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

[Mario Limonciello]

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@xxxxxxxxxxxxxxx
> > Fixes: 554b841d4703 ("tpm: Disable RNG for all AMD fTPMs")
> > Reported-by: Todd Brandt <todd.e.brandt@xxxxxxxxx>
> > Reported-by: Patrick Steinhardt <ps@xxxxxx>
> > Reported-by: Ronan Pigott <ronan@xxxxxx>
> > Reported-by: Raymond Jay Golo <rjgolo@xxxxxxxxx>
> > Closes: https://bugzilla.kernel.org/show_bug.cgi?id=217804
> > Signed-off-by: Mario Limonciello <mario.limonciello@xxxxxxx>
> > ---
> > 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.