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Tsirkin" To: "Jason A. Donenfeld" Subject: Re: propagating vmgenid outward and upward Message-ID: <20220302024137-mutt-send-email-mst@kernel.org> References: <223f858c-34c5-3ccd-b9e8-7585a976364d@redhat.com> <20220301121419-mutt-send-email-mst@kernel.org> MIME-Version: 1.0 In-Reply-To: Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=mst@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Received-SPF: pass client-ip=170.10.129.124; envelope-from=mst@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -28 X-Spam_score: -2.9 X-Spam_bar: -- X-Spam_report: (-2.9 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.082, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H5=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: "Brown, Len" , linux-hyperv@vger.kernel.org, Colm MacCarthaigh , Daniel =?iso-8859-1?Q?P=2E_Berrang=E9?= , adrian@parity.io, KVM list , Jann Horn , Greg Kroah-Hartman , Linux PM , "Rafael J. Wysocki" , LKML , Dominik Brodowski , QEMU Developers , Alexander Graf , Linux Crypto Mailing List , Pavel Machek , Theodore Ts'o , "Michael Kelley \(LINUX\)" , Laszlo Ersek , Arnd Bergmann Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Tue, Mar 01, 2022 at 07:37:06PM +0100, Jason A. Donenfeld wrote: > Hi Michael, > > On Tue, Mar 1, 2022 at 6:17 PM Michael S. Tsirkin wrote: > > Hmm okay, so it's a performance optimization... some batching then? Do > > you really need to worry about every packet? Every 64 packets not > > enough? Packets are after all queued at NICs etc, and VM fork can > > happen after they leave wireguard ... > > Unfortunately, yes, this is an "every packet" sort of thing -- if the > race is to be avoided in a meaningful way. It's really extra bad: > ChaCha20 and AES-CTR work by xoring a secret stream of bytes with > plaintext to produce a ciphertext. If you use that same secret stream > and xor it with a second plaintext and transmit that too, an attacker > can combine the two different ciphertexts to learn things about the > original plaintext. So what about the point about packets queued then? You don't fish packets out of qdisc queues, do you? > But, anyway, it seems like the race is here to stay given what we have > _currently_ available with the virtual hardware. That's why I'm > focused on trying to get something going that's the least bad with > what we've currently got, which is racy by design. How vitally > important is it to have something that doesn't race in the far future? > I don't know, really. It seems plausible that that ACPI notifier > triggers so early that nothing else really even has a chance, so the > race concern is purely theoretical. But I haven't tried to measure > that so I'm not sure. > > Jason