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 X-Spam-Level: X-Spam-Status: No, score=-6.0 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 1BA34C433ED for ; Mon, 12 Apr 2021 19:20:50 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id E745660200 for ; Mon, 12 Apr 2021 19:20:49 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S245191AbhDLTVC (ORCPT ); Mon, 12 Apr 2021 15:21:02 -0400 Received: from mail.kernel.org ([198.145.29.99]:59456 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S237286AbhDLTU6 (ORCPT ); Mon, 12 Apr 2021 15:20:58 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id D493961355; Mon, 12 Apr 2021 19:20:35 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1618255236; bh=us+Qc1vT3f53J+ggtKPb/+ymp1HxiNch+u06FxUBXUY=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=H0X16zKxKe1LhLzjb8sgtgoVRLivxcOvs85HWh8i3MZXStYMc6bJiG/IEnuSMsBtB honZi1B21HE09B6pMjjWxMemocS7T98zi1ELFCMl2i722cft2u5QaHP9OTVp2wGN8K +yKw1nFdN6FuyeQi75xUk5qmBfms3Ea7urByzkz6hJLRvp7e2vkO3TpjekzMzAjw6h Wlv/eTjgNx/11YByBp15yrd6lyqGFT7dppOn6D0cOSPQznN8HAzndO6H2g7yyP2Ig7 Cm+tYGAP4mlbDqfrQ9A8m4QT5vpUz6diV5WrKf47BaxLc4QTHwL3DxrtqY2iIA+bJz Y5ZSVNVrQuvGQ== Date: Mon, 12 Apr 2021 12:20:33 -0700 From: Eric Biggers To: Chris von Recklinghausen Cc: ardb@kernel.org, simo@redhat.com, rafael@kernel.org, decui@microsoft.com, linux-pm@vger.kernel.org, linux-crypto@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v6 1/1] use crc32 instead of md5 for hibernation e820 integrity check Message-ID: References: <20210412140932.31162-1-crecklin@redhat.com> <5795c815-7715-1ecb-dd83-65f3d18b9092@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <5795c815-7715-1ecb-dd83-65f3d18b9092@redhat.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Apr 12, 2021 at 03:04:58PM -0400, Chris von Recklinghausen wrote: > On 4/12/21 1:45 PM, Eric Biggers wrote: > > On Mon, Apr 12, 2021 at 10:09:32AM -0400, Chris von Recklinghausen wrote: > > > Suspend fails on a system in fips mode because md5 is used for the e820 > > > integrity check and is not available. Use crc32 instead. > > > > > > This patch changes the integrity check algorithm from md5 to crc32. > > > > > > The purpose of the integrity check is to detect possible differences > > > between the memory map used at the time when the hibernation image is > > > about to be loaded into memory and the memory map used at the image > > > creation time, because it is generally unsafe to load the image if the > > > current memory map doesn't match the one used when it was created. so > > > it is not intended as a cryptographic integrity check. > > This still doesn't actually explain why a non-cryptographic checksum is > > sufficient. "Detection of possible differences" could very well require > > cryptographic authentication; it depends on whether malicious changes need to be > > detected or not. > > Hi Eric, > > The cases that the commit comments for 62a03defeabd mention are the same as > for this patch, e.g. > >     1. Without this patch applied, it is possible that BIOS has >        provided an inconsistent memory map, but the resume kernel is still >        able to restore the image anyway(e.g, E820_RAM region is the superset >        of the previous one), although the system might be unstable. So this >        patch tries to treat any inconsistent e820 as illegal. > >     2. Another case is, this patch replies on comparing the e820_saved, but >        currently the e820_save might not be strictly the same across >        hibernation, even if BIOS has provided consistent e820 map - In >        theory mptable might modify the BIOS-provided e820_saved dynamically >        in early_reserve_e820_mpc_new, which would allocate a buffer from >        E820_RAM, and marks it from E820_RAM to E820_RESERVED). >        This is a potential and rare case we need to deal with in OS in >        the future. > > Maybe they should be added to the comments with this patch as well? In any > case, the above comments only mention detecting consequences of BIOS > issues/actions on the e820 map and not intrusions from attackers requiring > cryptographic protection. Does that seem to be a reasonable explanation to > you? If so I can add these to the commit comments. > > I'll make the other changes you suggest below. > > Thanks, > Those details are still missing the high-level point. Is this just meant to detect non-malicious changes (presumably caused by BIOS bugs), or is it meant to detect malicious changes? That's all that really needs to be mentioned. - Eric