lists  /  announce  owl-users  owl-dev  john-users  john-dev  passwdqc-users  yescrypt  popa3d-users  /  oss-security  kernel-hardening  musl  sabotage  tlsify  passwords  /  crypt-dev  xvendor  /  Bugtraq  Full-Disclosure  linux-kernel  linux-netdev  linux-ext4  linux-hardening  PHC 
Open Source and information security mailing list archives
Hash Suite: Windows password security audit tool. GUI, reports in PDF.
[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Date:   Wed, 27 May 2020 10:03:56 -0700
From:   "Daniel Xu" <>
To:     "Andrii Nakryiko" <>
Cc:     "Alexei Starovoitov" <>,
        "Daniel Borkmann" <>,
        "Martin Lau" <>, "Song Liu" <>,
        "Yonghong Song" <>, "Andrii Nakryiko" <>,
        "john fastabend" <>,
        "KP Singh" <>,
        "David S. Miller" <>,
        "Jakub Kicinski" <>,
        "Jesper Dangaard Brouer" <>,
        "bpf" <>, "Networking" <>,
        "open list" <>,
        "clang-built-linux" <>
Subject: Re: [PATCH bpf-next] libbpf: Export bpf_object__load_vmlinux_btf

Hi Andrii,

On Tue May 26, 2020 at 3:09 PM PST, Andrii Nakryiko wrote:
> On Tue, May 26, 2020 at 7:09 PM Daniel Xu <> wrote:
> >
> > Right now the libbpf model encourages loading the entire object at once.
> > In this model, libbpf handles loading BTF from vmlinux for us. However,
> > it can be useful to selectively load certain maps and programs inside an
> > object without loading everything else.
> There is no way to selectively load or not load a map. All maps are
> created, unless they are reusing map FD or pinned instances. See
> below, I'd like to understand the use case better.
> >
> > In the latter model, there was perviously no way to load BTF on-demand.
> > This commit exports the bpf_object__load_vmlinux_btf such that we are
> > able to load BTF on demand.
> >
> Let's start with the real problem, not a solution. Do you have
> specific use case where you need bpf_object__load_vmlinux_btf()? It
> might not do anything if none of BPF programs in the object requires
> BTF, because it's very much tightly coupled with loading bpf_object as
> a whole model. I'd like to understand what you are after with this,
> before exposing internal implementation details as an API.

If I try loading a program through the following sequence:


And the program require BTF (tp_btf), I get an unavoidable (to the best
of my knowledge) segfault in the following code path:

      libbpf_find_attach_btf_id()    <-- [0]
            btf__find_by_name_kind() <-- boom (btf->nr_types)

because [0] passes prog->obj->btf_vmlinux which is still null. So the
solution I'm proposing is exporting bpf_object__load_vmlinux_btf() and
calling that on struct bpf_object before performing prog loads.



Powered by blists - more mailing lists