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Tsirkin" To: "Jason A. Donenfeld" Cc: Laszlo Ersek , LKML , KVM list , QEMU Developers , linux-hyperv@vger.kernel.org, Linux Crypto Mailing List , Alexander Graf , "Michael Kelley (LINUX)" , Greg Kroah-Hartman , adrian@parity.io, Daniel =?iso-8859-1?Q?P=2E_Berrang=E9?= , Dominik Brodowski , Jann Horn , "Rafael J. Wysocki" , "Brown, Len" , Pavel Machek , Linux PM , Colm MacCarthaigh , Theodore Ts'o , Arnd Bergmann Subject: Re: propagating vmgenid outward and upward Message-ID: <20220302122640-mutt-send-email-mst@kernel.org> References: <20220302031738-mutt-send-email-mst@kernel.org> <20220302074503-mutt-send-email-mst@kernel.org> <20220302092149-mutt-send-email-mst@kernel.org> <20220302101602-mutt-send-email-mst@kernel.org> <20220302111737-mutt-send-email-mst@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-hyperv@vger.kernel.org On Wed, Mar 02, 2022 at 05:32:07PM +0100, Jason A. Donenfeld wrote: > Hi Michael, > > On Wed, Mar 02, 2022 at 11:22:46AM -0500, Michael S. Tsirkin wrote: > > > Because that 16 byte read of vmgenid is not atomic. Let's say you read > > > the first 8 bytes, and then the VM is forked. > > > > But at this point when VM was forked plaintext key and nonce are all in > > buffer, and you previously indicated a fork at this point is harmless. > > You wrote "If it changes _after_ that point of check ... it doesn't > > matter:" > > Ahhh, fair point. I think you're right. > > Alright, so all we're talking about here is an ordinary 16-byte read, > and 16 bytes of storage per keypair, and a 16-byte comparison. > > Still seems much worse than just having a single word... > > Jason And it is, I saw a 30% higher overhead, it is however 30% of a very low number ;) -- MST