linux-kernel - Re: [PATCH v4 2/6] tpm, tpm_tis: Claim and release locality only once

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Message-ID: <dd421552-40f8-b5c2-5d5a-cc9ce3bdb760@gmx.de>
Date:   Mon, 16 May 2022 22:23:54 +0200
From:   Lino Sanfilippo <LinoSanfilippo@....de>
To:     Jarkko Sakkinen <jarkko@...nel.org>
Cc:     peterhuewe@....de, jgg@...pe.ca, stefanb@...ux.vnet.ibm.com,
        linux@...ewoehner.de, linux-integrity@...r.kernel.org,
        linux-kernel@...r.kernel.org, lukas@...ner.de,
        p.rosenberger@...bus.com, Lino Sanfilippo <l.sanfilippo@...bus.com>
Subject: Re: [PATCH v4 2/6] tpm, tpm_tis: Claim and release locality only once

On 13.05.22 at 19:59, Jarkko Sakkinen wrote:
> On Wed, May 11, 2022 at 09:29:57PM +0200, Lino Sanfilippo wrote:
>>
>>
>> On 11.05.22 at 13:27, Jarkko Sakkinen wrote:
>>> On Mon, May 09, 2022 at 10:05:55AM +0200, Lino Sanfilippo wrote:
>>>> From: Lino Sanfilippo <l.sanfilippo@...bus.com>
>>>>
>>>> It is not necessary to claim and release the default locality for each TPM
>>>> command. Instead claim the locality once at driver startup and release it
>>>> at driver shutdown.
>>>>
>>>> Signed-off-by: Lino Sanfilippo <l.sanfilippo@...bus.com>
>>>
>>> We are doing what we're being because of Intel TXT:
>>>
>>> https://lore.kernel.org/tpmdd-devel/20170315055738.11088-1-jarkko.sakkinen@iki.fi/
>>>
>>> Unfortunately cannot accept this change.
>>>
>>
>> I do not see how the patch affects the crb code since the only changes concern the
>> tpm_class_ops of the tis core. AFAICS crb uses its own set of tpm_class_ops
>> which are still used to claim and release the locality.
>>
>> Or do I miss something?
>
> Ugh, yes breaking everything when TXT is used with tpm_tis.
>
>> Regards,
>> Lino
>
> BR, Jarkko
>

Ok, I got it now. The idea of this patch was to maintain the locality 0 for the whole
driver lifetime, so that we can always be sure that the locality is already claimed
when the interrupt status register is read or written in the interrupt handler.

But of course this does not work if some other instance like TXT also wants
to claim localities.

I will try another approach to make sure that the locality is already taken when the
irq handler is called and only released after the handler has finished.

Regards,
Lino