linux-kernel - Re: [PATCH bpf-next v5 3/7] bpf: lsm: provide attachment points for BPF LSM programs

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Date:   Mon, 23 Mar 2020 12:59:52 -0700
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     KP Singh <kpsingh@...omium.org>
Cc:     open list <linux-kernel@...r.kernel.org>,
        bpf <bpf@...r.kernel.org>, linux-security-module@...r.kernel.org,
        Brendan Jackman <jackmanb@...gle.com>,
        Florent Revest <revest@...gle.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        James Morris <jmorris@...ei.org>,
        Kees Cook <keescook@...omium.org>,
        Paul Turner <pjt@...gle.com>, Jann Horn <jannh@...gle.com>,
        Florent Revest <revest@...omium.org>,
        Brendan Jackman <jackmanb@...omium.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [PATCH bpf-next v5 3/7] bpf: lsm: provide attachment points for
 BPF LSM programs

On Mon, Mar 23, 2020 at 9:45 AM KP Singh <kpsingh@...omium.org> wrote:
>
> From: KP Singh <kpsingh@...gle.com>
>
> When CONFIG_BPF_LSM is enabled, nops functions, bpf_lsm_<hook_name>, are
> generated for each LSM hook. These nops are initialized as LSM hooks in
> a subsequent patch.
>
> Signed-off-by: KP Singh <kpsingh@...gle.com>
> Reviewed-by: Brendan Jackman <jackmanb@...gle.com>
> Reviewed-by: Florent Revest <revest@...gle.com>
> ---
>  include/linux/bpf_lsm.h | 21 +++++++++++++++++++++
>  kernel/bpf/bpf_lsm.c    | 19 +++++++++++++++++++
>  2 files changed, 40 insertions(+)
>  create mode 100644 include/linux/bpf_lsm.h
>
> diff --git a/include/linux/bpf_lsm.h b/include/linux/bpf_lsm.h
> new file mode 100644
> index 000000000000..c6423a140220
> --- /dev/null
> +++ b/include/linux/bpf_lsm.h
> @@ -0,0 +1,21 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +
> +/*
> + * Copyright (C) 2020 Google LLC.
> + */
> +
> +#ifndef _LINUX_BPF_LSM_H
> +#define _LINUX_BPF_LSM_H
> +
> +#include <linux/bpf.h>
> +#include <linux/lsm_hooks.h>
> +
> +#ifdef CONFIG_BPF_LSM
> +
> +#define LSM_HOOK(RET, NAME, ...) RET bpf_lsm_##NAME(__VA_ARGS__);
> +#include <linux/lsm_hook_names.h>
> +#undef LSM_HOOK
> +
> +#endif /* CONFIG_BPF_LSM */
> +
> +#endif /* _LINUX_BPF_LSM_H */
> diff --git a/kernel/bpf/bpf_lsm.c b/kernel/bpf/bpf_lsm.c
> index 82875039ca90..530d137f7a84 100644
> --- a/kernel/bpf/bpf_lsm.c
> +++ b/kernel/bpf/bpf_lsm.c
> @@ -7,6 +7,25 @@
>  #include <linux/filter.h>
>  #include <linux/bpf.h>
>  #include <linux/btf.h>
> +#include <linux/lsm_hooks.h>
> +#include <linux/bpf_lsm.h>
> +
> +/* For every LSM hook  that allows attachment of BPF programs, declare a NOP
> + * function where a BPF program can be attached as an fexit trampoline.
> + */
> +#define LSM_HOOK(RET, NAME, ...) LSM_HOOK_##RET(NAME, __VA_ARGS__)
> +
> +#define LSM_HOOK_int(NAME, ...)                        \
> +noinline __weak int bpf_lsm_##NAME(__VA_ARGS__)        \
> +{                                              \
> +       return 0;                               \
> +}
> +
> +#define LSM_HOOK_void(NAME, ...) \
> +noinline __weak void bpf_lsm_##NAME(__VA_ARGS__) {}
> +

Could unify with:

#define LSM_HOOK(RET, NAME, ...) noinline __weak RET bpf_lsm_##NAME(__VA_ARGS__)
{
    return (RET)0;
}

then you don't need LSM_HOOK_int and LSM_HOOK_void.

> +#include <linux/lsm_hook_names.h>
> +#undef LSM_HOOK
>
>  const struct bpf_prog_ops lsm_prog_ops = {
>  };
> --
> 2.20.1
>