linux-kernel - Re: [PATCH] tpm: Add upgrade/reduced mode support for TPM1.2 modules

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Date:   Thu, 2 Jun 2022 14:25:26 +0300
From:   Jarkko Sakkinen <jarkko@...nel.org>
To:     Stefan Mahnke-Hartmann <stefan.mahnke-hartmann@...ineon.com>
Cc:     linux-integrity@...r.kernel.org, linux-kernel@...r.kernel.org,
        peterhuewe@....de, jgg@...pe.ca
Subject: Re: [PATCH] tpm: Add upgrade/reduced mode support for TPM1.2 modules

On Wed, Jun 01, 2022 at 10:38:11AM +0200, Stefan Mahnke-Hartmann wrote:
> In case a TPM in failure mode is detected, the TPM should be accessible
> through a transparent communication channel for analysing purposes (e.g.
> TPM_GetTestResult) or a field upgrade. Since a TPM in failure mode has
> similar reduced functionality as in field upgrade mode, the flag
> TPM_CHIP_FLAG_FIRMWARE_UPGRADE_MODE is also valid.
> 
> As described in TCG TPM Main Part1 Design Principles, Revision 116,
> chapter 9.2.1. the TPM also allows an update function in case a TPM is
> in failure mode.
> 
> If the TPM in failure mode is detected, the function tpm1_auto_startup()
> sets TPM_CHIP_FLAG_FIRMWARE_UPGRADE_MODE flag. This patch simply follows
> the same rationale as TPM2 in field upgrade mode.

"following the rationale" does not give a clue what it does.

Also minor nit: write in imperative from, and please do not say "this
patch". It won't be a patch, once it is in git.

> Signed-off-by: Stefan Mahnke-Hartmann <stefan.mahnke-hartmann@...ineon.com>
> ---
> If you have any better suggestions, please let me know.
> 
>  drivers/char/tpm/tpm1-cmd.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/char/tpm/tpm1-cmd.c b/drivers/char/tpm/tpm1-cmd.c
> index f7dc986fa4a0..7a42d74c450c 100644
> --- a/drivers/char/tpm/tpm1-cmd.c
> +++ b/drivers/char/tpm/tpm1-cmd.c
> @@ -710,8 +710,10 @@ int tpm1_auto_startup(struct tpm_chip *chip)
>  		goto out;
>  	rc = tpm1_do_selftest(chip);
>  	if (rc) {
> -		dev_err(&chip->dev, "TPM self test failed\n");
> -		goto out;
> +		dev_err(&chip->dev, "TPM self test failed, so the TPM has limited functionality\n");
> +		/* A TPM in this state possibly allows or needs a firmware upgrade */
> +		chip->flags |= TPM_CHIP_FLAG_FIRMWARE_UPGRADE;
> +		rc = 0;
>  	}
>  
>  	return rc;
> -- 
> 2.25.1
> 

Why all error codes trigger this action, e.g. all possible TPM2
errors and -ETIME?

BR, Jarkko