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

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Date:   Fri, 17 Nov 2017 19:10:09 +0100
From:   Javier Martinez Canillas <javierm@...hat.com>
To:     Jason Gunthorpe <jgg@...pe.ca>
Cc:     linux-kernel@...r.kernel.org,
        Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>,
        Peter Huewe <peterhuewe@....de>,
        Philip Tricca <philip.b.tricca@...el.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 11/17/2017 06:58 PM, Jason Gunthorpe wrote:
> On Fri, Nov 17, 2017 at 06:56:09PM +0100, Javier Martinez Canillas wrote:
> 
>> Yes, the problem with that is user-space not having enough information about
>> what went wrong. Right now the TCTI layer just reports TSS2_BASE_RC_IO_ERROR
>> in this case and can't be blamed.
> 
> Well, if you care about the differnce between a transport failure and
> a kernel rejection due to validation, then it needs to report a
> different code :)
> 

Fair enough, the hard part I guess would be to decide which errno codes to use
that could better map to the actual TPM_RC_COMMAND_{CODE,SIZE} response codes.

I'll give some thought to this and also discuss with the tpm2 tools/tss folks.

>>> Regarding your specific issue, can you make the command you want to
>>> use validate? Would that make sense?
>>
>> Sorry, I'm not sure to understand what you meant. Could you please elaborate?
> 
> Make it so tpm_validate will accept the command being sent.
>

Right, that's what I understood indeed but wanted to be sure. The problem with
that approach is that would not scale.

Since this particular TPM2 doesn't have support for the TPM2_EncryptDecrypt2
command, but some chips may not support others commands. So I rather prefer to
have a consistent way for the kernel to report when a command is found to not
be supported and user-space to understand it.

> Jason
> 

Best regards,
-- 
Javier Martinez Canillas
Software Engineer - Desktop Hardware Enablement
Red Hat