When the XDP metadata area was used, it is expected that the same metadata can also be accessed from TC, as can be read in the description of the bpf_xdp_adjust_meta helper function. In the tun driver, this was not yet implemented.
To make this work, the skb that is being built on XDP_PASS should know of the current size of the metadata area. This is ensured by adding calls to skb_metadata_set. For the tun_xdp_one code path, an additional check is necessary to handle the case where the externally initialized xdp_buff has no metadata support (xdp->data_meta == xdp->data + 1).
More information about this feature can be found in the commit message of commit de8f3a83b0a0 ("bpf: add meta pointer for direct access").
Signed-off-by: Marcus Wichelmann marcus.wichelmann@hetzner-cloud.de Reviewed-by: Willem de Bruijn willemb@google.com Acked-by: Jason Wang jasowang@redhat.com --- drivers/net/tun.c | 25 ++++++++++++++++++++++--- 1 file changed, 22 insertions(+), 3 deletions(-)
diff --git a/drivers/net/tun.c b/drivers/net/tun.c index 4ec8fbd93c8d..70208b3a2e93 100644 --- a/drivers/net/tun.c +++ b/drivers/net/tun.c @@ -1600,7 +1600,8 @@ static bool tun_can_build_skb(struct tun_struct *tun, struct tun_file *tfile,
static struct sk_buff *__tun_build_skb(struct tun_file *tfile, struct page_frag *alloc_frag, char *buf, - int buflen, int len, int pad) + int buflen, int len, int pad, + int metasize) { struct sk_buff *skb = build_skb(buf, buflen);
@@ -1609,6 +1610,8 @@ static struct sk_buff *__tun_build_skb(struct tun_file *tfile,
skb_reserve(skb, pad); skb_put(skb, len); + if (metasize) + skb_metadata_set(skb, metasize); skb_set_owner_w(skb, tfile->socket.sk);
get_page(alloc_frag->page); @@ -1668,6 +1671,7 @@ static struct sk_buff *tun_build_skb(struct tun_struct *tun, char *buf; size_t copied; int pad = TUN_RX_PAD; + int metasize = 0; int err = 0;
rcu_read_lock(); @@ -1695,7 +1699,7 @@ static struct sk_buff *tun_build_skb(struct tun_struct *tun, if (hdr->gso_type || !xdp_prog) { *skb_xdp = 1; return __tun_build_skb(tfile, alloc_frag, buf, buflen, len, - pad); + pad, metasize); }
*skb_xdp = 0; @@ -1730,12 +1734,18 @@ static struct sk_buff *tun_build_skb(struct tun_struct *tun,
pad = xdp.data - xdp.data_hard_start; len = xdp.data_end - xdp.data; + + /* It is known that the xdp_buff was prepared with metadata + * support, so the metasize will never be negative. + */ + metasize = xdp.data - xdp.data_meta; } bpf_net_ctx_clear(bpf_net_ctx); rcu_read_unlock(); local_bh_enable();
- return __tun_build_skb(tfile, alloc_frag, buf, buflen, len, pad); + return __tun_build_skb(tfile, alloc_frag, buf, buflen, len, pad, + metasize);
out: bpf_net_ctx_clear(bpf_net_ctx); @@ -2452,6 +2462,7 @@ static int tun_xdp_one(struct tun_struct *tun, struct sk_buff_head *queue; u32 rxhash = 0, act; int buflen = hdr->buflen; + int metasize = 0; int ret = 0; bool skb_xdp = false; struct page *page; @@ -2506,6 +2517,14 @@ static int tun_xdp_one(struct tun_struct *tun, skb_reserve(skb, xdp->data - xdp->data_hard_start); skb_put(skb, xdp->data_end - xdp->data);
+ /* The externally provided xdp_buff may have no metadata support, which + * is marked by xdp->data_meta being xdp->data + 1. This will lead to a + * metasize of -1 and is the reason why the condition checks for > 0. + */ + metasize = xdp->data - xdp->data_meta; + if (metasize > 0) + skb_metadata_set(skb, metasize); + if (virtio_net_hdr_to_skb(skb, gso, tun_is_little_endian(tun))) { atomic_long_inc(&tun->rx_frame_errors); kfree_skb(skb);