| From: |
| Ingo Molnar <mingo-AT-kernel.org> |
| To: |
| Josef Bacik <josef-AT-toxicpanda.com> |
| Subject: |
| Re: [PATCH 1/2] bpf: add a bpf_override_function helper |
| Date: |
| Sat, 11 Nov 2017 09:14:55 +0100 |
| Message-ID: |
| <20171111081455.qx4rodxldofbzypb@gmail.com> |
| Cc: |
| rostedt-AT-goodmis.org, mingo-AT-redhat.com, davem-AT-davemloft.net, netdev-AT-vger.kernel.org, linux-kernel-AT-vger.kernel.org, ast-AT-kernel.org, kernel-team-AT-fb.com, daniel-AT-iogearbox.net, Josef Bacik <jbacik-AT-fb.com> |
* Josef Bacik <josef@toxicpanda.com> wrote:
> On Fri, Nov 10, 2017 at 10:34:59AM +0100, Ingo Molnar wrote:
> >
> > * Josef Bacik <josef@toxicpanda.com> wrote:
> >
> > > @@ -551,6 +578,10 @@ static const struct bpf_func_proto *kprobe_prog_func_proto(enum
bpf_func_id func
> > > return &bpf_get_stackid_proto;
> > > case BPF_FUNC_perf_event_read_value:
> > > return &bpf_perf_event_read_value_proto;
> > > + case BPF_FUNC_override_return:
> > > + pr_warn_ratelimited("%s[%d] is installing a program with bpf_override_return helper that
may cause unexpected behavior!",
> > > + current->comm, task_pid_nr(current));
> > > + return &bpf_override_return_proto;
> >
> > So if this new functionality is used we'll always print this into the syslog?
> >
> > The warning is also a bit passive aggressive about informing the user: what
> > unexpected behavior can happen, what is the worst case?
> >
>
> It's modeled after the other warnings bpf will spit out, but with this feature
> you are skipping a function and instead returning some arbitrary value, so
> anything could go wrong if you mess something up. For instance I screwed up my
> initial test case and made every IO submitted return an error instead of just on
> the one file system I was attempting to test, so all sorts of hilarity ensued.
Ok, then for the x86 bits:
NAK-ed-by: Ingo Molnar <mingo@kernel.org>
One of the major advantages of having an in-kernel BPF sandbox is to never crash
the kernel - and allowing BPF programs to just randomly modify the return value of
kernel functions sounds immensely broken to me.
(And yes, I realize that kprobes are used here as a vehicle, but the point
remains.)
Thanks,
Ingo
