On Wed, 2022-02-16 at 13:44 -0800, Andrii Nakryiko wrote:
> On Wed, Feb 9, 2022 at 10:43 AM Jakub Sitnicki <jakub@xxxxxxxxxxxxxx>
> wrote:
> >
> > Extend the context access tests for sk_lookup prog to cover the
> > surprising
> > case of a 4-byte load from the remote_port field, where the
> > expected value
> > is actually shifted by 16 bits.
> >
> > Acked-by: Yonghong Song <yhs@xxxxxx>
> > Signed-off-by: Jakub Sitnicki <jakub@xxxxxxxxxxxxxx>
> > ---
> > tools/include/uapi/linux/bpf.h | 3 ++-
> > tools/testing/selftests/bpf/progs/test_sk_lookup.c | 6 ++++++
> > 2 files changed, 8 insertions(+), 1 deletion(-)
> >
> > diff --git a/tools/include/uapi/linux/bpf.h
> > b/tools/include/uapi/linux/bpf.h
> > index a7f0ddedac1f..afe3d0d7f5f2 100644
> > --- a/tools/include/uapi/linux/bpf.h
> > +++ b/tools/include/uapi/linux/bpf.h
> > @@ -6453,7 +6453,8 @@ struct bpf_sk_lookup {
> > __u32 protocol; /* IP protocol (IPPROTO_TCP,
> > IPPROTO_UDP) */
> > __u32 remote_ip4; /* Network byte order */
> > __u32 remote_ip6[4]; /* Network byte order */
> > - __u32 remote_port; /* Network byte order */
> > + __be16 remote_port; /* Network byte order */
> > + __u16 :16; /* Zero padding */
> > __u32 local_ip4; /* Network byte order */
> > __u32 local_ip6[4]; /* Network byte order */
> > __u32 local_port; /* Host byte order */
> > diff --git a/tools/testing/selftests/bpf/progs/test_sk_lookup.c
> > b/tools/testing/selftests/bpf/progs/test_sk_lookup.c
> > index 83b0aaa52ef7..bf5b7caefdd0 100644
> > --- a/tools/testing/selftests/bpf/progs/test_sk_lookup.c
> > +++ b/tools/testing/selftests/bpf/progs/test_sk_lookup.c
> > @@ -392,6 +392,7 @@ int ctx_narrow_access(struct bpf_sk_lookup
> > *ctx)
> > {
> > struct bpf_sock *sk;
> > int err, family;
> > + __u32 val_u32;
> > bool v4;
> >
> > v4 = (ctx->family == AF_INET);
> > @@ -418,6 +419,11 @@ 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) */
> > + 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.
>
> [0]
> https://github.com/libbpf/libbpf/runs/5220996832?check_suite_focus=true
>
> > /* Narrow loads from local_port field. Expect DST_PORT. */
> > if (LSB(ctx->local_port, 0) != ((DST_PORT >> 0) & 0xff) ||
> > LSB(ctx->local_port, 1) != ((DST_PORT >> 8) & 0xff) ||
> > --
> > 2.31.1
> >
