linux-kernel - Re: [PATCH v6] tpm: add support for partial reads

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Date:   Wed, 21 Nov 2018 17:18:38 +0200
From:   Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
To:     Tadeusz Struk <tadeusz.struk@...el.com>
Cc:     jgg@...pe.ca, linux-integrity@...r.kernel.org,
        linux-security-module@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v6] tpm: add support for partial reads

On Wed, Nov 21, 2018 at 06:50:37AM -0800, Tadeusz Struk wrote:
> Currently to read a response from the TPM device an application needs
> provide big enough buffer for the whole response and read it in one go.
> The application doesn't know how big the response it beforehand so it
> always needs to maintain a 4K buffer and read the max (4K).
> In case if the user of the TSS library doesn't provide big enough
> buffer the TCTI spec says that the library should set the required
> size and return TSS2_TCTI_RC_INSUFFICIENT_BUFFER error code so that the
> application could allocate a bigger buffer and call receive again.
> To make it possible in the TSS library, this requires being able to do
> partial reads from the driver.
> The library would read the 10 bytes header first to get the actual size
> of the response from the header, and then read the rest of the response.
> 
> This patch adds support for partial reads, i.e. the user can read the
> response in one or multiple reads, until the whole response is consumed.
> The user can also read only part of the response and ignore
> the rest by issuing a new write to send a new command.
> 
> Signed-off-by: Tadeusz Struk <tadeusz.struk@...el.com>

Reviewed-by: Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>

/Jarkko