linux-kernel - Re: [RFC PATCH] tpm: don't return -EINVAL if TPM command validation fails

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Date:   Tue, 21 Nov 2017 01:15:12 +0200
From:   Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
To:     Javier Martinez Canillas <javierm@...hat.com>
Cc:     linux-kernel@...r.kernel.org, Peter Huewe <peterhuewe@....de>,
        Philip Tricca <philip.b.tricca@...el.com>,
        Jason Gunthorpe <jgunthorpe@...idianresearch.com>,
        linux-integrity@...r.kernel.org,
        William Roberts <william.c.roberts@...el.com>
Subject: Re: [RFC PATCH] tpm: don't return -EINVAL if TPM command validation
 fails

On Fri, Nov 17, 2017 at 11:07:24AM +0100, Javier Martinez Canillas wrote:
> According to the TPM Library Specification, a TPM device must do a command
> header validation before processing and return a TPM_RC_COMMAND_CODE code
> if the command is not implemented and the TPM_RC_COMMAND_SIZE code if the
> command buffer size is not correct.
> 
> So user-space will expect to handle these response codes as errors, but if
> the in-kernel resource manager is used (/dev/tpmrm?) then an -EINVAL errno
> code is returned instead if the command isn't implemented or the buffer
> size isn't correct. This confuses user-space since doesn't expect that.
> 
> This is also not consistent with the behavior when not using TPM spaces
> and accessing the TPM directly (/dev/tpm?), in this case the command is
> is sent to the TPM anyways and user-space can get an error from the TPM.
> 
> Instead of returning an -EINVAL errno code when the tpm_validate_command()
> function fails, allow the command to be sent to the TPM but just don't do
> any TPM space management. That way the TPM can report back a proper error
> and the behavior be consistent when using either /dev/tpm? or /dev/tpmrm?.
> 
> Signed-off-by: Javier Martinez Canillas <javierm@...hat.com>

It is not a virtual TPM so I don't think that matters. It at least
matters less than breaking the sandbox.

/Jarkko