From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 1D3B4C433EF for ; Wed, 2 Mar 2022 16:32:30 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S242281AbiCBQdJ (ORCPT ); Wed, 2 Mar 2022 11:33:09 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:38426 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S242543AbiCBQdC (ORCPT ); Wed, 2 Mar 2022 11:33:02 -0500 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 7E1B7C6255; Wed, 2 Mar 2022 08:32:19 -0800 (PST) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 1A2F6617F7; Wed, 2 Mar 2022 16:32:19 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 4FDCBC004E1; Wed, 2 Mar 2022 16:32:16 +0000 (UTC) Authentication-Results: smtp.kernel.org; dkim=pass (1024-bit key) header.d=zx2c4.com header.i=@zx2c4.com header.b="Jx2KF4SC" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=zx2c4.com; s=20210105; t=1646238734; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=pn15odJ1axHr1tSHXKM6R6gy8OQYz+UX/tuJV8kTZOI=; b=Jx2KF4SCMS6oQ81ruL+PmUOxb313LAgFJH4b+Nm/AbpnaHEQrJ93HFFJlkrZFljIclR1Ig 7MjMDAT88vIHvYQ5jVCXMswnqvnSTAn/DRep7zjTiB1RFfgW3eKlFxCp1420xGYalEM2Wc ntxUnKyAuMw/wp27G1pbbLokW2Kvk8w= Received: by mail.zx2c4.com (ZX2C4 Mail Server) with ESMTPSA id 6b026337 (TLSv1.3:AEAD-AES256-GCM-SHA384:256:NO); Wed, 2 Mar 2022 16:32:14 +0000 (UTC) Date: Wed, 2 Mar 2022 17:32:07 +0100 From: "Jason A. Donenfeld" To: "Michael S. Tsirkin" 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 =?utf-8?B?UC4gQmVycmFuZ8Op?= , 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: 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=utf-8 Content-Disposition: inline In-Reply-To: <20220302111737-mutt-send-email-mst@kernel.org> Precedence: bulk List-ID: X-Mailing-List: linux-crypto@vger.kernel.org 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 From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id B07C3C433EF for ; Wed, 2 Mar 2022 16:33:48 +0000 (UTC) Received: from localhost ([::1]:48318 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1nPRv9-0002W4-QN for qemu-devel@archiver.kernel.org; Wed, 02 Mar 2022 11:33:47 -0500 Received: from eggs.gnu.org ([209.51.188.92]:33182) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1nPRtt-0000Wg-1l for qemu-devel@nongnu.org; Wed, 02 Mar 2022 11:32:29 -0500 Received: from sin.source.kernel.org ([145.40.73.55]:37344) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1nPRtq-0000wM-Ot for qemu-devel@nongnu.org; Wed, 02 Mar 2022 11:32:28 -0500 Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by sin.source.kernel.org (Postfix) with ESMTPS id 33AA5CE2189; Wed, 2 Mar 2022 16:32:20 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 4FDCBC004E1; Wed, 2 Mar 2022 16:32:16 +0000 (UTC) Authentication-Results: smtp.kernel.org; dkim=pass (1024-bit key) header.d=zx2c4.com header.i=@zx2c4.com header.b="Jx2KF4SC" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=zx2c4.com; s=20210105; t=1646238734; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=pn15odJ1axHr1tSHXKM6R6gy8OQYz+UX/tuJV8kTZOI=; b=Jx2KF4SCMS6oQ81ruL+PmUOxb313LAgFJH4b+Nm/AbpnaHEQrJ93HFFJlkrZFljIclR1Ig 7MjMDAT88vIHvYQ5jVCXMswnqvnSTAn/DRep7zjTiB1RFfgW3eKlFxCp1420xGYalEM2Wc ntxUnKyAuMw/wp27G1pbbLokW2Kvk8w= Received: by mail.zx2c4.com (ZX2C4 Mail Server) with ESMTPSA id 6b026337 (TLSv1.3:AEAD-AES256-GCM-SHA384:256:NO); Wed, 2 Mar 2022 16:32:14 +0000 (UTC) Date: Wed, 2 Mar 2022 17:32:07 +0100 From: "Jason A. Donenfeld" To: "Michael S. Tsirkin" Subject: Re: propagating vmgenid outward and upward Message-ID: 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=utf-8 Content-Disposition: inline In-Reply-To: <20220302111737-mutt-send-email-mst@kernel.org> Received-SPF: pass client-ip=145.40.73.55; envelope-from=SRS0=fxzG=TN=zx2c4.com=Jason@kernel.org; helo=sin.source.kernel.org X-Spam_score_int: -67 X-Spam_score: -6.8 X-Spam_bar: ------ X-Spam_report: (-6.8 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, HEADER_FROM_DIFFERENT_DOMAINS=0.249, RCVD_IN_DNSWL_HI=-5, 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 =?utf-8?B?UC4gQmVycmFuZ8Op?= , 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" 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