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Re: [PATCH v2 0/2] block: Use 'read-zeroes=true' mode by default with 'n

From: Philippe Mathieu-Daudé
Subject: Re: [PATCH v2 0/2] block: Use 'read-zeroes=true' mode by default with 'null-co' driver
Date: Fri, 19 Feb 2021 15:09:43 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.7.0

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?

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).

>> Cannot we just somehow annotate it in a way that the checker can
>> understand (akin to how we provide coverity models) and be done?
> The question is, why wouldn’t we change the default?  read-zeroes=true
> seems the better default to me.  I consider silencing valgrind warnings
> and the like a nice side effect.
> Max

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