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

[Jarkko Sakkinen]

On Mon, Oct 14, 2019 at 10:00:33PM +0300, Jarkko Sakkinen wrote:
> 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.

As a ABI backwards compatibility workaround I'd agree most likely agree
with you. As a guideline for new features there should be a framework on
how to decide what to do.

/Jarkko