[v4,4/9] security: keys: trusted: use ASN.1 tpm2 key format for the blobs
diff mbox series

Message ID 20191230173802.8731-5-James.Bottomley@HansenPartnership.com
State New
Headers show
Series
  • TPM 2.0 trusted keys with attached policy
Related show

Commit Message

James Bottomley Dec. 30, 2019, 5:37 p.m. UTC
Modify the tpm2 key format blob output to export and import in the
ASN.1 form for tpm2 sealed object keys.  For compatibility with prior
trusted keys, the importer will also accept two tpm2b quantities
representing the public and private parts of the key.  However, the
export via keyctl pipe will only output the ASN.1 format.

The benefit of the ASN.1 format is that it's a standard and thus the
exported key can be used by userspace tools.  The format includes
policy specifications, thus it gets us out of having to construct
policy handles in userspace and the format includes the parent meaning
you don't have to keep passing it in each time.

This patch only implements basic handling for the ASN.1 format, so
keys with passwords but no policy.

Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>

v2: Updated encode API, added length checks
---
 security/keys/trusted-keys/Makefile       |   2 +-
 security/keys/trusted-keys/tpm2key.asn1   |  23 ++++
 security/keys/trusted-keys/trusted_tpm1.c |   2 +-
 security/keys/trusted-keys/trusted_tpm2.c | 187 +++++++++++++++++++++++++++++-
 4 files changed, 207 insertions(+), 7 deletions(-)
 create mode 100644 security/keys/trusted-keys/tpm2key.asn1

Comments

Jarkko Sakkinen Jan. 6, 2020, 9:53 p.m. UTC | #1
On Mon, 2019-12-30 at 09:37 -0800, James Bottomley wrote:

Again bad formatting in the short summary.

> Modify the tpm2 key format blob output to export and import in the
> ASN.1 form for tpm2 sealed object keys.  For compatibility with prior
> trusted keys, the importer will also accept two tpm2b quantities
> representing the public and private parts of the key.  However, the
> export via keyctl pipe will only output the ASN.1 format.

I think this is fair enough when it comes to backwards compatibility.

What you should do with the earlier patch is to document in the commit
message this framework for backwards compatibility. It is redundancy
but makes the commit log easier to follow. E.g. tell in that commit
message that ASN.1 loader will handle loading old blobs.

> The benefit of the ASN.1 format is that it's a standard and thus the
> exported key can be used by userspace tools.  The format includes
> policy specifications, thus it gets us out of having to construct
> policy handles in userspace and the format includes the parent meaning
> you don't have to keep passing it in each time.

Please be explicit with the tools you are referring. Point out what
you are using if there is variable number of choices.

In high-level the code change itself looks good.

/Jarkko

Patch
diff mbox series

diff --git a/security/keys/trusted-keys/Makefile b/security/keys/trusted-keys/Makefile
index 7b73cebbb378..e0198641eff2 100644
--- a/security/keys/trusted-keys/Makefile
+++ b/security/keys/trusted-keys/Makefile
@@ -5,4 +5,4 @@ 
 
 obj-$(CONFIG_TRUSTED_KEYS) += trusted.o
 trusted-y += trusted_tpm1.o
-trusted-y += trusted_tpm2.o
+trusted-y += trusted_tpm2.o tpm2key.asn1.o
diff --git a/security/keys/trusted-keys/tpm2key.asn1 b/security/keys/trusted-keys/tpm2key.asn1
new file mode 100644
index 000000000000..1851b7c80f08
--- /dev/null
+++ b/security/keys/trusted-keys/tpm2key.asn1
@@ -0,0 +1,23 @@ 
+---
+--- Note: This isn't quite the definition in the standard
+---       However, the Linux asn.1 parser doesn't understand
+---       [2] EXPLICIT SEQUENCE OF OPTIONAL
+---       So there's an extra intermediate TPMPolicySequence
+---       definition to work around this
+
+TPMKey ::= SEQUENCE {
+	type		OBJECT IDENTIFIER ({tpmkey_type}),
+	emptyAuth	[0] EXPLICIT BOOLEAN OPTIONAL,
+	policy		[1] EXPLICIT TPMPolicySequence OPTIONAL,
+	secret		[2] EXPLICIT OCTET STRING OPTIONAL,
+	parent		INTEGER ({tpmkey_parent}),
+	pubkey		OCTET STRING ({tpmkey_pub}),
+	privkey		OCTET STRING ({tpmkey_priv})
+	}
+
+TPMPolicySequence ::= SEQUENCE OF TPMPolicy
+
+TPMPolicy ::= SEQUENCE {
+	commandCode		[0] EXPLICIT INTEGER,
+	commandPolicy		[1] EXPLICIT OCTET STRING
+	}
diff --git a/security/keys/trusted-keys/trusted_tpm1.c b/security/keys/trusted-keys/trusted_tpm1.c
index ef15b6cda6ec..d92d45d759c6 100644
--- a/security/keys/trusted-keys/trusted_tpm1.c
+++ b/security/keys/trusted-keys/trusted_tpm1.c
@@ -1005,7 +1005,7 @@  static int trusted_instantiate(struct key *key,
 		goto out;
 	}
 
-	if (!options->keyhandle) {
+	if (!options->keyhandle && !tpm2) {
 		ret = -EINVAL;
 		goto out;
 	}
diff --git a/security/keys/trusted-keys/trusted_tpm2.c b/security/keys/trusted-keys/trusted_tpm2.c
index 11a331a94327..cd7008d499ba 100644
--- a/security/keys/trusted-keys/trusted_tpm2.c
+++ b/security/keys/trusted-keys/trusted_tpm2.c
@@ -4,6 +4,8 @@ 
  * Copyright (C) 2014 Intel Corporation
  */
 
+#include <linux/asn1_encoder.h>
+#include <linux/oid_registry.h>
 #include <linux/string.h>
 #include <linux/err.h>
 #include <linux/tpm.h>
@@ -12,6 +14,10 @@ 
 #include <keys/trusted-type.h>
 #include <keys/trusted_tpm.h>
 
+#include <asm/unaligned.h>
+
+#include "tpm2key.asn1.h"
+
 static struct tpm2_hash tpm2_hash_map[] = {
 	{HASH_ALGO_SHA1, TPM_ALG_SHA1},
 	{HASH_ALGO_SHA256, TPM_ALG_SHA256},
@@ -20,6 +26,158 @@  static struct tpm2_hash tpm2_hash_map[] = {
 	{HASH_ALGO_SM3_256, TPM_ALG_SM3_256},
 };
 
+static u32 tpm2key_oid[] = { 2,23,133,10,1,5 };
+
+static int tpm2_key_encode(struct trusted_key_payload *payload,
+			   struct trusted_key_options *options,
+			   u8 *src, u32 len)
+{
+	const int SCRATCH_SIZE = PAGE_SIZE;
+	u8 *scratch = kmalloc(SCRATCH_SIZE, GFP_KERNEL);
+	u8 *work = scratch, *work1;
+	u8 *end_work = scratch + SCRATCH_SIZE;
+	u8 *priv, *pub;
+	u16 priv_len, pub_len;
+
+	priv_len = get_unaligned_be16(src);
+	src += 2;
+	priv = src;
+	src += priv_len;
+	pub_len = get_unaligned_be16(src);
+	src += 2;
+	pub = src;
+
+	if (!scratch)
+		return -ENOMEM;
+
+	work = asn1_encode_oid(work, end_work, tpm2key_oid,
+			       asn1_oid_len(tpm2key_oid));
+	if (options->blobauth_len == 0) {
+		unsigned char bool[3], *w = bool;
+		/* tag 0 is emptyAuth */
+		w = asn1_encode_boolean(w, w + sizeof(bool), true);
+		if (WARN(IS_ERR(w), "BUG: Boolean failed to encode"))
+			return PTR_ERR(w);
+		work = asn1_encode_tag(work, end_work, 0, bool, w - bool);
+	}
+	/*
+	 * Assume both octet strings will encode to a 2 byte definite length
+	 *
+	 * Note: For a well behaved TPM, this warning should never
+	 * trigger, so if it does there's something nefarious going on
+	 */
+	if (WARN(work - scratch + pub_len + priv_len + 14 > SCRATCH_SIZE,
+		 "BUG: scratch buffer is too small"))
+		return -EINVAL;
+	work = asn1_encode_integer(work, end_work, options->keyhandle);
+	work = asn1_encode_octet_string(work, end_work, pub, pub_len);
+	work = asn1_encode_octet_string(work, end_work, priv, priv_len);
+
+	work1 = payload->blob;
+	work1 = asn1_encode_sequence(work1, work1 + sizeof(payload->blob),
+				     scratch, work - scratch);
+	if (WARN(IS_ERR(work1), "BUG: ASN.1 encoder failed"))
+		return PTR_ERR(work1);
+
+	return work1 - payload->blob;
+}
+
+struct tpm2key_context {
+	u32 parent;
+	const u8 *pub;
+	u32 pub_len;
+	const u8 *priv;
+	u32 priv_len;
+};
+
+static int tpm2_key_decode(struct trusted_key_payload *payload,
+			   struct trusted_key_options *options,
+			   u8 **buf)
+{
+	int ret;
+	struct tpm2key_context ctx;
+	u8 *blob;
+
+	ret = asn1_ber_decoder(&tpm2key_decoder, &ctx, payload->blob,
+			       payload->blob_len);
+	if (ret < 0)
+		return ret;
+
+	if (ctx.priv_len + ctx.pub_len > MAX_BLOB_SIZE)
+		return -EINVAL;
+
+	blob = kmalloc(ctx.priv_len + ctx.pub_len + 4, GFP_KERNEL);
+	if (!blob)
+		return -ENOMEM;
+
+	*buf = blob;
+	options->keyhandle = ctx.parent;
+	put_unaligned_be16(ctx.priv_len, blob);
+	blob += 2;
+	memcpy(blob, ctx.priv, ctx.priv_len);
+	blob += ctx.priv_len;
+	put_unaligned_be16(ctx.pub_len, blob);
+	blob += 2;
+	memcpy(blob, ctx.pub, ctx.pub_len);
+
+	return 0;
+}
+
+int tpmkey_parent(void *context, size_t hdrlen,
+		  unsigned char tag,
+		  const void *value, size_t vlen)
+{
+	struct tpm2key_context *ctx = context;
+	const u8 *v = value;
+	int i;
+
+	ctx->parent = 0;
+	for (i = 0; i < vlen; i++) {
+		ctx->parent <<= 8;
+		ctx->parent |= v[i];
+	}
+	return 0;
+}
+
+int tpmkey_type(void *context, size_t hdrlen,
+		unsigned char tag,
+		const void *value, size_t vlen)
+{
+	enum OID oid = look_up_OID(value, vlen);
+
+	if (oid != OID_TPMSealedData) {
+		char buffer[50];
+
+		sprint_oid(value, vlen, buffer, sizeof(buffer));
+		pr_debug("OID is \"%s\" which is not TPMSealedData\n",
+			 buffer);
+		return -EINVAL;
+	}
+	return 0;
+}
+
+int tpmkey_pub(void *context, size_t hdrlen,
+	       unsigned char tag,
+	       const void *value, size_t vlen)
+{
+	struct tpm2key_context *ctx = context;
+
+	ctx->pub = value;
+	ctx->pub_len = vlen;
+	return 0;
+}
+
+int tpmkey_priv(void *context, size_t hdrlen,
+		unsigned char tag,
+		const void *value, size_t vlen)
+{
+	struct tpm2key_context *ctx = context;
+
+	ctx->priv = value;
+	ctx->priv_len = vlen;
+	return 0;
+}
+
 /**
  * tpm_buf_append_auth() - append TPMS_AUTH_COMMAND to the buffer.
  *
@@ -79,6 +237,9 @@  int tpm2_seal_trusted(struct tpm_chip *chip,
 	if (i == ARRAY_SIZE(tpm2_hash_map))
 		return -EINVAL;
 
+	if (!options->keyhandle)
+		return -EINVAL;
+
 	rc = tpm_buf_init(&buf, TPM2_ST_SESSIONS, TPM2_CC_CREATE);
 	if (rc)
 		return rc;
@@ -145,8 +306,10 @@  int tpm2_seal_trusted(struct tpm_chip *chip,
 		goto out;
 	}
 
-	memcpy(payload->blob, &buf.data[TPM_HEADER_SIZE + 4], blob_len);
-	payload->blob_len = blob_len;
+	payload->blob_len =
+		tpm2_key_encode(payload, options,
+				&buf.data[TPM_HEADER_SIZE + 4],
+				blob_len);
 
 out:
 	tpm_buf_destroy(&buf);
@@ -157,6 +320,8 @@  int tpm2_seal_trusted(struct tpm_chip *chip,
 		else
 			rc = -EPERM;
 	}
+	if (payload->blob_len < 0)
+		return payload->blob_len;
 
 	return rc;
 }
@@ -183,13 +348,23 @@  static int tpm2_load_cmd(struct tpm_chip *chip,
 	unsigned int private_len;
 	unsigned int public_len;
 	unsigned int blob_len;
+	u8 *blob;
 	int rc;
 
-	private_len = be16_to_cpup((__be16 *) &payload->blob[0]);
+	rc = tpm2_key_decode(payload, options, &blob);
+	if (rc)
+		/* old form */
+		blob = payload->blob;
+
+	/* new format carries keyhandle but old format doesn't */
+	if (!options->keyhandle)
+		return -EINVAL;
+
+	private_len = be16_to_cpup((__be16 *) &blob[0]);
 	if (private_len > (payload->blob_len - 2))
 		return -E2BIG;
 
-	public_len = be16_to_cpup((__be16 *) &payload->blob[2 + private_len]);
+	public_len = be16_to_cpup((__be16 *) &blob[2 + private_len]);
 	blob_len = private_len + public_len + 4;
 	if (blob_len > payload->blob_len)
 		return -E2BIG;
@@ -205,7 +380,7 @@  static int tpm2_load_cmd(struct tpm_chip *chip,
 			     options->keyauth /* hmac */,
 			     TPM_DIGEST_SIZE);
 
-	tpm_buf_append(&buf, payload->blob, blob_len);
+	tpm_buf_append(&buf, blob, blob_len);
 
 	if (buf.flags & TPM_BUF_OVERFLOW) {
 		rc = -E2BIG;
@@ -218,6 +393,8 @@  static int tpm2_load_cmd(struct tpm_chip *chip,
 			(__be32 *) &buf.data[TPM_HEADER_SIZE]);
 
 out:
+	if (blob != payload->blob)
+		kfree(blob);
 	tpm_buf_destroy(&buf);
 
 	if (rc > 0)