ctx)
 {
-	struct bpf_dynptr meta;
 	const __u32 chunk_len = META_SIZE / 4;
-	const __u32 zero = 0;
+	__u8 meta_have[META_SIZE];
+	struct bpf_dynptr meta;
 	__u8 *dst, *src;
 
-	dst = bpf_map_lookup_elem(&test_result, &zero);
-	if (!dst)
-		return TC_ACT_SHOT;
+	dst = meta_have;
 
 	/* 1. Regular read */
 	bpf_dynptr_from_skb_meta(ctx, 0, &meta);
@@ -155,9 +150,14 @@ int ing_cls_dynptr_offset_rd(struct __sk_buff *ctx)
 	/* 4. Read from a slice starting at an offset */
 	src = bpf_dynptr_slice(&meta, 2 * chunk_len, NULL, chunk_len);
 	if (!src)
-		return TC_ACT_SHOT;
+		goto out;
 	__builtin_memcpy(dst, src, chunk_len);
 
+	if (__builtin_memcmp(meta_want, meta_have, META_SIZE))
+		goto out;
+
+	test_pass = true;
+out:
 	return TC_ACT_SHOT;
 }