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

Yu Chen
2018-08-07T07:32:30Z

On Mon, Aug 06, 2018 at 12:20:20PM +0200, Oliver Neukum wrote:
> On Mo, 2018-08-06 at 15:57 +0800, Yu Chen wrote:
> > Hi Oliver,
> > 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.
> >
> > Humm, I did not quite get the point here, let's take fscrypt
>
> While the system is running and the fs is mounted, your data
> is as secure as root access to your machine, right? You encrypt
> a disk primarily so data cannot be recovered (and altered) while
> the system is not running.
>
> Secure Boot does not trust root fully. There is a cryptographic
> chain of trust and user space is not part of it.
>
Okay, I see. So if we want to use secure boot mechanism for
hibernation encryption, user space is trusted.
> > for example, the kernel gets user generated key from user space,
> > and uses per-inode nonce(random bytes) as the master key to
> > do a KDF(key derivation function) on user provided key, and uses
> > that key for encryption. We can also added similar mechanism
> > to generate the key in kernel space but the key should be
> > original from user's provided key(password derived), because
> > the security boot/signature mechanism could not cover the case
> > that, two different users could resume to each other's context
> > because there isn't any certification during resume if it is
> > on the same physical hardware.
>
> Please explain. You will always have to suspend the whole machine
> with all tasks of all users. And STD with Secure Boot need not
> imply that you encrypt your discs. You need to encrypt only
> kernel memory to meet the requirements.
>
> As STD affects the whole machine it must require root rights.
> So I cannot see how you can talk about a session belonging
> to a user. Please explain.
>
The case is for physical access, not the 'user' in OS.
> It seems to me that you can in theory encrypt the password
> by a key coming from user space, so that you need to know
> an additional key to resume the system, but that seems to me
> above and beyond what Secure Boot requires.
>
Understand.

Best,
Yu
> Regards
> Oliver
>