tpm: Add NULL primary creation

The session handling code uses a "salted" session, meaning a session
whose salt is encrypted to the public part of another TPM key so an
observer cannot obtain it (and thus deduce the session keys).  This
patch creates and context saves in the tpm_chip area the primary key
of the NULL hierarchy for this purpose.

[jarkko@kernel.org: fixed documentation errors]
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>
Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org>
Tested-by: Jarkko Sakkinen <jarkko@kernel.org>
Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org>

drivers/char/tpm/Kconfig

@@ -27,6 +27,17 @@ menuconfig TCG_TPM
 
 if TCG_TPM
 
+config TCG_TPM2_HMAC
+	bool "Use HMAC and encrypted transactions on the TPM bus"
+	default y
+	help
+	  Setting this causes us to deploy a scheme which uses request
+	  and response HMACs in addition to encryption for
+	  communicating with the TPM to prevent or detect bus snooping
+	  and interposer attacks (see tpm-security.rst).  Saying Y
+	  here adds some encryption overhead to all kernel to TPM
+	  transactions.
+
 config HW_RANDOM_TPM
 	bool "TPM HW Random Number Generator support"
 	depends on TCG_TPM && HW_RANDOM && !(TCG_TPM=y && HW_RANDOM=m)

drivers/char/tpm/Makefile

@@ -17,6 +17,7 @@ tpm-y += eventlog/tpm1.o
 tpm-y += eventlog/tpm2.o
 tpm-y += tpm-buf.o
 
+tpm-$(CONFIG_TCG_TPM2_HMAC) += tpm2-sessions.o
 tpm-$(CONFIG_ACPI) += tpm_ppi.o eventlog/acpi.o
 tpm-$(CONFIG_EFI) += eventlog/efi.o
 tpm-$(CONFIG_OF) += eventlog/of.o

drivers/char/tpm/tpm.h

@@ -321,4 +321,14 @@ void tpm_bios_log_setup(struct tpm_chip *chip);
 void tpm_bios_log_teardown(struct tpm_chip *chip);
 int tpm_dev_common_init(void);
 void tpm_dev_common_exit(void);
+
+#ifdef CONFIG_TCG_TPM2_HMAC
+int tpm2_sessions_init(struct tpm_chip *chip);
+#else
+static inline int tpm2_sessions_init(struct tpm_chip *chip)
+{
+	return 0;
+}
+#endif
+
 #endif

drivers/char/tpm/tpm2-cmd.c

@@ -759,6 +759,11 @@ int tpm2_auto_startup(struct tpm_chip *chip)
 		rc = 0;
 	}
 
+	if (rc)
+		goto out;
+
+	rc = tpm2_sessions_init(chip);
+
 out:
 	/*
 	 * Infineon TPM in field upgrade mode will return no data for the number

drivers/char/tpm/tpm2-sessions.c

+// SPDX-License-Identifier: GPL-2.0
+
+/*
+ * Copyright (C) 2018 James.Bottomley@HansenPartnership.com
+ *
+ */
+
+#include "tpm.h"
+#include <asm/unaligned.h>
+
+/**
+ * tpm2_parse_create_primary() - parse the data returned from TPM_CC_CREATE_PRIMARY
+ *
+ * @chip:	The TPM the primary was created under
+ * @buf:	The response buffer from the chip
+ * @handle:	pointer to be filled in with the return handle of the primary
+ * @hierarchy:	The hierarchy the primary was created for
+ *
+ * Return:
+ * * 0		- OK
+ * * -errno	- A system error
+ * * TPM_RC	- A TPM error
+ */
+static int tpm2_parse_create_primary(struct tpm_chip *chip, struct tpm_buf *buf,
+				     u32 *handle, u32 hierarchy)
+{
+	struct tpm_header *head = (struct tpm_header *)buf->data;
+	off_t offset_r = TPM_HEADER_SIZE, offset_t;
+	u16 len = TPM_HEADER_SIZE;
+	u32 total_len = be32_to_cpu(head->length);
+	u32 val, param_len;
+
+	*handle = tpm_buf_read_u32(buf, &offset_r);
+	param_len = tpm_buf_read_u32(buf, &offset_r);
+	/*
+	 * param_len doesn't include the header, but all the other
+	 * lengths and offsets do, so add it to parm len to make
+	 * the comparisons easier
+	 */
+	param_len += TPM_HEADER_SIZE;
+
+	if (param_len + 8 > total_len)
+		return -EINVAL;
+	len = tpm_buf_read_u16(buf, &offset_r);
+	offset_t = offset_r;
+	/* now we have the public area, compute the name of the object */
+	put_unaligned_be16(TPM_ALG_SHA256, chip->null_key_name);
+	sha256(&buf->data[offset_r], len, chip->null_key_name + 2);
+
+	/* validate the public key */
+	val = tpm_buf_read_u16(buf, &offset_t);
+
+	/* key type (must be what we asked for) */
+	if (val != TPM_ALG_ECC)
+		return -EINVAL;
+	val = tpm_buf_read_u16(buf, &offset_t);
+
+	/* name algorithm */
+	if (val != TPM_ALG_SHA256)
+		return -EINVAL;
+	val = tpm_buf_read_u32(buf, &offset_t);
+
+	/* object properties */
+	if (val != TPM2_OA_TMPL)
+		return -EINVAL;
+
+	/* auth policy (empty) */
+	val = tpm_buf_read_u16(buf, &offset_t);
+	if (val != 0)
+		return -EINVAL;
+
+	/* symmetric key parameters */
+	val = tpm_buf_read_u16(buf, &offset_t);
+	if (val != TPM_ALG_AES)
+		return -EINVAL;
+
+	/* symmetric key length */
+	val = tpm_buf_read_u16(buf, &offset_t);
+	if (val != AES_KEY_BITS)
+		return -EINVAL;
+
+	/* symmetric encryption scheme */
+	val = tpm_buf_read_u16(buf, &offset_t);
+	if (val != TPM_ALG_CFB)
+		return -EINVAL;
+
+	/* signing scheme */
+	val = tpm_buf_read_u16(buf, &offset_t);
+	if (val != TPM_ALG_NULL)
+		return -EINVAL;
+
+	/* ECC Curve */
+	val = tpm_buf_read_u16(buf, &offset_t);
+	if (val != TPM2_ECC_NIST_P256)
+		return -EINVAL;
+
+	/* KDF Scheme */
+	val = tpm_buf_read_u16(buf, &offset_t);
+	if (val != TPM_ALG_NULL)
+		return -EINVAL;
+
+	/* extract public key (x and y points) */
+	val = tpm_buf_read_u16(buf, &offset_t);
+	if (val != EC_PT_SZ)
+		return -EINVAL;
+	memcpy(chip->null_ec_key_x, &buf->data[offset_t], val);
+	offset_t += val;
+	val = tpm_buf_read_u16(buf, &offset_t);
+	if (val != EC_PT_SZ)
+		return -EINVAL;
+	memcpy(chip->null_ec_key_y, &buf->data[offset_t], val);
+	offset_t += val;
+
+	/* original length of the whole TPM2B */
+	offset_r += len;
+
+	/* should have exactly consumed the TPM2B public structure */
+	if (offset_t != offset_r)
+		return -EINVAL;
+	if (offset_r > param_len)
+		return -EINVAL;
+
+	/* creation data (skip) */
+	len = tpm_buf_read_u16(buf, &offset_r);
+	offset_r += len;
+	if (offset_r > param_len)
+		return -EINVAL;
+
+	/* creation digest (must be sha256) */
+	len = tpm_buf_read_u16(buf, &offset_r);
+	offset_r += len;
+	if (len != SHA256_DIGEST_SIZE || offset_r > param_len)
+		return -EINVAL;
+
+	/* TPMT_TK_CREATION follows */
+	/* tag, must be TPM_ST_CREATION (0x8021) */
+	val = tpm_buf_read_u16(buf, &offset_r);
+	if (val != TPM2_ST_CREATION || offset_r > param_len)
+		return -EINVAL;
+
+	/* hierarchy */
+	val = tpm_buf_read_u32(buf, &offset_r);
+	if (val != hierarchy || offset_r > param_len)
+		return -EINVAL;
+
+	/* the ticket digest HMAC (might not be sha256) */
+	len = tpm_buf_read_u16(buf, &offset_r);
+	offset_r += len;
+	if (offset_r > param_len)
+		return -EINVAL;
+
+	/*
+	 * finally we have the name, which is a sha256 digest plus a 2
+	 * byte algorithm type
+	 */
+	len = tpm_buf_read_u16(buf, &offset_r);
+	if (offset_r + len != param_len + 8)
+		return -EINVAL;
+	if (len != SHA256_DIGEST_SIZE + 2)
+		return -EINVAL;
+
+	if (memcmp(chip->null_key_name, &buf->data[offset_r],
+		   SHA256_DIGEST_SIZE + 2) != 0) {
+		dev_err(&chip->dev, "NULL Seed name comparison failed\n");
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
+/**
+ * tpm2_create_primary() - create a primary key using a fixed P-256 template
+ *
+ * @chip:      the TPM chip to create under
+ * @hierarchy: The hierarchy handle to create under
+ * @handle:    The returned volatile handle on success
+ *
+ * For platforms that might not have a persistent primary, this can be
+ * used to create one quickly on the fly (it uses Elliptic Curve not
+ * RSA, so even slow TPMs can create one fast).  The template uses the
+ * TCG mandated H one for non-endorsement ECC primaries, i.e. P-256
+ * elliptic curve (the only current one all TPM2s are required to
+ * have) a sha256 name hash and no policy.
+ *
+ * Return:
+ * * 0		- OK
+ * * -errno	- A system error
+ * * TPM_RC	- A TPM error
+ */
+static int tpm2_create_primary(struct tpm_chip *chip, u32 hierarchy,
+			       u32 *handle)
+{
+	int rc;
+	struct tpm_buf buf;
+	struct tpm_buf template;
+
+	rc = tpm_buf_init(&buf, TPM2_ST_SESSIONS, TPM2_CC_CREATE_PRIMARY);
+	if (rc)
+		return rc;
+
+	rc = tpm_buf_init_sized(&template);
+	if (rc) {
+		tpm_buf_destroy(&buf);
+		return rc;
+	}
+
+	/*
+	 * create the template.  Note: in order for userspace to
+	 * verify the security of the system, it will have to create
+	 * and certify this NULL primary, meaning all the template
+	 * parameters will have to be identical, so conform exactly to
+	 * the TCG TPM v2.0 Provisioning Guidance for the SRK ECC
+	 * key H template (H has zero size unique points)
+	 */
+
+	/* key type */
+	tpm_buf_append_u16(&template, TPM_ALG_ECC);
+
+	/* name algorithm */
+	tpm_buf_append_u16(&template, TPM_ALG_SHA256);
+
+	/* object properties */
+	tpm_buf_append_u32(&template, TPM2_OA_TMPL);
+
+	/* sauth policy (empty) */
+	tpm_buf_append_u16(&template, 0);
+
+	/* BEGIN parameters: key specific; for ECC*/
+
+	/* symmetric algorithm */
+	tpm_buf_append_u16(&template, TPM_ALG_AES);
+
+	/* bits for symmetric algorithm */
+	tpm_buf_append_u16(&template, AES_KEY_BITS);
+
+	/* algorithm mode (must be CFB) */
+	tpm_buf_append_u16(&template, TPM_ALG_CFB);
+
+	/* scheme (NULL means any scheme) */
+	tpm_buf_append_u16(&template, TPM_ALG_NULL);
+
+	/* ECC Curve ID */
+	tpm_buf_append_u16(&template, TPM2_ECC_NIST_P256);
+
+	/* KDF Scheme */
+	tpm_buf_append_u16(&template, TPM_ALG_NULL);
+
+	/* unique: key specific; for ECC it is two zero size points */
+	tpm_buf_append_u16(&template, 0);
+	tpm_buf_append_u16(&template, 0);
+
+	/* END parameters */
+
+	/* primary handle */
+	tpm_buf_append_u32(&buf, hierarchy);
+	tpm_buf_append_empty_auth(&buf, TPM2_RS_PW);
+
+	/* sensitive create size is 4 for two empty buffers */
+	tpm_buf_append_u16(&buf, 4);
+
+	/* sensitive create auth data (empty) */
+	tpm_buf_append_u16(&buf, 0);
+
+	/* sensitive create sensitive data (empty) */
+	tpm_buf_append_u16(&buf, 0);
+
+	/* the public template */
+	tpm_buf_append(&buf, template.data, template.length);
+	tpm_buf_destroy(&template);
+
+	/* outside info (empty) */
+	tpm_buf_append_u16(&buf, 0);
+
+	/* creation PCR (none) */
+	tpm_buf_append_u32(&buf, 0);
+
+	rc = tpm_transmit_cmd(chip, &buf, 0,
+			      "attempting to create NULL primary");
+
+	if (rc == TPM2_RC_SUCCESS)
+		rc = tpm2_parse_create_primary(chip, &buf, handle, hierarchy);
+
+	tpm_buf_destroy(&buf);
+
+	return rc;
+}
+
+static int tpm2_create_null_primary(struct tpm_chip *chip)
+{
+	u32 null_key;
+	int rc;
+
+	rc = tpm2_create_primary(chip, TPM2_RH_NULL, &null_key);
+
+	if (rc == TPM2_RC_SUCCESS) {
+		unsigned int offset = 0; /* dummy offset for null key context */
+
+		rc = tpm2_save_context(chip, null_key, chip->null_key_context,
+				       sizeof(chip->null_key_context), &offset);
+		tpm2_flush_context(chip, null_key);
+	}
+
+	return rc;
+}
+
+/**
+ * tpm2_sessions_init() - start of day initialization for the sessions code
+ * @chip: TPM chip
+ *
+ * Derive and context save the null primary and allocate memory in the
+ * struct tpm_chip for the authorizations.
+ */
+int tpm2_sessions_init(struct tpm_chip *chip)
+{
+	int rc;
+
+	rc = tpm2_create_null_primary(chip);
+	if (rc)
+		dev_err(&chip->dev, "TPM: security failed (NULL seed derivation): %d\n", rc);
+
+	return rc;
+}

include/linux/tpm.h

@@ -23,6 +23,7 @@
 #include <linux/fs.h>
 #include <linux/highmem.h>
 #include <crypto/hash_info.h>
+#include <crypto/aes.h>
 
 #define TPM_DIGEST_SIZE 20	/* Max TPM v1.2 PCR size */
 #define TPM_MAX_DIGEST_SIZE SHA512_DIGEST_SIZE
@@ -35,12 +36,15 @@ struct trusted_key_options;
 enum tpm_algorithms {
 	TPM_ALG_ERROR		= 0x0000,
 	TPM_ALG_SHA1		= 0x0004,
+	TPM_ALG_AES		= 0x0006,
 	TPM_ALG_KEYEDHASH	= 0x0008,
 	TPM_ALG_SHA256		= 0x000B,
 	TPM_ALG_SHA384		= 0x000C,
 	TPM_ALG_SHA512		= 0x000D,
 	TPM_ALG_NULL		= 0x0010,
 	TPM_ALG_SM3_256		= 0x0012,
+	TPM_ALG_ECC		= 0x0023,
+	TPM_ALG_CFB		= 0x0043,
 };
 
 /*
@@ -49,6 +53,11 @@ enum tpm_algorithms {
  */
 #define TPM_MAX_HASHES	5
 
+enum tpm2_curves {
+	TPM2_ECC_NONE		= 0x0000,
+	TPM2_ECC_NIST_P256	= 0x0003,
+};
+
 struct tpm_digest {
 	u16 alg_id;
 	u8 digest[TPM_MAX_DIGEST_SIZE];
@@ -116,6 +125,20 @@ struct tpm_chip_seqops {
 	const struct seq_operations *seqops;
 };
 
+/* fixed define for the curve we use which is NIST_P256 */
+#define EC_PT_SZ	32
+
+/*
+ * fixed define for the size of a name.  This is actually HASHALG size
+ * plus 2, so 32 for SHA256
+ */
+#define TPM2_NAME_SIZE	34
+
+/*
+ * The maximum size for an object context
+ */
+#define TPM2_MAX_CONTEXT_SIZE 4096
+
 struct tpm_chip {
 	struct device dev;
 	struct device devs;
@@ -170,6 +193,17 @@ struct tpm_chip {
 
 	/* active locality */
 	int locality;
+
+#ifdef CONFIG_TCG_TPM2_HMAC
+	/* details for communication security via sessions */
+
+	/* saved context for NULL seed */
+	u8 null_key_context[TPM2_MAX_CONTEXT_SIZE];
+	 /* name of NULL seed */
+	u8 null_key_name[TPM2_NAME_SIZE];
+	u8 null_ec_key_x[EC_PT_SZ];
+	u8 null_ec_key_y[EC_PT_SZ];
+#endif
 };
 
 #define TPM_HEADER_SIZE		10
@@ -194,6 +228,7 @@ enum tpm2_timeouts {
 enum tpm2_structures {
 	TPM2_ST_NO_SESSIONS	= 0x8001,
 	TPM2_ST_SESSIONS	= 0x8002,
+	TPM2_ST_CREATION	= 0x8021,
 };
 
 /* Indicates from what layer of the software stack the error comes from */
@@ -243,6 +278,7 @@ enum tpm2_command_codes {
 };
 
 enum tpm2_permanent_handles {
+	TPM2_RH_NULL		= 0x40000007,
 	TPM2_RS_PW		= 0x40000009,
 };
 
@@ -318,9 +354,28 @@ struct tpm_buf {
 enum tpm2_object_attributes {
 	TPM2_OA_FIXED_TPM		= BIT(1),
 	TPM2_OA_FIXED_PARENT		= BIT(4),
+	TPM2_OA_SENSITIVE_DATA_ORIGIN	= BIT(5),
 	TPM2_OA_USER_WITH_AUTH		= BIT(6),
+	TPM2_OA_NO_DA			= BIT(10),
+	TPM2_OA_RESTRICTED		= BIT(16),
+	TPM2_OA_DECRYPT			= BIT(17),
 };
 
+/*
+ * definitions for the canonical template.  These are mandated
+ * by the TCG key template documents
+ */
+
+#define AES_KEY_BYTES	AES_KEYSIZE_128
+#define AES_KEY_BITS	(AES_KEY_BYTES*8)
+#define TPM2_OA_TMPL	(TPM2_OA_NO_DA |			\
+			 TPM2_OA_FIXED_TPM |			\
+			 TPM2_OA_FIXED_PARENT |			\
+			 TPM2_OA_SENSITIVE_DATA_ORIGIN |	\
+			 TPM2_OA_USER_WITH_AUTH |		\
+			 TPM2_OA_DECRYPT |			\
+			 TPM2_OA_RESTRICTED)
+
 enum tpm2_session_attributes {
 	TPM2_SA_CONTINUE_SESSION	= BIT(0),
 };
@@ -373,6 +428,16 @@ extern int tpm_pcr_extend(struct tpm_chip *chip, u32 pcr_idx,
 extern int tpm_get_random(struct tpm_chip *chip, u8 *data, size_t max);
 extern struct tpm_chip *tpm_default_chip(void);
 void tpm2_flush_context(struct tpm_chip *chip, u32 handle);
+
+static inline void tpm_buf_append_empty_auth(struct tpm_buf *buf, u32 handle)
+{
+	/* simple authorization for empty auth */
+	tpm_buf_append_u32(buf, 9);		/* total length of auth */
+	tpm_buf_append_u32(buf, handle);
+	tpm_buf_append_u16(buf, 0);		/* nonce len */
+	tpm_buf_append_u8(buf, 0);		/* attributes */
+	tpm_buf_append_u16(buf, 0);		/* hmac len */
+}
 #else
 static inline int tpm_is_tpm2(struct tpm_chip *chip)
 {
@@ -399,5 +464,9 @@ static inline struct tpm_chip *tpm_default_chip(void)
 {
 	return NULL;
 }
+
+static inline void tpm_buf_append_empty_auth(struct tpm_buf *buf, u32 handle)
+{
+}
 #endif
 #endif