[PATCH bpf-next v9 02/10] bpf: Add eBPF program subtype and is_valid_subtype() verifier

[Alexei Starovoitov]

On Tue, Jun 25, 2019 at 3:04 PM Mickaël Salaün <mic at digikod.net> wrote:
>
> The goal of the program subtype is to be able to have different static
> fine-grained verifications for a unique program type.
>
> The struct bpf_verifier_ops gets a new optional function:
> is_valid_subtype(). This new verifier is called at the beginning of the
> eBPF program verification to check if the (optional) program subtype is
> valid.
>
> The new helper bpf_load_program_xattr() enables to verify a program with
> subtypes.
>
> For now, only Landlock eBPF programs are using a program subtype (see
> next commits) but this could be used by other program types in the
> future.
>
> Signed-off-by: Mickaël Salaün <mic at digikod.net>
> Cc: Alexei Starovoitov <ast at kernel.org>
> Cc: Daniel Borkmann <daniel at iogearbox.net>
> Cc: David S. Miller <davem at davemloft.net>
> Link: https://lkml.kernel.org/r/20160827205559.GA43880@ast-mbp.thefacebook.com
> ---
>
> Changes since v8:
> * use bpf_load_program_xattr() instead of bpf_load_program() and add
>   bpf_verify_program_xattr() to deal with subtypes
> * remove put_extra() since there is no more "previous" field (for now)
>
> Changes since v7:
> * rename LANDLOCK_SUBTYPE_* to LANDLOCK_*
> * move subtype in bpf_prog_aux and use only one bit for has_subtype
>   (suggested by Alexei Starovoitov)

sorry to say, but I don't think the landlock will ever land,
since posting huge patches once a year is missing a lot of development
that is happening during that time.
This 2/10 patch is an example.
subtype concept was useful 2 years ago when v6 was posted.
Since then bpf developers faced very similar problem in other parts
and it was solved with 'expected_attach_type' field.
See commit 5e43f899b03a ("bpf: Check attach type at prog load time")
dated March 2018.