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

On Tue, Jun 25, 2019 at 3:04 PM Mickaël Salaün [off-list ref] 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@digikod.net>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Cc: David S. Miller <davem@davemloft.net>
Link: https://lkml.kernel.org/r/20160827205559.GA43880@ast-mbp.thefacebook.com
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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.