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[83.57.175.68]) by smtp.gmail.com with ESMTPSA id ck9sm12009559edb.36.2021.02.22.10.36.39 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 22 Feb 2021 10:36:40 -0800 (PST) Subject: Re: [PATCH v2 0/2] block: Use 'read-zeroes=true' mode by default with 'null-co' driver To: =?UTF-8?Q?Daniel_P=2e_Berrang=c3=a9?= 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> From: =?UTF-8?Q?Philippe_Mathieu-Daud=c3=a9?= Message-ID: Date: Mon, 22 Feb 2021 19:36:39 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.7.0 MIME-Version: 1.0 In-Reply-To: Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=philmd@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=63.128.21.124; envelope-from=philmd@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, NICE_REPLY_A=-0.001, 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=unavailable 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: 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 2/22/21 7:15 PM, Daniel P. Berrangé wrote: > 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. I simply wanted to help the security team by removing the amount of reports using the null-co driver. This is probably easier to resolve with one documentation line. As I am not understanding where this thread is heading, I am taking a step back with this topic. Please disregard this series. Regards, Phil.