linux-kernel - Re: [PATCH v14 2/7] tpm: tpm_tis: Fix expected bit handling and send all bytes in one shot without last byte in exception

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Date:   Tue, 14 Sep 2021 00:10:26 +0300
From:   Jarkko Sakkinen <jarkko@...nel.org>
To:     amirmizi6@...il.com, Eyal.Cohen@...oton.com,
        oshrialkoby85@...il.com, alexander.steffen@...ineon.com,
        robh+dt@...nel.org, mark.rutland@....com, peterhuewe@....de,
        jgg@...pe.ca, arnd@...db.de, gregkh@...uxfoundation.org,
        benoit.houyere@...com, eajames@...ux.ibm.com, joel@....id.au
Cc:     devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-integrity@...r.kernel.org, oshri.alkoby@...oton.com,
        tmaimon77@...il.com, gcwilson@...ibm.com, kgoldman@...ibm.com,
        Dan.Morav@...oton.com, oren.tanami@...oton.com,
        shmulik.hager@...oton.com, amir.mizinski@...oton.com
Subject: Re: [PATCH v14 2/7] tpm: tpm_tis: Fix expected bit handling and
 send all bytes in one shot without last byte in exception

On Mon, 2021-09-13 at 17:43 +0300, amirmizi6@...il.com wrote:
> From: Amir Mizinski <amirmizi6@...il.com>
> 
> Detected an incorrect implementation of the send command.
> Currently, the driver polls the TPM_STS.stsValid field until TRUE; then it
> reads TPM_STS register again to verify only that TPM_STS.expect field is
> FALSE (i.e., it ignores TPM_STS.stsValid).
> Since TPM_STS.stsValid represents the TPM_STS.expect validity, both fields
> fields should be checked in the same TPM_STS register read value.
> 
> This fix modifies the signature of 'wait_for_tpm_stat()', adding an
> additional "mask_result" parameter to its call and renaming it to
> 'tpm_tis_wait_for_stat()' for better alignment with other naming.
> 'tpm_tis_wait_for_stat()' is now polling the TPM_STS with a mask and waits
> for the value in mask_result. The fix adds the ability to check if certain
> TPM_STS bits have been cleared.

Use imprative form, e.g. "Modify the signature...".

> 
> This change is also aligned to verifying the CRC on I2C TPM. The CRC
> verification should be done after the TPM_STS.expect field is cleared
> (TPM received all expected command bytes and set the calculated CRC value
> in the register).

What does it mean when you "align to verifying"?

> In addition, the send command was changed to comply with
> TCG_DesignPrinciples_TPM2p0Driver_vp24_pubrev.pdf as follows:
> - send all command bytes in one loop
> - remove special handling of the last byte
> 
> Suggested-by: Benoit Houyere <benoit.houyere@...com>
> Signed-off-by: Amir Mizinski <amirmizi6@...il.com>


I don't think the rename is important enough to be done, and it
definitely should not be melded into another patch.

/Jarkko