netdev - Re: [PATCH bpf-next v2 2/2] selftests/bpf: Cover 4-byte load from remote_port in bpf_sk

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Message-ID: <87fsohea8q.fsf@cloudflare.com>
Date:   Thu, 17 Feb 2022 17:11:13 +0100
From:   Jakub Sitnicki <jakub@...udflare.com>
To:     Ilya Leoshkevich <iii@...ux.ibm.com>
Cc:     Andrii Nakryiko <andrii.nakryiko@...il.com>,
        bpf <bpf@...r.kernel.org>, Networking <netdev@...r.kernel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        kernel-team <kernel-team@...udflare.com>,
        Yonghong Song <yhs@...com>
Subject: Re: [PATCH bpf-next v2 2/2] selftests/bpf: Cover 4-byte load from
 remote_port in bpf_sk_lookup

On Thu, Feb 17, 2022 at 03:18 PM +01, Ilya Leoshkevich wrote:
> On Wed, 2022-02-16 at 13:44 -0800, Andrii Nakryiko wrote:
>> On Wed, Feb 9, 2022 at 10:43 AM Jakub Sitnicki <jakub@...udflare.com>
>> wrote:

[...]

>> > +       /* Load from remote_port field with zero padding (backward
>> > compatibility) */
>> > +       val_u32 = *(__u32 *)&ctx->remote_port;
>> > +       if (val_u32 != bpf_htonl(bpf_ntohs(SRC_PORT) << 16))
>> > +               return SK_DROP;
>> > +
>> 
>> Jakub, can you please double check that your patch set doesn't break
>> big-endian architectures? I've noticed that our s390x test runner is
>> now failing in the sk_lookup selftest. See [0]. Also CC'ing Ilya.
>
> I agree that this looks like an endianness issue. The new check seems
> to make little sense on big-endian to me, so I would just #ifdef it
> out.

We have a very similar check for a load from context in
progs/test_sock_fields.c, which is not causing problems:

static __noinline bool sk_dst_port__load_word(struct bpf_sock *sk)
{
	__u32 *word = (__u32 *)&sk->dst_port;
	return word[0] == bpf_htonl(0xcafe0000);
}

So I think I just messed something up here. Will dig into it.

[...]