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From: "Jason A. Donenfeld" <Jason@zx2c4.com>
To: "Michael S. Tsirkin" <mst@redhat.com>
Cc: "Laszlo Ersek" <lersek@redhat.com>,
	LKML <linux-kernel@vger.kernel.org>,
	"KVM list" <kvm@vger.kernel.org>,
	"QEMU Developers" <qemu-devel@nongnu.org>,
	linux-hyperv@vger.kernel.org,
	"Linux Crypto Mailing List" <linux-crypto@vger.kernel.org>,
	"Alexander Graf" <graf@amazon.com>,
	"Michael Kelley (LINUX)" <mikelley@microsoft.com>,
	"Greg Kroah-Hartman" <gregkh@linuxfoundation.org>,
	adrian@parity.io, "Daniel P. Berrangé" <berrange@redhat.com>,
	"Dominik Brodowski" <linux@dominikbrodowski.net>,
	"Jann Horn" <jannh@google.com>,
	"Rafael J. Wysocki" <rafael@kernel.org>,
	"Brown, Len" <len.brown@intel.com>, "Pavel Machek" <pavel@ucw.cz>,
	"Linux PM" <linux-pm@vger.kernel.org>,
	"Colm MacCarthaigh" <colmmacc@amazon.com>,
	"Theodore Ts'o" <tytso@mit.edu>, "Arnd Bergmann" <arnd@arndb.de>
Subject: Re: propagating vmgenid outward and upward
Date: Wed, 2 Mar 2022 16:14:56 +0100	[thread overview]
Message-ID: <CAHmME9rf7hQP78kReP2diWNeX=obPem=f8R-dC7Wkpic2xmffg@mail.gmail.com> (raw)
In-Reply-To: <20220302092149-mutt-send-email-mst@kernel.org>

Hi Michael,

On Wed, Mar 2, 2022 at 3:46 PM Michael S. Tsirkin <mst@redhat.com> wrote:
> I just don't see how "value changed while it was read" is so different
> from "value changed one clock after it was read".  Since we don't detect
> the latter I don't see why we should worry about the former.

The "barrier" is at the point where the plaintext has been chosen AND
the nonce for a given keypair has been selected. So, if you have
plaintext in a buffer, and a key in a buffer, and the nonce for that
encryption in a buffer, and then after those are all selected, you
check to see if the vmgenid has changed since the birth of that key,
then you're all set. If it changes _after_ that point of check (your
"one clock after"), it doesn't matter: you'll just be
double-transmitting the same ciphertext, which is something that flaky
wifi sometimes does _anyway_ (and attackers can do intentionally), so
network protocols already are resilient to replay. This is the same
case you asked about earlier, and then answered yourself, when you
were wondering about reaching down into qdiscs.

Jason

WARNING: multiple messages have this Message-ID (diff)
From: "Jason A. Donenfeld" <Jason@zx2c4.com>
To: "Michael S. Tsirkin" <mst@redhat.com>
Cc: "Brown, Len" <len.brown@intel.com>,
	linux-hyperv@vger.kernel.org,
	"Colm MacCarthaigh" <colmmacc@amazon.com>,
	"Daniel P. Berrangé" <berrange@redhat.com>,
	adrian@parity.io, "KVM list" <kvm@vger.kernel.org>,
	"Jann Horn" <jannh@google.com>,
	"Greg Kroah-Hartman" <gregkh@linuxfoundation.org>,
	"Linux PM" <linux-pm@vger.kernel.org>,
	"Rafael J. Wysocki" <rafael@kernel.org>,
	LKML <linux-kernel@vger.kernel.org>,
	"Dominik Brodowski" <linux@dominikbrodowski.net>,
	"QEMU Developers" <qemu-devel@nongnu.org>,
	"Alexander Graf" <graf@amazon.com>,
	"Linux Crypto Mailing List" <linux-crypto@vger.kernel.org>,
	"Pavel Machek" <pavel@ucw.cz>, "Theodore Ts'o" <tytso@mit.edu>,
	"Michael Kelley (LINUX)" <mikelley@microsoft.com>,
	"Laszlo Ersek" <lersek@redhat.com>,
	"Arnd Bergmann" <arnd@arndb.de>
Subject: Re: propagating vmgenid outward and upward
Date: Wed, 2 Mar 2022 16:14:56 +0100	[thread overview]
Message-ID: <CAHmME9rf7hQP78kReP2diWNeX=obPem=f8R-dC7Wkpic2xmffg@mail.gmail.com> (raw)
In-Reply-To: <20220302092149-mutt-send-email-mst@kernel.org>

Hi Michael,

On Wed, Mar 2, 2022 at 3:46 PM Michael S. Tsirkin <mst@redhat.com> wrote:
> I just don't see how "value changed while it was read" is so different
> from "value changed one clock after it was read".  Since we don't detect
> the latter I don't see why we should worry about the former.

The "barrier" is at the point where the plaintext has been chosen AND
the nonce for a given keypair has been selected. So, if you have
plaintext in a buffer, and a key in a buffer, and the nonce for that
encryption in a buffer, and then after those are all selected, you
check to see if the vmgenid has changed since the birth of that key,
then you're all set. If it changes _after_ that point of check (your
"one clock after"), it doesn't matter: you'll just be
double-transmitting the same ciphertext, which is something that flaky
wifi sometimes does _anyway_ (and attackers can do intentionally), so
network protocols already are resilient to replay. This is the same
case you asked about earlier, and then answered yourself, when you
were wondering about reaching down into qdiscs.

Jason


  reply	other threads:[~2022-03-02 15:15 UTC|newest]

Thread overview: 61+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-03-01 15:42 propagating vmgenid outward and upward Jason A. Donenfeld
2022-03-01 16:15 ` Laszlo Ersek
2022-03-01 16:28   ` Jason A. Donenfeld
2022-03-01 16:28     ` Jason A. Donenfeld
2022-03-01 17:17     ` Michael S. Tsirkin
2022-03-01 17:17       ` Michael S. Tsirkin
2022-03-01 18:37       ` Jason A. Donenfeld
2022-03-01 18:37         ` Jason A. Donenfeld
2022-03-02  7:42         ` Michael S. Tsirkin
2022-03-02  7:42           ` Michael S. Tsirkin
2022-03-02  7:48           ` Michael S. Tsirkin
2022-03-02  7:48             ` Michael S. Tsirkin
2022-03-02  8:30         ` Michael S. Tsirkin
2022-03-02  8:30           ` Michael S. Tsirkin
2022-03-02 11:26           ` Jason A. Donenfeld
2022-03-02 11:26             ` Jason A. Donenfeld
2022-03-02 12:58             ` Michael S. Tsirkin
2022-03-02 12:58               ` Michael S. Tsirkin
2022-03-02 13:55               ` Jason A. Donenfeld
2022-03-02 13:55                 ` Jason A. Donenfeld
2022-03-02 14:46                 ` Michael S. Tsirkin
2022-03-02 14:46                   ` Michael S. Tsirkin
2022-03-02 15:14                   ` Jason A. Donenfeld [this message]
2022-03-02 15:14                     ` Jason A. Donenfeld
2022-03-02 15:20                     ` Michael S. Tsirkin
2022-03-02 15:20                       ` Michael S. Tsirkin
2022-03-02 15:36                       ` Jason A. Donenfeld
2022-03-02 15:36                         ` Jason A. Donenfeld
2022-03-02 16:22                         ` Michael S. Tsirkin
2022-03-02 16:22                           ` Michael S. Tsirkin
2022-03-02 16:32                           ` Jason A. Donenfeld
2022-03-02 16:32                             ` Jason A. Donenfeld
2022-03-02 17:27                             ` Michael S. Tsirkin
2022-03-02 17:27                               ` Michael S. Tsirkin
2022-03-03 13:07                             ` Michael S. Tsirkin
2022-03-03 13:07                               ` Michael S. Tsirkin
2022-03-02 16:29                         ` Michael S. Tsirkin
2022-03-02 16:29                           ` Michael S. Tsirkin
2022-03-01 16:21 ` Michael S. Tsirkin
2022-03-01 16:21   ` Michael S. Tsirkin
2022-03-01 16:35   ` Jason A. Donenfeld
2022-03-01 16:35     ` Jason A. Donenfeld
2022-03-01 18:01 ` Greg KH
2022-03-01 18:01   ` Greg KH
2022-03-01 18:24   ` Jason A. Donenfeld
2022-03-01 18:24     ` Jason A. Donenfeld
2022-03-01 19:41     ` Greg KH
2022-03-01 19:41       ` Greg KH
2022-03-01 23:12       ` Jason A. Donenfeld
2022-03-01 23:12         ` Jason A. Donenfeld
2022-03-02 14:35 ` Jason A. Donenfeld
2022-03-09 10:10 ` Alexander Graf
2022-03-09 22:02   ` Jason A. Donenfeld
2022-03-09 22:02     ` Jason A. Donenfeld
2022-03-10 11:18     ` Alexander Graf
2022-03-20 22:53       ` Michael S. Tsirkin
2022-03-20 22:53         ` Michael S. Tsirkin
2022-04-19 15:12       ` Jason A. Donenfeld
2022-04-19 15:12         ` Jason A. Donenfeld
2022-04-19 16:43         ` Michael S. Tsirkin
2022-04-19 16:43           ` Michael S. Tsirkin

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