linux-kernel - Re: [PATCH] KEYS: asym_tpm: Switch to get_random

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Date:   Thu, 3 Oct 2019 14:43:44 +0300
From:   Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
To:     Mimi Zohar <zohar@...ux.ibm.com>
Cc:     linux-integrity@...r.kernel.org, stable@...r.kernel.org,
        David Howells <dhowells@...hat.com>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        "David S. Miller" <davem@...emloft.net>,
        "open list:ASYMMETRIC KEYS" <keyrings@...r.kernel.org>,
        "open list:CRYPTO API" <linux-crypto@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] KEYS: asym_tpm: Switch to get_random_bytes()

On Thu, Oct 03, 2019 at 02:41:19PM +0300, Jarkko Sakkinen wrote:
> On Wed, Oct 02, 2019 at 10:00:19AM -0400, Mimi Zohar wrote:
> > On Thu, 2019-09-26 at 20:16 +0300, Jarkko Sakkinen wrote:
> > > Only the kernel random pool should be used for generating random numbers.
> > > TPM contributes to that pool among the other sources of entropy. In here it
> > > is not, agreed, absolutely critical because TPM is what is trusted anyway
> > > but in order to remove tpm_get_random() we need to first remove all the
> > > call sites.
> > 
> > At what point during boot is the kernel random pool available?  Does
> > this imply that you're planning on changing trusted keys as well?
> 
> Well trusted keys *must* be changed to use it. It is not a choice
> because using a proprietary random number generator instead of defacto
> one in the kernel can be categorized as a *regression*.
> 
> Also, TEE trusted keys cannot use the TPM option.
> 
> If it was not initialized early enough we would need fix that too.
> 
> I don't think there should be a problem anyway since encrypted keys is
> already using get_random_bytes().

Looking at asym_tpm.c the implementation copies all the anti-patterns
from trusted keys, which is really unfortunate. I don't know how that
has passed through all the filters.

/Jarkko