netdev - Re: [PATCH bpf-next 1/2] libbpf: stop enforcing kern

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Date:   Fri, 18 Oct 2019 07:49:13 -0700
From:   John Fastabend <john.fastabend@...il.com>
To:     John Fastabend <john.fastabend@...il.com>,
        Andrii Nakryiko <andrii.nakryiko@...il.com>,
        Alexei Starovoitov <ast@...com>
Cc:     John Fastabend <john.fastabend@...il.com>,
        Andrii Nakryiko <andriin@...com>, bpf <bpf@...r.kernel.org>,
        Networking <netdev@...r.kernel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Kernel Team <Kernel-team@...com>
Subject: Re: [PATCH bpf-next 1/2] libbpf: stop enforcing kern_version,
 populate it for users

John Fastabend wrote:
> Andrii Nakryiko wrote:
> > On Fri, Oct 4, 2019 at 7:36 AM Alexei Starovoitov <ast@...com> wrote:
> > >
> > > On 10/4/19 7:32 AM, Andrii Nakryiko wrote:
> > > >> If we are not going to validate the section should we also skip collect'ing it?
> > > > Well, if user supplied version, we will parse and use it to override
> > > > out prepopulated one, so in that sense we do have validation.
> > > >
> > > > But I think it's fine just to drop it altogether. Will do in v3.
> > > >
> > >
> > > what about older kernel that still enforce it?
> > > May be populate it in bpf_attr while loading, but
> > > don't check it in elf from libbpf?
> > 
> > That's what my change does. I pre-populate correct kernel version in
> > bpf_object->kern_version from uname(). If ELF has "version" section,
> > we still parse it and override bpf_object->kern_version.
> > bpf_object->kern_version then is always specified as part of
> > bpf_prog_load->kern_version.
> > 
> > So what we are discussing here is to not even look at user-provided
> > version, but just always specify correct current kernel version. So I
> > don't think we are going to break anything, except we might allow to
> > pass some programs that were failing before due to unspecified or zero
> > version.
> > 
> > So with that, do you think it's ok to get rid of version section altogether?
> 
> Should be fine on my side. Go for it.

... Actually it turns out this broke some kernels that report via uname()
incorrect version info. Sent a patch out to add just the bits back we need
to get it working again.

To bad but I can't fix distributions that are deployed so...