linux-kernel - Re: [PATCH 2/2] random: add fork_event sysctl for polling VM forks

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Message-ID: <YnAnCgxmPBrMdKt5@zx2c4.com>
Date:   Mon, 2 May 2022 20:46:34 +0200
From:   "Jason A. Donenfeld" <Jason@...c4.com>
To:     Alexander Graf <graf@...zon.com>
Cc:     Lennart Poettering <mzxreary@...inter.de>,
        linux-kernel@...r.kernel.org, linux-crypto@...r.kernel.org,
        Dominik Brodowski <linux@...inikbrodowski.net>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Theodore Ts'o <tytso@....edu>,
        Colm MacCarthaigh <colmmacc@...zon.com>,
        Torben Hansen <htorben@...zon.co.uk>,
        Jann Horn <jannh@...gle.com>,
        "Michael Kelley (LINUX)" <mikelley@...rosoft.com>
Subject: Re: [PATCH 2/2] random: add fork_event sysctl for polling VM forks

On Mon, May 02, 2022 at 08:34:38PM +0200, Alexander Graf wrote:
> Michael, since we already changed the CID in the spec, can we add a 
> property to the device that indicates the first 4 bytes of the UUID will 
> always be different between parent and child?
> 
> That should give us the ability to mmap the vmgenid directly to user 
> space and act based on a simple u32 compare for clone notification, no?

That is not a good idea. We want an _additional_ 4 bytes, so that we can
keep the first 16 bytes (128 bits) as a kernel space secret.

Jason