linux-kernel - Re: [PATCH v18 1/6] tpm_tis: Fix expected bit handling and send all bytes in one shot without last byte in exception

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Date:   Tue, 02 Nov 2021 22:23:42 +0200
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 v18 1/6] tpm_tis: Fix expected bit handling and send all
 bytes in one shot without last byte in exception

On Tue, 2021-11-02 at 17:20 +0200, amirmizi6@...il.com wrote:
> From: Amir Mizinski <amirmizi6@...il.com>
> 
> 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, a check of
> only one of these fields is wrong. Fix this condition so that both fields
> are checked in the same TPM_STS register read.
> 
> Modify the signature of wait_for_tpm_stat() to tpm_tis_wait_for_stat(),
> adding an additional "expected" parameter to its call.
> tpm_tis_wait_for_stat() is now polling the TPM_STS with a mask and waits
> for the value in "expected". This modification adds the ability to check if
> certain TPM_STS bits have been cleared.
> For example, use the new parameter to check in status that TPM_STS_VALID
> is set and also that TPM_STS_EXPECT is zeroed. This prevents a racy
> check.
> 
> Suggested-by: Benoit Houyere <benoit.houyere@...com>
> Signed-off-by: Amir Mizinski <amirmizi6@...il.com>

Thank you, this looks legit now!

Reviewed-by: Jarkko Sakkinen <jarkko@...nel.org>

/Jarkko