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 4FB06EE49B0 for ; Wed, 23 Aug 2023 10:25:56 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233615AbjHWKZy (ORCPT ); Wed, 23 Aug 2023 06:25:54 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:51708 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233546AbjHWKZt (ORCPT ); Wed, 23 Aug 2023 06:25:49 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 5AAB7193; Wed, 23 Aug 2023 03:25:45 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id CB458619FD; Wed, 23 Aug 2023 10:25:44 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 8125AC433C7; Wed, 23 Aug 2023 10:25:43 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1692786344; bh=1SoNFlSDBESEpcUsmvCkcrZqM4mjft2HogS2NbeyGmE=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=E+vlYrSdAnPcxsYLLO0ChKFjh+9XZ9zyLgRhKIgkovbbZIZeZ7KMiIpxNmZSyQsib XUqttnDDlRKi8yHkzUyoVLIAFjZE9HQ5iBqaYvdUxO7HHNVceekz6YVg0Z/+PIoVXk 2qGQRJCr5xBydAuNg9TMlrZGkrvrkOt1txoiQ3ag= Date: Wed, 23 Aug 2023 12:25:41 +0200 From: Greg KH To: Babis Chalios Cc: Olivia Mackall , Herbert Xu , Theodore Ts'o , "Jason A. Donenfeld" , "Michael S. Tsirkin" , Jason Wang , Xuan Zhuo , linux-crypto@vger.kernel.org, linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org, graf@amazon.de, xmarcalx@amazon.co.uk, aams@amazon.de, dwmw@amazon.co.uk Subject: Re: [RFC PATCH 1/2] random: emit reseed notifications for PRNGs Message-ID: <2023082317-bauble-appeasing-90c0@gregkh> References: <20230823090107.65749-1-bchalios@amazon.es> <20230823090107.65749-2-bchalios@amazon.es> <2023082322-semester-heave-e5bc@gregkh> <2023082340-daybreak-lagged-f157@gregkh> <89ce1064-e4a3-461f-8a78-88e72e5b6419@amazon.es> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <89ce1064-e4a3-461f-8a78-88e72e5b6419@amazon.es> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Aug 23, 2023 at 12:08:35PM +0200, Babis Chalios wrote: > > > On 23/8/23 12:06, Greg KH wrote: > > CAUTION: This email originated from outside of the organization. Do not click links or open attachments unless you can confirm the sender and know the content is safe. > > > > > > > > On Wed, Aug 23, 2023 at 11:27:11AM +0200, Babis Chalios wrote: > > > Hi Greg, > > > > > > On 23/8/23 11:08, Greg KH wrote: > > > > CAUTION: This email originated from outside of the organization. Do not click links or open attachments unless you can confirm the sender and know the content is safe. > > > > > > > > > > > > > > > > On Wed, Aug 23, 2023 at 11:01:05AM +0200, Babis Chalios wrote: > > > > > Sometimes, PRNGs need to reseed. For example, on a regular timer > > > > > interval, to ensure nothing consumes a random value for longer than e.g. > > > > > 5 minutes, or when VMs get cloned, to ensure seeds don't leak in to > > > > > clones. > > > > > > > > > > The notification happens through a 32bit epoch value that changes every > > > > > time cached entropy is no longer valid, hence PRNGs need to reseed. User > > > > > space applications can get hold of a pointer to this value through > > > > > /dev/(u)random. We introduce a new ioctl() that returns an anonymous > > > > > file descriptor. From this file descriptor we can mmap() a single page > > > > > which includes the epoch at offset 0. > > > > > > > > > > random.c maintains the epoch value in a global shared page. It exposes > > > > > a registration API for kernel subsystems that are able to notify when > > > > > reseeding is needed. Notifiers register with random.c and receive a > > > > > unique 8bit ID and a pointer to the epoch. When they need to report a > > > > > reseeding event they write a new epoch value which includes the > > > > > notifier ID in the first 8 bits and an increasing counter value in the > > > > > remaining 24 bits: > > > > > > > > > > RNG epoch > > > > > *-------------*---------------------* > > > > > | notifier id | epoch counter value | > > > > > *-------------*---------------------* > > > > > 8 bits 24 bits > > > > Why not just use 32/32 for a full 64bit value, or better yet, 2 > > > > different variables? Why is 32bits and packing things together here > > > > somehow simpler? > > > We made it 32 bits so that we can read/write it atomically in all 32bit > > > architectures. > > > Do you think that's not a problem? > > What 32bit platforms care about this type of interface at all? > > I think, any 32bit platform that gets random bytes from the kernel. You are making a new api, for some new functionality, for what I thought was virtual machines (hence the virtio driver), none of which work in a 32bit system. I thought this was an ioctl for userspace, which can handle 64bits at once (or 2 32bit numbers). For internal kernel stuff, a lock should be fine, or better yet, a 64bit atomic value read (horrible on 32bit platforms, I know...) Just asking, it feels odd to pack bits in these days for when 90% of the cpus really don't need it. greg k-h