linux-kernel - Re: [PATCH] tpm: require to compile as part of the kernel

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Date:   Fri, 29 Jun 2018 09:31:41 -0600
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
Cc:     linux-integrity@...r.kernel.org,
        linux-security-module@...r.kernel.org,
        Peter Huewe <peterhuewe@....de>, Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Winkler, Tomas" <tomas.winkler@...el.com>,
        Azhar Shaikh <azhar.shaikh@...el.com>,
        Stefan Berger <stefanb@...ux.vnet.ibm.com>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] tpm: require to compile as part of the kernel

On Fri, Jun 29, 2018 at 06:10:02PM +0300, Jarkko Sakkinen wrote:
> Do not allow to compile TPM core as a module. TPM defines a root of
> trust for integrity and keyring subsystems and should be always
> available and not be loaded from the user space. There is no a
> reasonable use case for a loadable module existing.
> 
> Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
> ---
>  drivers/char/tpm/Kconfig | 2 +-
>  include/linux/tpm.h      | 3 +--
>  2 files changed, 2 insertions(+), 3 deletions(-)

This doesn't really make sense..

The kconfig method is that if IMA requires TPM it should declare so
and TPM will become non-modular because IMA is non-modular.

There are lots of legitimate use cases for TPM that don't involve IMA
or keyring.

> diff --git a/drivers/char/tpm/Kconfig b/drivers/char/tpm/Kconfig
> index 18c81cbe4704..9728771aecbd 100644
> --- a/drivers/char/tpm/Kconfig
> +++ b/drivers/char/tpm/Kconfig
> @@ -3,7 +3,7 @@
>  #
>  
>  menuconfig TCG_TPM
> -	tristate "TPM Hardware Support"
> +	bool "TPM Hardware Support"
>  	depends on HAS_IOMEM
>  	select SECURITYFS
>  	select CRYPTO
> diff --git a/include/linux/tpm.h b/include/linux/tpm.h
> index 4609b94142d4..cefa61b12891 100644
> --- a/include/linux/tpm.h
> +++ b/include/linux/tpm.h
> @@ -50,8 +50,7 @@ struct tpm_class_ops {
>  	void (*clk_enable)(struct tpm_chip *chip, bool value);
>  };
>  
> -#if defined(CONFIG_TCG_TPM) || defined(CONFIG_TCG_TPM_MODULE)
> -
> +#if defined(CONFIG_TCG_TPM)

Huh. This new version is certainly right

Jason