[v10,7/8] security: keys: trusted: add ability to specify arbitrary policy
diff mbox series

Message ID 20200616160229.8018-8-James.Bottomley@HansenPartnership.com
State New
Headers show
Series
  • TPM 2.0 trusted keys with attached policy
Related show

Commit Message

James Bottomley June 16, 2020, 4:02 p.m. UTC
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       | 16 ++++++
 security/keys/trusted-keys/tpm2-policy.c      | 53 +++++++++++++++++++
 security/keys/trusted-keys/tpm2-policy.h      |  1 +
 security/keys/trusted-keys/trusted_tpm1.c     | 15 ++++++
 4 files changed, 85 insertions(+)

Comments

Jarkko Sakkinen June 17, 2020, 11:42 p.m. UTC | #1
On Tue, Jun 16, 2020 at 09:02:28AM -0700, 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.

Never heard of policymaker before and did not find TCG spec for it.

/Jarkko
James Bottomley June 18, 2020, 12:27 a.m. UTC | #2
On Thu, 2020-06-18 at 02:42 +0300, Jarkko Sakkinen wrote:
> On Tue, Jun 16, 2020 at 09:02:28AM -0700, 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.
> 
> Never heard of policymaker before and did not find TCG spec for it.

It's not part of the spec.  Both the IBM and Intel TSSs define a
policymaker tool to help you build policy hashes.  The format is simply
a set of numbers that if hashed a line at a time produce the policy
hash.

James
Jarkko Sakkinen June 18, 2020, 7:12 a.m. UTC | #3
On Wed, Jun 17, 2020 at 05:27:43PM -0700, James Bottomley wrote:
> On Thu, 2020-06-18 at 02:42 +0300, Jarkko Sakkinen wrote:
> > On Tue, Jun 16, 2020 at 09:02:28AM -0700, 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.
> > 
> > Never heard of policymaker before and did not find TCG spec for it.
> 
> It's not part of the spec.  Both the IBM and Intel TSSs define a
> policymaker tool to help you build policy hashes.  The format is simply
> a set of numbers that if hashed a line at a time produce the policy
> hash.

OK, so they both use this 'policymaker' format? Where is it documented?

/Jarkko
James Bottomley June 18, 2020, 7:45 p.m. UTC | #4
On Thu, 2020-06-18 at 10:12 +0300, Jarkko Sakkinen wrote:
> On Wed, Jun 17, 2020 at 05:27:43PM -0700, James Bottomley wrote:
> > On Thu, 2020-06-18 at 02:42 +0300, Jarkko Sakkinen wrote:
> > > On Tue, Jun 16, 2020 at 09:02:28AM -0700, 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.
> > > 
> > > Never heard of policymaker before and did not find TCG spec for
> > > it.
> > 
> > It's not part of the spec.  Both the IBM and Intel TSSs define a
> > policymaker tool to help you build policy hashes.  The format is
> > simply
> > a set of numbers that if hashed a line at a time produce the policy
> > hash.
> 
> OK, so they both use this 'policymaker' format? Where is it
> documented?

I don't think it is except in the source code of the tools.  It's
basically a sequence of TPM2_PolicyXX statements laid out in binary end
to end one per line as the TPM2 command value says they are hashed.  I
can just say that if you prefer.  The example given is

TPM2_PolicyPCR(policydigest, selection)
TPM2_PolicyAuthValue()

So if you look in the manual, TPM2_PolicyPCR says the hash is
calculated as

H_policyAlg (policyDigest_old || TPM_CC_PolicyPCR || pcrs || digestTPM)

So the policymaker statement is

TPM_CC_PolicyPCR || pcrs || digestTPM

Which in hex is

0000017F 00000001000B 03000001303095B49BE85E381E5B20E557E46363EF55B0F43B132C2D8E3DE9AC436656F2

And TPM2_PolicyAuthValue simply says

H_policyAlg (policyDigest_old || TPM_CC_PolicyAuthValue )

So the policymaker statement is

TPM_CC_PolicyAuthValue

or in hex

0000016b

James
Jarkko Sakkinen June 23, 2020, 12:46 a.m. UTC | #5
On Thu, Jun 18, 2020 at 12:45:14PM -0700, James Bottomley wrote:
> On Thu, 2020-06-18 at 10:12 +0300, Jarkko Sakkinen wrote:
> > On Wed, Jun 17, 2020 at 05:27:43PM -0700, James Bottomley wrote:
> > > On Thu, 2020-06-18 at 02:42 +0300, Jarkko Sakkinen wrote:
> > > > On Tue, Jun 16, 2020 at 09:02:28AM -0700, 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.
> > > > 
> > > > Never heard of policymaker before and did not find TCG spec for
> > > > it.
> > > 
> > > It's not part of the spec.  Both the IBM and Intel TSSs define a
> > > policymaker tool to help you build policy hashes.  The format is
> > > simply
> > > a set of numbers that if hashed a line at a time produce the policy
> > > hash.
> > 
> > OK, so they both use this 'policymaker' format? Where is it
> > documented?
> 
> I don't think it is except in the source code of the tools.  It's
> basically a sequence of TPM2_PolicyXX statements laid out in binary end
> to end one per line as the TPM2 command value says they are hashed.  I
> can just say that if you prefer.  The example given is

There is no "the tools". There are multiple user space stacks.

I think that the format should be documented to Documents/security/tpm.

/Jarkko

Patch
diff mbox series

diff --git a/Documentation/security/keys/trusted-encrypted.rst b/Documentation/security/keys/trusted-encrypted.rst
index 053344c4df5b..b68d3eb73f00 100644
--- a/Documentation/security/keys/trusted-encrypted.rst
+++ b/Documentation/security/keys/trusted-encrypted.rst
@@ -76,6 +76,9 @@  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.
@@ -168,6 +171,19 @@  zeros (the value of PCR 16)::
     $ dd if=/dev/zero bs=1 count=20 2>/dev/null|sha1sum
     6768033e216468247bd031a0a2d9876d79818f8f
 
+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 a trusted key under new pcr values::
 
     $ keyctl update 268728824 "update pcrinfo=`cat pcr.blob`"
diff --git a/security/keys/trusted-keys/tpm2-policy.c b/security/keys/trusted-keys/tpm2-policy.c
index 080a76e879fd..87a13e607eca 100644
--- a/security/keys/trusted-keys/tpm2-policy.c
+++ b/security/keys/trusted-keys/tpm2-policy.c
@@ -370,3 +370,56 @@  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 46bf1f0a9325..0da013116c1c 100644
--- a/security/keys/trusted-keys/tpm2-policy.h
+++ b/security/keys/trusted-keys/tpm2-policy.h
@@ -28,3 +28,4 @@  int tpm2_generate_policy_digest(struct tpm2_policies *pols, u32 hash,
 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,
 			    u32 *handle);
+int tpm2_parse_policies(struct tpm2_policies **ppols, char *str);
diff --git a/security/keys/trusted-keys/trusted_tpm1.c b/security/keys/trusted-keys/trusted_tpm1.c
index 9f735bbe9eef..d8b073ebe167 100644
--- a/security/keys/trusted-keys/trusted_tpm1.c
+++ b/security/keys/trusted-keys/trusted_tpm1.c
@@ -29,6 +29,8 @@ 
 
 #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;
@@ -709,6 +711,7 @@  enum {
 	Opt_hash,
 	Opt_policydigest,
 	Opt_policyhandle,
+	Opt_policy,
 };
 
 static const match_table_t key_tokens = {
@@ -724,6 +727,7 @@  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}
 };
 
@@ -855,6 +859,17 @@  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;
 		}