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[70.163.223.149]) by smtp.gmail.com with ESMTPSA id l3sm2318388ioj.7.2019.10.04.11.33.43 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 04 Oct 2019 11:33:43 -0700 (PDT) Date: Fri, 4 Oct 2019 11:33:42 -0700 From: Jerry Snitselaar To: James Bottomley Cc: Jarkko Sakkinen , Mimi Zohar , David Safford , linux-integrity@vger.kernel.org, stable@vger.kernel.org, David Howells , Herbert Xu , "David S. Miller" , "open list:ASYMMETRIC KEYS" , "open list:CRYPTO API" , open list Subject: Re: [PATCH] KEYS: asym_tpm: Switch to get_random_bytes() Message-ID: <20191004183342.y63qdvspojyf3m55@cantor> Reply-To: Jerry Snitselaar Mail-Followup-To: James Bottomley , Jarkko Sakkinen , Mimi Zohar , David Safford , linux-integrity@vger.kernel.org, stable@vger.kernel.org, David Howells , Herbert Xu , "David S. Miller" , "open list:ASYMMETRIC KEYS" , "open list:CRYPTO API" , open list References: <20191003114119.GF8933@linux.intel.com> <1570107752.4421.183.camel@linux.ibm.com> <20191003175854.GB19679@linux.intel.com> <1570128827.5046.19.camel@linux.ibm.com> <20191003215125.GA30511@linux.intel.com> <20191003215743.GB30511@linux.intel.com> <1570140491.5046.33.camel@linux.ibm.com> <1570147177.10818.11.camel@HansenPartnership.com> <20191004182216.GB6945@linux.intel.com> <1570213491.3563.27.camel@HansenPartnership.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Disposition: inline In-Reply-To: <1570213491.3563.27.camel@HansenPartnership.com> User-Agent: NeoMutt/20180716 Sender: linux-integrity-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-integrity@vger.kernel.org On Fri Oct 04 19, James Bottomley wrote: >On Fri, 2019-10-04 at 21:22 +0300, Jarkko Sakkinen wrote: >> 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 random >> > bytes first extracts bytes from the TPM RNG and places it into >> > the kernel entropy pool and then asks for 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. > >That doesn't seem to work: when I trace what happens I see us inject 32 >bytes of entropy at boot time, but never again. I think the problem is >the kernel entropy pool is push not pull and we have no triggering >event in the TPM to get us to push. I suppose we could set a timer to >do this or perhaps there is a pull hook and we haven't wired it up >correctly? > >James > Shouldn't hwrng_fillfn be pulling from it?