Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
MIME-Version: 1.0
References: <20220711083220.2175036-1-asavkov@redhat.com> <YswAqrJrMKIZPpcz@krava>
In-Reply-To: <YswAqrJrMKIZPpcz@krava>
From:   Daniel Vacek <neelx@redhat.com>
Date:   Mon, 1 Aug 2022 15:58:24 +0200
Message-ID: <CACjP9X-HWHhFD6D1TsuhWOgj2v=dMkwVCjQCQzQqa054yKiqeg@mail.gmail.com>
Subject: Re: [RFC PATCH bpf-next 0/4] bpf_panic() helper
To:     Jiri Olsa <olsajiri@gmail.com>
Cc:     Artem Savkov <asavkov@redhat.com>,
        Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Andrii Nakryiko <andrii@kernel.org>, bpf@vger.kernel.org,
        netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
        Andrea Arcangeli <aarcange@redhat.com>
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

On Mon, Jul 11, 2022 at 12:51 PM Jiri Olsa <olsajiri@gmail.com> wrote:
>
> On Mon, Jul 11, 2022 at 10:32:16AM +0200, Artem Savkov wrote:
> > eBPF is often used for kernel debugging, and one of the widely used and
> > powerful debugging techniques is post-mortem debugging with a full memory dump.
> > Triggering a panic at exactly the right moment allows the user to get such a
> > dump and thus a better view at the system's state. This patchset adds
> > bpf_panic() helper to do exactly that.
>
> FWIW I was asked for such helper some time ago from Daniel Vacek, cc-ed

Nice :-)
This is totally welcome. Though, IIRC, I was asking if I could do a
NULL pointer dereference within perf probe (or ftrace) back then.
Still, the outcome is similar. So kudos to Artem.

--nX

> jirka
>
> >
> > I realize that even though there are multiple guards present, a helper like
> > this is contrary to BPF being "safe", so this is sent as RFC to have a
> > discussion on whether adding destructive capabilities is deemed acceptable.
> >
> > Artem Savkov (4):
> >   bpf: add a sysctl to enable destructive bpf helpers
> >   bpf: add BPF_F_DESTRUCTIVE flag for BPF_PROG_LOAD
> >   bpf: add bpf_panic() helper
> >   selftests/bpf: bpf_panic selftest
> >
> >  include/linux/bpf.h                           |   8 +
> >  include/uapi/linux/bpf.h                      |  13 ++
> >  kernel/bpf/core.c                             |   1 +
> >  kernel/bpf/helpers.c                          |  13 ++
> >  kernel/bpf/syscall.c                          |  33 +++-
> >  kernel/bpf/verifier.c                         |   7 +
> >  kernel/trace/bpf_trace.c                      |   2 +
> >  tools/include/uapi/linux/bpf.h                |  13 ++
> >  .../selftests/bpf/prog_tests/bpf_panic.c      | 144 ++++++++++++++++++
> >  9 files changed, 233 insertions(+), 1 deletion(-)
> >  create mode 100644 tools/testing/selftests/bpf/prog_tests/bpf_panic.c
> >
> > --
> > 2.35.3
> >
>