linux-kernel - Re: tpm_tis_spi takes minutes to probe

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Date: Fri, 17 May 2024 18:57:42 +0300
From: "Jarkko Sakkinen" <jarkko@...nel.org>
To: "Jarkko Sakkinen" <jarkko@...nel.org>, "Vitor Soares"
 <ivitro@...il.com>, <linux-integrity@...r.kernel.org>,
 <linux-kernel@...r.kernel.org>
Cc: <jgg@...pe.ca>, <peterhuewe@....de>, <vitor.soares@...adex.com>
Subject: Re: tpm_tis_spi takes minutes to probe

On Fri May 17, 2024 at 6:42 PM EEST, Jarkko Sakkinen wrote:
> On Fri May 17, 2024 at 5:53 PM EEST, Vitor Soares wrote:
> > Greetings,
> >
> > I'm using the tpm_tis_spi.ko module and it is taking several minutes to probe on
> > kernel:
> >  - commit ea5f6ad9ad96 ("Merge tag 'platform-drivers-x86-v6.10-1' of
> > git://git.kernel.org/pub/scm/linux/kernel/git/pdx86/platform-drivers-x86")
> >
> > root@...din-imx8mm-07317726:~# time modprobe tpm_tis_spi 
> > [   57.534597] SPI driver tpm_tis_spi has no spi_device_id for atmel,attpm20p
>
> This was added in 6.9:
>
> $ git --no-pager log -1 3c45308c44eda
> commit 3c45308c44eda6cc3343a48341a82b96753c8a13
> Author: Lukas Wunner <lukas@...ner.de>
> Date:   Sat Jan 13 18:10:52 2024 +0100
>
>     tpm_tis_spi: Add compatible string atmel,attpm20p
>     
>     Commit 4f2a348aa365 ("arm64: dts: imx8mm-venice-gw73xx: add TPM device")
>     added a devicetree node for the Trusted Platform Module on certain
>     Gateworks boards.
>     
>     The commit only used the generic "tcg,tpm_tis-spi" compatible string,
>     but public documentation shows that the chip is an ATTPM20P from Atmel
>     (nowadays Microchip):
>     https://trac.gateworks.com/wiki/tpm
>     
>     Add the chip to the supported compatible strings of the TPM TIS SPI
>     driver.
>     
>     For reference, a datasheet is available at:
>     https://ww1.microchip.com/downloads/en/DeviceDoc/ATTPM20P-Trusted-Platform-Module-TPM-2.0-SPI-Interface-Summary-Data-Sheet-DS40002082A.pdf
>     
>     Signed-off-by: Lukas Wunner <lukas@...ner.de>
>     Reviewed-by: Jarkko Sakkinen <jarkko.sakkinen@...nel.org>
>     Cc: Tim Harvey <tharvey@...eworks.com>
>     Signed-off-by: Jarkko Sakkinen <jarkko@...nel.org>
>
> linux-tpmdd on  tpm2_key 
> $ git describe --contains 3c45308c44eda
> tpmdd-v6.9-rc1~2
>
> > [   57.560684] tpm_tis_spi spi2.1: 2.0 TPM (device-id 0x3205, rev-id 1)
> > [   57.584943] tpm tpm0: A TPM error (256) occurred attempting the self test
>
> Course of event is I think:
>
> 	rc = tpm2_do_selftest(chip);
> 	if (rc && rc != TPM2_RC_INITIALIZE)
> 		goto out;
>
> 	/* 1. TPM_RC_INITIALIZE */
> 	if (rc == TPM2_RC_INITIALIZE) {
> 		/* 2. Branches here. */
> 		rc = tpm2_startup(chip);
> 		if (rc)
> 			goto out;
>
> 		rc = tpm2_do_selftest(chip);
> 		if (rc)
> 			goto out;
> 	}
>
> 	/* 4. Second self-test successful. */
>
> It is possible that there is a performance regression given multitude
> of HMAC changes. It would likely had to be in tpm2_do_selftest(), since
> it is the most time-consuming function.
>
> I checked the timeouts etc. but in the first seek did find anything
> obvious.

Right, the extra time comes from probably null key creation, even though
tpm2_do_selftest() does not itself invoke tpm2_start_auth_session().

If you don't want that to happen, then you should disable
CONFIG_TCG_TPM2_HMAC but also bus encrypted sessions to trusted keys
random number generation and PCR extension.

BR, Jarkko