Re: nfp: bpf: perf event output helpers support

From: Kees Cook
Date: Thu Jun 07 2018 - 15:14:00 EST


On Thu, Jun 7, 2018 at 9:33 AM, Jakub Kicinski
<jakub.kicinski@xxxxxxxxxxxxx> 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