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Date:   Fri, 1 Jul 2022 22:53:36 +0200
From:   "Jason A. Donenfeld" <Jason@zx2c4.com>
To:     Jonathan Corbet <corbet@lwn.net>
Cc:     John Stultz <jstultz@google.com>,
        Kalesh Singh <kaleshsingh@google.com>,
        Christoph Hellwig <hch@lst.de>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Arve =?utf-8?B?SGrDuG5uZXbDpWc=?= <arve@android.com>,
        Todd Kjos <tkjos@android.com>,
        Martijn Coenen <maco@android.com>,
        Joel Fernandes <joel@joelfernandes.org>,
        Christian Brauner <brauner@kernel.org>,
        Hridya Valsaraju <hridya@google.com>,
        Suren Baghdasaryan <surenb@google.com>,
        Theodore Ts'o <tytso@mit.edu>,
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        Lai Jiangshan <jiangshanlai@gmail.com>,
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Subject: Re: [PATCH] remove CONFIG_ANDROID
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Hi Jon,

On Fri, Jul 01, 2022 at 02:22:38PM -0600, Jonathan Corbet wrote:
> So please forgive the noise from the peanut gallery

Yuh oh, I sure hope this isn't newsworthy for LWN. This has already
consumed me for two days...

> myself wondering...do you really need a knob for this?  The kernel
> itself can observe how often (and for how long) the system is suspended,
> and might well be able to do the right thing without explicit input from
> user space.  If it works it would eliminate a potential configuration
> problem and also perhaps respond correctly to changing workloads.
> 
> For example, rather than testing a knob, avoid resetting keys on resume
> if the suspend time is less than (say) 30s?
> 
> Educate me on what I'm missing here, please :)

What you're missing is that wireguard needs to do this before going to
sleep, not when waking up, because one of the objectives is forward
secrecy. See
https://git.zx2c4.com/wireguard-linux/tree/drivers/net/wireguard/device.c#n63

	if (IS_ENABLED(CONFIG_PM_AUTOSLEEP) || IS_ENABLED(CONFIG_ANDROID))
		return 0;
	if (action != PM_HIBERNATION_PREPARE && action != PM_SUSPEND_PREPARE)
		return 0;
	[...]
	wg_noise_handshake_clear(&peer->handshake);
	wg_noise_keypairs_clear(&peer->keypairs);

Somebody asked the same question on wgml here -
https://lore.kernel.org/wireguard/CAHmME9p2OYSTX2C5M0faKtw2N8jiyohvRqnAPKa=e7BWynF7fQ@mail.gmail.com/T/
- and then eventually suggested that I should wake up computers from
sleep to clear that memory. No way jose.

Anyway, this matter has been resolved in this thread here:
https://lore.kernel.org/lkml/20220630191230.235306-1-kaleshsingh@google.com/T/
And this Android change:
https://android-review.googlesource.com/c/kernel/common/+/2142693/1
Resulting in these two commits landing in Greg's tree:
https://git.kernel.org/pub/scm/linux/kernel/git/gregkh/char-misc.git/commit/?id=261e224d6a5c43e2bb8a07b7662f9b4ec425cfec
https://git.kernel.org/pub/scm/linux/kernel/git/gregkh/char-misc.git/commit/?id=1045a06724f322ed61f1ffb994427c7bdbe64647
So hopefully this thread can come to an end and I can get back to work.

Jason