netdev - Re: [RFC PATCH bpf-next 0/4] bpf

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Date:   Mon, 1 Aug 2022 15:58:24 +0200
From:   Daniel Vacek <neelx@...hat.com>
To:     Jiri Olsa <olsajiri@...il.com>
Cc:     Artem Savkov <asavkov@...hat.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>, bpf@...r.kernel.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        Andrea Arcangeli <aarcange@...hat.com>
Subject: Re: [RFC PATCH bpf-next 0/4] bpf_panic() helper

On Mon, Jul 11, 2022 at 12:51 PM Jiri Olsa <olsajiri@...il.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
> >
>