veth: Adjust hard_start offset on redirect XDP frames
[ Upstream commit5c8572251f
] When native XDP redirect into a veth device, the frame arrives in the xdp_frame structure. It is then processed in veth_xdp_rcv_one(), which can run a new XDP bpf_prog on the packet. Doing so requires converting xdp_frame to xdp_buff, but the tricky part is that xdp_frame memory area is located in the top (data_hard_start) memory area that xdp_buff will point into. The current code tried to protect the xdp_frame area, by assigning xdp_buff.data_hard_start past this memory. This results in 32 bytes less headroom to expand into via BPF-helper bpf_xdp_adjust_head(). This protect step is actually not needed, because BPF-helper bpf_xdp_adjust_head() already reserve this area, and don't allow BPF-prog to expand into it. Thus, it is safe to point data_hard_start directly at xdp_frame memory area. Fixes:9fc8d518d9
("veth: Handle xdp_frames in xdp napi ring") Reported-by: Mao Wenan <maowenan@huawei.com> Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com> Signed-off-by: Alexei Starovoitov <ast@kernel.org> Acked-by: Toshiaki Makita <toshiaki.makita1@gmail.com> Acked-by: Toke Høiland-Jørgensen <toke@redhat.com> Link: https://lore.kernel.org/bpf/158945338331.97035.5923525383710752178.stgit@firesoul Signed-off-by: Sasha Levin <sashal@kernel.org>
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@ -510,13 +510,15 @@ static struct sk_buff *veth_xdp_rcv_one(struct veth_rq *rq,
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struct veth_xdp_tx_bq *bq)
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{
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void *hard_start = frame->data - frame->headroom;
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void *head = hard_start - sizeof(struct xdp_frame);
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int len = frame->len, delta = 0;
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struct xdp_frame orig_frame;
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struct bpf_prog *xdp_prog;
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unsigned int headroom;
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struct sk_buff *skb;
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/* bpf_xdp_adjust_head() assures BPF cannot access xdp_frame area */
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hard_start -= sizeof(struct xdp_frame);
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rcu_read_lock();
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xdp_prog = rcu_dereference(rq->xdp_prog);
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if (likely(xdp_prog)) {
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@ -538,7 +540,6 @@ static struct sk_buff *veth_xdp_rcv_one(struct veth_rq *rq,
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break;
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case XDP_TX:
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orig_frame = *frame;
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xdp.data_hard_start = head;
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xdp.rxq->mem = frame->mem;
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if (unlikely(veth_xdp_tx(rq->dev, &xdp, bq) < 0)) {
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trace_xdp_exception(rq->dev, xdp_prog, act);
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@ -550,7 +551,6 @@ static struct sk_buff *veth_xdp_rcv_one(struct veth_rq *rq,
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goto xdp_xmit;
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case XDP_REDIRECT:
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orig_frame = *frame;
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xdp.data_hard_start = head;
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xdp.rxq->mem = frame->mem;
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if (xdp_do_redirect(rq->dev, &xdp, xdp_prog)) {
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frame = &orig_frame;
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@ -572,7 +572,7 @@ static struct sk_buff *veth_xdp_rcv_one(struct veth_rq *rq,
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rcu_read_unlock();
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headroom = sizeof(struct xdp_frame) + frame->headroom - delta;
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skb = veth_build_skb(head, headroom, len, 0);
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skb = veth_build_skb(hard_start, headroom, len, 0);
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if (!skb) {
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xdp_return_frame(frame);
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goto err;
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