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From:   Evan Green <evgreen@chromium.org>
To:     linux-kernel@vger.kernel.org
Cc:     corbet@lwn.net, linux-integrity@vger.kernel.org,
        Eric Biggers <ebiggers@kernel.org>, gwendal@chromium.org,
        dianders@chromium.org, apronin@chromium.org,
        Pavel Machek <pavel@ucw.cz>, Ben Boeckel <me@benboeckel.net>,
        rjw@rjwysocki.net, jejb@linux.ibm.com,
        Kees Cook <keescook@chromium.org>, dlunev@google.com,
        zohar@linux.ibm.com, Matthew Garrett <mgarrett@aurora.tech>,
        jarkko@kernel.org, linux-pm@vger.kernel.org,
        Evan Green <evgreen@chromium.org>,
        David Howells <dhowells@redhat.com>,
        James Morris <jmorris@namei.org>,
        Paul Moore <paul@paul-moore.com>,
        "Serge E. Hallyn" <serge@hallyn.com>, keyrings@vger.kernel.org,
        linux-security-module@vger.kernel.org
Subject: [PATCH v5 04/11] security: keys: trusted: Include TPM2 creation data
Date:   Fri, 11 Nov 2022 15:16:29 -0800
Message-Id: <20221111151451.v5.4.Ieb1215f598bc9df56b0e29e5977eae4fcca25e15@changeid>
In-Reply-To: <20221111231636.3748636-1-evgreen@chromium.org>
References: <20221111231636.3748636-1-evgreen@chromium.org>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

In addition to the private key and public key, the TPM2_Create
command may also return creation data, a creation hash, and a creation
ticket. These fields allow the TPM to attest to the contents of a
specified set of PCRs at the time the trusted key was created. Encrypted
hibernation will use this to ensure that PCRs settable only by the
kernel were set properly at the time of creation, indicating this is an
authentic hibernate key.

Encode these additional parameters into the ASN.1 created to represent
the key blob. The new fields are made optional so that they don't bloat
key blobs which don't need them, and to ensure interoperability with
old blobs.

Signed-off-by: Evan Green <evgreen@chromium.org>
---

Changes in v5:
 - Factored some math out to a helper function (Kees)
 - Constified src in tpm2_key_encode().

Changes in v3:
 - Fix SoB and -- note ordering (Kees)
 - Add comments describing the TPM2 spec type names for the new fields
   in tpm2key.asn1 (Kees)
 - Add len buffer checks in tpm2_key_encode() (Kees)

This is a replacement for Matthew's original patch here:
https://patchwork.kernel.org/patch/12096489/

That patch was written before the exported key format was switched to
ASN.1. This patch accomplishes the same thing (saving, loading, and
getting pointers to the creation data) while utilizing the new ASN.1
format.

---
 include/keys/trusted-type.h               |   8 +
 security/keys/trusted-keys/tpm2key.asn1   |  15 +-
 security/keys/trusted-keys/trusted_tpm2.c | 253 +++++++++++++++++++---
 3 files changed, 245 insertions(+), 31 deletions(-)

diff --git a/include/keys/trusted-type.h b/include/keys/trusted-type.h
index 4eb64548a74f1a..209086fed240a5 100644
--- a/include/keys/trusted-type.h
+++ b/include/keys/trusted-type.h
@@ -22,15 +22,23 @@
 #define MAX_BLOB_SIZE			512
 #define MAX_PCRINFO_SIZE		64
 #define MAX_DIGEST_SIZE			64
+#define MAX_CREATION_DATA		412
+#define MAX_TK				76
 
 struct trusted_key_payload {
 	struct rcu_head rcu;
 	unsigned int key_len;
 	unsigned int blob_len;
+	unsigned int creation_len;
+	unsigned int creation_hash_len;
+	unsigned int tk_len;
 	unsigned char migratable;
 	unsigned char old_format;
 	unsigned char key[MAX_KEY_SIZE + 1];
 	unsigned char blob[MAX_BLOB_SIZE];
+	unsigned char *creation;
+	unsigned char *creation_hash;
+	unsigned char *tk;
 };
 
 struct trusted_key_options {
diff --git a/security/keys/trusted-keys/tpm2key.asn1 b/security/keys/trusted-keys/tpm2key.asn1
index f57f869ad60068..608f8d9ca95fa8 100644
--- a/security/keys/trusted-keys/tpm2key.asn1
+++ b/security/keys/trusted-keys/tpm2key.asn1
@@ -7,5 +7,18 @@ TPMKey ::= SEQUENCE {
 	emptyAuth	[0] EXPLICIT BOOLEAN OPTIONAL,
 	parent		INTEGER ({tpm2_key_parent}),
 	pubkey		OCTET STRING ({tpm2_key_pub}),
-	privkey		OCTET STRING ({tpm2_key_priv})
+	privkey		OCTET STRING ({tpm2_key_priv}),
+	---
+	--- A TPM2B_CREATION_DATA struct as returned from the TPM2_Create command.
+	---
+	creationData	[1] EXPLICIT OCTET STRING OPTIONAL ({tpm2_key_creation_data}),
+	---
+	--- A TPM2B_DIGEST of the creationHash as returned from the TPM2_Create
+	--- command.
+	---
+	creationHash	[2] EXPLICIT OCTET STRING OPTIONAL ({tpm2_key_creation_hash}),
+	---
+	--- A TPMT_TK_CREATION ticket as returned from the TPM2_Create command.
+	---
+	creationTk	[3] EXPLICIT OCTET STRING OPTIONAL ({tpm2_key_creation_tk})
 	}
diff --git a/security/keys/trusted-keys/trusted_tpm2.c b/security/keys/trusted-keys/trusted_tpm2.c
index 2b2c8eb258d5bd..ff2aede8986236 100644
--- a/security/keys/trusted-keys/trusted_tpm2.c
+++ b/security/keys/trusted-keys/trusted_tpm2.c
@@ -28,24 +28,86 @@ static struct tpm2_hash tpm2_hash_map[] = {
 
 static u32 tpm2key_oid[] = { 2, 23, 133, 10, 1, 5 };
 
+/* Helper function to advance past a __be16 length + buffer safely */
+static const u8 *get_sized_section(const u8 *src, const u8 *end, u16 *len)
+{
+	u32 length;
+
+	if (src + sizeof(u16) > end)
+		return NULL;
+
+	/* Include the size field in the returned section length. */
+	length = get_unaligned_be16(src) + sizeof(u16);
+	*len = length;
+	if (*len != length)
+		return NULL;
+
+	src += *len;
+	if (src > end)
+		return NULL;
+
+	return src;
+}
+
 static int tpm2_key_encode(struct trusted_key_payload *payload,
 			   struct trusted_key_options *options,
-			   u8 *src, u32 len)
+			   const u8 *src, u32 len)
 {
 	const int SCRATCH_SIZE = PAGE_SIZE;
+	const u8 *end = src + len;
 	u8 *scratch = kmalloc(SCRATCH_SIZE, GFP_KERNEL);
 	u8 *work = scratch, *work1;
 	u8 *end_work = scratch + SCRATCH_SIZE;
-	u8 *priv, *pub;
+	const u8 *priv, *pub;
+	const u8 *creation_data = NULL, *creation_hash = NULL, *creation_tk = NULL;
+	u16 creation_data_len, creation_hash_len = 0, creation_tk_len = 0;
 	u16 priv_len, pub_len;
+	int rc;
 
-	priv_len = get_unaligned_be16(src) + 2;
 	priv = src;
+	src = get_sized_section(src, end, &priv_len);
+	if (!src)
+		return -EINVAL;
 
-	src += priv_len;
-
-	pub_len = get_unaligned_be16(src) + 2;
 	pub = src;
+	src = get_sized_section(src, end, &pub_len);
+	if (!src)
+		return -EINVAL;
+
+	creation_data = src;
+	src = get_sized_section(src, end, &creation_data_len);
+	if (!src)
+		return -EINVAL;
+
+	/*
+	 * If the creation data has content, pull out the creation hash and
+	 * ticket as well. Otherwise pretend it doesn't exist.
+	 */
+	if (creation_data_len > sizeof(u16)) {
+		creation_hash = src;
+		src = get_sized_section(src, end, &creation_hash_len);
+		if (!src)
+			return -EINVAL;
+
+		/*
+		 * The creation ticket (TPMT_TK_CREATION) consists of a 2 byte
+		 * tag, 4 byte handle, and then a TPM2B_DIGEST, which is a 2
+		 * byte length followed by data.
+		 */
+		if (src + 8 > end)
+			return -EINVAL;
+
+		creation_tk = src;
+		src = get_sized_section(src + 6, end, &creation_tk_len);
+		if (!src)
+			return -EINVAL;
+
+		creation_tk_len += 6;
+
+	} else {
+		creation_data_len = 0;
+		creation_data = NULL;
+	}
 
 	if (!scratch)
 		return -ENOMEM;
@@ -63,26 +125,81 @@ static int tpm2_key_encode(struct trusted_key_payload *payload,
 	}
 
 	/*
-	 * Assume both octet strings will encode to a 2 byte definite length
+	 * Assume each octet string will encode to a 2 byte definite length.
+	 * Each optional octet string consumes one extra byte.
 	 *
-	 * Note: For a well behaved TPM, this warning should never
-	 * trigger, so if it does there's something nefarious going on
+	 * 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;
+	if (WARN(work - scratch + pub_len + priv_len + creation_data_len +
+		 creation_hash_len + creation_tk_len + (7 * 5) + 3 >
+		 SCRATCH_SIZE,
+		 "BUG: scratch buffer is too small")) {
+		rc = -EINVAL;
+		goto err;
+	}
 
 	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);
+	if (creation_data_len) {
+		u8 *scratch2 = kmalloc(SCRATCH_SIZE, GFP_KERNEL);
+		u8 *work2;
+		u8 *end_work2 = scratch2 + SCRATCH_SIZE;
+
+		if (!scratch2) {
+			rc = -ENOMEM;
+			goto err;
+		}
+
+		work2 = asn1_encode_octet_string(scratch2,
+						 end_work2,
+						 creation_data,
+						 creation_data_len);
+
+		work = asn1_encode_tag(work,
+				       end_work,
+				       1,
+				       scratch2,
+				       work2 - scratch2);
+
+		work2 = asn1_encode_octet_string(scratch2,
+						 end_work2,
+						 creation_hash,
+						 creation_hash_len);
+
+		work = asn1_encode_tag(work,
+				       end_work,
+				       2,
+				       scratch2,
+				       work2 - scratch2);
+
+		work2 = asn1_encode_octet_string(scratch2,
+						 end_work2,
+						 creation_tk,
+						 creation_tk_len);
+
+		work = asn1_encode_tag(work,
+				       end_work,
+				       3,
+				       scratch2,
+				       work2 - scratch2);
+
+		kfree(scratch2);
+	}
 
 	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);
+	if (WARN(IS_ERR(work1), "BUG: ASN.1 encoder failed")) {
+		rc = PTR_ERR(work1);
+		goto err;
+	}
 
 	return work1 - payload->blob;
+err:
+	kfree(scratch);
+	return rc;
 }
 
 struct tpm2_key_context {
@@ -91,15 +208,21 @@ struct tpm2_key_context {
 	u32 pub_len;
 	const u8 *priv;
 	u32 priv_len;
+	const u8 *creation_data;
+	u32 creation_data_len;
+	const u8 *creation_hash;
+	u32 creation_hash_len;
+	const u8 *creation_tk;
+	u32 creation_tk_len;
 };
 
 static int tpm2_key_decode(struct trusted_key_payload *payload,
-			   struct trusted_key_options *options,
-			   u8 **buf)
+			   struct trusted_key_options *options)
 {
+	u64 data_len;
 	int ret;
 	struct tpm2_key_context ctx;
-	u8 *blob;
+	u8 *blob, *buf;
 
 	memset(&ctx, 0, sizeof(ctx));
 
@@ -108,21 +231,57 @@ static int tpm2_key_decode(struct trusted_key_payload *payload,
 	if (ret < 0)
 		return ret;
 
-	if (ctx.priv_len + ctx.pub_len > MAX_BLOB_SIZE)
+	data_len = ctx.priv_len + ctx.pub_len + ctx.creation_data_len +
+		   ctx.creation_hash_len + ctx.creation_tk_len;
+
+	if (data_len > MAX_BLOB_SIZE)
 		return -EINVAL;
 
-	blob = kmalloc(ctx.priv_len + ctx.pub_len + 4, GFP_KERNEL);
-	if (!blob)
+	buf = kmalloc(data_len + 4, GFP_KERNEL);
+	if (!buf)
 		return -ENOMEM;
 
-	*buf = blob;
+	blob = buf;
 	options->keyhandle = ctx.parent;
 
 	memcpy(blob, ctx.priv, ctx.priv_len);
 	blob += ctx.priv_len;
 
 	memcpy(blob, ctx.pub, ctx.pub_len);
+	blob += ctx.pub_len;
+	if (ctx.creation_data_len) {
+		memcpy(blob, ctx.creation_data, ctx.creation_data_len);
+		blob += ctx.creation_data_len;
+	}
 
+	if (ctx.creation_hash_len) {
+		memcpy(blob, ctx.creation_hash, ctx.creation_hash_len);
+		blob += ctx.creation_hash_len;
+	}
+
+	if (ctx.creation_tk_len) {
+		memcpy(blob, ctx.creation_tk, ctx.creation_tk_len);
+		blob += ctx.creation_tk_len;
+	}
+
+	/*
+	 * Copy the buffer back into the payload blob since the creation
+	 * info will be used after loading.
+	 */
+	payload->blob_len = blob - buf;
+	memcpy(payload->blob, buf, payload->blob_len);
+	if (ctx.creation_data_len) {
+		payload->creation = payload->blob + ctx.priv_len + ctx.pub_len;
+		payload->creation_len = ctx.creation_data_len;
+		payload->creation_hash = payload->creation + ctx.creation_data_len;
+		payload->creation_hash_len = ctx.creation_hash_len;
+		payload->tk = payload->creation_hash +
+			      payload->creation_hash_len;
+
+		payload->tk_len = ctx.creation_tk_len;
+	}
+
+	kfree(buf);
 	return 0;
 }
 
@@ -185,6 +344,42 @@ int tpm2_key_priv(void *context, size_t hdrlen,
 	return 0;
 }
 
+int tpm2_key_creation_data(void *context, size_t hdrlen,
+			   unsigned char tag,
+			   const void *value, size_t vlen)
+{
+	struct tpm2_key_context *ctx = context;
+
+	ctx->creation_data = value;
+	ctx->creation_data_len = vlen;
+
+	return 0;
+}
+
+int tpm2_key_creation_hash(void *context, size_t hdrlen,
+			   unsigned char tag,
+			   const void *value, size_t vlen)
+{
+	struct tpm2_key_context *ctx = context;
+
+	ctx->creation_hash = value;
+	ctx->creation_hash_len = vlen;
+
+	return 0;
+}
+
+int tpm2_key_creation_tk(void *context, size_t hdrlen,
+			 unsigned char tag,
+			 const void *value, size_t vlen)
+{
+	struct tpm2_key_context *ctx = context;
+
+	ctx->creation_tk = value;
+	ctx->creation_tk_len = vlen;
+
+	return 0;
+}
+
 /**
  * tpm_buf_append_auth() - append TPMS_AUTH_COMMAND to the buffer.
  *
@@ -229,6 +424,7 @@ int tpm2_seal_trusted(struct tpm_chip *chip,
 		      struct trusted_key_options *options)
 {
 	int blob_len = 0;
+	unsigned int offset;
 	struct tpm_buf buf;
 	u32 hash;
 	u32 flags;
@@ -317,13 +513,14 @@ int tpm2_seal_trusted(struct tpm_chip *chip,
 		rc = -E2BIG;
 		goto out;
 	}
-	if (tpm_buf_length(&buf) < TPM_HEADER_SIZE + 4 + blob_len) {
+	offset = TPM_HEADER_SIZE + 4;
+	if (tpm_buf_length(&buf) < offset + blob_len) {
 		rc = -EFAULT;
 		goto out;
 	}
 
 	blob_len = tpm2_key_encode(payload, options,
-				   &buf.data[TPM_HEADER_SIZE + 4],
+				   &buf.data[offset],
 				   blob_len);
 
 out:
@@ -370,13 +567,11 @@ static int tpm2_load_cmd(struct tpm_chip *chip,
 	int rc;
 	u32 attrs;
 
-	rc = tpm2_key_decode(payload, options, &blob);
-	if (rc) {
-		/* old form */
-		blob = payload->blob;
+	rc = tpm2_key_decode(payload, options);
+	if (rc)
 		payload->old_format = 1;
-	}
 
+	blob = payload->blob;
 	/* new format carries keyhandle but old format doesn't */
 	if (!options->keyhandle)
 		return -EINVAL;
@@ -433,8 +628,6 @@ 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)
-- 
2.38.1.431.g37b22c650d-goog