Re: [PATCH bpf-next v1 0/6] Introduce eBPF support for HID devices

[Yonghong Song <yhs@fb.com>]

On 2/24/22 5:49 AM, Benjamin Tissoires wrote:
> Hi Greg,
> 
> Thanks for the quick answer :)
> 
> On Thu, Feb 24, 2022 at 12:31 PM Greg KH <gregkh@linuxfoundation.org> wrote:
>>
>> On Thu, Feb 24, 2022 at 12:08:22PM +0100, Benjamin Tissoires wrote:
>>> Hi there,
>>>
>>> This series introduces support of eBPF for HID devices.
>>>
>>> I have several use cases where eBPF could be interesting for those
>>> input devices:
>>>
>>> - simple fixup of report descriptor:
>>>
>>> In the HID tree, we have half of the drivers that are "simple" and
>>> that just fix one key or one byte in the report descriptor.
>>> Currently, for users of such devices, the process of fixing them
>>> is long and painful.
>>> With eBPF, we could externalize those fixups in one external repo,
>>> ship various CoRe bpf programs and have those programs loaded at boot
>>> time without having to install a new kernel (and wait 6 months for the
>>> fix to land in the distro kernel)
>>
>> Why would a distro update such an external repo faster than they update
>> the kernel?  Many sane distros update their kernel faster than other
>> packages already, how about fixing your distro?  :)
> 
> Heh, I'm going to try to dodge the incoming rhel bullet :)
> 
> It's true that thanks to the work of the stable folks we don't have to
> wait 6 months for a fix to come in. However, I think having a single
> file to drop in a directory would be easier for development/testing
> (and distribution of that file between developers/testers) than
> requiring people to recompile their kernel.
> 
> Brain fart: is there any chance we could keep the validated bpf
> programs in the kernel tree?

Yes, see kernel/bpf/preload/iterators/iterators.bpf.c.

> 
>>
>> I'm all for the idea of using ebpf for HID devices, but now we have to
>> keep track of multiple packages to be in sync here.  Is this making
>> things harder overall?
> 
> Probably, and this is also maybe opening a can of worms. Vendors will
> be able to say "use that bpf program for my HID device because the
> firmware is bogus".
> 
> OTOH, as far as I understand, you can not load a BPF program in the
> kernel that uses GPL-declared functions if your BPF program is not
> GPL. Which means that if firmware vendors want to distribute blobs
> through BPF, either it's GPL and they have to provide the sources, or
> it's not happening.
> 
> I am not entirely clear on which plan I want to have for userspace.
> I'd like to have libinput on board, but right now, Peter's stance is
> "not in my garden" (and he has good reasons for it).
> So my initial plan is to cook and hold the bpf programs in hid-tools,
> which is the repo I am using for the regression tests on HID.
> 
> I plan on building a systemd intrinsic that would detect the HID
> VID/PID and then load the various BPF programs associated with the
> small fixes.
> Note that everything can not be fixed through eBPF, simply because at
> boot we don't always have the root partition mounted.
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