Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
MIME-Version: 1.0
References: <20210716081722.4130161-1-andreas@rammhold.de> <0a684d56-66d0-184e-4853-9faafa2d243d@pengutronix.de>
In-Reply-To: <0a684d56-66d0-184e-4853-9faafa2d243d@pengutronix.de>
From:   Sumit Garg <sumit.garg@linaro.org>
Date:   Mon, 19 Jul 2021 13:36:09 +0530
Message-ID: <CAFA6WYNC2xasX4uKmgcK+ZmA4HUh5PhCci+e12VFWPfF0b0eWQ@mail.gmail.com>
Subject: Re: [PATCH] KEYS: trusted: Fix trusted key backends when building as module
To:     Ahmad Fatoum <a.fatoum@pengutronix.de>
Cc:     Andreas Rammhold <andreas@rammhold.de>,
        James Bottomley <jejb@linux.ibm.com>,
        Jarkko Sakkinen <jarkko@kernel.org>,
        Mimi Zohar <zohar@linux.ibm.com>,
        David Howells <dhowells@redhat.com>,
        James Morris <jmorris@namei.org>,
        "Serge E . Hallyn" <serge@hallyn.com>,
        linux-integrity <linux-integrity@vger.kernel.org>,
        "open list:ASYMMETRIC KEYS" <keyrings@vger.kernel.org>,
        "open list:SECURITY SUBSYSTEM" 
        <linux-security-module@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Pengutronix Kernel Team <kernel@pengutronix.de>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
Precedence: bulk

On Mon, 19 Jul 2021 at 12:40, Ahmad Fatoum <a.fatoum@pengutronix.de> wrote:
>
> Hello Andreas,
>
> On 16.07.21 10:17, Andreas Rammhold wrote:
> > Before this commit the kernel could end up with no trusted key sources
> > even thought both of the currently supported backends (tpm & tee) were
> > compoiled as modules. This manifested in the trusted key type not being
> > registered at all.
>
> I assume (TPM) trusted key module use worked before the TEE rework? If so=
,
>
> an appropriate Fixes: Tag would then be in order.
>
> > When checking if a CONFIG_=E2=80=A6 preprocessor variable is defined we=
 only
> > test for the builtin (=3Dy) case and not the module (=3Dm) case. By usi=
ng
> > the IS_ENABLE(=E2=80=A6) macro we to test for both cases.
>
> It looks to me like you could now provoke a link error if TEE is a module
> and built-in trusted key core tries to link against trusted_key_tee_ops.
>

That's true.

> One solution for that IS_REACHABLE(). Another is to address the root caus=
e,
> which is the inflexible trusted keys Kconfig description:
>
> - Trusted keys despite TEE support can still only be built when TCG_TPM i=
s enabled
> - There is no support to have TEE or TPM enabled without using those for
>   enabled trusted keys as well
> - As you noticed, module build of the backend has issues
>
> I addressed these three issues in a patch[1], a month ago, but have yet t=
o
> receive feedback.

That's an oversight on my part since this patch was part of the new
CAAM trust source patch-set. Although I do admit that it was on my
TODO list. So I have provided some feedback on that patch. Can you
post the next version as an independent fix patch?

-Sumit

>
> [1]: https://lore.kernel.org/linux-integrity/f8285eb0135ba30c9d846cf9dd39=
5d1f5f8b1efc.1624364386.git-series.a.fatoum@pengutronix.de/
>
> Cheers,
> Ahmad
>
> > Signed-off-by: Andreas Rammhold <andreas@rammhold.de>
> > ---
> >  security/keys/trusted-keys/trusted_core.c | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/security/keys/trusted-keys/trusted_core.c b/security/keys/=
trusted-keys/trusted_core.c
> > index d5c891d8d353..fd640614b168 100644
> > --- a/security/keys/trusted-keys/trusted_core.c
> > +++ b/security/keys/trusted-keys/trusted_core.c
> > @@ -27,10 +27,10 @@ module_param_named(source, trusted_key_source, char=
p, 0);
> >  MODULE_PARM_DESC(source, "Select trusted keys source (tpm or tee)");
> >
> >  static const struct trusted_key_source trusted_key_sources[] =3D {
> > -#if defined(CONFIG_TCG_TPM)
> > +#if IS_ENABLED(CONFIG_TCG_TPM)
> >       { "tpm", &trusted_key_tpm_ops },
> >  #endif
> > -#if defined(CONFIG_TEE)
> > +#if IS_ENABLED(CONFIG_TEE)
> >       { "tee", &trusted_key_tee_ops },
> >  #endif
> >  };
> >
>
>
> --
> Pengutronix e.K.                           |                             =
|
> Steuerwalder Str. 21                       | http://www.pengutronix.de/  =
|
> 31137 Hildesheim, Germany                  | Phone: +49-5121-206917-0    =
|
> Amtsgericht Hildesheim, HRA 2686           | Fax:   +49-5121-206917-5555 =
|