linux-kernel - Re: [PATCH v2] tpm: Don't make vendor check required for probe

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Date:   Tue, 22 Aug 2023 09:05:13 -0500
From:   Mario Limonciello <mario.limonciello@....com>
To:     Jarkko Sakkinen <jarkko@...nel.org>
Cc:     linux-integrity@...r.kernel.org, linux-kernel@...r.kernel.org,
        stable@...r.kernel.org, Todd Brandt <todd.e.brandt@...el.com>,
        Patrick Steinhardt <ps@....im>, Ronan Pigott <ronan@....ie>,
        Raymond Jay Golo <rjgolo@...il.com>
Subject: Re: [PATCH v2] tpm: Don't make vendor check required for probe

On 8/22/2023 08:22, Jarkko Sakkinen wrote:
> On Mon Aug 21, 2023 at 5:02 PM EEST, Mario Limonciello wrote:
>> The vendor check introduced by commit 554b841d4703 ("tpm: Disable RNG for
>> all AMD fTPMs") doesn't work properly on a number of Intel fTPMs.  On the
>> reported systems the TPM doesn't reply at bootup and returns back the
>> command code. This makes the TPM fail probe.
>>
>> As this isn't crucial for anything but AMD fTPM and AMD fTPM works, check
>> the chip vendor and if it's not AMD don't run the checks.
>>
>> Cc: stable@...r.kernel.org
>> Fixes: 554b841d4703 ("tpm: Disable RNG for all AMD fTPMs")
>> Reported-by: Todd Brandt <todd.e.brandt@...el.com>
>> Reported-by: Patrick Steinhardt <ps@....im>
>> Reported-by: Ronan Pigott <ronan@....ie>
>> Reported-by: Raymond Jay Golo <rjgolo@...il.com>
>> Closes: https://bugzilla.kernel.org/show_bug.cgi?id=217804
>> Signed-off-by: Mario Limonciello <mario.limonciello@....com>
>> ---
>> v1->v2:
>>   * Check x86 vendor for AMD
>> ---
>>   drivers/char/tpm/tpm_crb.c | 7 ++++++-
>>   1 file changed, 6 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/char/tpm/tpm_crb.c b/drivers/char/tpm/tpm_crb.c
>> index 9eb1a18590123..7faf670201ccc 100644
>> --- a/drivers/char/tpm/tpm_crb.c
>> +++ b/drivers/char/tpm/tpm_crb.c
>> @@ -465,8 +465,12 @@ static bool crb_req_canceled(struct tpm_chip *chip, u8 status)
>>   
>>   static int crb_check_flags(struct tpm_chip *chip)
>>   {
>> +	int ret = 0;
>> +#ifdef CONFIG_X86
>>   	u32 val;
>> -	int ret;
>> +
>> +	if (boot_cpu_data.x86_vendor != X86_VENDOR_AMD)
>> +		return ret;
>>   
>>   	ret = crb_request_locality(chip, 0);
>>   	if (ret)
>> @@ -481,6 +485,7 @@ static int crb_check_flags(struct tpm_chip *chip)
>>   
>>   release:
>>   	crb_relinquish_locality(chip, 0);
>> +#endif
> 
> Looks much better but the main question here is that is this combination
> possible:
> 
> 1. AMD CPU
> 2. Non-AMD fTPM (i.e. manufacturer property differs)
> 
> BR, Jarkko

Yes that combination is possible.

Pluton TPM uses the tpm_crb driver.