From 3fd9dcd689a5582e682fde57b3139066d032367a Mon Sep 17 00:00:00 2001 From: Jesper Dangaard Brouer Date: Wed, 1 Feb 2023 18:31:50 +0100 Subject: [PATCH] selftests/bpf: xdp_hw_metadata clear metadata when -EOPNOTSUPP 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: 297a3f124155 ("selftests/bpf: Simple program to dump XDP RX metadata") Signed-off-by: Jesper Dangaard Brouer Signed-off-by: Daniel Borkmann Acked-by: Stanislav Fomichev Link: https://lore.kernel.org/bpf/167527271027.937063.5177725618616476592.stgit@firesoul --- tools/testing/selftests/bpf/progs/xdp_hw_metadata.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) diff --git a/tools/testing/selftests/bpf/progs/xdp_hw_metadata.c b/tools/testing/selftests/bpf/progs/xdp_hw_metadata.c index 25b8178..4c55b4d 100644 --- a/tools/testing/selftests/bpf/progs/xdp_hw_metadata.c +++ b/tools/testing/selftests/bpf/progs/xdp_hw_metadata.c @@ -70,10 +70,14 @@ int rx(struct xdp_md *ctx) } if (!bpf_xdp_metadata_rx_timestamp(ctx, &meta->rx_timestamp)) - bpf_printk("populated rx_timestamp with %u", meta->rx_timestamp); + bpf_printk("populated rx_timestamp with %llu", meta->rx_timestamp); + else + meta->rx_timestamp = 0; /* Used by AF_XDP as not avail signal */ if (!bpf_xdp_metadata_rx_hash(ctx, &meta->rx_hash)) bpf_printk("populated rx_hash with %u", meta->rx_hash); + else + meta->rx_hash = 0; /* Used by AF_XDP as not avail signal */ return bpf_redirect_map(&xsk, ctx->rx_queue_index, XDP_PASS); } -- 2.7.4