[dm-devel] dm-integrity

[Renesanso]

I have other question: why you dont use AEAD idea from redhad for 
dm-crypt (cryptsetup, that works, as they present), that realise AES-GCM 
(as, example ZFS use)? Why do you want to merge dm-integrity and 
dm-crypt? 
https://mbroz.fedorapeople.org/talks/DevConf2017/devconf2017-aead.pdf

07.07.2017 13:47, Milan Broz пишет:
> On 07/05/2017 06:45 PM, Renesanso wrote:
>> 1. And in this (
>> https://kernel.googlesource.com/pub/scm/linux/kernel/git/kasatkin/linux-digsig/+/2dfa67a1a4c049fd33fcc6abcb1c8ca57b17a268/Documentation/device-mapper/dm-integrity.txt
>> ) implementation gives variant to use external device for metadata and
>> journal. It really affect perfomance, I think. Do you plan do analogue
>> functions?
> Not yet. The design was meant for authenticated extension and cryptsetup
> has only one device as a backend (I really do not want to make it another volume manager :)
> (It is not easy task to solve the situation when the separate devices are out of sync,
> and security implications only complicates it more.)
>
> But I can imagine that if there is some strong use case, it can be added there.
>
> (As said, it was not means as straight replacement of the module mentioned above;
> the name clash is just my stupid coincidence.)
>
>> 2. And other question: in your implementation tags write rarery after
>> data (eg. data[512b], tag[32b], data [512b], tag[32b]) or data stores in
>> one "half" of disk and tags in another (in end of disk, example)? Second
>> variant gives VERY HUGE penalty on hdd's.
> Tags are written into metadata sectors that are interleaved with normal
> data sectors. (This allow us to resize the device later.)
>
> There are multiple tags in one metadata sector and dm-integrity
> provides all the infrastructure to perform atomic write of sector+metadata.
>
>> 3. And can, as I see there many options (as journal, buffers and other).
>> Can you give me example of parameters configuration, that fully
>> correctly work in production (KVMs- VMs -> raw -> EXT4 -> LVM -> MD ->
>> multiple dm-integrity on multiple phisical disks )?
> Sorry, I do not have any "good practices" or any configurations yet.
> In fact, I am still curious what use cases people can find for it :)
>
> There is a lot of things to fine-tune though. But the initial
> penalty of using data journal will be always big.
> (You can switch journalling off if it is already on higher layer.)
>
> The whole integrity/crypt stack was meant for experiments with
> authenticated encryption on the sector level (and with expected
> performance penalty - security is the first class citizen here).
>
> I will try to put some more info into some blog soon.
>
> Thanks,
> Milan