linux-kernel - Re: [tpmdd-devel] [PATCH 4/4] keys, trusted: seal/unseal with TPM 2.0 chips

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Message-ID: <20151003102655.GA9372@intel.com>
Date:	Sat, 3 Oct 2015 13:26:55 +0300
From:	Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
To:	"Fuchs, Andreas" <andreas.fuchs@....fraunhofer.de>
Cc:	"tpmdd-devel@...ts.sourceforge.net" 
	<tpmdd-devel@...ts.sourceforge.net>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	David Howells <dhowells@...hat.com>,
	"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
	"open list:KEYS-TRUSTED" <linux-security-module@...r.kernel.org>,
	"open list:KEYS-TRUSTED" <keyrings@...r.kernel.org>,
	James Morris <james.l.morris@...cle.com>,
	David Safford <safford@...ibm.com>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"Serge E. Hallyn" <serge@...lyn.com>
Subject: Re: [tpmdd-devel] [PATCH 4/4] keys,	trusted: seal/unseal with TPM
 2.0 chips

On Sat, Oct 03, 2015 at 10:00:59AM +0000, Fuchs, Andreas wrote:
> Hi Jarkko,
> 
> [snip]
> 
> diff --git a/security/keys/trusted.h b/security/keys/trusted.h
> index ff001a5..fc32c47 100644
> --- a/security/keys/trusted.h
> +++ b/security/keys/trusted.h
> @@ -12,6 +12,13 @@
>  #define TPM_RETURN_OFFSET              6
>  #define TPM_DATA_OFFSET                        10
> 
> +/* Transient object handles start from 0x80000000 in TPM 2.0, which makes it
> + * a sane default.
> + */
> +
> +#define TPM1_SRKHANDLE 0x40000000
> +#define TPM2_SRKHANDLE 0x80000000
> +
>  #define LOAD32(buffer, offset) (ntohl(*(uint32_t *)&buffer[offset]))
>  #define LOAD32N(buffer, offset)        (*(uint32_t *)&buffer[offset])
>  #define LOAD16(buffer, offset) (ntohs(*(uint16_t *)&buffer[offset]))
> 
> This TPM2_SRKHANDLE is unfortunately wrong.
> 
> Transient handles are assigned and returned by the TPM following the
> commands TPM2_CreatePrimary, TPM2_LoadObject and TPM2_ContextLoad. You
> can only use transient handles as returned by the TPM in order to
> refer to the corresponding object created inside the TPM via these
> commands. They can never assumed to be constant. The fact that TPMs
> return 0x80000000 for the first loaded Object and 0x80000001 for the
> second is merely a coincidence... ;-)
> 
> TPM2 also has no (single) SRK anymore. You have to create your own SRK
> / Storage Primary Keys via TPM2_CreatePrimary and use the transient
> handle returned from there. This however requires SH-authorization,
> usually via Policy IMHO, so not easy to manage. So IMHO, this might be
> something for the future but for the moment relying on a persistent
> key would be better...
> 
> For persistent SRKs it should become a convention to have those
> around. Those handles start with 0x81000000 and the SRKs (or Storage
> primary Keys) shall live within 0x81000000 to 0x8100FFFF (see
> http://www.trustedcomputinggroup.org/resources/registry_of_reserved_tpm_20_handles_and_localities)
> 
> I'd recommend to rely on the existence of a handle inside this range
> with an empty auth-value. So maybe install a persistent SRK to
> 0x81000000 via TPM2_EvictControl and then use this from within the
> kernel for anything following.
> P.S. You should check for the key's TPMA_OBJECT to have fixedTPM SET.
> I don't know if there is an actual test for owner-generated SRK
> testing. I'll ask around though...
> 
> Note: you can query for handles in this range via
> TPM2_GetCapability(TPM_CAP_HANDLES, 0x81000000) and then look for
> fitting keys.
> 
> 
> Feel free to discuss other approaches.

I'm fully aware of all what you said. My take was to use 0x800000000 as
a default value if you don't the handle ID explicitly in 'description'
parameter of the add_key() syscall.

> Cheers,
> Andreas

/Jarkko
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