Re: [PATCH] KEYS: asym_tpm: Switch to get_random_bytes()

[Jarkko Sakkinen]

On Wed, Oct 09, 2019 at 12:11:06PM +0000, Safford, David (GE Global Research, US) wrote:
> 
> > From: Jarkko Sakkinen <jarkko.sakkinen@xxxxxxxxxxxxxxx>
> > Sent: Tuesday, October 8, 2019 7:54 PM
> > To: Ken Goldman <kgold@xxxxxxxxxxxxx>
> > Cc: Safford, David (GE Global Research, US) <david.safford@xxxxxx>; Mimi
> > Zohar <zohar@xxxxxxxxxxxxx>; linux-integrity@xxxxxxxxxxxxxxx;
> > stable@xxxxxxxxxxxxxxx; open list:ASYMMETRIC KEYS
> > <keyrings@xxxxxxxxxxxxxxx>; open list:CRYPTO API <linux-
> > crypto@xxxxxxxxxxxxxxx>; open list <linux-kernel@xxxxxxxxxxxxxxx>
> > Subject: EXT: Re: [PATCH] KEYS: asym_tpm: Switch to get_random_bytes()
> > 
> > On Wed, Oct 09, 2019 at 02:49:35AM +0300, Jarkko Sakkinen wrote:
> > > On Mon, Oct 07, 2019 at 06:13:01PM -0400, Ken Goldman wrote:
> > > > The TPM library specification states that the TPM must comply with
> > > > NIST
> > > > SP800-90 A.
> > > >
> > > > https://trustedcomputinggroup.org/membership/certification/tpm-certi
> > > > fied-products/
> > > >
> > > > shows that the TPMs get third party certification, Common Criteria EAL 4+.
> > > >
> > > > While it's theoretically possible that an attacker could compromise
> > > > both the TPM vendors and the evaluation agencies, we do have EAL 4+
> > > > assurance against both 1 and 2.
> > >
> > > Certifications do not equal to trust.
> > 
> > And for trusted keys the least trust solution is to do generation with the kernel
> > assets and sealing with TPM. With TEE the least trust solution is equivalent.
> > 
> > Are you proposing that the kernel random number generation should be
> > removed? That would be my conclusion of this discussion if I would agree any
> > of this (I don't).
> > 
> > /Jarkko
> 
> No one is suggesting that.
> 
> You are suggesting changing the documented behavior of trusted keys, and
> that would cause problems for some of our use cases. While certification
> may not in your mind be equal to trust, it is equal to compliance with 
> mandatory regulations.
> 
> Perhaps rather than arguing past each other, we should look into 
> providing users the ability to choose, as an argument to keyctl?
> 
> dave

I'm taking my words back in the regression part as regression would need
really a failing system. Definitely the fixes tag should be removed from
my patch.

What is anyway the role of the kernel rng? Why does it exist and when
exactly it should be used? This exactly where the whole review process
throughout the "chain of command" failed misserably with tpm_asym.c.

The commit message for tpm_asym.c does not document the design choice in
any possible way and still was merged to the mainline.

Before knowning the answer to the "existential" question we are
somewhat paralyzed on moving forward with trusted keys (e.g. paralyzed
to merge TEE backend).

Your proposal might make sense but I don't really want to say anything
since I'm completely cluesless of the role of the kernel rng. Looks like
everyone who participated to the review process of tpm_asym.c, is too.

/Jarkko