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=-11.1 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=ham 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 6D418C433E4 for ; Fri, 21 Aug 2020 12:40:11 +0000 (UTC) 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 mail.kernel.org (Postfix) with ESMTPS id 3AFBE207DA for ; Fri, 21 Aug 2020 12:40:11 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="CzF0fOBH" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 3AFBE207DA Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:49534 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1k96L4-0003Kv-Hk for qemu-devel@archiver.kernel.org; Fri, 21 Aug 2020 08:40:10 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:34718) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1k96KJ-0002XZ-Ov for qemu-devel@nongnu.org; Fri, 21 Aug 2020 08:39:23 -0400 Received: from us-smtp-1.mimecast.com ([207.211.31.81]:56914 helo=us-smtp-delivery-1.mimecast.com) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1k96KG-0002BJ-IA for qemu-devel@nongnu.org; Fri, 21 Aug 2020 08:39:23 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1598013559; 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: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=exZ6e8JZ5+9mEgtc0J7odTL5oVSyrezyCyIp/SW25tE=; b=CzF0fOBHEvKC7x/IHNLkgWV/o/oAGgN8s1a5Frgp+se5i0F8U+r7RCntI9NG48VFd09Kuc ec1H5gOGKJgH/FJDdakXwpTtg3LPlHmMqSBx9KecJMd/Lf+YeB4zWPkMsQHZ9OZR4o8zKB EBkQxw43R2F0rUAfN5+1QKRoISUU35Y= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-579-zomGM9XRPz-kKLoZn4nUNQ-1; Fri, 21 Aug 2020 08:39:16 -0400 X-MC-Unique: zomGM9XRPz-kKLoZn4nUNQ-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 9BE9480733D; Fri, 21 Aug 2020 12:39:14 +0000 (UTC) Received: from work-vm (ovpn-113-246.ams2.redhat.com [10.36.113.246]) by smtp.corp.redhat.com (Postfix) with ESMTPS id A96D374E2A; Fri, 21 Aug 2020 12:39:12 +0000 (UTC) Date: Fri, 21 Aug 2020 13:39:10 +0100 From: "Dr. David Alan Gilbert" To: Daniel =?iso-8859-1?Q?P=2E_Berrang=E9?= Subject: Re: [PATCH v3 05/10] migration/dirtyrate: Record hash results for each sampled page Message-ID: <20200821123910.GC2655@work-vm> References: <1597634433-18809-1-git-send-email-zhengchuan@huawei.com> <1597634433-18809-6-git-send-email-zhengchuan@huawei.com> <20200820173009.GM2664@work-vm> <20200820175149.GA244434@redhat.com> <20200820175512.GQ2664@work-vm> <95894cf7-ba09-9862-357a-1073a192e934@huawei.com> <20200821123014.GK348677@redhat.com> MIME-Version: 1.0 In-Reply-To: <20200821123014.GK348677@redhat.com> User-Agent: Mutt/1.14.6 (2020-07-11) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=dgilbert@redhat.com X-Mimecast-Spam-Score: 0.002 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Content-Disposition: inline Received-SPF: pass client-ip=207.211.31.81; envelope-from=dgilbert@redhat.com; helo=us-smtp-delivery-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/08/21 05:15:56 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -40 X-Spam_score: -4.1 X-Spam_bar: ---- X-Spam_report: (-4.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=-1, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, URIBL_BLOCKED=0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: alex.chen@huawei.com, zhang.zhanghailiang@huawei.com, quintela@redhat.com, linyilu@huawei.com, qemu-devel@nongnu.org, Zheng Chuan , ann.zhuangyanying@huawei.com, fangying1@huawei.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" * Daniel P. Berrangé (berrange@redhat.com) wrote: > On Fri, Aug 21, 2020 at 08:22:06PM +0800, Zheng Chuan wrote: > > > > > > On 2020/8/21 1:55, Dr. David Alan Gilbert wrote: > > > * Daniel P. Berrangé (berrange@redhat.com) wrote: > > >> On Thu, Aug 20, 2020 at 06:30:09PM +0100, Dr. David Alan Gilbert wrote: > > >>> * Chuan Zheng (zhengchuan@huawei.com) wrote: > > >>>> Record hash results for each sampled page. > > >>>> > > >>>> Signed-off-by: Chuan Zheng > > >>>> Signed-off-by: YanYing Zhuang > > >>>> --- > > >>>> migration/dirtyrate.c | 144 ++++++++++++++++++++++++++++++++++++++++++++++++++ > > >>>> migration/dirtyrate.h | 7 +++ > > >>>> 2 files changed, 151 insertions(+) > > >>>> > > >>>> diff --git a/migration/dirtyrate.c b/migration/dirtyrate.c > > >>>> index c4304ef..62b6f69 100644 > > >>>> --- a/migration/dirtyrate.c > > >>>> +++ b/migration/dirtyrate.c > > >>>> @@ -25,6 +25,7 @@ > > >>>> #include "dirtyrate.h" > > >>>> > > >>>> CalculatingDirtyRateState CalculatingState = CAL_DIRTY_RATE_INIT; > > >>>> +static unsigned long int qcrypto_hash_len = QCRYPTO_HASH_LEN; > > >>> > > >>> Why do we need this static rather than just using the QCRYPTO_HASH_LEN ? > > >>> It's never going to change is it? > > >>> (and anyway it's just a MD5 len?) > > >> > > >> I wouldn't want to bet on that given that this is use of MD5. We might > > >> claim this isn't security critical, but surprises happen, and we will > > >> certainly be dinged on security audits for introducing new use of MD5 > > >> no matter what. > > >> > > >> If a cryptographic hash is required, then sha256 should be the choice > > >> for any new code that doesn't have back compat requirements. > > >> > > >> If a cryptographic hash is not required then how about crc32 > > > > > > It doesn't need to be cryptographic; is crc32 the fastest reasonable hash for use > > > in large areas? > > > > > > Dave > > > > > >> IOW, it doesn't make a whole lot of sense to say we need a cryptographic > > >> hash, but then pick the most insecure one. > > >> > > >> sha256 is slower than md5, but it is conceivable that in future we might > > >> gain support for something like Blake2b which is similar security level > > >> to SHA3, while being faster than MD5. > > >> > > >> Overall I'm pretty unethusiastic about use of MD5 being introduced and > > >> worse, being hardcoded as the only option. > > >> > > >> Regards, > > >> Daniel > > >> -- > > >> |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| > > >> |: https://libvirt.org -o- https://fstop138.berrange.com :| > > >> |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :| > > > > Hi, Daniel, Dave. > > > > I do compare MD5 and SHA256 with vm memory of 128G under mempress of 100G. > > > > 1. Calculation speed > > 1） MD5 takes about 500ms to sample and hash all pages by record_ramblock_hash_info(). > > 2) SHA256 takes about 750ms to sample all pages by record_ramblock_hash_info(). > > > > 2. CPU Consumption > > 1) MD5 may have instant rise up to 48% for dirtyrate thread > > 2) SHA256 may have instant rise up to 75% for dirtyrate thread > > > > 3. Memory Consumption > > SHA256 may need twice memory than MD5 due to its HASH_LEN. > > > > I am trying to consider if crc32 is more faster and takes less memory and is more safer than MD5? > > No, crc32 is absolutely *weaker* than MD5. It is NOT a cryptographic > hash so does not try to guarantee collision resistance. It only has > 2^32 possible outputs. > > MD5 does try to guarantee collision resistance, but MD5 is considered > broken these days, so a malicious attacker can cause collisions if they > are motivated enough. > > IOW if you need collision resistance that SHA256 should be used. There's no need to guard against malicious behaviour here - this is just a stat to guide migration. If CRC32 is likely to be faster than md5 I suspect it's enough. Dave > > Regards, > Daniel > -- > |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| > |: https://libvirt.org -o- https://fstop138.berrange.com :| > |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :| -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK