Re: [PATCH 4/6] KEYS: trusted: add ability to specify arbitrary policy

["Jarkko Sakkinen" <jarkko@kernel.org>]

On Fri May 24, 2024 at 4:04 PM EEST, James Bottomley wrote:
> This patch adds a policy= argument to key creation.  The policy is the
> standard tss policymaker format and each separate policy line must
> have a newline after it.
>
> Thus to construct a policy requiring authorized value and pcr 16
> locking using a sha256 hash, the policy (policy.txt) file would be two
> lines:
>
> 0000017F00000001000B03000001303095B49BE85E381E5B20E557E46363EF55B0F43B132C2D8E3DE9AC436656F2
> 0000016b
>
> This can be inserted into the key with
>
> keyctl add trusted kmk "new 32 policy=`cat policy.txt` keyhandle=0x81000001 hash=sha256" @u
>
> Note that although a few policies work like this, most require special
> handling which must be added to the kernel policy construction
> routine.
>
> Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>
> ---
>  .../security/keys/trusted-encrypted.rst       | 17 +++++-
>  security/keys/trusted-keys/tpm2-policy.c      | 53 +++++++++++++++++++
>  security/keys/trusted-keys/tpm2-policy.h      |  5 ++
>  security/keys/trusted-keys/trusted_tpm1.c     | 15 ++++++
>  4 files changed, 89 insertions(+), 1 deletion(-)
>
> diff --git a/Documentation/security/keys/trusted-encrypted.rst b/Documentation/security/keys/trusted-encrypted.rst
> index c37c08956ec1..fbb41cf16f30 100644
> --- a/Documentation/security/keys/trusted-encrypted.rst
> +++ b/Documentation/security/keys/trusted-encrypted.rst
> @@ -233,6 +233,9 @@ Usage::
>         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.
> +       policy=       specify an arbitrary set of policies.  These must
> +                     be in policymaker format with each separate
> +                     policy line newline terminated.
>  
>  "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.
> @@ -377,6 +380,19 @@ the sha1 pcr16 bank you'd say::
>  
>  because the trailing hash is the sha256sum of 20 zero bytes.
>  
> +You can also specify arbitrary policy in policymaker format, so a two
> +value policy (the pcr example above and authvalue) would look like
> +this in policymaker format::
> +
> +    0000017F000000010004030000016768033e216468247bd031a0a2d9876d79818f8f
> +    0000016b
> +
> +This can be placed in a file (say policy.txt) and then added to the key as::
> +
> +    $ keyctl add trusted kmk "new 32 keyhandle=0x81000001 hash=sha1 policy=`cat policy.txt`" @u
> +
> +The newlines in the file policy.txt will be automatically processed.
> +
>  Reseal (TPM specific) a trusted key under new PCR values::
>  
>      $ keyctl update 268728824 "update pcrinfo=`cat pcr.blob`"
> @@ -447,7 +463,6 @@ Another new format 'enc32' has been defined in order to support encrypted keys
>  with payload size of 32 bytes. This will initially be used for nvdimm security
>  but may expand to other usages that require 32 bytes payload.
>  
> -
>  TPM 2.0 ASN.1 Key Format
>  ------------------------
>  
> diff --git a/security/keys/trusted-keys/tpm2-policy.c b/security/keys/trusted-keys/tpm2-policy.c
> index 8c3a09762c10..a731c10d9bba 100644
> --- a/security/keys/trusted-keys/tpm2-policy.c
> +++ b/security/keys/trusted-keys/tpm2-policy.c

Ditto.

> @@ -323,3 +323,56 @@ int tpm2_get_policy_session(struct tpm_chip *chip, struct tpm2_policies *pols)
>  
>  	return 0;
>  }
> +
> +int tpm2_parse_policies(struct tpm2_policies **ppols, char *str)
> +{
> +	struct tpm2_policies *pols;
> +	char *p;
> +	u8 *ptr;
> +	int i = 0, left = PAGE_SIZE, res;
> +
> +	pols = kmalloc(left, GFP_KERNEL);
> +	if (!pols)
> +		return -ENOMEM;
> +
> +	ptr = (u8 *)(pols + 1);
> +	left -= ptr - (u8 *)pols;
> +
> +	while ((p = strsep(&str, "\n"))) {
> +		if (*p == '\0' || *p == '\n')
> +			continue;
> +
> +		pols->len[i] = strlen(p)/2;
> +		if (pols->len[i] > left) {
> +			res = -E2BIG;
> +			goto err;
> +		}
> +
> +		res = hex2bin(ptr, p, pols->len[i]);
> +		if (res)
> +			goto err;
> +
> +		/* get command code and skip past */
> +		pols->code[i] = get_unaligned_be32(ptr);
> +		pols->policies[i] = ptr + 4;
> +		ptr += pols->len[i];
> +		left -= pols->len[i];
> +		pols->len[i] -= 4;
> +
> +		/*
> +		 * FIXME: this does leave the code embedded in dead
> +		 * regions of the memory, but it's easier than
> +		 * hexdumping to a temporary or copying over
> +		 */
> +		i++;
> +	}
> +
> +	pols->count = i;
> +	*ppols = pols;
> +
> +	return 0;
> +
> + err:
> +	kfree(pols);
> +	return res;
> +}
> diff --git a/security/keys/trusted-keys/tpm2-policy.h b/security/keys/trusted-keys/tpm2-policy.h
> index b20e9c3e2f06..8ddf235b3fec 100644
> --- a/security/keys/trusted-keys/tpm2-policy.h
> +++ b/security/keys/trusted-keys/tpm2-policy.h
> @@ -28,6 +28,7 @@ int tpm2_generate_policy_digest(struct tpm2_policies *pols, u32 hash,
>  				u8 *policydigest, u32 *plen);
>  int tpm2_encode_policy(struct tpm2_policies *pols, u8 **data, u32 *len);
>  int tpm2_get_policy_session(struct tpm_chip *chip, struct tpm2_policies *pols);
> +int tpm2_parse_policies(struct tpm2_policies **ppols, char *str);
>  #else
>  static inline int tpm2_key_policy_process(struct tpm2_key_context *ctx,
>  					  struct trusted_key_payload *payload)
> @@ -50,4 +51,8 @@ static inline int tpm2_get_policy_session(struct tpm_chip *chip,
>  {
>  	return -EINVAL;
>  }
> +static inline int tpm2_parse_policies(struct tpm2_policies **ppols, char *str)
> +{
> +	return -EINVAL;
> +}
>  #endif
> diff --git a/security/keys/trusted-keys/trusted_tpm1.c b/security/keys/trusted-keys/trusted_tpm1.c
> index 89c9798d1800..4dcc1373dd05 100644
> --- a/security/keys/trusted-keys/trusted_tpm1.c
> +++ b/security/keys/trusted-keys/trusted_tpm1.c
> @@ -22,6 +22,8 @@
>  
>  #include <keys/trusted_tpm.h>
>  
> +#include "tpm2-policy.h"
> +
>  static const char hmac_alg[] = "hmac(sha1)";
>  static const char hash_alg[] = "sha1";
>  static struct tpm_chip *chip;
> @@ -724,6 +726,7 @@ enum {
>  	Opt_hash,
>  	Opt_policydigest,
>  	Opt_policyhandle,
> +	Opt_policy,
>  };
>  
>  static const match_table_t key_tokens = {
> @@ -736,6 +739,7 @@ static const match_table_t key_tokens = {
>  	{Opt_hash, "hash=%s"},
>  	{Opt_policydigest, "policydigest=%s"},
>  	{Opt_policyhandle, "policyhandle=%s"},
> +	{Opt_policy, "policy=%s"},
>  	{Opt_err, NULL}
>  };
>  
> @@ -869,6 +873,17 @@ static int getoptions(char *c, struct trusted_key_payload *pay,
>  				return -EINVAL;
>  			opt->policyhandle = handle;
>  			break;
> +
> +		case Opt_policy:
> +			if (pay->policies)
> +				return -EINVAL;
> +			if (!tpm2)
> +				return -EINVAL;
> +			res = tpm2_parse_policies(&pay->policies, args[0].from);
> +			if (res)
> +				return res;
> +			break;
> +
>  		default:
>  			return -EINVAL;
>  		}

BR, Jarkko