linux-kernel - Re: [PATCH 3/3] tpm: Drop CONFIG_HW_RANDOM

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Date:   Thu, 03 Aug 2023 12:01:59 +0300
From:   "Jarkko Sakkinen" <jarkko@...nel.org>
To:     "Mario Limonciello" <mario.limonciello@....com>,
        <peterhuewe@....de>
Cc:     <linux-kernel@...r.kernel.org>, <linux-integrity@...r.kernel.org>,
        <Jason@...c4.com>, <dragonn@...pl>
Subject: Re: [PATCH 3/3] tpm: Drop CONFIG_HW_RANDOM_TPM

On Thu Aug 3, 2023 at 4:50 AM EEST, Mario Limonciello wrote:
> As the behavior of whether a TPM is registered for hwrng can be controlled
> by command line, drop the kernel configuration option.
>
> Cc: Mateusz Schyboll <dragonn@...pl>
> Signed-off-by: Mario Limonciello <mario.limonciello@....com>
> ---
>  drivers/char/tpm/Kconfig    | 11 -----------
>  drivers/char/tpm/tpm-chip.c |  6 +++---
>  2 files changed, 3 insertions(+), 14 deletions(-)
>
> diff --git a/drivers/char/tpm/Kconfig b/drivers/char/tpm/Kconfig
> index 927088b2c3d3f..69aaa730dc208 100644
> --- a/drivers/char/tpm/Kconfig
> +++ b/drivers/char/tpm/Kconfig
> @@ -27,17 +27,6 @@ menuconfig TCG_TPM
>  
>  if TCG_TPM
>  
> -config HW_RANDOM_TPM
> -	bool "TPM HW Random Number Generator support"
> -	depends on TCG_TPM && HW_RANDOM && !(TCG_TPM=y && HW_RANDOM=m)
> -	default y
> -	help
> -	  This setting exposes the TPM's Random Number Generator as a hwrng
> -	  device. This allows the kernel to collect randomness from the TPM at
> -	  boot, and provides the TPM randomines in /dev/hwrng.
> -
> -	  If unsure, say Y.
> -
>  config TCG_TIS_CORE
>  	tristate
>  	help
> diff --git a/drivers/char/tpm/tpm-chip.c b/drivers/char/tpm/tpm-chip.c
> index 8fb42232bd7a5..0d69335743469 100644
> --- a/drivers/char/tpm/tpm-chip.c
> +++ b/drivers/char/tpm/tpm-chip.c
> @@ -533,7 +533,7 @@ static int tpm_add_hwrng(struct tpm_chip *chip)
>  	if (!trust_tpm)
>  		chip->flags |= TPM_CHIP_FLAG_HWRNG_DISABLED;
>  
> -	if (!IS_ENABLED(CONFIG_HW_RANDOM_TPM) || tpm_is_firmware_upgrade(chip) ||
> +	if (tpm_is_firmware_upgrade(chip) ||
>  	    chip->flags & TPM_CHIP_FLAG_HWRNG_DISABLED)
>  		return 0;
>  
> @@ -639,7 +639,7 @@ int tpm_chip_register(struct tpm_chip *chip)
>  	return 0;
>  
>  out_hwrng:
> -	if (IS_ENABLED(CONFIG_HW_RANDOM_TPM) && !tpm_is_firmware_upgrade(chip) &&
> +	if (!tpm_is_firmware_upgrade(chip) &&
>  	    !(chip->flags & TPM_CHIP_FLAG_HWRNG_DISABLED))
>  		hwrng_unregister(&chip->hwrng);
>  out_ppi:
> @@ -665,7 +665,7 @@ EXPORT_SYMBOL_GPL(tpm_chip_register);
>  void tpm_chip_unregister(struct tpm_chip *chip)
>  {
>  	tpm_del_legacy_sysfs(chip);
> -	if (IS_ENABLED(CONFIG_HW_RANDOM_TPM) && !tpm_is_firmware_upgrade(chip) &&
> +	if (!tpm_is_firmware_upgrade(chip) &&
>  	    !(chip->flags & TPM_CHIP_FLAG_HWRNG_DISABLED))
>  		hwrng_unregister(&chip->hwrng);
>  	tpm_bios_log_teardown(chip);
> -- 
> 2.34.1

I don't understand this but please take it a way from patch set, which
should only contain critical fixes, which this definitely is not.

BR, Jarkko