netdev - Re: [PATCH bpf-next v1 1/3] bpf/xdp: Add bpf_load_hdr

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Date:   Fri, 1 Oct 2021 15:47:55 -0700
From:   Song Liu <song@...nel.org>
To:     Joanne Koong <joannekoong@...com>
Cc:     bpf <bpf@...r.kernel.org>, Martin KaFai Lau <kafai@...com>,
        Networking <netdev@...r.kernel.org>,
        Kernel Team <Kernel-team@...com>
Subject: Re: [PATCH bpf-next v1 1/3] bpf/xdp: Add bpf_load_hdr_opt support for xdp

On Fri, Oct 1, 2021 at 3:04 PM Joanne Koong <joannekoong@...com> wrote:
>
> This patch enables XDP programs to use the bpf_load_hdr_opt helper
> function to load header options.
>
> The upper 16 bits of "flags" is used to denote the offset to the tcp
> header. No other flags are, at this time, used by XDP programs.
> In the future, more flags can be included to support other types of
> header options.
>
> Much of the logic for loading header options can be shared between
> sockops and xdp programs. In net/core/filter.c, this common shared
> logic is refactored into a separate function both sockops and xdp
> use.
>
> Signed-off-by: Joanne Koong <joannekoong@...com>

Looks good over all.

Acked-by: Song Liu <songliubraving@...com>

Just a nitpick below.

> ---
>  include/uapi/linux/bpf.h       | 26 ++++++----
>  net/core/filter.c              | 88 ++++++++++++++++++++++++++--------
>  tools/include/uapi/linux/bpf.h | 26 ++++++----
>  3 files changed, 103 insertions(+), 37 deletions(-)
>

[...]

> +
> +BPF_CALL_4(bpf_xdp_load_hdr_opt, struct xdp_buff *, xdp,
> +          void *, search_res, u32, len, u64, flags)
> +{
> +       const void *op, *opend;
> +       struct tcphdr *th;
> +
> +       /* The upper 16 bits of flags contain the offset to the tcp header.
> +        * No other bits should be set.
> +        */
> +       if (flags & 0xffffffffffff)

Maybe use (1ULL << BPF_LOAD_HDR_OPT_TCP_OFFSET_SHIFT) - 1

> +               return -EINVAL;
> +
> +       th = xdp->data + (flags >> BPF_LOAD_HDR_OPT_TCP_OFFSET_SHIFT);
> +       op = (void *)th + sizeof(struct tcphdr);
> +       if (unlikely(op > xdp->data_end))
> +               return -EINVAL;

[...]