selftests/bpf: Cover write access to skb metadata via dynptr

Add tests what exercise writes to skb metadata in two ways:
1. indirectly, using bpf_dynptr_write helper,
2. directly, using a read-write dynptr slice.

Signed-off-by: Jakub Sitnicki <jakub@cloudflare.com>
Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>
Reviewed-by: Jesse Brandeburg <jbrandeburg@cloudflare.com>
Acked-by: Eduard Zingerman <eddyz87@gmail.com>
Link: https://patch.msgid.link/20250814-skb-metadata-thru-dynptr-v7-7-8a39e636e0fb@cloudflare.com

diff --git a/tools/testing/selftests/bpf/prog_tests/xdp_context_test_run.c b/tools/testing/selftests/bpf/prog_tests/xdp_context_test_run.c
index 7e4526461a4cb6ad6a39ac99dc4f2096c156c075..79c4c58276e6727396f182d18f8d40921557228b 100644 (file)
--- a/tools/testing/selftests/bpf/prog_tests/xdp_context_test_run.c
+++ b/tools/testing/selftests/bpf/prog_tests/xdp_context_test_run.c
@@ -269,7 +269,8 @@ close:
 }
 
 static void test_tuntap(struct bpf_program *xdp_prog,
-                       struct bpf_program *tc_prog,
+                       struct bpf_program *tc_prio_1_prog,
+                       struct bpf_program *tc_prio_2_prog,
                        struct bpf_map *result_map)
 {
        LIBBPF_OPTS(bpf_tc_hook, tc_hook, .attach_point = BPF_TC_INGRESS);
@@ -302,11 +303,20 @@ static void test_tuntap(struct bpf_program *xdp_prog,
        if (!ASSERT_OK(ret, "bpf_tc_hook_create"))
                goto close;
 
-       tc_opts.prog_fd = bpf_program__fd(tc_prog);
+       tc_opts.prog_fd = bpf_program__fd(tc_prio_1_prog);
        ret = bpf_tc_attach(&tc_hook, &tc_opts);
        if (!ASSERT_OK(ret, "bpf_tc_attach"))
                goto close;
 
+       if (tc_prio_2_prog) {
+               LIBBPF_OPTS(bpf_tc_opts, tc_opts, .handle = 1, .priority = 2,
+                           .prog_fd = bpf_program__fd(tc_prio_2_prog));
+
+               ret = bpf_tc_attach(&tc_hook, &tc_opts);
+               if (!ASSERT_OK(ret, "bpf_tc_attach"))
+                       goto close;
+       }
+
        ret = bpf_xdp_attach(tap_ifindex, bpf_program__fd(xdp_prog),
                             0, NULL);
        if (!ASSERT_GE(ret, 0, "bpf_xdp_attach"))
@@ -341,13 +351,29 @@ void test_xdp_context_tuntap(void)
                return;
 
        if (test__start_subtest("data_meta"))
-               test_tuntap(skel->progs.ing_xdp, skel->progs.ing_cls,
+               test_tuntap(skel->progs.ing_xdp,
+                           skel->progs.ing_cls,
+                           NULL, /* tc prio 2 */
                            skel->maps.test_result);
        if (test__start_subtest("dynptr_read"))
-               test_tuntap(skel->progs.ing_xdp, skel->progs.ing_cls_dynptr_read,
+               test_tuntap(skel->progs.ing_xdp,
+                           skel->progs.ing_cls_dynptr_read,
+                           NULL, /* tc prio 2 */
                            skel->maps.test_result);
        if (test__start_subtest("dynptr_slice"))
-               test_tuntap(skel->progs.ing_xdp, skel->progs.ing_cls_dynptr_slice,
+               test_tuntap(skel->progs.ing_xdp,
+                           skel->progs.ing_cls_dynptr_slice,
+                           NULL, /* tc prio 2 */
+                           skel->maps.test_result);
+       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);
+       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);
 
        test_xdp_meta__destroy(skel);

diff --git a/tools/testing/selftests/bpf/progs/test_xdp_meta.c b/tools/testing/selftests/bpf/progs/test_xdp_meta.c
index 0ba647fb1b1d7be7871288d1edd7d58d0b81cd45..e7879860f4039a6500d46fe8bb5303b1d91e3262 100644 (file)
--- a/tools/testing/selftests/bpf/progs/test_xdp_meta.c
+++ b/tools/testing/selftests/bpf/progs/test_xdp_meta.c
@@ -60,6 +60,24 @@ int ing_cls_dynptr_read(struct __sk_buff *ctx)
        return TC_ACT_SHOT;
 }
 
+/* Write to metadata using bpf_dynptr_write helper */
+SEC("tc")
+int ing_cls_dynptr_write(struct __sk_buff *ctx)
+{
+       struct bpf_dynptr data, meta;
+       __u8 *src;
+
+       bpf_dynptr_from_skb(ctx, 0, &data);
+       src = bpf_dynptr_slice(&data, sizeof(struct ethhdr), NULL, META_SIZE);
+       if (!src)
+               return TC_ACT_SHOT;
+
+       bpf_dynptr_from_skb_meta(ctx, 0, &meta);
+       bpf_dynptr_write(&meta, 0, src, META_SIZE, 0);
+
+       return TC_ACT_UNSPEC; /* pass */
+}
+
 /* Read from metadata using read-only dynptr slice */
 SEC("tc")
 int ing_cls_dynptr_slice(struct __sk_buff *ctx)
@@ -82,6 +100,55 @@ int ing_cls_dynptr_slice(struct __sk_buff *ctx)
        return TC_ACT_SHOT;
 }
 
+/* Write to metadata using writeable dynptr slice */
+SEC("tc")
+int ing_cls_dynptr_slice_rdwr(struct __sk_buff *ctx)
+{
+       struct bpf_dynptr data, meta;
+       __u8 *src, *dst;
+
+       bpf_dynptr_from_skb(ctx, 0, &data);
+       src = bpf_dynptr_slice(&data, sizeof(struct ethhdr), NULL, META_SIZE);
+       if (!src)
+               return TC_ACT_SHOT;
+
+       bpf_dynptr_from_skb_meta(ctx, 0, &meta);
+       dst = bpf_dynptr_slice_rdwr(&meta, 0, NULL, META_SIZE);
+       if (!dst)
+               return TC_ACT_SHOT;
+
+       __builtin_memcpy(dst, src, META_SIZE);
+
+       return TC_ACT_UNSPEC; /* pass */
+}
+
+/* Reserve and clear space for metadata but don't populate it */
+SEC("xdp")
+int ing_xdp_zalloc_meta(struct xdp_md *ctx)
+{
+       struct ethhdr *eth = ctx_ptr(ctx, data);
+       __u8 *meta;
+       int ret;
+
+       /* Drop any non-test packets */
+       if (eth + 1 > ctx_ptr(ctx, data_end))
+               return XDP_DROP;
+       if (eth->h_proto != 0)
+               return XDP_DROP;
+
+       ret = bpf_xdp_adjust_meta(ctx, -META_SIZE);
+       if (ret < 0)
+               return XDP_DROP;
+
+       meta = ctx_ptr(ctx, data_meta);
+       if (meta + META_SIZE > ctx_ptr(ctx, data))
+               return XDP_DROP;
+
+       __builtin_memset(meta, 0, META_SIZE);
+
+       return XDP_PASS;
+}
+
 SEC("xdp")
 int ing_xdp(struct xdp_md *ctx)
 {