linux-kernel - Re: [tpmdd-devel] [PATCH] tpm: remove chip

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Date:   Tue, 24 Oct 2017 10:11:18 -0600
From:   Jason Gunthorpe <jgunthorpe@...idianresearch.com>
To:     PrasannaKumar Muralidharan <prasannatsmkumar@...il.com>
Cc:     Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>,
        Stefan Berger <stefanb@...ux.vnet.ibm.com>,
        linux-integrity@...r.kernel.org,
        David Howells <dhowells@...hat.com>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        "open list:INTEGRITY MEASUREMENT ARCHITECTURE IMA" 
        <linux-ima-user@...ts.sourceforge.net>,
        Dmitry Kasatkin <dmitry.kasatkin@...il.com>,
        open list <linux-kernel@...r.kernel.org>,
        linux-security-module@...r.kernel.org,
        "moderated list:TPM DEVICE DRIVER" 
        <tpmdd-devel@...ts.sourceforge.net>,
        "open list:KEYS-TRUSTED" <keyrings@...r.kernel.org>,
        "open list:HARDWARE RANDOM NUMBER GENERATOR CORE" 
        <linux-crypto@...r.kernel.org>,
        James Morris <james.l.morris@...cle.com>,
        Matt Mackall <mpm@...enic.com>,
        "open list:INTEGRITY MEASUREMENT ARCHITECTURE IMA" 
        <linux-ima-devel@...ts.sourceforge.net>,
        David Safford <safford@...ibm.com>,
        Mimi Zohar <zohar@...ux.vnet.ibm.com>,
        "Serge E. Hallyn" <serge@...lyn.com>
Subject: Re: [tpmdd-devel] [PATCH] tpm: remove chip_num parameter from
 in-kernel API

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@...idianresearch.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.

> The RFC is just a sample use case of the API.

Well, a wrong example not to be emulated, and I think, further shows
how Jarkko's direction is the right one.

Jason