linux-kernel - Re: [RFC PATCH 0/2] seccomp: Split set filter into two steps

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Date:   Fri, 6 Oct 2023 15:58:40 +0800
From:   Hengqi Chen <hengqi.chen@...il.com>
To:     Kees Cook <keescook@...omium.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>
Cc:     linux-kernel@...r.kernel.org, bpf@...r.kernel.org,
        luto@...capital.net, wad@...omium.org, alexyonghe@...cent.com
Subject: Re: [RFC PATCH 0/2] seccomp: Split set filter into two steps

+ BPF maintainers

On Wed, Oct 4, 2023 at 2:02 AM Kees Cook <keescook@...omium.org> wrote:
>
> On Tue, Oct 03, 2023 at 08:38:34AM +0000, Hengqi Chen wrote:
> > This patchset introduces two new operations which essentially
> > splits the SECCOMP_SET_MODE_FILTER process into two steps:
> > SECCOMP_LOAD_FILTER and SECCOMP_ATTACH_FILTER.
> >
> > The SECCOMP_LOAD_FILTER loads the filter and returns a fd
> > which can be pinned to bpffs. This extends the lifetime of the
> > filter and thus can be reused by different processes.
> > With this new operation, we can eliminate a hot path of JITing
> > BPF program (the filter) where we apply the same seccomp filter
> > to thousands of micro VMs on a bare metal instance.
> >
> > The SECCOMP_ATTACH_FILTER is used to attach a loaded filter.
> > The filter is represented by a fd which is either returned
> > from SECCOMP_LOAD_FILTER or obtained from bpffs using bpf syscall.
>
> Interesting! I like this idea, thanks for writing it up.
>
> Two design notes:
>
> - Can you reuse/refactor seccomp_prepare_filter() instead of duplicating
>   the logic into two new functions?
>

Sure, will do.

> - Is there a way to make sure the BPF program coming from the fd is one
>   that was built via SECCOMP_LOAD_FILTER? (I want to make sure we can
>   never confuse a non-seccomp program into getting loaded into seccomp.)
>

Maybe we can add a new prog type enum like BPF_PROG_TYPE_SECCOMP
for seccomp filter.

> -Kees
>
> --
> Kees Cook
>

Cheers,
--
Hengqi