Re: [PATCH 0/4][RFC v2] Introduce the in-kernel hibernation encryption

Yu Chen
2018-08-03T03:31:50Z

Hi Joey,
On Tue, Jul 31, 2018 at 01:04:15AM +0800, joeyli wrote:
> Hi all,
>
> On Thu, Jul 26, 2018 at 04:14:04PM +0800, joeyli wrote:
> > On Thu, Jul 26, 2018 at 09:30:46AM +0200, Oliver Neukum wrote:
> > > On Di, 2018-07-24 at 00:23 +0800, Yu Chen wrote:
> > > >
> > > > Good point, we once tried to generate key in kernel, but people
> > > > suggest to generate key in userspace and provide it to the
> > > > kernel, which is what ecryptfs do currently, so it seems this
> > > > should also be safe for encryption in kernel.
> > > > https://www.spinics.net/lists/linux-crypto/msg33145.html
> > > > Thus Chun-Yi's signature can use EFI key and both the key from
> > > > user space.
> > >
> > > Hi,
> > >
> > > ecryptfs can trust user space. It is supposed to keep data
> > > safe while the system is inoperative. The whole point of Secure
> > > Boot is a cryptographic system of trust that does not include
> > > user space.
> > >
> > > I seriously doubt we want to use trusted computing here. So the
> > > key needs to be generated in kernel space and stored in a safe
> > > manner. As we have a saolution doing that, can we come to ausable
> > > synthesis?
> > >
> > > Regards
> > > Oliver
> >
> > Crurently there have two solutions, they are trusted key and EFI key.
> > Both of them are generated in kernel and are not visible in user space.
> >
> > The trusted key is generated by kernel then sealed by the TPM's
> > SRK. So the trusted key can be stored in anywhere then be enrolled
> > to kernel when we need it. EVM already uses it.
> >
> > The EFI key is Jiri Kosina's idea. It is stored in boot services
> > variable, which means that it can only be access by signed EFI binary
> > (e.g. signed EFI boot stub) when secure boot be enabled. SLE applied
> > this solution a couple of years.
> >
> > I am working on put the EFI key to key retention service. Then
> > EFI key can be a master key of encrypted key. EVM can also use
> > it:
> > https://github.com/joeyli/linux-s4sign/commit/bae39460393ada4c0226dd07cd5e3afcef86b71f
> > https://github.com/joeyli/linux-s4sign/commit/f552f97cc3cca5acd84f424b7f946ffb5fe8e9ec
> >
> > That's why I want to use key retention service in hibernation
> > encryption/authentication. Which means that we can use key
> > API to access trusted key and EFI key.
> >
>
> Here is a proof of concept for using the key retention service
> to encrypt/sign snapshot image. It's using EFI key now, I will
> add encrypted key support in the key handler later:
> https://github.com/joeyli/linux-s4sign/commit/6311e97038974bc5de8121769fb4d34470009566
>
Thanks for the work, I have two questions here:
1. Could you please describe a little more about the scenario on
how the user could use the secret key for hibernation encryption?
A requirement is that, the user should provide a passphrase(for key derivation, i.e.)
during resume. I was thinking how user could interact with
the security key mechanism here.

2. The generation of secret key in EFI boot environment is
using a non standard derivation method in generate_secret_key(),
I'm not sure if this is safe enough. This is why we tried to put
PBKDF2 into kernel at first and leave it to the user space then.

Best,
Yu

> My next step is that cleaning up the my EFI key type patches and
> submit it to EFI/keys subsystem ASAP. Then I will clean up
> my hibernation encryption/authentication solution for reviewing.
>
> Thanks
> Joey Lee