Re: [PATCH bpf-next v4 02/10] bpf: xfrm: Add bpf_xdp_get_xfrm_state() kfunc

[Eyal Birger]

On Mon, Dec 4, 2023 at 12:57 PM Daniel Xu <dxu@xxxxxxxxx> wrote:
>
> This commit adds an unstable kfunc helper to access internal xfrm_state
> associated with an SA. This is intended to be used for the upcoming
> IPsec pcpu work to assign special pcpu SAs to a particular CPU. In other
> words: for custom software RSS.
>
> That being said, the function that this kfunc wraps is fairly generic
> and used for a lot of xfrm tasks. I'm sure people will find uses
> elsewhere over time.
>
> Co-developed-by: Antony Antony <antony.antony@xxxxxxxxxxx>
> Signed-off-by: Antony Antony <antony.antony@xxxxxxxxxxx>
> Signed-off-by: Daniel Xu <dxu@xxxxxxxxx>
> ---
>  include/net/xfrm.h     |   9 ++++
>  net/xfrm/xfrm_bpf.c    | 102 +++++++++++++++++++++++++++++++++++++++++
>  net/xfrm/xfrm_policy.c |   2 +
>  3 files changed, 113 insertions(+)
>
> diff --git a/include/net/xfrm.h b/include/net/xfrm.h
> index c9bb0f892f55..1d107241b901 100644
> --- a/include/net/xfrm.h
> +++ b/include/net/xfrm.h
> @@ -2190,4 +2190,13 @@ static inline int register_xfrm_interface_bpf(void)
>
>  #endif
>
> +#if IS_ENABLED(CONFIG_DEBUG_INFO_BTF)
> +int register_xfrm_state_bpf(void);
> +#else
> +static inline int register_xfrm_state_bpf(void)
> +{
> +       return 0;
> +}
> +#endif
> +
>  #endif /* _NET_XFRM_H */
> diff --git a/net/xfrm/xfrm_bpf.c b/net/xfrm/xfrm_bpf.c
> index 3d3018b87f96..3d6cac7345ca 100644
> --- a/net/xfrm/xfrm_bpf.c
> +++ b/net/xfrm/xfrm_bpf.c
> @@ -6,9 +6,11 @@
>   */
>
>  #include <linux/bpf.h>
> +#include <linux/btf.h>
>  #include <linux/btf_ids.h>
>
>  #include <net/dst_metadata.h>
> +#include <net/xdp.h>
>  #include <net/xfrm.h>
>
>  #if IS_BUILTIN(CONFIG_XFRM_INTERFACE) || \
> @@ -112,3 +114,103 @@ int __init register_xfrm_interface_bpf(void)
>  }
>
>  #endif /* xfrm interface */
> +
> +/* bpf_xfrm_state_opts - Options for XFRM state lookup helpers
> + *
> + * Members:
> + * @error      - Out parameter, set for any errors encountered
> + *              Values:
> + *                -EINVAL - netns_id is less than -1
> + *                -EINVAL - opts__sz isn't BPF_XFRM_STATE_OPTS_SZ
> + *                -ENONET - No network namespace found for netns_id
> + * @netns_id   - Specify the network namespace for lookup
> + *              Values:
> + *                BPF_F_CURRENT_NETNS (-1)
> + *                  Use namespace associated with ctx
> + *                [0, S32_MAX]
> + *                  Network Namespace ID
> + * @mark       - XFRM mark to match on
> + * @daddr      - Destination address to match on
> + * @spi                - Security parameter index to match on
> + * @proto      - L3 protocol to match on
> + * @family     - L3 protocol family to match on
> + */
> +struct bpf_xfrm_state_opts {
> +       s32 error;
> +       s32 netns_id;
> +       u32 mark;
> +       xfrm_address_t daddr;
> +       __be32 spi;
> +       u8 proto;
> +       u16 family;
> +};
> +
> +enum {
> +       BPF_XFRM_STATE_OPTS_SZ = sizeof(struct bpf_xfrm_state_opts),
> +};
> +
> +__bpf_kfunc_start_defs();
> +
> +/* bpf_xdp_get_xfrm_state - Get XFRM state
> + *
> + * Parameters:
> + * @ctx        - Pointer to ctx (xdp_md) in XDP program
> + *                 Cannot be NULL
> + * @opts       - Options for lookup (documented above)
> + *                 Cannot be NULL
> + * @opts__sz   - Length of the bpf_xfrm_state_opts structure
> + *                 Must be BPF_XFRM_STATE_OPTS_SZ
> + */
> +__bpf_kfunc struct xfrm_state *
> +bpf_xdp_get_xfrm_state(struct xdp_md *ctx, struct bpf_xfrm_state_opts *opts, u32 opts__sz)
> +{
> +       struct xdp_buff *xdp = (struct xdp_buff *)ctx;
> +       struct net *net = dev_net(xdp->rxq->dev);
> +       struct xfrm_state *x;
> +
> +       if (!opts || opts__sz < sizeof(opts->error))
> +               return NULL;
> +
> +       if (opts__sz != BPF_XFRM_STATE_OPTS_SZ) {
> +               opts->error = -EINVAL;
> +               return NULL;
> +       }
> +
> +       if (unlikely(opts->netns_id < BPF_F_CURRENT_NETNS)) {
> +               opts->error = -EINVAL;
> +               return NULL;
> +       }
> +
> +       if (opts->netns_id >= 0) {
> +               net = get_net_ns_by_id(net, opts->netns_id);
> +               if (unlikely(!net)) {
> +                       opts->error = -ENONET;
> +                       return NULL;
> +               }
> +       }
> +
> +       x = xfrm_state_lookup(net, opts->mark, &opts->daddr, opts->spi,
> +                             opts->proto, opts->family);
> +
> +       if (opts->netns_id >= 0)
> +               put_net(net);

Maybe opts->error should be set to something like -ENOENT if x == NULL?

> +
> +       return x;
> +}
> +
> +__bpf_kfunc_end_defs();
> +
> +BTF_SET8_START(xfrm_state_kfunc_set)
> +BTF_ID_FLAGS(func, bpf_xdp_get_xfrm_state, KF_RET_NULL | KF_ACQUIRE)
> +BTF_SET8_END(xfrm_state_kfunc_set)
> +
> +static const struct btf_kfunc_id_set xfrm_state_xdp_kfunc_set = {
> +       .owner = THIS_MODULE,
> +       .set   = &xfrm_state_kfunc_set,
> +};
> +
> +int __init register_xfrm_state_bpf(void)
> +{
> +       return register_btf_kfunc_id_set(BPF_PROG_TYPE_XDP,
> +                                        &xfrm_state_xdp_kfunc_set);
> +}
> diff --git a/net/xfrm/xfrm_policy.c b/net/xfrm/xfrm_policy.c
> index c13dc3ef7910..1b7e75159727 100644
> --- a/net/xfrm/xfrm_policy.c
> +++ b/net/xfrm/xfrm_policy.c
> @@ -4218,6 +4218,8 @@ void __init xfrm_init(void)
>  #ifdef CONFIG_XFRM_ESPINTCP
>         espintcp_init();
>  #endif
> +
> +       register_xfrm_state_bpf();
>  }
>
>  #ifdef CONFIG_AUDITSYSCALL
> --
> 2.42.1
>
>