linux-kernel - Re: [PATCH bpf-next] bpf: allow loading instructions from a fd

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Message-ID: <20200714173154.i2wxhm4n4ob7sfpd@ast-mbp.dhcp.thefacebook.com>
Date:   Tue, 14 Jul 2020 10:31:54 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Matteo Croce <mcroce@...ux.microsoft.com>
Cc:     bpf@...r.kernel.org, linux-kernel@...r.kernel.org,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>
Subject: Re: [PATCH bpf-next] bpf: allow loading instructions from a fd

On Mon, Jul 13, 2020 at 03:05:11PM +0200, Matteo Croce wrote:
> From: Matteo Croce <mcroce@...rosoft.com>
> 
> Allow to load the BPF instructons from a file descriptor,
> other than a pointer.
> 
> This is required by the Integrity Subsystem to validate the source of
> the instructions.
> 
> In bpf_attr replace 'insns', which is an u64, to a union containing also
> the file descriptor as int.
> A new BPF_F_LOAD_BY_FD flag tells bpf_prog_load() to load
> the instructions from file descriptor and ignore the pointer.
> 
> As BPF files usually are regular ELF files, start reading from the
> current file position, so the userspace can skip the ELF header and jump
> to the right section.

That is not the case at all.
Have you looked at amount of work libbpf is doing with elf file before
raw instructions become suitable to be loaded by the kernel?