Received-SPF: softfail (google.com: domain of transitioning linux-kernel-owner@vger.kernel.org does not designate 23.128.96.19 as permitted sender) client-ip=23.128.96.19;
Date:   Mon, 2 May 2022 20:46:34 +0200
From:   "Jason A. Donenfeld" <Jason@zx2c4.com>
To:     Alexander Graf <graf@amazon.com>
Cc:     Lennart Poettering <mzxreary@0pointer.de>,
        linux-kernel@vger.kernel.org, linux-crypto@vger.kernel.org,
        Dominik Brodowski <linux@dominikbrodowski.net>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Theodore Ts'o <tytso@mit.edu>,
        Colm MacCarthaigh <colmmacc@amazon.com>,
        Torben Hansen <htorben@amazon.co.uk>,
        Jann Horn <jannh@google.com>,
        "Michael Kelley (LINUX)" <mikelley@microsoft.com>
Subject: Re: [PATCH 2/2] random: add fork_event sysctl for polling VM forks
Message-ID: <YnAnCgxmPBrMdKt5@zx2c4.com>
References: <20220502140602.130373-1-Jason@zx2c4.com>
 <20220502140602.130373-2-Jason@zx2c4.com>
 <Ym/7UlgQ5VjjC76P@gardel-login>
 <YnAC00VtU8MGb7vO@zx2c4.com>
 <YnAMBzhcJhGR5XOK@gardel-login>
 <YnAc4hwPyByF4kZ5@zx2c4.com>
 <480469e6-0eb0-8d76-0b8d-111579e73701@amazon.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Disposition: inline
In-Reply-To: <480469e6-0eb0-8d76-0b8d-111579e73701@amazon.com>
Precedence: bulk

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