linux-kernel - Re: [PATCH v4] KEYS: encrypted: Instantiate key with user-provided decrypted data

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Message-ID: <YfFe9+XDPDIdSqF1@iki.fi>
Date:   Wed, 26 Jan 2022 16:47:19 +0200
From:   Jarkko Sakkinen <jarkko@...nel.org>
To:     Martin Ross <mross@...ox.com>
Cc:     corbet@....net, dhowells@...hat.com, jejb@...ux.ibm.com,
        jmorris@...ei.org, keyrings@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-integrity@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        linux-security-module@...r.kernel.org, serge@...lyn.com,
        Yael Tiomkin <yaelt@...gle.com>,
        Mimi Zohar <zohar@...ux.ibm.com>
Subject: Re: [PATCH v4] KEYS: encrypted: Instantiate key with user-provided
 decrypted data

On Tue, Jan 18, 2022 at 01:26:05PM -0500, Martin Ross wrote:
> Hi Jarkko,
> 
> I have been working with Yael on this project so I thought I might add
> a bit of background here around the use case that this series of
> patches is trying to address.
> 
> At a high level we are trying to provide users of encryption that have
> key management hierarchies a better tradeoff between security and
> availability.  For available and performance reasons master keys often
> need to be released (or derived/wrapped keys created) outside of a KMS
> to clients (which may in turn further wrap those keys in a series of
> levels).  What we are trying to do is provide a mechanism where the
> wrapping/unwrapping of these keys is not dependent on a remote call at
> runtime.  e.g.  To unwrap a key if you are using AWS KMS or Google
> Service you need to make an RPC.  In practice to defend against
> availability or performance issues, designers end up building their
> own kms and effectively encrypting everything with a DEK.  The DEK
> encrypts same set as the master key thereby eliminating the security
> benefit of keeping the master key segregated in the first place.
> 
> We are building a mechanism to  create a security boundary in the
> kernel that allows these master keys to be stored in the kernel and
> used to wrap/unwrap keys via less trusted user processes.  The other
> goal here is to eliminate the complexity and statefulness required to
> do this today which would be to create a trusted daemon or process on
> the machine.  Concretely this means that since the user process will
> not have the master key the system designer has better options.  One
> obvious advantage is that any core dumps or code injection attacks
> won't be able to trivially grab the master key from the process or the
> linux keyring.  Once in the kernel this functionality can be
> transparently integrated into user space crypto libraries that have
> existing key management functionality.
> 
> Hope this helps and happy to answer any further questions!
> 
> M

Thank you.

It indeed does. I think it is a good explanation. Maybe the way to move
forward would be bring this context at leat a bit to the documentation
update?

/Jarkko