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Message-Id: <20250630-skb-metadata-thru-dynptr-v1-10-f17da13625d8@cloudflare.com>
Date: Mon, 30 Jun 2025 16:55:43 +0200
From: Jakub Sitnicki <jakub@...udflare.com>
To: bpf@...r.kernel.org
Cc: Alexei Starovoitov <ast@...nel.org>,
Arthur Fabre <arthur@...hurfabre.com>, Eric Dumazet <edumazet@...gle.com>,
Jakub Kicinski <kuba@...nel.org>, Jesper Dangaard Brouer <hawk@...nel.org>,
Jesse Brandeburg <jbrandeburg@...udflare.com>,
Joanne Koong <joannelkoong@...il.com>,
Lorenzo Bianconi <lorenzo@...nel.org>,
Toke Høiland-Jørgensen <thoiland@...hat.com>,
Yan Zhai <yan@...udflare.com>, netdev@...r.kernel.org,
kernel-team@...udflare.com, Stanislav Fomichev <sdf@...ichev.me>
Subject: [PATCH bpf-next 10/13] selftests/bpf: Cover read access to skb
metadata via dynptr
Exercise reading from SKB metadata area in two new ways:
1. indirectly, with bpf_dynptr_read(), and
2. directly, with bpf_dynptr_slice().
Signed-off-by: Jakub Sitnicki <jakub@...udflare.com>
---
tools/include/uapi/linux/bpf.h | 9 +++++
.../bpf/prog_tests/xdp_context_test_run.c | 21 +++++++++++
tools/testing/selftests/bpf/progs/test_xdp_meta.c | 42 ++++++++++++++++++++++
3 files changed, 72 insertions(+)
diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index 719ba230032f..ab5730d2fb29 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -7591,4 +7591,13 @@ enum bpf_kfunc_flags {
BPF_F_PAD_ZEROS = (1ULL << 0),
};
+/**
+ * enum bpf_dynptr_from_skb_flags - Flags for bpf_dynptr_from_skb()
+ *
+ * @BPF_DYNPTR_F_SKB_METADATA: Create dynptr to the SKB metadata area
+ */
+enum bpf_dynptr_from_skb_flags {
+ BPF_DYNPTR_F_SKB_METADATA = (1ULL << 0),
+};
+
#endif /* _UAPI__LINUX_BPF_H__ */
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 6c66e27e5bc7..7e4526461a4c 100644
--- a/tools/testing/selftests/bpf/prog_tests/xdp_context_test_run.c
+++ b/tools/testing/selftests/bpf/prog_tests/xdp_context_test_run.c
@@ -171,6 +171,18 @@ static void assert_test_result(const struct bpf_map *result_map)
"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);
@@ -268,6 +280,9 @@ static void test_tuntap(struct bpf_program *xdp_prog,
int tap_ifindex;
int ret;
+ if (!clear_test_result(result_map))
+ return;
+
ns = netns_new(TAP_NETNS, true);
if (!ASSERT_OK_PTR(ns, "create and open ns"))
return;
@@ -328,6 +343,12 @@ void test_xdp_context_tuntap(void)
if (test__start_subtest("data_meta"))
test_tuntap(skel->progs.ing_xdp, skel->progs.ing_cls,
skel->maps.test_result);
+ if (test__start_subtest("dynptr_read"))
+ test_tuntap(skel->progs.ing_xdp, skel->progs.ing_cls_dynptr_read,
+ skel->maps.test_result);
+ if (test__start_subtest("dynptr_slice"))
+ test_tuntap(skel->progs.ing_xdp, 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 fcf6ca14f2ea..6b11134520be 100644
--- a/tools/testing/selftests/bpf/progs/test_xdp_meta.c
+++ b/tools/testing/selftests/bpf/progs/test_xdp_meta.c
@@ -1,8 +1,10 @@
+#include <stdbool.h>
#include <linux/bpf.h>
#include <linux/if_ether.h>
#include <linux/pkt_cls.h>
#include <bpf/bpf_helpers.h>
+#include "bpf_kfuncs.h"
#define META_SIZE 32
@@ -40,6 +42,46 @@ int ing_cls(struct __sk_buff *ctx)
return TC_ACT_SHOT;
}
+/* Read from metadata using bpf_dynptr_read helper */
+SEC("tc")
+int ing_cls_dynptr_read(struct __sk_buff *ctx)
+{
+ 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(ctx, BPF_DYNPTR_F_SKB_METADATA, &meta);
+ bpf_dynptr_read(dst, META_SIZE, &meta, 0, 0);
+
+ return TC_ACT_SHOT;
+}
+
+/* Read from metadata using read-only dynptr slice */
+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;
+
+ bpf_dynptr_from_skb(ctx, BPF_DYNPTR_F_SKB_METADATA, &meta);
+ src = bpf_dynptr_slice(&meta, 0, NULL, META_SIZE);
+ if (!src)
+ return TC_ACT_SHOT;
+
+ __builtin_memcpy(dst, src, META_SIZE);
+
+ return TC_ACT_SHOT;
+}
+
SEC("xdp")
int ing_xdp(struct xdp_md *ctx)
{
--
2.43.0
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