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From: Willy Tarreau <w@1wt.eu>
To: Jann Horn <jannh@google.com>
Cc: Jason Donenfeld <Jason@zx2c4.com>, KVM list <kvm@vger.kernel.org>,
	"open list:DOCUMENTATION" <linux-doc@vger.kernel.org>,
	ghammer@redhat.com, "Weiss, Radu" <raduweis@amazon.com>,
	Qemu Developers <qemu-devel@nongnu.org>,
	"open list:VIRTIO GPU DRIVER"
	<virtualization@lists.linux-foundation.org>,
	Pavel Machek <pavel@ucw.cz>,
	Colm MacCarthaigh <colmmacc@amazon.com>,
	Jonathan Corbet <corbet@lwn.net>,
	"Michael S. Tsirkin" <mst@redhat.com>,
	Eric Biggers <ebiggers@kernel.org>,
	"Singh, Balbir" <sblbir@amazon.com>,
	bonzini@gnu.org, "Graf \(AWS\), Alexander" <graf@amazon.de>,
	oridgar@gmail.com, "Catangiu, Adrian Costin" <acatan@amazon.com>,
	Andy Lutomirski <luto@kernel.org>,
	Michal Hocko <mhocko@kernel.org>,
	"Theodore Y. Ts'o" <tytso@mit.edu>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	kernel list <linux-kernel@vger.kernel.org>,
	Linux API <linux-api@vger.kernel.org>,
	"Rafael J. Wysocki" <rafael@kernel.org>,
	"Woodhouse, David" <dwmw@amazon.co.uk>
Subject: Re: [PATCH] drivers/virt: vmgenid: add vm generation id driver
Date: Sat, 17 Oct 2020 09:17:21 +0200
Message-ID: <20201017071721.GA14143@1wt.eu> (raw)
In-Reply-To: <CAG48ez3pXLC+eqAXDCniM0a+5yP2XJODDkZqiUTZUOttCE_LbA@mail.gmail.com>

On Sat, Oct 17, 2020 at 08:55:34AM +0200, Jann Horn wrote:
> My suggestion is to use a counter *in the UAPI*, not in the hypervisor
> protocol. (And as long as that counter can only miss increments in a
> cryptographically negligible fraction of cases, everything's fine.)

OK I got it now and I agree.

> > If what is sought is pure
> > randomness (in the sense that it's unpredictable, which I don't think
> > is needed here), then randoms are better.
> 
> And this is what *the hypervisor protocol* gives us (which could be
> very useful for reseeding the kernel RNG).

As an external source, yes very likely, as long as it's not trivially
observable by everyone under the same hypervisor :-)

> > Now the initial needs in the forwarded message are not entirely clear
> > to me but I wanted to rule out the apparent mismatch between the expressed
> > needs for uniqueness and the proposed solutions solely based on randomness.
> 
> Sure, from a theoretical standpoint, it would be a little bit nicer if
> the hypervisor protocol included a generation number along with the
> 128-bit random value. But AFAIU it doesn't, so if we want this to just
> work under Microsoft's existing hypervisor, we'll have to make do with
> checking whether the random value changed. :P

OK got it, thanks for the explanation!

Willy


  reply index

Thread overview: 30+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <AQHWo8lIfZnFKGe8nkGmhTCXwq5R3w==>
2020-10-16 14:33 ` Catangiu, Adrian Costin
2020-10-16 15:00   ` Catangiu, Adrian Costin
2020-10-16 15:14   ` gregkh
2020-10-17  1:40   ` Jann Horn
2020-10-17  3:36     ` Willy Tarreau
2020-10-17  4:02       ` Jann Horn
2020-10-17  4:34         ` Colm MacCarthaigh
2020-10-17  5:01           ` Jann Horn
2020-10-17  5:29             ` Colm MacCarthaigh
2020-10-17  5:37             ` Willy Tarreau
2020-10-17  5:52               ` Jann Horn
2020-10-17  6:44                 ` Willy Tarreau
2020-10-17  6:55                   ` Jann Horn
2020-10-17  7:17                     ` Willy Tarreau [this message]
2020-10-17 13:24                     ` Jason A. Donenfeld
2020-10-17 18:06                       ` Catangiu, Adrian Costin
2020-10-17 18:09                       ` Alexander Graf
2020-10-18  2:08                         ` Jann Horn
2020-10-20  9:35                         ` Christian Borntraeger
2020-10-20  9:54                           ` Alexander Graf
2020-10-20 16:54                         ` Catangiu, Adrian Costin
2020-10-18  3:14                       ` Colm MacCarthaigh
2020-10-18 15:52                       ` Michael S. Tsirkin
2020-10-18 15:54                         ` Andy Lutomirski
2020-10-18 15:59                           ` Michael S. Tsirkin
2020-10-18 16:14                             ` Andy Lutomirski
2020-10-19 15:00                               ` Michael S. Tsirkin
2020-10-17 18:10     ` Andy Lutomirski
2020-10-19 17:15       ` Mathieu Desnoyers
2020-10-20 10:00         ` Alexander Graf

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