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

Jerry Snitselaar
2023-08-22T19:50:52Z

On Tue, Aug 22, 2023 at 05:56:03PM +0300, Jarkko Sakkinen wrote:
> On Tue Aug 22, 2023 at 5:05 PM EEST, Mario Limonciello wrote:
> > 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@vger.kernel.org
> > >> Fixes: 554b841d4703 ("tpm: Disable RNG for all AMD fTPMs")
> > >> Reported-by: Todd Brandt <todd.e.brandt@intel.com>
> > >> Reported-by: Patrick Steinhardt <ps@pks.im>
> > >> Reported-by: Ronan Pigott <ronan@rjp.ie>
> > >> Reported-by: Raymond Jay Golo <rjgolo@gmail.com>
> > >> Closes: https://bugzilla.kernel.org/show_bug.cgi?id=217804
> > >> Signed-off-by: Mario Limonciello <mario.limonciello@amd.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.
>
> Then I guess we'll go with this for now. Thanks for the effort.
>
> Tested-by: Jarkko Sakkinen <jarkko@kernel.org> # QEMU + swtpm
> Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org>
>
> I'm planning to send a pull request right after this with the fix so it
> will land to v6.6-rc1 or v6.6-rc2:
> https://lore.kernel.org/linux-integrity/20230817201935.31399-1-jarkko@kernel.org/
>
> BR, Jarkko

Super minor nit that isn't this patch in particular so don't hold this
up, but it seems like the function name for the earlier attempt to
solve this issue that mentioned amd and ftpm was a clearer description
of what was happening than crb_check_flags.

Regards,
Jerry