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

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Message-ID: <25a21516-7201-4ee4-be2b-f67edaf97e2a@amd.com>
Date:   Fri, 18 Aug 2023 17:38:10 -0500
From:   "Limonciello, Mario" <mario.limonciello@....com>
To:     Jarkko Sakkinen <jarkko@...nel.org>
Cc:     linux-integrity@...r.kernel.org, linux-kernel@...r.kernel.org,
        Thorsten Leemhuis <regressions@...mhuis.info>,
        charles.d.prestopine@...el.com, rafael.j.wysocki@...el.com,
        len.brown@...el.com, stable@...r.kernel.org,
        Todd Brandt <todd.e.brandt@...el.com>
Subject: Re: [PATCH] tpm: Don't make vendor check required for probe



On 8/18/2023 5:07 PM, Jarkko Sakkinen wrote:
> On Fri Aug 18, 2023 at 6:15 PM UTC, Mario Limonciello wrote:
>> The vendor check introduced by commit 554b841d4703 ("tpm: Disable RNG for
>> all AMD fTPMs") doesn't work properly on Intel fTPM.  The TPM doesn't reply
>> at bootup and returns back the command code.
> 
> Is this reproducible with any production hardware? You are stating it
> as it was reproducible categorically with any Intel fTPM.
> 

Yes, it's affecting production hardware too.
Someone came to the kernel bugzilla and reported a regression on 6.4.11 
on a Lenovo Intel laptop as well.

>> As this isn't crucial for anything but AMD fTPM and AMD fTPM works, throw
>> away the error code to let Intel fTPM continue to work.
>>
>> Cc: stable@...r.kernel.org
>> Fixes: 554b841d4703 ("tpm: Disable RNG for all AMD fTPMs")
> 
> It does make sense not to exercise this outside of AMD CPus but since
> there is no production hardware failing, it cannot be categorized as a
> bug fix.

See above (and also kernel bugzilla).

> 
>> Reported-by: Todd Brandt <todd.e.brandt@...el.com>
>> Closes: https://bugzilla.kernel.org/show_bug.cgi?id=217804
>> Signed-off-by: Mario Limonciello <mario.limonciello@....com>
>> ---
>>   drivers/char/tpm/tpm_crb.c | 3 +--
>>   1 file changed, 1 insertion(+), 2 deletions(-)
>>
>> diff --git a/drivers/char/tpm/tpm_crb.c b/drivers/char/tpm/tpm_crb.c
>> index 9eb1a18590123..b0e9931fe436c 100644
>> --- a/drivers/char/tpm/tpm_crb.c
>> +++ b/drivers/char/tpm/tpm_crb.c
>> @@ -472,8 +472,7 @@ static int crb_check_flags(struct tpm_chip *chip)
>>   	if (ret)
>>   		return ret;
>>   
>> -	ret = tpm2_get_tpm_pt(chip, TPM2_PT_MANUFACTURER, &val, NULL);
>> -	if (ret)
>> +	if (tpm2_get_tpm_pt(chip, TPM2_PT_MANUFACTURER, &val, NULL))
>>   		goto release;
> 
> It would be better not to exercise a potentially failing code path at
> all. This initiates full transaction with the TPM.

So why does a full transaction not work in this case?

> 
>>   
>>   	if (val == 0x414D4400U /* AMD */)
>> -- 
>> 2.34.1
> 
> BR, Jarkko