Re: [RFC PATCH 1/5] bpf: add PHYS_DEV prog type for early driver filter

[Tom Herbert <tom@herbertland.com>]

On Fri, Apr 1, 2016 at 9:21 PM, Brenden Blanco <bblanco@plumgrid.com> wrote:
> Add a new bpf prog type that is intended to run in early stages of the
> packet rx path. Only minimal packet metadata will be available, hence a new
> context type, struct xdp_metadata, is exposed to userspace. So far only
> expose the readable packet length, and only in read mode.
>
This would eventually be a generic abstraction of receive descriptors?

> The PHYS_DEV name is chosen to represent that the program is meant only
> for physical adapters, rather than all netdevs.
>
Is there a hard restriction that this could only work with physical devices?

> While the user visible struct is new, the underlying context must be
> implemented as a minimal skb in order for the packet load_* instructions
> to work. The skb filled in by the driver must have skb->len, skb->head,
> and skb->data set, and skb->data_len == 0.
>
> Signed-off-by: Brenden Blanco <bblanco@plumgrid.com>
> ---
>  include/uapi/linux/bpf.h |  5 ++++
>  kernel/bpf/verifier.c    |  1 +
>  net/core/filter.c        | 68 ++++++++++++++++++++++++++++++++++++++++++++++++
>  3 files changed, 74 insertions(+)
>
> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> index 924f537..b8a4ef2 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -92,6 +92,7 @@ enum bpf_prog_type {
>         BPF_PROG_TYPE_KPROBE,
>         BPF_PROG_TYPE_SCHED_CLS,
>         BPF_PROG_TYPE_SCHED_ACT,
> +       BPF_PROG_TYPE_PHYS_DEV,
>  };
>
>  #define BPF_PSEUDO_MAP_FD      1
> @@ -367,6 +368,10 @@ struct __sk_buff {
>         __u32 tc_classid;
>  };
>
> +struct xdp_metadata {
> +       __u32 len;
> +};
> +
>  struct bpf_tunnel_key {
>         __u32 tunnel_id;
>         union {
> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> index 2e08f8e..804ca70 100644
> --- a/kernel/bpf/verifier.c
> +++ b/kernel/bpf/verifier.c
> @@ -1340,6 +1340,7 @@ static bool may_access_skb(enum bpf_prog_type type)
>         case BPF_PROG_TYPE_SOCKET_FILTER:
>         case BPF_PROG_TYPE_SCHED_CLS:
>         case BPF_PROG_TYPE_SCHED_ACT:
> +       case BPF_PROG_TYPE_PHYS_DEV:
>                 return true;
>         default:
>                 return false;
> diff --git a/net/core/filter.c b/net/core/filter.c
> index b7177d0..c417db6 100644
> --- a/net/core/filter.c
> +++ b/net/core/filter.c
> @@ -2018,6 +2018,12 @@ tc_cls_act_func_proto(enum bpf_func_id func_id)
>         }
>  }
>
> +static const struct bpf_func_proto *
> +phys_dev_func_proto(enum bpf_func_id func_id)
> +{
> +       return sk_filter_func_proto(func_id);
> +}
> +
>  static bool __is_valid_access(int off, int size, enum bpf_access_type type)
>  {
>         /* check bounds */
> @@ -2073,6 +2079,36 @@ static bool tc_cls_act_is_valid_access(int off, int size,
>         return __is_valid_access(off, size, type);
>  }
>
> +static bool __is_valid_xdp_access(int off, int size,
> +                                 enum bpf_access_type type)
> +{
> +       if (off < 0 || off >= sizeof(struct xdp_metadata))
> +               return false;
> +
> +       if (off % size != 0)
> +               return false;
> +
> +       if (size != 4)
> +               return false;
> +
> +       return true;
> +}
> +
> +static bool phys_dev_is_valid_access(int off, int size,
> +                                    enum bpf_access_type type)
> +{
> +       if (type == BPF_WRITE)
> +               return false;
> +
> +       switch (off) {
> +       case offsetof(struct xdp_metadata, len):
> +               break;
> +       default:
> +               return false;
> +       }
> +       return __is_valid_xdp_access(off, size, type);
> +}
> +
>  static u32 bpf_net_convert_ctx_access(enum bpf_access_type type, int dst_reg,
>                                       int src_reg, int ctx_off,
>                                       struct bpf_insn *insn_buf,
> @@ -2210,6 +2246,26 @@ static u32 bpf_net_convert_ctx_access(enum bpf_access_type type, int dst_reg,
>         return insn - insn_buf;
>  }
>
> +static u32 bpf_phys_dev_convert_ctx_access(enum bpf_access_type type,
> +                                          int dst_reg, int src_reg,
> +                                          int ctx_off,
> +                                          struct bpf_insn *insn_buf,
> +                                          struct bpf_prog *prog)
> +{
> +       struct bpf_insn *insn = insn_buf;
> +
> +       switch (ctx_off) {
> +       case offsetof(struct xdp_metadata, len):
> +               BUILD_BUG_ON(FIELD_SIZEOF(struct sk_buff, len) != 4);
> +
> +               *insn++ = BPF_LDX_MEM(BPF_W, dst_reg, src_reg,
> +                                     offsetof(struct sk_buff, len));
> +               break;
> +       }
> +
> +       return insn - insn_buf;
> +}
> +
>  static const struct bpf_verifier_ops sk_filter_ops = {
>         .get_func_proto = sk_filter_func_proto,
>         .is_valid_access = sk_filter_is_valid_access,
> @@ -2222,6 +2278,12 @@ static const struct bpf_verifier_ops tc_cls_act_ops = {
>         .convert_ctx_access = bpf_net_convert_ctx_access,
>  };
>
> +static const struct bpf_verifier_ops phys_dev_ops = {
> +       .get_func_proto = phys_dev_func_proto,
> +       .is_valid_access = phys_dev_is_valid_access,
> +       .convert_ctx_access = bpf_phys_dev_convert_ctx_access,
> +};
> +
>  static struct bpf_prog_type_list sk_filter_type __read_mostly = {
>         .ops = &sk_filter_ops,
>         .type = BPF_PROG_TYPE_SOCKET_FILTER,
> @@ -2237,11 +2299,17 @@ static struct bpf_prog_type_list sched_act_type __read_mostly = {
>         .type = BPF_PROG_TYPE_SCHED_ACT,
>  };
>
> +static struct bpf_prog_type_list phys_dev_type __read_mostly = {
> +       .ops = &phys_dev_ops,
> +       .type = BPF_PROG_TYPE_PHYS_DEV,
> +};
> +
>  static int __init register_sk_filter_ops(void)
>  {
>         bpf_register_prog_type(&sk_filter_type);
>         bpf_register_prog_type(&sched_cls_type);
>         bpf_register_prog_type(&sched_act_type);
> +       bpf_register_prog_type(&phys_dev_type);
>
>         return 0;
>  }
> --
> 2.8.0
>