linux-kernel - Re: [PATCH 2/2] tpm: Add Field Upgrade mode support for Infineon TPM2 modules

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Date:   Mon, 9 May 2022 14:50:18 +0200
From:   Stefan Mahnke-Hartmann <stefan.mahnke-hartmann@...ineon.com>
To:     <jarkko@...nel.org>
CC:     <Marten.Lindahl@...s.com>, <jgg@...pe.ca>,
        <johannes.holland@...ineon.com>, <jsnitsel@...hat.com>,
        <linux-integrity@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <martenli@...s.com>, <nayna@...ux.vnet.ibm.com>,
        <peterhuewe@....de>, <stefan.mahnke-hartmann@...ineon.com>
Subject: Re: [PATCH 2/2] tpm: Add Field Upgrade mode support for Infineon TPM2 modules

On 07.05.22 21:43, Jarkko Sakkinen wrote:
> On Fri, May 06, 2022 at 02:31:48PM +0200, Stefan Mahnke-Hartmann wrote:
>> TPM2_GetCapability with a capability that has the property type value
>> of TPM_PT_TOTAL_COMMANDS returns a zero length list, when an Infineon
>> TPM2 is in Field Upgrade mode.
>> Since an Infineon TPM2.0 in Field Upgrade mode returns RC_SUCCESS on
>> TPM2_Startup, the Field Upgrade mode has to be detected by
>> TPM2_GetCapability.
>>
>> Signed-off-by: Stefan Mahnke-Hartmann <stefan.mahnke-hartmann@...ineon.com>
>> ---
>>  drivers/char/tpm/tpm2-cmd.c | 6 ++++++
>>  1 file changed, 6 insertions(+)
>>
>> diff --git a/drivers/char/tpm/tpm2-cmd.c b/drivers/char/tpm/tpm2-cmd.c
>> index e62a644ce26b..659130e2936e 100644
>> --- a/drivers/char/tpm/tpm2-cmd.c
>> +++ b/drivers/char/tpm/tpm2-cmd.c
>> @@ -746,6 +746,12 @@ int tpm2_auto_startup(struct tpm_chip *chip)
>>  	}
>>  
>>  	rc = tpm2_get_cc_attrs_tbl(chip);
>> +	/*
>> +	 * Infineon TPM in Field Upgrade mode will return no data for the number
>> +	 * of supported commands.
>> +	 */
>> +	if (rc == -ENODATA)
>> +		rc = TPM2_RC_UPGRADE;
>
> Injecting hardware error codes like this is not considered a great idea.

Resetting the error code was to avoid code duplication, while following the
same rationale as Mårten's patch. I can also add the -ENODATA to the if clause
below or duplicate the code block (similar to Mårten's). Do you have a better
suggestion?

>
>>  
>>  out:
>>  	if (rc == TPM2_RC_UPGRADE) {
>> -- 
>> 2.25.1
>>
>
> BR, Jarkko