linux-kernel - Re: [PATCH bpf-next v2 1/7] bpf: Refactor trampoline update code

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Message-ID: <CAEf4BzZ58iymCdqqCe=p-7BSF_kt+Dd19taEjTJBEt_ZBZz0=Q@mail.gmail.com>
Date:   Tue, 3 Mar 2020 20:49:02 -0800
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     KP Singh <kpsingh@...omium.org>
Cc:     linux-security-module@...r.kernel.org,
        open list <linux-kernel@...r.kernel.org>,
        bpf <bpf@...r.kernel.org>, Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Paul Turner <pjt@...gle.com>, Jann Horn <jannh@...gle.com>,
        Florent Revest <revest@...omium.org>,
        Brendan Jackman <jackmanb@...omium.org>
Subject: Re: [PATCH bpf-next v2 1/7] bpf: Refactor trampoline update code

On Tue, Mar 3, 2020 at 5:56 PM KP Singh <kpsingh@...omium.org> wrote:
>
> From: KP Singh <kpsingh@...gle.com>
>
> As we need to introduce a third type of attachment for trampolines, the
> flattened signature of arch_prepare_bpf_trampoline gets even more
> complicated.
>
> Refactor the prog and count argument to arch_prepare_bpf_trampoline to
> use bpf_tramp_progs to simplify the addition and accounting for new
> attachment types.
>
> Signed-off-by: KP Singh <kpsingh@...gle.com>
> ---

See note about const-ification of trampoline and naming suggestion,
but looks good overall:

Acked-by: Andrii Nakryiko <andriin@...com>


>  arch/x86/net/bpf_jit_comp.c | 31 ++++++++++---------
>  include/linux/bpf.h         | 13 ++++++--
>  kernel/bpf/bpf_struct_ops.c | 12 ++++++-
>  kernel/bpf/trampoline.c     | 62 +++++++++++++++++++++----------------
>  4 files changed, 73 insertions(+), 45 deletions(-)
>

[...]

> diff --git a/kernel/bpf/trampoline.c b/kernel/bpf/trampoline.c
> index 704fa787fec0..cfe96d4cd89f 100644
> --- a/kernel/bpf/trampoline.c
> +++ b/kernel/bpf/trampoline.c
> @@ -190,40 +190,49 @@ static int register_fentry(struct bpf_trampoline *tr, void *new_addr)
>         return ret;
>  }
>
> -/* Each call __bpf_prog_enter + call bpf_func + call __bpf_prog_exit is ~50
> - * bytes on x86.  Pick a number to fit into BPF_IMAGE_SIZE / 2
> - */
> -#define BPF_MAX_TRAMP_PROGS 40
> +static struct bpf_tramp_progs *
> +bpf_trampoline_update_progs(struct bpf_trampoline *tr, int *total)

reading the code again, seems like bpf_trampoline_update_progs is
really more like bpf_trampoline_get_progs, no? It doesn't modify
trampoline itself, so might as well mark tr as const pointer.


> +{
> +       struct bpf_tramp_progs *tprogs;
> +       struct bpf_prog **progs;
> +       struct bpf_prog_aux *aux;
> +       int kind;
> +

[...]