linux-kernel - Re: [PATCH v3 6/6] gpiolib: notify user-space about in-kernel line state changes

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CAMRc=Mefz=EBd6us-eK8kqk8zL0=LsEWUkP3JB7a0M7xcT8z8Q@mail.gmail.com>
Date: Wed, 16 Oct 2024 12:12:10 +0200
From: Bartosz Golaszewski <brgl@...ev.pl>
To: Kent Gibson <warthog618@...il.com>
Cc: Linus Walleij <linus.walleij@...aro.org>, linux-gpio@...r.kernel.org, 
	linux-kernel@...r.kernel.org, 
	Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
Subject: Re: [PATCH v3 6/6] gpiolib: notify user-space about in-kernel line
 state changes

On Wed, Oct 16, 2024 at 11:43 AM Kent Gibson <warthog618@...il.com> wrote:
>
> On Wed, Oct 16, 2024 at 11:22:07AM +0200, Bartosz Golaszewski wrote:
> > On Wed, Oct 16, 2024 at 11:17 AM Kent Gibson <warthog618@...il.com> wrote:
> > >
> > > > >
> > > >
> > > > You mean, you get a CHANGED_CONFIG event but the debounce value is not
> > > > in the associated line info?
> > > >
> > >
> > > Correct.
> > >
> >
> > Ok, let me see.
> >
>
> When setting from userspace the issue is that linereq_set_config() setting the
> direction will emit, quite possibly before the debounce has been set.  The
> edge_detector_setup() that does set it can also emit, though only if the
> hardware supports debounce.  And then there could be a race between the
> notifier being called and the period being set in the supinfo.
> (the set will probably win that one)
>
> Debounce set from the kernel side is going to be an issue as cdev
> catches and stores the value from userspace to report in the supinfo - that
> isn't the case for kernel calls to gpiod_set_config().
>
> Seems moving the debounce value out of the desc and into cdev, which seemed a
> good idea at the time, might come back and bite now if it is no longer
> restricted to being cdev specific.  Now there is an actual reason to
> store it in the desc :(.
>

I'm seeing commit:

commit 9344e34e7992fec95ce6210d95ac01437dd327ab
Author: Kent Gibson <warthog618@...il.com>
Date:   Tue Dec 19 08:41:54 2023 +0800

    gpiolib: cdev: relocate debounce_period_us from struct gpio_desc

    Store the debounce period for a requested line locally, rather than in
    the debounce_period_us field in the gpiolib struct gpio_desc.

    Add a global tree of lines containing supplemental line information
    to make the debounce period available to be reported by the
    GPIO_V2_GET_LINEINFO_IOCTL and the line change notifier.

    Signed-off-by: Kent Gibson <warthog618@...il.com>
    Reviewed-by: Andy Shevchenko <andy@...nel.org>
    Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@...aro.org>

But it doesn't explain *why* we did this and I don't remember the
story behind this change.

How bad would it be to go back to storing the debounce setting in the
descriptor?

Bart