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 DEA8FEE4993 for ; Wed, 23 Aug 2023 09:21:22 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234797AbjHWJVN (ORCPT ); Wed, 23 Aug 2023 05:21:13 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:56560 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235579AbjHWJSo (ORCPT ); Wed, 23 Aug 2023 05:18:44 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 722C33A93; Wed, 23 Aug 2023 02:08:09 -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 0841462C55; Wed, 23 Aug 2023 09:08:09 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 99F3CC433C7; Wed, 23 Aug 2023 09:08:07 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1692781688; bh=io4Q0PxusKKtCDplWhMVdna1pz9TzX1YUrlW8pFjO1A=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=XAA2JrXx6qAAt+nZq1vahQ+uXOCJ1xlcmx538cqtPSkgfM9aaoHDFrV5McTfaba+x CM20rqIIJEXxfCH5pGV8PZS/PwKcnRSImWu5BPjBARP75nnyoDPFwhYhue8KiQhZgK ei+3vUUWk1gKp9TlE80sWmmW0qv/JNHNV+1+PVvY= Date: Wed, 23 Aug 2023 11:08:05 +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: <2023082322-semester-heave-e5bc@gregkh> References: <20230823090107.65749-1-bchalios@amazon.es> <20230823090107.65749-2-bchalios@amazon.es> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230823090107.65749-2-bchalios@amazon.es> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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? thanks, greg k-h