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bh=BIYDINmA+s9L1cgWv2wqmURWttMuM0iVhSPANY/Lxn0=; b=Lr0/KFGULb8jdk12v9k9vmRc6DFMgnnFMnvk4o8m9xIzUt6p0KhzlQuABDpoOTa7riX3e9 FL/2DtSBGq3VjpdgwaaQx+//WKXL3mt8cfehegPsZXAbGZd/r91XUL7ttHoo7VeOflKAcu XLNmi0BQlBTmR29Qp46PpoBtD7Taaog= 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-34-5TIESmLUPS2mKTk-B8U5_w-1; Mon, 22 Feb 2021 13:15:31 -0500 X-MC-Unique: 5TIESmLUPS2mKTk-B8U5_w-1 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id CA7C6107ACF2; Mon, 22 Feb 2021 18:15:30 +0000 (UTC) Received: from redhat.com (ovpn-115-70.ams2.redhat.com [10.36.115.70]) by smtp.corp.redhat.com (Postfix) with ESMTPS id E253219725; Mon, 22 Feb 2021 18:15:16 +0000 (UTC) Date: Mon, 22 Feb 2021 18:15:13 +0000 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Philippe =?utf-8?Q?Mathieu-Daud=C3=A9?= Subject: Re: [PATCH v2 0/2] block: Use 'read-zeroes=true' mode by default with 'null-co' driver Message-ID: References: <20210211142656.3818078-1-philmd@redhat.com> <20210213215448.GA67780@ip-172-44-255-31> <3da6a2aa-472e-d9e1-b803-303891513274@redhat.com> <38dd38eb-af59-8baf-b908-fb6c4e842cd1@redhat.com> MIME-Version: 1.0 In-Reply-To: <38dd38eb-af59-8baf-b908-fb6c4e842cd1@redhat.com> User-Agent: Mutt/2.0.5 (2021-01-21) X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=berrange@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=170.10.133.124; envelope-from=berrange@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -27 X-Spam_score: -2.8 X-Spam_bar: -- X-Spam_report: (-2.8 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-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: , Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Cc: Fam Zheng , Laurent Vivier , Thomas Huth , qemu-block@nongnu.org, Markus Armbruster , qemu-devel@nongnu.org, Wainer dos Santos Moschetta , Max Reitz , Alexander Bulekov , Bandan Das , Paolo Bonzini , Stefan Hajnoczi , Cleber Rosa , Kevin Wolf Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Fri, Feb 19, 2021 at 03:09:43PM +0100, Philippe Mathieu-Daudé wrote: > On 2/19/21 12:07 PM, Max Reitz wrote: > > On 13.02.21 22:54, Fam Zheng wrote: > >> On 2021-02-11 15:26, Philippe Mathieu-Daudé wrote: > >>> The null-co driver doesn't zeroize buffer in its default config, > >>> because it is designed for testing and tests want to run fast. > >>> However this confuses security researchers (access to uninit > >>> buffers). > >> > >> I'm a little surprised. > >> > >> Is changing default the only way to fix this? I'm not opposed to > >> changing the default but I'm not convinced this is the easiest way. > >> block/nvme.c also doesn't touch the memory, but defers to the device > >> DMA, why doesn't that confuse the security checker? > > Generally speaking, there is a balance between security and performance. > We try to provide both, but when we can't, my understanding is security > is more important. > > Customers expect a secure product. If they prefer performance and > at the price of security, it is also possible by enabling an option > that is not the default. > > I'm not sure why you mention block/nvme here. I have the understanding > the null-co driver is only useful for testing. Are there production > cases where null-co is used? Do we have any real world figures for the performance of null-co with & without zero'ing ? Before worrying about a tradeoff of security vs performance, it'd be good to know if there is actually a real world performance problem in the first place. Personally I'd go for zero'ing by defualt unless the performance hit was really bad. > BTW block/nvme is a particular driver where performance matters more > than security (but we have to make sure the users are aware of that). 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 :|