On 04/09/2019 04:06 PM, Alan Maguire wrote:
> commit 868d523535c2 ("bpf: add bpf_skb_adjust_room encap flags")
> introduced support to bpf_skb_adjust_room for GSO-friendly GRE
> and UDP encapsulation.
>
> For GSO to work for skbs, the inner headers (mac and network) need to
> be marked. For L3 encapsulation using bpf_skb_adjust_room, the mac
> and network headers are identical. Here we provide a way of specifying
> the inner mac header length for cases where L2 encap is desired. Such
> an approach can support encapsulated ethernet headers, MPLS headers etc.
> For example to convert from a packet of form [eth][ip][tcp] to
> [eth][ip][udp][inner mac][ip][tcp], something like the following could
> be done:
>
> headroom = sizeof(iph) + sizeof(struct udphdr) + inner_maclen;
>
> ret = bpf_skb_adjust_room(skb, headroom, BPF_ADJ_ROOM_MAC,
> BPF_F_ADJ_ROOM_ENCAP_L4_UDP |
> BPF_F_ADJ_ROOM_ENCAP_L3_IPV4 |
> BPF_F_ADJ_ROOM_ENCAP_L2(inner_maclen));
>
> Signed-off-by: Alan Maguire <alan.maguire@xxxxxxxxxx>
> ---
> include/uapi/linux/bpf.h | 10 ++++++++++
> net/core/filter.c | 12 ++++++++----
> 2 files changed, 18 insertions(+), 4 deletions(-)
>
> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> index 8370245..912391c 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -1500,6 +1500,10 @@ struct bpf_stack_build_id {
> * * **BPF_F_ADJ_ROOM_ENCAP_L4_UDP **:
> * Use with ENCAP_L3 flags to further specify the tunnel type.
> *
> + * * **BPF_F_ADJ_ROOM_ENCAP_L2(len) **:
> + * Use with ENCAP_L3/L4 flags to further specify the tunnel
> + * type; **len** is the length of the inner MAC header.
> + *
> * A call to this helper is susceptible to change the underlaying
> * packet buffer. Therefore, at load time, all checks on pointers
> * previously done by the verifier are invalidated and must be
> @@ -2641,10 +2645,16 @@ enum bpf_func_id {
> /* BPF_FUNC_skb_adjust_room flags. */
> #define BPF_F_ADJ_ROOM_FIXED_GSO (1ULL << 0)
>
> +#define BPF_ADJ_ROOM_ENCAP_L2_MASK 0xff
> +#define BPF_ADJ_ROOM_ENCAP_L2_SHIFT 56
Would appreciate a small whitespace cleanup in that tab after the define
is replaced with a normal space like in the rest of the file.
> #define BPF_F_ADJ_ROOM_ENCAP_L3_IPV4 (1ULL << 1)
> #define BPF_F_ADJ_ROOM_ENCAP_L3_IPV6 (1ULL << 2)
> #define BPF_F_ADJ_ROOM_ENCAP_L4_GRE (1ULL << 3)
> #define BPF_F_ADJ_ROOM_ENCAP_L4_UDP (1ULL << 4)
> +#define BPF_F_ADJ_ROOM_ENCAP_L2(len) (((__u64)len & \
> + BPF_ADJ_ROOM_ENCAP_L2_MASK) \
> + << BPF_ADJ_ROOM_ENCAP_L2_SHIFT)
Ditto here.
> /* Mode for BPF_FUNC_skb_adjust_room helper. */
> enum bpf_adj_room_mode {
> diff --git a/net/core/filter.c b/net/core/filter.c
> index 22eb2ed..a1654ef62 100644
> --- a/net/core/filter.c
> +++ b/net/core/filter.c
> @@ -2969,11 +2969,14 @@ static u32 bpf_skb_net_base_len(const struct sk_buff *skb)
> #define BPF_F_ADJ_ROOM_MASK (BPF_F_ADJ_ROOM_FIXED_GSO | \
> BPF_F_ADJ_ROOM_ENCAP_L3_MASK | \
> BPF_F_ADJ_ROOM_ENCAP_L4_GRE | \
> - BPF_F_ADJ_ROOM_ENCAP_L4_UDP)
> + BPF_F_ADJ_ROOM_ENCAP_L4_UDP | \
> + BPF_F_ADJ_ROOM_ENCAP_L2( \
> + BPF_ADJ_ROOM_ENCAP_L2_MASK))
>
> static int bpf_skb_net_grow(struct sk_buff *skb, u32 off, u32 len_diff,
> u64 flags)
> {
One thing that it seems missing in this but also in Willem's earlier set
is that we reject these flags in bpf_skb_net_shrink(). Both are called from
bpf_skb_adjust_room(), so if we don't support decap yet we should reject
such flags so we can extend in future. Could you or Willem send a follow-up?
Thanks!
> + u8 inner_mac_len = flags >> BPF_ADJ_ROOM_ENCAP_L2_SHIFT;
> bool encap = flags & BPF_F_ADJ_ROOM_ENCAP_L3_MASK;
> u16 mac_len = 0, inner_net = 0, inner_trans = 0;
> unsigned int gso_type = SKB_GSO_DODGY;
> @@ -3008,6 +3011,8 @@ static int bpf_skb_net_grow(struct sk_buff *skb, u32 off, u32 len_diff,
>
> mac_len = skb->network_header - skb->mac_header;
> inner_net = skb->network_header;
> + if (inner_mac_len > len_diff)
> + return -EINVAL;
> inner_trans = skb->transport_header;
> }
>
> @@ -3016,8 +3021,7 @@ static int bpf_skb_net_grow(struct sk_buff *skb, u32 off, u32 len_diff,
> return ret;
>
> if (encap) {
> - /* inner mac == inner_net on l3 encap */
> - skb->inner_mac_header = inner_net;
> + skb->inner_mac_header = inner_net - inner_mac_len;
> skb->inner_network_header = inner_net;
> skb->inner_transport_header = inner_trans;
> skb_set_inner_protocol(skb, skb->protocol);
> @@ -3031,7 +3035,7 @@ static int bpf_skb_net_grow(struct sk_buff *skb, u32 off, u32 len_diff,
> gso_type |= SKB_GSO_GRE;
> else if (flags & BPF_F_ADJ_ROOM_ENCAP_L3_IPV6)
> gso_type |= SKB_GSO_IPXIP6;
> - else
> + else if (flags & BPF_F_ADJ_ROOM_ENCAP_L3_IPV4)
> gso_type |= SKB_GSO_IPXIP4;
>
> if (flags & BPF_F_ADJ_ROOM_ENCAP_L4_GRE ||
>
