linux-kernel - Re: [PATCH] security/keys/trusted: Allow operation without hardware TPM

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Message-ID: <CAPcyv4j+4WMFsEbT_TDQfNs2ZG6+ME6b07RaqmT9kfbTStWgJQ@mail.gmail.com>
Date:   Tue, 19 Mar 2019 16:01:51 -0700
From:   Dan Williams <dan.j.williams@...el.com>
To:     Mimi Zohar <zohar@...ux.ibm.com>
Cc:     James Bottomley <jejb@...ux.ibm.com>,
        Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>,
        "linux-nvdimm@...ts.01.org" <linux-nvdimm@...ts.01.org>,
        Roberto Sassu <roberto.sassu@...wei.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        David Howells <dhowells@...hat.com>, keyrings@...r.kernel.org
Subject: Re: [PATCH] security/keys/trusted: Allow operation without hardware TPM

On Tue, Mar 19, 2019 at 3:56 PM Mimi Zohar <zohar@...ux.ibm.com> wrote:
>
> Hi Dan,
>
> On Mon, 2019-03-18 at 17:30 -0700, Dan Williams wrote:
>
> Sorry for the late reply.
>
> > On Mon, Mar 18, 2019 at 5:24 PM James Bottomley <jejb@...ux.ibm.com> wrote:
> > >
> > > On Mon, 2019-03-18 at 16:45 -0700, Dan Williams wrote:
> > > > Rather than fail initialization of the trusted.ko module, arrange for
> > > > the module to load, but rely on trusted_instantiate() to fail
> > > > trusted-key operations.
> > >
> > > What actual problem is this fixing?  To me it would seem like an
> > > enhancement to make the trusted module fail at load time if there's no
> > > TPM rather than waiting until first use to find out it can never work.
> > > Is there some piece of user code that depends on the successful
> > > insertion of trusted.ko?
> >
> > The module dependency chain relies on it. If that can be broken that
> > would also be an acceptable fix.
> >
> > I found this through the following dependency chain: libnvdimm.ko ->
> > encrypted_keys.ko -> trusted.ko.
> >
> > "key_type_trusted" is the symbol that encrypted_keys needs regardless
> > of whether the tpm is present.
>
> Commit 982e617a313b ("encrypted-keys: remove trusted-keys dependency")
> removed the dependency on trusted keys.  masterkey_trusted.c should
> only be included if "CONFIG_TRUSTED_KEYS" is enabled.  Is
> CONFIG_TRUSTED_KEYS enabled?

Yes, TRUSTED_KEYS is enabled, the module is built/available, and tries
to load when encrypted_keys.ko loads. The problem is that it fails to
load due an error returned from init_trusted(). The error is new for
v5.1. So, instead of requiring the module dependencies to resolve
successfully, and init_trusted() to return 0, the proposal is to just
lookup the key types by name.