The AF_XDP userspace part of xdp_hw_metadata see non-zero as a signal of
the availability of rx_timestamp and rx_hash in data_meta area. The
kernel-side BPF-prog code doesn't initialize these members when kernel
returns an error e.g. -EOPNOTSUPP. This memory area is not guaranteed to
be zeroed, and can contain garbage/previous values, which will be read
and interpreted by AF_XDP userspace side.
Tested this on different drivers. The experiences are that for most
packets they will have zeroed this data_meta area, but occasionally it
will contain garbage data.
Example of failure tested on ixgbe:
poll: 1 (0)
xsk_ring_cons__peek: 1
0x18ec788: rx_desc[0]->addr=100000000008000 addr=8100 comp_addr=8000
rx_hash: 3697961069
rx_timestamp: 9024981991734834796 (sec:9024981991.7348)
0x18ec788: complete idx=8 addr=8000
Converting to date:
date -d @9024981991
2255-12-28T20:26:31 CET
I choose a simple fix in this patch. When kfunc fails or isn't supported
assign zero to the corresponding struct meta value.
It's up to the individual BPF-programmer to do something smarter e.g.
that fits their use-case, like getting a software timestamp and marking
a flag that gives the type of timestamp.
Fixes: 297a3f1241 ("selftests/bpf: Simple program to dump XDP RX metadata")
Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Stanislav Fomichev <sdf@google.com>
Link: https://lore.kernel.org/bpf/167527271027.937063.5177725618616476592.stgit@firesoul
To be used for verification of driver implementations. Note that
the skb path is gone from the series, but I'm still keeping the
implementation for any possible future work.
$ xdp_hw_metadata <ifname>
On the other machine:
$ echo -n xdp | nc -u -q1 <target> 9091 # for AF_XDP
$ echo -n skb | nc -u -q1 <target> 9092 # for skb
Sample output:
# xdp
xsk_ring_cons__peek: 1
0x19f9090: rx_desc[0]->addr=100000000008000 addr=8100 comp_addr=8000
rx_timestamp_supported: 1
rx_timestamp: 1667850075063948829
0x19f9090: complete idx=8 addr=8000
# skb
found skb hwtstamp = 1668314052.854274681
Decoding:
# xdp
rx_timestamp=1667850075.063948829
$ date -d @1667850075
Mon Nov 7 11:41:15 AM PST 2022
$ date
Mon Nov 7 11:42:05 AM PST 2022
# skb
$ date -d @1668314052
Sat Nov 12 08:34:12 PM PST 2022
$ date
Sat Nov 12 08:37:06 PM PST 2022
Cc: John Fastabend <john.fastabend@gmail.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Martin KaFai Lau <martin.lau@linux.dev>
Cc: Jakub Kicinski <kuba@kernel.org>
Cc: Willem de Bruijn <willemb@google.com>
Cc: Jesper Dangaard Brouer <brouer@redhat.com>
Cc: Anatoly Burakov <anatoly.burakov@intel.com>
Cc: Alexander Lobakin <alexandr.lobakin@intel.com>
Cc: Magnus Karlsson <magnus.karlsson@gmail.com>
Cc: Maryam Tahhan <mtahhan@redhat.com>
Cc: xdp-hints@xdp-project.net
Cc: netdev@vger.kernel.org
Signed-off-by: Stanislav Fomichev <sdf@google.com>
Link: https://lore.kernel.org/r/20230119221536.3349901-18-sdf@google.com
Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>
