@@ -418,9 +418,15 @@ int ctx_narrow_access(struct bpf_sk_lookup *ctx)
if (LSW(ctx->remote_port, 0) != SRC_PORT)
return SK_DROP;
- /* Load from remote_port field with zero padding (backward compatibility) */
+ /*
+ * NOTE: 4-byte load from bpf_sk_lookup at remote_port offset
+ * is quirky. It gets rewritten by the access converter to a
+ * 2-byte load for backward compatibility. Treating the load
+ * result as a be16 value makes the code portable across
+ * little- and big-endian platforms.
+ */
val_u32 = *(__u32 *)&ctx->remote_port;
- if (val_u32 != bpf_htonl(bpf_ntohs(SRC_PORT) << 16))
+ if (val_u32 != SRC_PORT)
return SK_DROP;
/* Narrow loads from local_port field. Expect DST_PORT. */
The context access converter rewrites the 4-byte load from bpf_sk_lookup->remote_port to a 2-byte load from bpf_sk_lookup_kern structure. It means that we cannot treat the destination register contents as a 32-bit value, or the code will not be portable across big- and little-endian architectures. This is exactly the same case as with 4-byte loads from bpf_sock->dst_port so follow the approach outlined in [1] and treat the register contents as a 16-bit value in the test. [1]: https://lore.kernel.org/bpf/20220317113920.1068535-5-jakub@cloudflare.com/ Fixes: 2ed0dc5937d3 ("selftests/bpf: Cover 4-byte load from remote_port in bpf_sk_lookup") Acked-by: Martin KaFai Lau <kafai@fb.com> Signed-off-by: Jakub Sitnicki <jakub@cloudflare.com> --- tools/testing/selftests/bpf/progs/test_sk_lookup.c | 10 ++++++++-- 1 file changed, 8 insertions(+), 2 deletions(-)