Re: [PATCH v2 3/3] keys, trusted: seal with a TPM2 authorization policy

[Jarkko Sakkinen]

On Mon, Dec 14, 2015 at 08:49:00AM -0500, Mimi Zohar wrote:
> On Sun, 2015-12-13 at 17:42 +0200, Jarkko Sakkinen wrote:
> > TPM2 supports authorization policies, which are essentially
> > combinational logic statements repsenting the conditions where the data
> > can be unsealed based on the TPM state. This patch enables to use
> > authorization policies to seal trusted keys.
> > 
> > Two following new options have been added for trusted keys:
> > 
> > * 'policydigest=': provide an auth policy digest for sealing.
> > * 'policyhandle=': provide a policy session handle for unsealing.
> > 
> > If 'hash=' option is supplied after 'policydigest=' option, this
> > will result an error because the state of the option would become
> > mixed.
> > 
> > Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@xxxxxxxxxxxxxxx>
> > Tested-by: Colin Ian King <colin.king@xxxxxxxxxxxxx>
> > ---
> >  Documentation/security/keys-trusted-encrypted.txt | 34 +++++++++++++----------
> >  drivers/char/tpm/tpm2-cmd.c                       | 24 +++++++++++++---
> >  include/keys/trusted-type.h                       |  4 +++
> >  security/keys/trusted.c                           | 26 +++++++++++++++++
> >  4 files changed, 70 insertions(+), 18 deletions(-)
> > 
> > diff --git a/Documentation/security/keys-trusted-encrypted.txt b/Documentation/security/keys-trusted-encrypted.txt
> > index fd2565b..324ddf5 100644
> > --- a/Documentation/security/keys-trusted-encrypted.txt
> > +++ b/Documentation/security/keys-trusted-encrypted.txt
> > @@ -27,20 +27,26 @@ Usage:
> >      keyctl print keyid
> > 
> >      options:
> > -       keyhandle= ascii hex value of sealing key default 0x40000000 (SRK)
> > -       keyauth=	  ascii hex auth for sealing key default 0x00...i
> > -		  (40 ascii zeros)
> > -       blobauth=  ascii hex auth for sealed data default 0x00...
> > -		  (40 ascii zeros)
> > -       blobauth=  ascii hex auth for sealed data default 0x00...
> > -		  (40 ascii zeros)
> > -       pcrinfo=	  ascii hex of PCR_INFO or PCR_INFO_LONG (no default)
> > -       pcrlock=	  pcr number to be extended to "lock" blob
> > -       migratable= 0|1 indicating permission to reseal to new PCR values,
> > -                   default 1 (resealing allowed)
> > -       hash=      hash algorithm name as a string. For TPM 1.x the only
> > -                  allowed value is sha1. For TPM 2.x the allowed values
> > -		  are sha1, sha256, sha384, sha512 and sm3-256.
> > +       keyhandle=    ascii hex value of sealing key default 0x40000000 (SRK)
> > +       keyauth=	     ascii hex auth for sealing key default 0x00...i
> > +                     (40 ascii zeros)
> > +       blobauth=     ascii hex auth for sealed data default 0x00...
> > +                     (40 ascii zeros)
> > +       blobauth=     ascii hex auth for sealed data default 0x00...
> > +                     (40 ascii zeros)
> > +       pcrinfo=	     ascii hex of PCR_INFO or PCR_INFO_LONG (no default)
> > +       pcrlock=	     pcr number to be extended to "lock" blob
> > +       migratable=   0|1 indicating permission to reseal to new PCR values,
> > +                     default 1 (resealing allowed)
> > +       hash=         hash algorithm name as a string. For TPM 1.x the only
> > +                     allowed value is sha1. For TPM 2.x the allowed values
> > +                     are sha1, sha256, sha384, sha512 and sm3-256.
> > +       policydigest= digest for the authorization policy. must be calculated
> > +                     with the same hash algorithm as specified by the 'hash='
> > +                     option.
> > +       policyhandle= handle to an authorization policy session that defines the
> > +                     same policy and with the same hash algorithm as was used to
> > +                     seal the key.
> > 
> >  "keyctl print" returns an ascii hex copy of the sealed key, which is in standard
> >  TPM_STORED_DATA format.  The key length for new keys are always in bytes.
> > diff --git a/drivers/char/tpm/tpm2-cmd.c b/drivers/char/tpm/tpm2-cmd.c
> > index d9d0822..45a6340 100644
> > --- a/drivers/char/tpm/tpm2-cmd.c
> > +++ b/drivers/char/tpm/tpm2-cmd.c
> > @@ -478,12 +478,26 @@ int tpm2_seal_trusted(struct tpm_chip *chip,
> >  	tpm_buf_append_u8(&buf, payload->migratable);
> > 
> >  	/* public */
> > -	tpm_buf_append_u16(&buf, 14);
> > +	if (options->policydigest)
> > +		tpm_buf_append_u16(&buf, 14 + options->digest_len);
> > +	else
> > +		tpm_buf_append_u16(&buf, 14);
> > 
> >  	tpm_buf_append_u16(&buf, TPM2_ALG_KEYEDHASH);
> >  	tpm_buf_append_u16(&buf, hash);
> > -	tpm_buf_append_u32(&buf, TPM2_ATTR_USER_WITH_AUTH);
> > -	tpm_buf_append_u16(&buf, 0); /* policy digest size */
> > +
> > +	/* policy */
> > +	if (options->policydigest) {
> > +		tpm_buf_append_u32(&buf, 0);
> > +		tpm_buf_append_u16(&buf, options->digest_len);
> > +		tpm_buf_append(&buf, options->policydigest,
> > +			       options->digest_len);
> > +	} else {
> > +		tpm_buf_append_u32(&buf, TPM2_ATTR_USER_WITH_AUTH);
> > +		tpm_buf_append_u16(&buf, 0);
> > +	}
> > +
> > +	/* public parameters */
> >  	tpm_buf_append_u16(&buf, TPM2_ALG_NULL);
> >  	tpm_buf_append_u16(&buf, 0);
> > 
> > @@ -613,7 +627,9 @@ static int tpm2_unseal(struct tpm_chip *chip,
> >  		return rc;
> > 
> >  	tpm_buf_append_u32(&buf, blob_handle);
> > -	tpm2_buf_append_auth(&buf, TPM2_RS_PW,
> > +	tpm2_buf_append_auth(&buf,
> > +			     options->policyhandle ?
> > +			     options->policyhandle : TPM2_RS_PW,
> >  			     NULL /* nonce */, 0,
> >  			     0 /* session_attributes */,
> >  			     options->blobauth /* hmac */,
> > diff --git a/include/keys/trusted-type.h b/include/keys/trusted-type.h
> > index a6a1008..42cf2d9 100644
> > --- a/include/keys/trusted-type.h
> > +++ b/include/keys/trusted-type.h
> > @@ -18,6 +18,7 @@
> >  #define MAX_KEY_SIZE			128
> >  #define MAX_BLOB_SIZE			512
> >  #define MAX_PCRINFO_SIZE		64
> > +#define MAX_DIGEST_SIZE			64
> > 
> >  struct trusted_key_payload {
> >  	struct rcu_head rcu;
> > @@ -37,6 +38,9 @@ struct trusted_key_options {
> >  	unsigned char pcrinfo[MAX_PCRINFO_SIZE];
> >  	int pcrlock;
> >  	uint32_t hash;
> > +	uint32_t digest_len;
> > +	unsigned char policydigest[MAX_DIGEST_SIZE];
> > +	uint32_t policyhandle;
> >  };
> > 
> >  extern struct key_type key_type_trusted;
> > diff --git a/security/keys/trusted.c b/security/keys/trusted.c
> > index 8f1300c..e15baf7 100644
> > --- a/security/keys/trusted.c
> > +++ b/security/keys/trusted.c
> > @@ -713,6 +713,8 @@ enum {
> >  	Opt_keyhandle, Opt_keyauth, Opt_blobauth,
> >  	Opt_pcrinfo, Opt_pcrlock, Opt_migratable,
> >  	Opt_hash,
> > +	Opt_policydigest,
> > +	Opt_policyhandle,
> >  };
> > 
> >  static const match_table_t key_tokens = {
> > @@ -726,6 +728,8 @@ static const match_table_t key_tokens = {
> >  	{Opt_pcrlock, "pcrlock=%s"},
> >  	{Opt_migratable, "migratable=%s"},
> >  	{Opt_hash, "hash=%s"},
> > +	{Opt_policydigest, "policydigest=%s"},
> > +	{Opt_policyhandle, "policyhandle=%s"},
> >  	{Opt_err, NULL}
> >  };
> > 
> > @@ -748,6 +752,7 @@ static int getoptions(char *c, struct trusted_key_payload *pay,
> >  		return tpm2;
> > 
> >  	opt->hash = tpm2 ? HASH_ALGO_SHA256 : HASH_ALGO_SHA1;
> > +	opt->digest_len = hash_digest_size[opt->hash];
> > 
> >  	while ((p = strsep(&c, " \t"))) {
> >  		if (*p == '\0' || *p == ' ' || *p == '\t')
> > @@ -802,9 +807,13 @@ static int getoptions(char *c, struct trusted_key_payload *pay,
> >  			opt->pcrlock = lock;
> >  			break;
> >  		case Opt_hash:
> > +			if (test_bit(Opt_policydigest, &token_mask))
> > +				return -EINVAL;
> 
> Thanks!  Definitely better than having the test at the end of the while
> loop.

Yup, retrospectively the previous version looked like a mess. This is
now nicely localized change that cannot easily break the existing
functionality.

> Mimi

/Jarkko

> 
> >  			for (i = 0; i < HASH_ALGO__LAST; i++) {
> >  				if (!strcmp(args[0].from, hash_algo_name[i])) {
> >  					opt->hash = i;
> > +					opt->digest_len =
> > +						hash_digest_size[opt->hash];
> >  					break;
> >  				}
> >  			}
> > @@ -815,6 +824,23 @@ static int getoptions(char *c, struct trusted_key_payload *pay,
> >  				return -EINVAL;
> >  			}
> >  			break;
> > +		case Opt_policydigest:
> > +			if (!tpm2 ||
> > +			    strlen(args[0].from) != (2 * opt->digest_len))
> > +				return -EINVAL;
> > +			res = hex2bin(opt->policydigest, args[0].from,
> > +				      opt->digest_len);
> > +			if (res < 0)
> > +				return -EINVAL;
> > +			break;
> > +		case Opt_policyhandle:
> > +			if (!tpm2)
> > +				return -EINVAL;
> > +			res = kstrtoul(args[0].from, 16, &handle);
> > +			if (res < 0)
> > +				return -EINVAL;
> > +			opt->policyhandle = handle;
> > +			break;
> >  		default:
> >  			return -EINVAL;
> >  		}
> 
> 

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