linux-kernel - Re: [PATCH bpf-next v1 09/13] bpf: lsm: Add a helper function bpf_lsm_event

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Date:   Mon, 23 Dec 2019 22:36:08 -0800
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,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        James Morris <jmorris@...ei.org>,
        Kees Cook <keescook@...omium.org>,
        Thomas Garnier <thgarnie@...omium.org>,
        Michael Halcrow <mhalcrow@...gle.com>,
        Paul Turner <pjt@...gle.com>,
        Brendan Gregg <brendan.d.gregg@...il.com>,
        Jann Horn <jannh@...gle.com>,
        Matthew Garrett <mjg59@...gle.com>,
        Christian Brauner <christian@...uner.io>,
        Mickaël Salaün <mic@...ikod.net>,
        Florent Revest <revest@...omium.org>,
        Brendan Jackman <jackmanb@...omium.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        "Serge E. Hallyn" <serge@...lyn.com>,
        Mauro Carvalho Chehab <mchehab+samsung@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Nicolas Ferre <nicolas.ferre@...rochip.com>,
        Stanislav Fomichev <sdf@...gle.com>,
        Quentin Monnet <quentin.monnet@...ronome.com>,
        Andrey Ignatov <rdna@...com>, Joe Stringer <joe@...d.net.nz>
Subject: Re: [PATCH bpf-next v1 09/13] bpf: lsm: Add a helper function bpf_lsm_event_output

On Fri, Dec 20, 2019 at 7:43 AM KP Singh <kpsingh@...omium.org> wrote:
>
> From: KP Singh <kpsingh@...gle.com>
>
> This helper is similar to bpf_perf_event_output except that
> it does need a ctx argument which is more usable in the
> BTF based LSM programs where the context is converted to
> the signature of the attacthed BTF type.
>
> An example usage of this function would be:
>
> struct {
>          __uint(type, BPF_MAP_TYPE_PERF_EVENT_ARRAY);
>          __uint(key_size, sizeof(int));
>          __uint(value_size, sizeof(u32));
> } perf_map SEC(".maps");
>
> BPF_TRACE_1(bpf_prog1, "lsm/bprm_check_security,
>             struct linux_binprm *, bprm)
> {
>         char buf[BUF_SIZE];
>         int len;
>         u64 flags = BPF_F_CURRENT_CPU;
>
>         /* some logic that fills up buf with len data */
>         len = fill_up_buf(buf);
>         if (len < 0)
>                 return len;
>         if (len > BU)
>                 return 0;
>
>         bpf_lsm_event_output(&perf_map, flags, buf, len);

This seems to be generally useful and not LSM-specific, so maybe name
it more generically as bpf_event_output instead?

I'm also curious why we needed both bpf_perf_event_output and
bpf_perf_event_output_raw_tp, if it could be done as simply as you did
it here. What's different between those three and why your
bpf_lsm_event_output doesn't need pt_regs passed into them?

>         return 0;
> }
>
> Signed-off-by: KP Singh <kpsingh@...gle.com>
> ---
>  include/uapi/linux/bpf.h       | 10 +++++++++-
>  kernel/bpf/verifier.c          |  1 +
>  security/bpf/ops.c             | 21 +++++++++++++++++++++
>  tools/include/uapi/linux/bpf.h | 10 +++++++++-
>  4 files changed, 40 insertions(+), 2 deletions(-)
>

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