linux-kernel - Re: [RFC PATCH bpf-next 4/5] bpf: load and verify kernel module BTFs

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Message-ID: <CAEf4Bza6CGgJO6eOSU66mj-usbaGuFgZhRz1i+mFjg_f75Jn5A@mail.gmail.com>
Date:   Thu, 5 Nov 2020 11:01:15 -0800
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Jakub Kicinski <kuba@...nel.org>,
        Andrii Nakryiko <andrii@...nel.org>, bpf <bpf@...r.kernel.org>,
        Networking <netdev@...r.kernel.org>,
        Alexei Starovoitov <ast@...com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Kernel Team <kernel-team@...com>,
        Arnaldo Carvalho de Melo <acme@...hat.com>,
        Jessica Yu <jeyu@...nel.org>,
        open list <linux-kernel@...r.kernel.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>
Subject: Re: [RFC PATCH bpf-next 4/5] bpf: load and verify kernel module BTFs

On Thu, Nov 5, 2020 at 8:45 AM Greg Kroah-Hartman
<gregkh@...uxfoundation.org> wrote:
>
> On Thu, Nov 05, 2020 at 08:39:25AM -0800, Jakub Kicinski wrote:
> > On Wed, 4 Nov 2020 20:51:39 -0800 Andrii Nakryiko wrote:
> > > Add kernel module listener that will load/validate and unload module BTF.
> > > Module BTFs gets ID generated for them, which makes it possible to iterate
> > > them with existing BTF iteration API. They are given their respective module's
> > > names, which will get reported through GET_OBJ_INFO API. They are also marked
> > > as in-kernel BTFs for tooling to distinguish them from user-provided BTFs.
> > >
> > > Also, similarly to vmlinux BTF, kernel module BTFs are exposed through
> > > sysfs as /sys/kernel/btf/<module-name>. This is convenient for user-space
> > > tools to inspect module BTF contents and dump their types with existing tools:
> >
> > Is there any precedent for creating per-module files under a new
> > sysfs directory structure? My intuition would be that these files
> > belong under /sys/module/
>
> Ick, why?  What's wrong with them under btf?  The module core code
> "owns" the /sys/modules/ tree.  If you want others to mess with that, it
> will get tricky.
>
>
> > Also the CC list on these patches is quite narrow. You should have
> > at least CCed the module maintainer. Adding some folks now.
> >
> > > [vmuser@...hvm bpf]$ ls -la /sys/kernel/btf
> > > total 0
> > > drwxr-xr-x  2 root root       0 Nov  4 19:46 .
> > > drwxr-xr-x 13 root root       0 Nov  4 19:46 ..
> > >
> > > ...
> > >
> > > -r--r--r--  1 root root     888 Nov  4 19:46 irqbypass
> > > -r--r--r--  1 root root  100225 Nov  4 19:46 kvm
> > > -r--r--r--  1 root root   35401 Nov  4 19:46 kvm_intel
> > > -r--r--r--  1 root root     120 Nov  4 19:46 pcspkr
> > > -r--r--r--  1 root root     399 Nov  4 19:46 serio_raw
> > > -r--r--r--  1 root root 4094095 Nov  4 19:46 vmlinux
> > >
> > > Signed-off-by: Andrii Nakryiko <andrii@...nel.org>
> > > ---
> > >  include/linux/bpf.h    |   2 +
> > >  include/linux/module.h |   4 +
> > >  kernel/bpf/btf.c       | 193 +++++++++++++++++++++++++++++++++++++++++
> > >  kernel/bpf/sysfs_btf.c |   2 +-
> > >  kernel/module.c        |  32 +++++++
> > >  5 files changed, 232 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> > > index 2fffd30e13ac..3cb89cd7177b 100644
> > > --- a/include/linux/bpf.h
> > > +++ b/include/linux/bpf.h
> > > @@ -36,9 +36,11 @@ struct seq_operations;
> > >  struct bpf_iter_aux_info;
> > >  struct bpf_local_storage;
> > >  struct bpf_local_storage_map;
> > > +struct kobject;
> > >
> > >  extern struct idr btf_idr;
> > >  extern spinlock_t btf_idr_lock;
> > > +extern struct kobject *btf_kobj;
>
> I don't see any Documentation/ABI/ updates for the sysfs changes here,
> did I miss it?
>

Nope, my bad, completely forgot to add it. Last time I touched sysfs
was quite a while ago, I forgot about adding ABI description. Will add
in the next version.

> thanks,
>
> greg k-h