[dm-crypt] How to suspend to disk with random encrypted swap

Sven Eschenberg sven at whgl.uni-frankfurt.de
Sun Oct 23 19:01:24 CEST 2016


Short answer:

No gentoo does not have direct support for encrypted rootfs/swap (for 
hibernate). However, I've heard that there's a strong pushing towards 
dracut for initramfs handling (well parts of the dev community however), 
if genkernel does not fulfil your needs. That is however from an OpenRC 
POV, I'd say. Systemd handles encrypted block devices a little different 
and you might end up with a lot more mambo jambo, than a little shell 
scripting, to get things into place.

Certainly the gentoo community might have pointers to various 
possibilities including those some of them tried already ;-).


Regards

-Sven


P.S.: https://wiki.gentoo.org/wiki/Initramfs/Guide for Gentoo'S 
initramfs approaches...

Am 23.10.2016 um 12:52 schrieb Heiko Rosemann:
> Hi David,
>
> [cropped]
> I don't know if gentoo has a similar setup ready out of the box.
>
> Good luck, and remember to backup early and often ;)
> Heiko
>
>
> On 10/23/2016 12:27 AM, Sven Eschenberg wrote:
>> Not really a cryptsetup question.
>>
>> You should be aware of the fact, that suspend to disk on a randomly
>> encrypted swap cannot work (for obvious reasons). In any way, you'll
>> need to start the kernel and give it a way to read the disk image. The
>> diskimage however should be encrypted for obvious reasons.
>>
>> How can you resolve the hen and egg problem?
>>
>> You can't with complete randomness.
>>
>> You'll have to either:
>> 1.) have a fixed passphrase for your swap, unlock swap during boot and
>> then resume
>> 2.) store your in memory image at some other place than swap, again,
>> that place should be encrypted - you could possibly store the image on
>> /, then you'll have to unlock / during boot to resume.
>> 3.) forget about suspend alltogether.
>>
>> To answer your questions to some extent:
>> The kernel will first try to find a suspend image signature on the
>> default swap partition, the location can however be overridden with
>> resume=, the gory details are in the kernel's documentation on boot
>> parameters. The kernel will resume, if there's an image accessible, this
>> can however be overridden with hibernate= .
>>
>> Regards
>>
>> -Sven
>>
>>
>> Am 22.10.2016 um 15:55 schrieb David Niklas:
>>> Hello,
>>> I use a random encrypted swap partition, and I want to suspend my system
>>> to disk. I'm having two problems.
>>> 1. How does the kernel know where to resume from/at all?
>>> 2. How do I get the random passphrase for decrypting the swap (and
>>> remember it)?
>>>
>>> Gentoo linux
>>> cryptsetup 1.7.2
>>>
>>> ###### /etc/conf.d/dmcrypt #########
>>>
>>> swap=swap
>>> options=' -c aes -h sha256 -d /dev/urandom '
>>> source='/dev/sda2'
>>>
>>> ####################################
>>>
>>> Thanks,
>>> David
>>> _______________________________________________
>>> dm-crypt mailing list
>>> dm-crypt at saout.de
>>> http://www.saout.de/mailman/listinfo/dm-crypt
>>>
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>
>
>
>
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