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

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Message-Id: <CUZ3T3G99JG2.29X1G67HRO9QT@suppilovahvero>
Date:   Tue, 22 Aug 2023 16:22:21 +0300
From:   "Jarkko Sakkinen" <jarkko@...nel.org>
To:     "Mario Limonciello" <mario.limonciello@....com>
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 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