Commit 5c857225 authored by Jesper Dangaard Brouer's avatar Jesper Dangaard Brouer Committed by Alexei Starovoitov

veth: Adjust hard_start offset on redirect XDP frames

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: 9fc8d518 ("veth: Handle xdp_frames in xdp napi ring")
Reported-by: default avatarMao Wenan <maowenan@huawei.com>
Signed-off-by: default avatarJesper Dangaard Brouer <brouer@redhat.com>
Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
Acked-by: default avatarToshiaki Makita <toshiaki.makita1@gmail.com>
Acked-by: default avatarToke Høiland-Jørgensen <toke@redhat.com>
Link: https://lore.kernel.org/bpf/158945338331.97035.5923525383710752178.stgit@firesoul
parent db612f74
...@@ -564,13 +564,15 @@ static struct sk_buff *veth_xdp_rcv_one(struct veth_rq *rq, ...@@ -564,13 +564,15 @@ static struct sk_buff *veth_xdp_rcv_one(struct veth_rq *rq,
struct veth_stats *stats) struct veth_stats *stats)
{ {
void *hard_start = frame->data - frame->headroom; void *hard_start = frame->data - frame->headroom;
void *head = hard_start - sizeof(struct xdp_frame);
int len = frame->len, delta = 0; int len = frame->len, delta = 0;
struct xdp_frame orig_frame; struct xdp_frame orig_frame;
struct bpf_prog *xdp_prog; struct bpf_prog *xdp_prog;
unsigned int headroom; unsigned int headroom;
struct sk_buff *skb; struct sk_buff *skb;
/* bpf_xdp_adjust_head() assures BPF cannot access xdp_frame area */
hard_start -= sizeof(struct xdp_frame);
rcu_read_lock(); rcu_read_lock();
xdp_prog = rcu_dereference(rq->xdp_prog); xdp_prog = rcu_dereference(rq->xdp_prog);
if (likely(xdp_prog)) { if (likely(xdp_prog)) {
...@@ -592,7 +594,6 @@ static struct sk_buff *veth_xdp_rcv_one(struct veth_rq *rq, ...@@ -592,7 +594,6 @@ static struct sk_buff *veth_xdp_rcv_one(struct veth_rq *rq,
break; break;
case XDP_TX: case XDP_TX:
orig_frame = *frame; orig_frame = *frame;
xdp.data_hard_start = head;
xdp.rxq->mem = frame->mem; xdp.rxq->mem = frame->mem;
if (unlikely(veth_xdp_tx(rq, &xdp, bq) < 0)) { if (unlikely(veth_xdp_tx(rq, &xdp, bq) < 0)) {
trace_xdp_exception(rq->dev, xdp_prog, act); trace_xdp_exception(rq->dev, xdp_prog, act);
...@@ -605,7 +606,6 @@ static struct sk_buff *veth_xdp_rcv_one(struct veth_rq *rq, ...@@ -605,7 +606,6 @@ static struct sk_buff *veth_xdp_rcv_one(struct veth_rq *rq,
goto xdp_xmit; goto xdp_xmit;
case XDP_REDIRECT: case XDP_REDIRECT:
orig_frame = *frame; orig_frame = *frame;
xdp.data_hard_start = head;
xdp.rxq->mem = frame->mem; xdp.rxq->mem = frame->mem;
if (xdp_do_redirect(rq->dev, &xdp, xdp_prog)) { if (xdp_do_redirect(rq->dev, &xdp, xdp_prog)) {
frame = &orig_frame; frame = &orig_frame;
...@@ -629,7 +629,7 @@ static struct sk_buff *veth_xdp_rcv_one(struct veth_rq *rq, ...@@ -629,7 +629,7 @@ static struct sk_buff *veth_xdp_rcv_one(struct veth_rq *rq,
rcu_read_unlock(); rcu_read_unlock();
headroom = sizeof(struct xdp_frame) + frame->headroom - delta; headroom = sizeof(struct xdp_frame) + frame->headroom - delta;
skb = veth_build_skb(head, headroom, len, 0); skb = veth_build_skb(hard_start, headroom, len, 0);
if (!skb) { if (!skb) {
xdp_return_frame(frame); xdp_return_frame(frame);
stats->rx_drops++; stats->rx_drops++;
......
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