Messages in this thread | | | From | Geert Uytterhoeven <> | Date | Mon, 6 Jan 2020 09:06:53 +0100 | Subject | Re: [PATCH v3 6/7] docs: gpio: Add GPIO Aggregator/Repeater documentation |
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Hi Linus,
On Sat, Jan 4, 2020 at 1:21 AM Linus Walleij <linus.walleij@linaro.org> wrote: > On Thu, Dec 12, 2019 at 3:48 PM Geert Uytterhoeven <geert@linux-m68k.org> wrote: > > On Thu, Dec 12, 2019 at 3:42 PM Linus Walleij <linus.walleij@linaro.org> wrote: > > > On Wed, Nov 27, 2019 at 9:43 AM Geert Uytterhoeven > > > <geert+renesas@glider.be> wrote: > > > > +The GPIO Aggregator allows access control for individual GPIOs, by aggregating > > > > +them into a new gpio_chip, which can be assigned to a group or user using > > > > +standard UNIX file ownership and permissions. Furthermore, this simplifies and > > > > +hardens exporting GPIOs to a virtual machine, as the VM can just grab the full > > > > +GPIO controller, and no longer needs to care about which GPIOs to grab and > > > > +which not, reducing the attack surface. > > > > + > > > > +Aggregated GPIO controllers are instantiated and destroyed by writing to > > > > +write-only attribute files in sysfs. > > > > > > I suppose virtual machines will have a lengthy config file where > > > they specify which GPIO lines to pick and use for their GPIO > > > aggregator, and that will all be fine, the VM starts and the aggregator > > > is there and we can start executing. > > > > > > I would perhaps point out a weakness as with all sysfs and with the current > > > gpio sysfs: if a process creates an aggregator device, and then that > > > process crashes, what happens when you try to restart the process and > > > run e.g. your VM again? > > > > > > Time for a hard reboot? Or should we add some design guidelines for > > > these machines so that they can cleanly tear down aggregators > > > previously created by the crashed VM? > > > > No, the VM does not create the aggregator. > > > > The idea is for the user to create one or more aggregators, set up > > permissions on /dev/gpiochipX, and launch the VM, passing the aggregated > > /dev/gpiochipX as parameters. > > If the VM crashes, just launch it again. > > > > Destroying the aggregators is a manual and independent process, after > > the VM has exited. > > I'm thinking about someone making some industrial application for some > control of a machinery say a robotic arm. > > And do make sure this VM is only controlling these GPIOs related to > this robotic arm, they create a GPIO aggregator. And we care about > cases like that since we provide this security argument. > > Surely that machine will be rebooted. > > Surely they don't have a printed paper with all the commands lying > at the console, and asking whoever powers it back on to manually > type it all in again. That feels a bit 1981. > > So they will have a script for this I suppose. Possibly in some > initscript so it is set up on boot. And this script echos stuff > all over the place to set up the aggregator. > > Is this the use case you're thinking of?
Exactly.
And they can configure that by echoing the GPIO specifiers to /sys/bus/platform/drivers/gpio-aggregator/new_device.
If their system has DT, another option is to describe the device in DT, and add its compatible value to gpio_aggregator_dt_ids[], cfr. the frobnicator example.
> I just like to have the whole picture here.
Sure. If anything is still unclear, please let me know! Thanks!
Gr{oetje,eeting}s,
Geert
-- Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org
In personal conversations with technical people, I call myself a hacker. But when I'm talking to journalists I just say "programmer" or something like that. -- Linus Torvalds
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