Commit ce523680 authored Mar 19, 2022 by Jakub Sitnicki Committed by Alexei Starovoitov Mar 20, 2022

selftests/bpf: Fix test for 4-byte load from remote_port on big-endian

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: 2ed0dc59 ("selftests/bpf: Cover 4-byte load from remote_port in bpf_sk_lookup")
Signed-off-by: Jakub Sitnicki <jakub@cloudflare.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Martin KaFai Lau <kafai@fb.com>
Link: https://lore.kernel.org/bpf/20220319183356.233666-4-jakub@cloudflare.com

parent 3c69611b

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

+8 −2

Original line number	Diff line number	Diff line
		@@ -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. */