From: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Subject: Re: [tpmdd-devel] [PATCH] tpm: remove chip_num parameter from
 in-kernel API
Date: Tue, 24 Oct 2017 20:15:12 +0200
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Cc: Jason Gunthorpe <jgunthorpe@obsidianresearch.com>,
        PrasannaKumar Muralidharan <prasannatsmkumar@gmail.com>,
        Stefan Berger <stefanb@linux.vnet.ibm.com>,
        linux-integrity@vger.kernel.org,
        David Howells <dhowells@redhat.com>,
        Herbert Xu <herbert@gondor.apana.org.au>,
        "open list:INTEGRITY MEASUREMENT ARCHITECTURE IMA"
        <linux-ima-user@lists.sourceforge.net>,
        Dmitry Kasatkin <dmitry.kasatkin@gmail.com>,
        open list <linux-kernel@vger.kernel.org>,
        linux-security-module@vger.kernel.org,
        "moderated list:TPM DEVICE DRIVER"
        <tpmdd-devel@lists.sourceforge.net>,
        "open list:KEYS-TRUSTED" <keyrings@vger.kernel.org>,
        "open list:HARDWARE RANDOM NUMBER GENERATOR CORE"
        <linux-crypto@vger.kernel.org>,
        James Morris <james.l.morris@oracle.com>,
        Matt Mackall <mpm@selenic.c
To: Dmitry Torokhov <dmitry.torokhov@gmail.com>
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On Tue, Oct 24, 2017 at 10:02:00AM -0700, Dmitry Torokhov wrote:
> On Tue, Oct 24, 2017 at 9:11 AM, Jason Gunthorpe
> <jgunthorpe@obsidianresearch.com> wrote:
> > On Tue, Oct 24, 2017 at 09:37:33PM +0530, PrasannaKumar Muralidharan wrote:
> >> Hi Jason,
> >>
> >> On 24 October 2017 at 21:25, Jason Gunthorpe
> >> <jgunthorpe@obsidianresearch.com> wrote:
> >> > On Tue, Oct 24, 2017 at 09:21:15PM +0530, PrasannaKumar Muralidharan wrote:
> >> >
> >> >> Please check the RFC [1]. It does use chip id. The rfc has issues and
> >> >> has to be fixed but still there could be users of the API.
> >> >>
> >> >> 1. https://www.spinics.net/lists/linux-crypto/msg28282.html
> >> >
> >> > That patch isn't safe at all. You need to store a kref to th chip in
> >> > the hwrng, not parse a string.
> >>
> >> The drivers/char/hw_random/tpm-rng.c module does not store the chip
> >> reference so I guess the usage is safe.
> >
> > It is using the default TPM, it is always safe to use the default tpm.
> 
> tpm-rng is abomination that should be kicked out as soon as possible.
> It wrecks havoc with the power management (TPM chip drivers may go
> into suspend state, but tpm_rng does not do any power management and
> happily forwards requests to suspended hardware) and may be available
> when there is no TPM at all yet (the drivers have not been probed yet,
> or have gotten a deferral, etc).
> 
> TPM core should register HWRNGs when chips are ready.
> 
> Thanks.
> 
> -- 
> Dmitry

I'm fine to review a two patch set where:

1. Patch 1 removes the existing TPM rng driver
2. Patch 2 makes the TPM driver as rng producer

Unrelate to patch that I'm proposing now but this sounds sensible.

/Jarkko