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Thu, 20 Aug 2020 17:55:15 +0000 (UTC) Date: Thu, 20 Aug 2020 18:55:12 +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: <20200820175512.GQ2664@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> MIME-Version: 1.0 In-Reply-To: <20200820175149.GA244434@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=iso-8859-1 Content-Transfer-Encoding: 8bit Content-Disposition: inline Received-SPF: pass client-ip=205.139.110.61; envelope-from=dgilbert@redhat.com; helo=us-smtp-delivery-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/08/20 03:03:34 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, Chuan Zheng , 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 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 :| -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK