linux-kernel - Re: [PATCH bpf-next 2/2] bpf: Expose bpf_d

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Date:   Thu, 12 Nov 2020 10:50:46 -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>, Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Jann Horn <jannh@...gle.com>,
        Hao Luo <haoluo@...gle.com>,
        Florent Revest <revest@...omium.org>,
        Brendan Jackman <jackmanb@...omium.org>
Subject: Re: [PATCH bpf-next 2/2] bpf: Expose bpf_d_path helper to sleepable
 LSM hooks

On Thu, Nov 12, 2020 at 9:20 AM KP Singh <kpsingh@...omium.org> wrote:
>
> From: KP Singh <kpsingh@...gle.com>
>
> Sleepable hooks are never called from an NMI/interrupt context, so it is
> safe to use the bpf_d_path helper in LSM programs attaching to these
> hooks.
>
> The helper is not restricted to sleepable programs and merely uses the
> list of sleeable hooks as the initial subset of LSM hooks where it can
> be used.
>
> Signed-off-by: KP Singh <kpsingh@...gle.com>
> ---

LGTM.

Acked-by: Andrii Nakryiko <andrii@...nel.org>


>  kernel/trace/bpf_trace.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
> index e4515b0f62a8..eab1af02c90d 100644
> --- a/kernel/trace/bpf_trace.c
> +++ b/kernel/trace/bpf_trace.c
> @@ -16,6 +16,7 @@
>  #include <linux/syscalls.h>
>  #include <linux/error-injection.h>
>  #include <linux/btf_ids.h>
> +#include <linux/bpf_lsm.h>
>
>  #include <uapi/linux/bpf.h>
>  #include <uapi/linux/btf.h>
> @@ -1178,7 +1179,11 @@ BTF_SET_END(btf_allowlist_d_path)
>
>  static bool bpf_d_path_allowed(const struct bpf_prog *prog)
>  {
> -       return btf_id_set_contains(&btf_allowlist_d_path, prog->aux->attach_btf_id);
> +       if (prog->type == BPF_PROG_TYPE_LSM)
> +               return bpf_lsm_is_sleepable_hook(prog->aux->attach_btf_id);
> +
> +       return btf_id_set_contains(&btf_allowlist_d_path,
> +                                  prog->aux->attach_btf_id);
>  }
>
>  BTF_ID_LIST_SINGLE(bpf_d_path_btf_ids, struct, path)
> --
> 2.29.2.222.g5d2a92d10f8-goog
>