linux-kernel - Re: nfp: bpf: perf event output helpers support

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Message-ID: <CAGXu5jJ7bygKKAzq-cP85XjB1OLzGAX6qr2VdCbSJ9_ZD=CZEw@mail.gmail.com>
Date:   Thu, 7 Jun 2018 12:13:49 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Jakub Kicinski <jakub.kicinski@...ronome.com>
Cc:     Quentin Monnet <quentin.monnet@...ronome.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Network Development <netdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: nfp: bpf: perf event output helpers support

On Thu, Jun 7, 2018 at 9:33 AM, Jakub Kicinski
<jakub.kicinski@...ronome.com> wrote:
> On Wed, 6 Jun 2018 22:15:04 -0700, Kees Cook wrote:
>> > +       rcu_read_lock();
>> > +       if (!rhashtable_lookup_fast(&bpf->maps_neutral, &map,
>> > +                                   nfp_bpf_maps_neutral_params)) {
>> > +               rcu_read_unlock();
>> > +               pr_warn("perf event: dest map pointer %px not recognized, dropping event\n",
>> > +                       map);
>>
>> Please don't use %px on kernel pointers unless you absolutely have
>> to[1]. It seems like this value wouldn't be actionable here, so likely
>> it's best to just remove its use entirely.
>
> We're using kernel pointer as an opaque handle when communicating with
> the device.  We need the actual value to correlate things.  Maybe I used
> the %px slightly out of spite there, because I forgot %p is now useless
> and wasted half an hour on debugging an endian issue :S
>
> This message can only really trigger when root loads a specific BPF map
> onto the device and FW is buggy.  Can I fix it in -next?  I'm making
> changes to this part of the code anyway.

That'd be fine by me, thanks!

-Kees

-- 
Kees Cook
Pixel Security