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

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Message-ID: <20191004182216.GB6945@linux.intel.com>
Date:   Fri, 4 Oct 2019 21:22:16 +0300
From:   Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
To:     James Bottomley <James.Bottomley@...senPartnership.com>
Cc:     Mimi Zohar <zohar@...ux.ibm.com>,
        David Safford <david.safford@...com>,
        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 04:59:37PM -0700, James Bottomley wrote:
> I think the principle of using multiple RNG sources for strong keys is
> a sound one, so could I propose a compromise:  We have a tpm subsystem
> random number generator that, when asked for <n> random bytes first
> extracts <n> bytes from the TPM RNG and places it into the kernel
> entropy pool and then asks for <n> random bytes from the kernel RNG? 
> That way, it will always have the entropy to satisfy the request and in
> the worst case, where the kernel has picked up no other entropy sources
> at all it will be equivalent to what we have now (single entropy
> source) but usually it will be a much better mixed entropy source.

I think we should rely the existing architecture where TPM is
contributing to the entropy pool as hwrng.

/Jarkko