[PATCH v2 00/10] Encrypted Hibernation

[PATCH v2 00/10] Encrypted Hibernation

[Evan Green]

We are exploring enabling hibernation in some new scenarios. However,
our security team has a few requirements, listed below:
1. The hibernate image must be encrypted with protection derived from
   both the platform (eg TPM) and user authentication data (eg
   password).
2. Hibernation must not be a vector by which a malicious userspace can
   escalate to the kernel.

Requirement #1 can be achieved solely with uswsusp, however requirement
2 necessitates mechanisms in the kernel to guarantee integrity of the
hibernate image. The kernel needs a way to authenticate that it generated
the hibernate image being loaded, and that the image has not been tampered
with. Adding support for in-kernel AEAD encryption with a TPM-sealed key
allows us to achieve both requirements with a single computation pass.

Matthew Garrett published a series [1] that aligns closely with this
goal. His series utilized the fact that PCR23 is a resettable PCR that
can be blocked from access by usermode. The TPM can create a sealed key
tied to PCR23 in two ways. First, the TPM can attest to the value of
PCR23 when the key was created, which the kernel can use on resume to
verify that the kernel must have created the key (since it is the only
one capable of modifying PCR23). It can also create a policy that enforces
PCR23 be set to a specific value as a condition of unsealing the key,
preventing usermode from unsealing the key by talking directly to the
TPM.

This series adopts that primitive as a foundation, tweaking and building
on it a bit. Where Matthew's series used the TPM-backed key to encrypt a
hash of the image, this series uses the key directly as a gcm(aes)
encryption key, which the kernel uses to encrypt and decrypt the
hibernate image in chunks of 16 pages. This provides both encryption and
integrity, which turns out to be a noticeable performance improvement over
separate passes for encryption and hashing.

The series also introduces the concept of mixing user key material into
the encryption key. This allows usermode to introduce key material
based on unspecified external authentication data (in our case derived
from something like the user password or PIN), without requiring
usermode to do a separate encryption pass.

Matthew also documented issues his series had [2] related to generating
fake images by booting alternate kernels without the PCR23 limiting.
With access to PCR23 on the same machine, usermode can create fake
hibernate images that are indistinguishable to the new kernel from
genuine ones. His post outlines a solution that involves adding more
PCRs into the creation data and policy, with some gyrations to make this
work well on a standard PC.

Our approach would be similar: on our machines PCR 0 indicates whether
the system is booted in secure/verified mode or developer mode. By
adding PCR0 to the policy, we can reject hibernate images made in
developer mode while in verified mode (or vice versa).

Additionally, mixing in the user authentication data limits both
data exfiltration attacks (eg a stolen laptop) and forged hibernation
image attacks to attackers that already know the authentication data (eg
user's password). This, combined with our relatively sealed userspace
(dm-verity on the rootfs), and some judicious clearing of the hibernate
image (such as across an OS update) further reduce the risk of an online
attack. The remaining attack space of a forgery from someone with
physical access to the device and knowledge of the authentication data
is out of scope for us, given that flipping to developer mode or
reflashing RO firmware trivially achieves the same thing.

A couple of patches still need to be written on top of this series. The
generalized functionality to OR in additional PCRs via Kconfig (like PCR
0 or 5) still needs to be added. We'll also need a patch that disallows
unencrypted forms of resume from hibernation, to fully close the door
to malicious userspace. However, I wanted to get this series out first
and get reactions from upstream before continuing to add to it.

[1] https://patchwork.kernel.org/project/linux-pm/cover/20210220013255.1083202-1-matthewgarrett@google.com/
[2] https://mjg59.dreamwidth.org/58077.html

Changes in v2:
 - Fixed sparse warnings
 - Adjust hash len by 2 due to new ASN.1 storage, and add underflow
   check.
 - Rework load/create_kernel_key() to eliminate a label (Andrey)
 - Call put_device() needed from calling tpm_default_chip().
 - Add missing static on snapshot_encrypted_byte_count()
 - Fold in only the used kernel key bytes to the user key.
 - Make the user key length 32 (Eric)
 - Use CRYPTO_LIB_SHA256 for less boilerplate (Eric)
 - Fixed some sparse warnings
 - Use CRYPTO_LIB_SHA256 to get rid of sha256_data() (Eric)
 - Adjusted offsets due to new ASN.1 format, and added a creation data
   length check.
 - Fix sparse warnings
 - Fix session type comment (Andrey)
 - Eliminate extra label in get/create_kernel_key() (Andrey)
 - Call tpm_try_get_ops() before calling tpm2_flush_context().

Evan Green (7):
  security: keys: trusted: Include TPM2 creation data
  security: keys: trusted: Verify creation data
  PM: hibernate: Add kernel-based encryption
  PM: hibernate: Use TPM-backed keys to encrypt image
  PM: hibernate: Mix user key in encrypted hibernate
  PM: hibernate: Verify the digest encryption key
  PM: hibernate: seal the encryption key with a PCR policy

Matthew Garrett (3):
  tpm: Add support for in-kernel resetting of PCRs
  tpm: Allow PCR 23 to be restricted to kernel-only use
  security: keys: trusted: Allow storage of PCR values in creation data

 Documentation/power/userland-swsusp.rst       |    8 +
 .../security/keys/trusted-encrypted.rst       |    4 +
 drivers/char/tpm/Kconfig                      |   10 +
 drivers/char/tpm/tpm-dev-common.c             |    8 +
 drivers/char/tpm/tpm-interface.c              |   28 +
 drivers/char/tpm/tpm.h                        |   23 +
 drivers/char/tpm/tpm1-cmd.c                   |   69 ++
 drivers/char/tpm/tpm2-cmd.c                   |   58 +
 drivers/char/tpm/tpm2-space.c                 |    2 +-
 include/keys/trusted-type.h                   |    9 +
 include/linux/tpm.h                           |   12 +
 include/uapi/linux/suspend_ioctls.h           |   28 +-
 kernel/power/Kconfig                          |   16 +
 kernel/power/Makefile                         |    1 +
 kernel/power/power.h                          |    1 +
 kernel/power/snapenc.c                        | 1037 +++++++++++++++++
 kernel/power/snapshot.c                       |    5 +
 kernel/power/user.c                           |   44 +-
 kernel/power/user.h                           |  114 ++
 security/keys/trusted-keys/tpm2key.asn1       |    5 +-
 security/keys/trusted-keys/trusted_tpm1.c     |    9 +
 security/keys/trusted-keys/trusted_tpm2.c     |  304 ++++-
 22 files changed, 1754 insertions(+), 41 deletions(-)
 create mode 100644 kernel/power/snapenc.c
 create mode 100644 kernel/power/user.h

-- 
2.31.0

[PATCH v2 03/10] security: keys: trusted: Include TPM2 creation data

[Evan Green]

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.

---

(no changes since v1)

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.

Signed-off-by: Evan Green <evgreen@chromium.org>
---
 include/keys/trusted-type.h               |   8 +
 security/keys/trusted-keys/tpm2key.asn1   |   5 +-
 security/keys/trusted-keys/trusted_tpm2.c | 202 +++++++++++++++++++---
 3 files changed, 190 insertions(+), 25 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..1bfbf290e523a3 100644
--- a/security/keys/trusted-keys/tpm2key.asn1
+++ b/security/keys/trusted-keys/tpm2key.asn1
@@ -7,5 +7,8 @@ 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}),
+	creationData	[1] EXPLICIT OCTET STRING OPTIONAL ({tpm2_key_creation_data}),
+	creationHash	[2] EXPLICIT OCTET STRING OPTIONAL ({tpm2_key_creation_hash}),
+	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..1f166d4fa307a9 100644
--- a/security/keys/trusted-keys/trusted_tpm2.c
+++ b/security/keys/trusted-keys/trusted_tpm2.c
@@ -37,7 +37,10 @@ static int tpm2_key_encode(struct trusted_key_payload *payload,
 	u8 *work = scratch, *work1;
 	u8 *end_work = scratch + SCRATCH_SIZE;
 	u8 *priv, *pub;
+	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;
@@ -46,6 +49,26 @@ static int tpm2_key_encode(struct trusted_key_payload *payload,
 
 	pub_len = get_unaligned_be16(src) + 2;
 	pub = src;
+	src += pub_len;
+
+	creation_data_len = get_unaligned_be16(src);
+	if (creation_data_len) {
+		creation_data_len += 2;
+		creation_data = src;
+		src += creation_data_len;
+
+		creation_hash_len = get_unaligned_be16(src) + 2;
+		creation_hash = src;
+		src += creation_hash_len;
+
+		/*
+		 * 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.
+		 */
+		creation_tk_len = get_unaligned_be16(src + 6) + 8;
+		creation_tk = src;
+	}
 
 	if (!scratch)
 		return -ENOMEM;
@@ -63,26 +86,81 @@ 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 +169,21 @@ 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 +192,57 @@ 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 +305,42 @@ 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 +385,7 @@ 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 +474,14 @@ 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 +528,11 @@ 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 +589,6 @@ 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)
-- 
2.31.0

[PATCH v2 04/10] security: keys: trusted: Allow storage of PCR values in creation data

[Evan Green]

From: Matthew Garrett <matthewgarrett@google.com>

When TPMs generate keys, they can also generate some information
describing the state of the PCRs at creation time. This data can then
later be certified by the TPM, allowing verification of the PCR values.
This allows us to determine the state of the system at the time a key
was generated. Add an additional argument to the trusted key creation
options, allowing the user to provide the set of PCRs that should have
their values incorporated into the creation data.

From: Matthew Garrett <mjg59@google.com>
Signed-off-by: Matthew Garrett <mjg59@google.com>

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

---
Matthew's original version of this patch is at:
https://patchwork.kernel.org/patch/12096503/

(no changes since v1)

 .../security/keys/trusted-encrypted.rst       |  4 +++
 include/keys/trusted-type.h                   |  1 +
 security/keys/trusted-keys/trusted_tpm1.c     |  9 +++++++
 security/keys/trusted-keys/trusted_tpm2.c     | 25 +++++++++++++++++--
 4 files changed, 37 insertions(+), 2 deletions(-)

diff --git a/Documentation/security/keys/trusted-encrypted.rst b/Documentation/security/keys/trusted-encrypted.rst
index 0bfb4c33974890..dc9e11bb4824da 100644
--- a/Documentation/security/keys/trusted-encrypted.rst
+++ b/Documentation/security/keys/trusted-encrypted.rst
@@ -199,6 +199,10 @@ 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.
+       creationpcrs= hex integer representing the set of PCR values to be
+                     included in the PCR creation data. The bit corresponding
+		     to each PCR should be 1 to be included, 0 to be ignored.
+		     TPM2 only.
 
 "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.
diff --git a/include/keys/trusted-type.h b/include/keys/trusted-type.h
index 209086fed240a5..8523d41507b2a4 100644
--- a/include/keys/trusted-type.h
+++ b/include/keys/trusted-type.h
@@ -54,6 +54,7 @@ struct trusted_key_options {
 	uint32_t policydigest_len;
 	unsigned char policydigest[MAX_DIGEST_SIZE];
 	uint32_t policyhandle;
+	uint32_t creation_pcrs;
 };
 
 struct trusted_key_ops {
diff --git a/security/keys/trusted-keys/trusted_tpm1.c b/security/keys/trusted-keys/trusted_tpm1.c
index aa108bea6739b3..2975827c01bec0 100644
--- a/security/keys/trusted-keys/trusted_tpm1.c
+++ b/security/keys/trusted-keys/trusted_tpm1.c
@@ -713,6 +713,7 @@ enum {
 	Opt_hash,
 	Opt_policydigest,
 	Opt_policyhandle,
+	Opt_creationpcrs,
 };
 
 static const match_table_t key_tokens = {
@@ -725,6 +726,7 @@ static const match_table_t key_tokens = {
 	{Opt_hash, "hash=%s"},
 	{Opt_policydigest, "policydigest=%s"},
 	{Opt_policyhandle, "policyhandle=%s"},
+	{Opt_creationpcrs, "creationpcrs=%s"},
 	{Opt_err, NULL}
 };
 
@@ -858,6 +860,13 @@ static int getoptions(char *c, struct trusted_key_payload *pay,
 				return -EINVAL;
 			opt->policyhandle = handle;
 			break;
+		case Opt_creationpcrs:
+			if (!tpm2)
+				return -EINVAL;
+			res = kstrtoint(args[0].from, 16, &opt->creation_pcrs);
+			if (res < 0)
+				return -EINVAL;
+			break;
 		default:
 			return -EINVAL;
 		}
diff --git a/security/keys/trusted-keys/trusted_tpm2.c b/security/keys/trusted-keys/trusted_tpm2.c
index 1f166d4fa307a9..1d1470b880ca01 100644
--- a/security/keys/trusted-keys/trusted_tpm2.c
+++ b/security/keys/trusted-keys/trusted_tpm2.c
@@ -389,7 +389,7 @@ int tpm2_seal_trusted(struct tpm_chip *chip,
 	struct tpm_buf buf;
 	u32 hash;
 	u32 flags;
-	int i;
+	int i, j;
 	int rc;
 
 	for (i = 0; i < ARRAY_SIZE(tpm2_hash_map); i++) {
@@ -458,7 +458,28 @@ int tpm2_seal_trusted(struct tpm_chip *chip,
 	tpm_buf_append_u16(&buf, 0);
 
 	/* creation PCR */
-	tpm_buf_append_u32(&buf, 0);
+	if (options->creation_pcrs) {
+		/* One bank */
+		tpm_buf_append_u32(&buf, 1);
+		/* Which bank to use */
+		tpm_buf_append_u16(&buf, hash);
+		/* Length of the PCR bitmask */
+		tpm_buf_append_u8(&buf, 3);
+		/* PCR bitmask */
+		for (i = 0; i < 3; i++) {
+			char tmp = 0;
+
+			for (j = 0; j < 8; j++) {
+				char bit = (i * 8) + j;
+
+				if (options->creation_pcrs & (1 << bit))
+					tmp |= (1 << j);
+			}
+			tpm_buf_append_u8(&buf, tmp);
+		}
+	} else {
+		tpm_buf_append_u32(&buf, 0);
+	}
 
 	if (buf.flags & TPM_BUF_OVERFLOW) {
 		rc = -E2BIG;
-- 
2.31.0

[PATCH v2 05/10] security: keys: trusted: Verify creation data

[Evan Green]

If a loaded key contains creation data, ask the TPM to verify that
creation data. This allows users like encrypted hibernate to know that
the loaded and parsed creation data has not been tampered with.

Partially-sourced-from: Matthew Garrett <mjg59@google.com>
Signed-off-by: Evan Green <evgreen@chromium.org>

---
Source material for this change is at:
https://patchwork.kernel.org/project/linux-pm/patch/20210220013255.1083202-9-matthewgarrett@google.com/

Changes in v2:
 - Adjust hash len by 2 due to new ASN.1 storage, and add underflow
   check.

 include/linux/tpm.h                       |  1 +
 security/keys/trusted-keys/trusted_tpm2.c | 77 ++++++++++++++++++++++-
 2 files changed, 77 insertions(+), 1 deletion(-)

diff --git a/include/linux/tpm.h b/include/linux/tpm.h
index 8320cbac6f4009..438f8bc0a50582 100644
--- a/include/linux/tpm.h
+++ b/include/linux/tpm.h
@@ -224,6 +224,7 @@ enum tpm2_command_codes {
 	TPM2_CC_SELF_TEST	        = 0x0143,
 	TPM2_CC_STARTUP		        = 0x0144,
 	TPM2_CC_SHUTDOWN	        = 0x0145,
+	TPM2_CC_CERTIFYCREATION	        = 0x014A,
 	TPM2_CC_NV_READ                 = 0x014E,
 	TPM2_CC_CREATE		        = 0x0153,
 	TPM2_CC_LOAD		        = 0x0157,
diff --git a/security/keys/trusted-keys/trusted_tpm2.c b/security/keys/trusted-keys/trusted_tpm2.c
index 1d1470b880ca01..f81c6578c7f783 100644
--- a/security/keys/trusted-keys/trusted_tpm2.c
+++ b/security/keys/trusted-keys/trusted_tpm2.c
@@ -691,6 +691,74 @@ static int tpm2_unseal_cmd(struct tpm_chip *chip,
 	return rc;
 }
 
+/**
+ * tpm2_certify_creation() - execute a TPM2_CertifyCreation command
+ *
+ * @chip: TPM chip to use
+ * @payload: the key data in clear and encrypted form
+ * @blob_handle: the loaded TPM handle of the key
+ *
+ * Return: 0 on success
+ *         -EINVAL on tpm error status
+ *         < 0 error from tpm_send or tpm_buf_init
+ */
+static int tpm2_certify_creation(struct tpm_chip *chip,
+				 struct trusted_key_payload *payload,
+				 u32 blob_handle)
+{
+	struct tpm_header *head;
+	struct tpm_buf buf;
+	int rc;
+
+	rc = tpm_buf_init(&buf, TPM2_ST_SESSIONS, TPM2_CC_CERTIFYCREATION);
+	if (rc)
+		return rc;
+
+	/* Use TPM_RH_NULL for signHandle */
+	tpm_buf_append_u32(&buf, 0x40000007);
+
+	/* Object handle */
+	tpm_buf_append_u32(&buf, blob_handle);
+
+	/* Auth */
+	tpm_buf_append_u32(&buf, 9);
+	tpm_buf_append_u32(&buf, TPM2_RS_PW);
+	tpm_buf_append_u16(&buf, 0);
+	tpm_buf_append_u8(&buf, 0);
+	tpm_buf_append_u16(&buf, 0);
+
+	/* Qualifying data */
+	tpm_buf_append_u16(&buf, 0);
+
+	/* Creation data hash */
+	if (payload->creation_hash_len < 2) {
+		rc = -EINVAL;
+		goto out;
+	}
+
+	tpm_buf_append_u16(&buf, payload->creation_hash_len - 2);
+	tpm_buf_append(&buf, payload->creation_hash + 2,
+		       payload->creation_hash_len - 2);
+
+	/* signature scheme */
+	tpm_buf_append_u16(&buf, TPM_ALG_NULL);
+
+	/* creation ticket */
+	tpm_buf_append(&buf, payload->tk, payload->tk_len);
+
+	rc = tpm_transmit_cmd(chip, &buf, 6, "certifying creation data");
+	if (rc)
+		goto out;
+
+	head = (struct tpm_header *)buf.data;
+
+	if (head->return_code != 0)
+		rc = -EINVAL;
+out:
+	tpm_buf_destroy(&buf);
+	return rc;
+}
+
 /**
  * tpm2_unseal_trusted() - unseal the payload of a trusted key
  *
@@ -716,8 +784,15 @@ int tpm2_unseal_trusted(struct tpm_chip *chip,
 		goto out;
 
 	rc = tpm2_unseal_cmd(chip, payload, options, blob_handle);
-	tpm2_flush_context(chip, blob_handle);
+	if (rc)
+		goto flush;
+
+	if (payload->creation_len)
+		rc = tpm2_certify_creation(chip, payload, blob_handle);
 
+
+flush:
+	tpm2_flush_context(chip, blob_handle);
 out:
 	tpm_put_ops(chip);
 
-- 
2.31.0

Re: [PATCH v2 04/10] security: keys: trusted: Allow storage of PCR values in creation data

[Ben Boeckel]

On Tue, Aug 23, 2022 at 15:25:20 -0700, Evan Green wrote:
> diff --git a/Documentation/security/keys/trusted-encrypted.rst b/Documentation/security/keys/trusted-encrypted.rst
> index 0bfb4c33974890..dc9e11bb4824da 100644
> --- a/Documentation/security/keys/trusted-encrypted.rst
> +++ b/Documentation/security/keys/trusted-encrypted.rst
> @@ -199,6 +199,10 @@ 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.
> +       creationpcrs= hex integer representing the set of PCR values to be
> +                     included in the PCR creation data. The bit corresponding
> +		     to each PCR should be 1 to be included, 0 to be ignored.
> +		     TPM2 only.

There's inconsistent whitespace here. Given the context, I suspect the
tabs should be expanded to spaces.

As for the docs themselves, this might preferrably mention how large
this is supposed to be. It seems to be limited to 32bits by the code.
What happens if fewer are provided? More? Will there always be at most
32 PCR values? Also, how are the bits interpreted? I presume bit 0 is
for PCR value 0?

Thanks for including docs.

Thanks,

--Ben

Re: [PATCH v2 04/10] security: keys: trusted: Allow storage of PCR values in creation data

[Evan Green]

On Wed, Aug 24, 2022 at 4:56 AM Ben Boeckel <me@benboeckel.net> wrote:
>
> On Tue, Aug 23, 2022 at 15:25:20 -0700, Evan Green wrote:
> > diff --git a/Documentation/security/keys/trusted-encrypted.rst b/Documentation/security/keys/trusted-encrypted.rst
> > index 0bfb4c33974890..dc9e11bb4824da 100644
> > --- a/Documentation/security/keys/trusted-encrypted.rst
> > +++ b/Documentation/security/keys/trusted-encrypted.rst
> > @@ -199,6 +199,10 @@ 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.
> > +       creationpcrs= hex integer representing the set of PCR values to be
> > +                     included in the PCR creation data. The bit corresponding
> > +                  to each PCR should be 1 to be included, 0 to be ignored.
> > +                  TPM2 only.
>
> There's inconsistent whitespace here. Given the context, I suspect the
> tabs should be expanded to spaces.
>
> As for the docs themselves, this might preferrably mention how large
> this is supposed to be. It seems to be limited to 32bits by the code.
> What happens if fewer are provided? More? Will there always be at most
> 32 PCR values? Also, how are the bits interpreted? I presume bit 0 is
> for PCR value 0?

Makes sense, I'll pin down the specification a bit better here and fix
up the spacing.

>
> Thanks for including docs.

Thanks for looking at them!

-Evan

Re: [PATCH v2 00/10] Encrypted Hibernation

[Limonciello, Mario]

On 8/23/2022 17:25, Evan Green wrote:
> We are exploring enabling hibernation in some new scenarios. However,
> our security team has a few requirements, listed below:
> 1. The hibernate image must be encrypted with protection derived from
>     both the platform (eg TPM) and user authentication data (eg
>     password).
> 2. Hibernation must not be a vector by which a malicious userspace can
>     escalate to the kernel.
> 
> Requirement #1 can be achieved solely with uswsusp, however requirement
> 2 necessitates mechanisms in the kernel to guarantee integrity of the
> hibernate image. The kernel needs a way to authenticate that it generated
> the hibernate image being loaded, and that the image has not been tampered
> with. Adding support for in-kernel AEAD encryption with a TPM-sealed key
> allows us to achieve both requirements with a single computation pass.
> 
> Matthew Garrett published a series [1] that aligns closely with this
> goal. His series utilized the fact that PCR23 is a resettable PCR that
> can be blocked from access by usermode. The TPM can create a sealed key
> tied to PCR23 in two ways. First, the TPM can attest to the value of
> PCR23 when the key was created, which the kernel can use on resume to
> verify that the kernel must have created the key (since it is the only
> one capable of modifying PCR23). It can also create a policy that enforces
> PCR23 be set to a specific value as a condition of unsealing the key,
> preventing usermode from unsealing the key by talking directly to the
> TPM.
> 
> This series adopts that primitive as a foundation, tweaking and building
> on it a bit. Where Matthew's series used the TPM-backed key to encrypt a
> hash of the image, this series uses the key directly as a gcm(aes)
> encryption key, which the kernel uses to encrypt and decrypt the
> hibernate image in chunks of 16 pages. This provides both encryption and
> integrity, which turns out to be a noticeable performance improvement over
> separate passes for encryption and hashing.
> 
> The series also introduces the concept of mixing user key material into
> the encryption key. This allows usermode to introduce key material
> based on unspecified external authentication data (in our case derived
> from something like the user password or PIN), without requiring
> usermode to do a separate encryption pass.
> 
> Matthew also documented issues his series had [2] related to generating
> fake images by booting alternate kernels without the PCR23 limiting.
> With access to PCR23 on the same machine, usermode can create fake
> hibernate images that are indistinguishable to the new kernel from
> genuine ones. His post outlines a solution that involves adding more
> PCRs into the creation data and policy, with some gyrations to make this
> work well on a standard PC.
> 
> Our approach would be similar: on our machines PCR 0 indicates whether
> the system is booted in secure/verified mode or developer mode. By
> adding PCR0 to the policy, we can reject hibernate images made in
> developer mode while in verified mode (or vice versa).
> 
> Additionally, mixing in the user authentication data limits both
> data exfiltration attacks (eg a stolen laptop) and forged hibernation
> image attacks to attackers that already know the authentication data (eg
> user's password). This, combined with our relatively sealed userspace
> (dm-verity on the rootfs), and some judicious clearing of the hibernate
> image (such as across an OS update) further reduce the risk of an online
> attack. The remaining attack space of a forgery from someone with
> physical access to the device and knowledge of the authentication data
> is out of scope for us, given that flipping to developer mode or
> reflashing RO firmware trivially achieves the same thing.
> 
> A couple of patches still need to be written on top of this series. The
> generalized functionality to OR in additional PCRs via Kconfig (like PCR
> 0 or 5) still needs to be added. We'll also need a patch that disallows
> unencrypted forms of resume from hibernation, to fully close the door
> to malicious userspace. However, I wanted to get this series out first
> and get reactions from upstream before continuing to add to it.

Something else to think about in this series is what happens with 
`hibernation_available` in kernel/power/hibernate.c.  Currently if the 
system is locked down hibernate is disabled, but I would think that
with a setup like that described here that should no longer be necessary.

> 
> [1] https://patchwork.kernel.org/project/linux-pm/cover/20210220013255.1083202-1-matthewgarrett@google.com/
> [2] https://mjg59.dreamwidth.org/58077.html
> 
> Changes in v2:
>   - Fixed sparse warnings
>   - Adjust hash len by 2 due to new ASN.1 storage, and add underflow
>     check.
>   - Rework load/create_kernel_key() to eliminate a label (Andrey)
>   - Call put_device() needed from calling tpm_default_chip().
>   - Add missing static on snapshot_encrypted_byte_count()
>   - Fold in only the used kernel key bytes to the user key.
>   - Make the user key length 32 (Eric)
>   - Use CRYPTO_LIB_SHA256 for less boilerplate (Eric)
>   - Fixed some sparse warnings
>   - Use CRYPTO_LIB_SHA256 to get rid of sha256_data() (Eric)
>   - Adjusted offsets due to new ASN.1 format, and added a creation data
>     length check.
>   - Fix sparse warnings
>   - Fix session type comment (Andrey)
>   - Eliminate extra label in get/create_kernel_key() (Andrey)
>   - Call tpm_try_get_ops() before calling tpm2_flush_context().
> 
> Evan Green (7):
>    security: keys: trusted: Include TPM2 creation data
>    security: keys: trusted: Verify creation data
>    PM: hibernate: Add kernel-based encryption
>    PM: hibernate: Use TPM-backed keys to encrypt image
>    PM: hibernate: Mix user key in encrypted hibernate
>    PM: hibernate: Verify the digest encryption key
>    PM: hibernate: seal the encryption key with a PCR policy
> 
> Matthew Garrett (3):
>    tpm: Add support for in-kernel resetting of PCRs
>    tpm: Allow PCR 23 to be restricted to kernel-only use
>    security: keys: trusted: Allow storage of PCR values in creation data
> 
>   Documentation/power/userland-swsusp.rst       |    8 +
>   .../security/keys/trusted-encrypted.rst       |    4 +
>   drivers/char/tpm/Kconfig                      |   10 +
>   drivers/char/tpm/tpm-dev-common.c             |    8 +
>   drivers/char/tpm/tpm-interface.c              |   28 +
>   drivers/char/tpm/tpm.h                        |   23 +
>   drivers/char/tpm/tpm1-cmd.c                   |   69 ++
>   drivers/char/tpm/tpm2-cmd.c                   |   58 +
>   drivers/char/tpm/tpm2-space.c                 |    2 +-
>   include/keys/trusted-type.h                   |    9 +
>   include/linux/tpm.h                           |   12 +
>   include/uapi/linux/suspend_ioctls.h           |   28 +-
>   kernel/power/Kconfig                          |   16 +
>   kernel/power/Makefile                         |    1 +
>   kernel/power/power.h                          |    1 +
>   kernel/power/snapenc.c                        | 1037 +++++++++++++++++
>   kernel/power/snapshot.c                       |    5 +
>   kernel/power/user.c                           |   44 +-
>   kernel/power/user.h                           |  114 ++
>   security/keys/trusted-keys/tpm2key.asn1       |    5 +-
>   security/keys/trusted-keys/trusted_tpm1.c     |    9 +
>   security/keys/trusted-keys/trusted_tpm2.c     |  304 ++++-
>   22 files changed, 1754 insertions(+), 41 deletions(-)
>   create mode 100644 kernel/power/snapenc.c
>   create mode 100644 kernel/power/user.h
> 

Re: [PATCH v2 00/10] Encrypted Hibernation

[Evan Green]

On Wed, Aug 31, 2022 at 11:35 AM Limonciello, Mario
<mario.limonciello@amd.com> wrote:
>
> On 8/23/2022 17:25, Evan Green wrote:
> > We are exploring enabling hibernation in some new scenarios. However,
> > our security team has a few requirements, listed below:
> > 1. The hibernate image must be encrypted with protection derived from
> >     both the platform (eg TPM) and user authentication data (eg
> >     password).
> > 2. Hibernation must not be a vector by which a malicious userspace can
> >     escalate to the kernel.
> >
> > Requirement #1 can be achieved solely with uswsusp, however requirement
> > 2 necessitates mechanisms in the kernel to guarantee integrity of the
> > hibernate image. The kernel needs a way to authenticate that it generated
> > the hibernate image being loaded, and that the image has not been tampered
> > with. Adding support for in-kernel AEAD encryption with a TPM-sealed key
> > allows us to achieve both requirements with a single computation pass.
> >
> > Matthew Garrett published a series [1] that aligns closely with this
> > goal. His series utilized the fact that PCR23 is a resettable PCR that
> > can be blocked from access by usermode. The TPM can create a sealed key
> > tied to PCR23 in two ways. First, the TPM can attest to the value of
> > PCR23 when the key was created, which the kernel can use on resume to
> > verify that the kernel must have created the key (since it is the only
> > one capable of modifying PCR23). It can also create a policy that enforces
> > PCR23 be set to a specific value as a condition of unsealing the key,
> > preventing usermode from unsealing the key by talking directly to the
> > TPM.
> >
> > This series adopts that primitive as a foundation, tweaking and building
> > on it a bit. Where Matthew's series used the TPM-backed key to encrypt a
> > hash of the image, this series uses the key directly as a gcm(aes)
> > encryption key, which the kernel uses to encrypt and decrypt the
> > hibernate image in chunks of 16 pages. This provides both encryption and
> > integrity, which turns out to be a noticeable performance improvement over
> > separate passes for encryption and hashing.
> >
> > The series also introduces the concept of mixing user key material into
> > the encryption key. This allows usermode to introduce key material
> > based on unspecified external authentication data (in our case derived
> > from something like the user password or PIN), without requiring
> > usermode to do a separate encryption pass.
> >
> > Matthew also documented issues his series had [2] related to generating
> > fake images by booting alternate kernels without the PCR23 limiting.
> > With access to PCR23 on the same machine, usermode can create fake
> > hibernate images that are indistinguishable to the new kernel from
> > genuine ones. His post outlines a solution that involves adding more
> > PCRs into the creation data and policy, with some gyrations to make this
> > work well on a standard PC.
> >
> > Our approach would be similar: on our machines PCR 0 indicates whether
> > the system is booted in secure/verified mode or developer mode. By
> > adding PCR0 to the policy, we can reject hibernate images made in
> > developer mode while in verified mode (or vice versa).
> >
> > Additionally, mixing in the user authentication data limits both
> > data exfiltration attacks (eg a stolen laptop) and forged hibernation
> > image attacks to attackers that already know the authentication data (eg
> > user's password). This, combined with our relatively sealed userspace
> > (dm-verity on the rootfs), and some judicious clearing of the hibernate
> > image (such as across an OS update) further reduce the risk of an online
> > attack. The remaining attack space of a forgery from someone with
> > physical access to the device and knowledge of the authentication data
> > is out of scope for us, given that flipping to developer mode or
> > reflashing RO firmware trivially achieves the same thing.
> >
> > A couple of patches still need to be written on top of this series. The
> > generalized functionality to OR in additional PCRs via Kconfig (like PCR
> > 0 or 5) still needs to be added. We'll also need a patch that disallows
> > unencrypted forms of resume from hibernation, to fully close the door
> > to malicious userspace. However, I wanted to get this series out first
> > and get reactions from upstream before continuing to add to it.
>
> Something else to think about in this series is what happens with
> `hibernation_available` in kernel/power/hibernate.c.  Currently if the
> system is locked down hibernate is disabled, but I would think that
> with a setup like that described here that should no longer be necessary.
>

Correct, I think that would be a reasonable followup to this series.

-Evan

Re: [PATCH v2 00/10] Encrypted Hibernation

[Pavel Machek]

[-- Attachment #1: Type: text/plain, Size: 636 bytes --]

Hi!

> We are exploring enabling hibernation in some new scenarios. However,
> our security team has a few requirements, listed below:
> 1. The hibernate image must be encrypted with protection derived from
>    both the platform (eg TPM) and user authentication data (eg
>    password).
> 2. Hibernation must not be a vector by which a malicious userspace can
>    escalate to the kernel.

Why is #2 reasonable requirement?

We normally allow userspace with appropriate permissions to update the
kernel, for example.

Best regards,
								Pavel
-- 
People of Russia, stop Putin before his war on Ukraine escalates.

[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 195 bytes --]

Re: [PATCH v2 00/10] Encrypted Hibernation

[Evan Green]

On Tue, Sep 20, 2022 at 1:46 AM Pavel Machek <pavel@ucw.cz> wrote:
>
> Hi!
>
> > We are exploring enabling hibernation in some new scenarios. However,
> > our security team has a few requirements, listed below:
> > 1. The hibernate image must be encrypted with protection derived from
> >    both the platform (eg TPM) and user authentication data (eg
> >    password).
> > 2. Hibernation must not be a vector by which a malicious userspace can
> >    escalate to the kernel.
>
> Why is #2 reasonable requirement?
>
> We normally allow userspace with appropriate permissions to update the
> kernel, for example.

I'll take a stab at answering this. I've also CCed one of our security
folks to keep me honest and add any needed additional context.

ChromeOS takes an approach of attempting to limit the blast radius of
any given vulnerability as much as possible. A vulnerable system
service may be running as root, but may also still be fairly
constrained by sandboxing: it may not have access to all processes,
the entire file system, or all capability bits. With Verified Boot
[1], our kernel and rootfs are statically signed by Google (or
yourself if firmware has been reflashed). Even if a full root
compromise occurs, it's difficult for the attacker to persist across a
reboot, since they cannot update the kernel or init flow on disk
without the signing key.

We do our best to lock down other escalation vectors from root to
kernel as well. For instance, features like LoadPin help prevent a
malicious root from simply loading up a payload via insmod.

So in cases like ours, jumping from root execution to kernel execution
represents a real escalation in privilege. Hibernate as it exists
today represents a wide open door for root to become kernel, so we're
forced to disable the Kconfigs for it. This series, along with another
patch to restrict unencrypted resume, would add the guardrails we need
to prevent arbitrary code from moving into the kernel via resume.

-Evan

[1] https://www.chromium.org/chromium-os/chromiumos-design-docs/verified-boot/

Re: [PATCH v2 00/10] Encrypted Hibernation

[Kees Cook]

On Tue, Aug 23, 2022 at 03:25:16PM -0700, Evan Green wrote:
> This series adopts that primitive as a foundation, tweaking and building
> on it a bit. Where Matthew's series used the TPM-backed key to encrypt a
> hash of the image, this series uses the key directly as a gcm(aes)
> encryption key, which the kernel uses to encrypt and decrypt the
> hibernate image in chunks of 16 pages. This provides both encryption and
> integrity, which turns out to be a noticeable performance improvement over
> separate passes for encryption and hashing.

I like this series! I would ask that someone more familiar with the
cryptographic constraints here confirm that the primitives you're using
are going to actually provide you the constraints you want (i.e.
encryption, integrity, etc). My understanding is that gcm(aes) is
exactly right, but I Am Not A Cryptographer. ;)

I'll reply more to individual patches ...

-- 
Kees Cook

Re: [PATCH v2 03/10] security: keys: trusted: Include TPM2 creation data

[Kees Cook]

On Tue, Aug 23, 2022 at 03:25:19PM -0700, Evan Green wrote:
> 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.
> 
> ---
> 
> (no changes since v1)
> 
> 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.

This part (between your S-o-b and the "---") should got below the "---"
after your S-o-b, otherwise tooling will include it in the commit log
(or lose your S-o-b).

> 
> Signed-off-by: Evan Green <evgreen@chromium.org>
> ---
>  include/keys/trusted-type.h               |   8 +
>  security/keys/trusted-keys/tpm2key.asn1   |   5 +-
>  security/keys/trusted-keys/trusted_tpm2.c | 202 +++++++++++++++++++---
>  3 files changed, 190 insertions(+), 25 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..1bfbf290e523a3 100644
> --- a/security/keys/trusted-keys/tpm2key.asn1
> +++ b/security/keys/trusted-keys/tpm2key.asn1
> @@ -7,5 +7,8 @@ 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}),
> +	creationData	[1] EXPLICIT OCTET STRING OPTIONAL ({tpm2_key_creation_data}),
> +	creationHash	[2] EXPLICIT OCTET STRING OPTIONAL ({tpm2_key_creation_hash}),
> +	creationTk	[3] EXPLICIT OCTET STRING OPTIONAL ({tpm2_key_creation_tk})
>  	}

Maybe include a link (or named reference) to these fields from the TPM
spec?

> [...]
> @@ -46,6 +49,26 @@ static int tpm2_key_encode(struct trusted_key_payload *payload,
>  
>  	pub_len = get_unaligned_be16(src) + 2;
>  	pub = src;
> +	src += pub_len;
> +
> +	creation_data_len = get_unaligned_be16(src);
> +	if (creation_data_len) {
> +		creation_data_len += 2;
> +		creation_data = src;
> +		src += creation_data_len;
> +
> +		creation_hash_len = get_unaligned_be16(src) + 2;
> +		creation_hash = src;
> +		src += creation_hash_len;
> +
> +		/*
> +		 * 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.
> +		 */
> +		creation_tk_len = get_unaligned_be16(src + 6) + 8;
> +		creation_tk = src;
> +	}
>  
>  	if (!scratch)
>  		return -ENOMEM;

I don't see anything in this code (even before your patch) actually
checking length against the "len" argument to tpm2_key_encode(). I think
that needs to be fixed so proper bounds checking can be done here.
Otherwise how do we know if we're running off the end of "src"?

Yes, I realize if we have a malicious TPM everything goes out the
window, but TPMs don't always behave -- this code should likely be more
defensive. Or, I've misunderstood where "src" is coming from.
Regardless, my question stands: what is checking "len"?

> @@ -63,26 +86,81 @@ 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;

I find the addition of the word "BUG" in a WARN() to be confusing. :) I
realize this is just copying the existing style, though.

> +	}
>  
>  	return work1 - payload->blob;
> +err:
> +	kfree(scratch);
> +	return rc;
>  }
>  
>  struct tpm2_key_context {
> @@ -91,15 +169,21 @@ 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 +192,57 @@ 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 +305,42 @@ 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;
> +}

What is hdrlen here? Or rather, what kinds of bounds checking is needed
here?

> +
> +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 +385,7 @@ 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 +474,14 @@ 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 +528,11 @@ 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 +589,6 @@ 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)
> -- 
> 2.31.0
> 

Otherwise looks good!

-Kees

-- 
Kees Cook

Re: [PATCH v2 05/10] security: keys: trusted: Verify creation data

[Kees Cook]

On Tue, Aug 23, 2022 at 03:25:21PM -0700, Evan Green wrote:
> If a loaded key contains creation data, ask the TPM to verify that
> creation data. This allows users like encrypted hibernate to know that
> the loaded and parsed creation data has not been tampered with.
> 
> Partially-sourced-from: Matthew Garrett <mjg59@google.com>
> Signed-off-by: Evan Green <evgreen@chromium.org>
> 
> ---
> Source material for this change is at:
> https://patchwork.kernel.org/project/linux-pm/patch/20210220013255.1083202-9-matthewgarrett@google.com/
> 
> Changes in v2:
>  - Adjust hash len by 2 due to new ASN.1 storage, and add underflow
>    check.
> 
>  include/linux/tpm.h                       |  1 +
>  security/keys/trusted-keys/trusted_tpm2.c | 77 ++++++++++++++++++++++-
>  2 files changed, 77 insertions(+), 1 deletion(-)
> 
> diff --git a/include/linux/tpm.h b/include/linux/tpm.h
> index 8320cbac6f4009..438f8bc0a50582 100644
> --- a/include/linux/tpm.h
> +++ b/include/linux/tpm.h
> @@ -224,6 +224,7 @@ enum tpm2_command_codes {
>  	TPM2_CC_SELF_TEST	        = 0x0143,
>  	TPM2_CC_STARTUP		        = 0x0144,
>  	TPM2_CC_SHUTDOWN	        = 0x0145,
> +	TPM2_CC_CERTIFYCREATION	        = 0x014A,
>  	TPM2_CC_NV_READ                 = 0x014E,
>  	TPM2_CC_CREATE		        = 0x0153,
>  	TPM2_CC_LOAD		        = 0x0157,
> diff --git a/security/keys/trusted-keys/trusted_tpm2.c b/security/keys/trusted-keys/trusted_tpm2.c
> index 1d1470b880ca01..f81c6578c7f783 100644
> --- a/security/keys/trusted-keys/trusted_tpm2.c
> +++ b/security/keys/trusted-keys/trusted_tpm2.c
> @@ -691,6 +691,74 @@ static int tpm2_unseal_cmd(struct tpm_chip *chip,
>  	return rc;
>  }
>  
> +/**
> + * tpm2_certify_creation() - execute a TPM2_CertifyCreation command
> + *
> + * @chip: TPM chip to use
> + * @payload: the key data in clear and encrypted form
> + * @blob_handle: the loaded TPM handle of the key
> + *
> + * Return: 0 on success
> + *         -EINVAL on tpm error status
> + *         < 0 error from tpm_send or tpm_buf_init
> + */
> +static int tpm2_certify_creation(struct tpm_chip *chip,
> +				 struct trusted_key_payload *payload,
> +				 u32 blob_handle)
> +{
> +	struct tpm_header *head;
> +	struct tpm_buf buf;
> +	int rc;
> +
> +	rc = tpm_buf_init(&buf, TPM2_ST_SESSIONS, TPM2_CC_CERTIFYCREATION);
> +	if (rc)
> +		return rc;
> +
> +	/* Use TPM_RH_NULL for signHandle */
> +	tpm_buf_append_u32(&buf, 0x40000007);
> +
> +	/* Object handle */
> +	tpm_buf_append_u32(&buf, blob_handle);
> +
> +	/* Auth */
> +	tpm_buf_append_u32(&buf, 9);
> +	tpm_buf_append_u32(&buf, TPM2_RS_PW);
> +	tpm_buf_append_u16(&buf, 0);
> +	tpm_buf_append_u8(&buf, 0);
> +	tpm_buf_append_u16(&buf, 0);
> +
> +	/* Qualifying data */
> +	tpm_buf_append_u16(&buf, 0);
> +
> +	/* Creation data hash */
> +	if (payload->creation_hash_len < 2) {
> +		rc = -EINVAL;
> +		goto out;
> +	}
> +
> +	tpm_buf_append_u16(&buf, payload->creation_hash_len - 2);
> +	tpm_buf_append(&buf, payload->creation_hash + 2,
> +		       payload->creation_hash_len - 2);
> +
> +	/* signature scheme */
> +	tpm_buf_append_u16(&buf, TPM_ALG_NULL);
> +
> +	/* creation ticket */
> +	tpm_buf_append(&buf, payload->tk, payload->tk_len);
> +
> +	rc = tpm_transmit_cmd(chip, &buf, 6, "certifying creation data");
> +	if (rc)
> +		goto out;
> +
> +	head = (struct tpm_header *)buf.data;
> +
> +	if (head->return_code != 0)
> +		rc = -EINVAL;

Do you have a reference to this TPM command spec? I have a dim memory of
some of these commands having success/failure listed separately from
other things in the reply. Is that true here? (i.e. is the return_code
only about "yes I replied" and there is a missing "but the answer is no"
check?)

> +out:
> +	tpm_buf_destroy(&buf);
> +	return rc;
> +}
> +
>  /**
>   * tpm2_unseal_trusted() - unseal the payload of a trusted key
>   *
> @@ -716,8 +784,15 @@ int tpm2_unseal_trusted(struct tpm_chip *chip,
>  		goto out;
>  
>  	rc = tpm2_unseal_cmd(chip, payload, options, blob_handle);
> -	tpm2_flush_context(chip, blob_handle);
> +	if (rc)
> +		goto flush;
> +
> +	if (payload->creation_len)
> +		rc = tpm2_certify_creation(chip, payload, blob_handle);
>  
> +
> +flush:
> +	tpm2_flush_context(chip, blob_handle);
>  out:
>  	tpm_put_ops(chip);
>  
> -- 
> 2.31.0
> 

Otherwise looks good to me. :)

-- 
Kees Cook

Re: [PATCH v2 00/10] Encrypted Hibernation

[Jason Gunthorpe]

On Tue, Sep 20, 2022 at 10:46:48AM +0200, Pavel Machek wrote:
> Hi!
> 
> > We are exploring enabling hibernation in some new scenarios. However,
> > our security team has a few requirements, listed below:
> > 1. The hibernate image must be encrypted with protection derived from
> >    both the platform (eg TPM) and user authentication data (eg
> >    password).
> > 2. Hibernation must not be a vector by which a malicious userspace can
> >    escalate to the kernel.
> 
> Why is #2 reasonable requirement?

These days with kernel lockdown we don't allow userspace to enter the
kernel

> We normally allow userspace with appropriate permissions to update the
> kernel, for example.

And in a lockdown secure boot environment only a signed kernel can be
booted in the first place.

A series like this is effectively carrying the secure boot trust
across the hibernation

Jason

Re: [PATCH v2 03/10] security: keys: trusted: Include TPM2 creation data

[Evan Green]

On Tue, Sep 20, 2022 at 4:04 PM Kees Cook <keescook@chromium.org> wrote:
>
> On Tue, Aug 23, 2022 at 03:25:19PM -0700, Evan Green wrote:
> > 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.
> >
> > ---
> >
> > (no changes since v1)
> >
> > 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.
>
> This part (between your S-o-b and the "---") should got below the "---"
> after your S-o-b, otherwise tooling will include it in the commit log
> (or lose your S-o-b).

Will fix.

>
> >
> > Signed-off-by: Evan Green <evgreen@chromium.org>
> > ---
> >  include/keys/trusted-type.h               |   8 +
> >  security/keys/trusted-keys/tpm2key.asn1   |   5 +-
> >  security/keys/trusted-keys/trusted_tpm2.c | 202 +++++++++++++++++++---
> >  3 files changed, 190 insertions(+), 25 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..1bfbf290e523a3 100644
> > --- a/security/keys/trusted-keys/tpm2key.asn1
> > +++ b/security/keys/trusted-keys/tpm2key.asn1
> > @@ -7,5 +7,8 @@ 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}),
> > +     creationData    [1] EXPLICIT OCTET STRING OPTIONAL ({tpm2_key_creation_data}),
> > +     creationHash    [2] EXPLICIT OCTET STRING OPTIONAL ({tpm2_key_creation_hash}),
> > +     creationTk      [3] EXPLICIT OCTET STRING OPTIONAL ({tpm2_key_creation_tk})
> >       }
>
> Maybe include a link (or named reference) to these fields from the TPM
> spec?

Sure. The TPM spec names their structure types (TPM2B_CREATION_DATA,
TPM2B_DIGEST, etc), so I'll add comments with the names of the types
as well as the command they came out of.

>
> > [...]
> > @@ -46,6 +49,26 @@ static int tpm2_key_encode(struct trusted_key_payload *payload,
> >
> >       pub_len = get_unaligned_be16(src) + 2;
> >       pub = src;
> > +     src += pub_len;
> > +
> > +     creation_data_len = get_unaligned_be16(src);
> > +     if (creation_data_len) {
> > +             creation_data_len += 2;
> > +             creation_data = src;
> > +             src += creation_data_len;
> > +
> > +             creation_hash_len = get_unaligned_be16(src) + 2;
> > +             creation_hash = src;
> > +             src += creation_hash_len;
> > +
> > +             /*
> > +              * 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.
> > +              */
> > +             creation_tk_len = get_unaligned_be16(src + 6) + 8;
> > +             creation_tk = src;
> > +     }
> >
> >       if (!scratch)
> >               return -ENOMEM;
>
> I don't see anything in this code (even before your patch) actually
> checking length against the "len" argument to tpm2_key_encode(). I think
> that needs to be fixed so proper bounds checking can be done here.
> Otherwise how do we know if we're running off the end of "src"?
>
> Yes, I realize if we have a malicious TPM everything goes out the
> window, but TPMs don't always behave -- this code should likely be more
> defensive. Or, I've misunderstood where "src" is coming from.
> Regardless, my question stands: what is checking "len"?

Sure, will add checks of len to my hunk and the bit above.

>
> > @@ -63,26 +86,81 @@ 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;
>
> I find the addition of the word "BUG" in a WARN() to be confusing. :) I
> realize this is just copying the existing style, though.

It wasn't my favorite either, but I felt an urge to be consistent. So
far I've lft this as-is, holler if I should change it.

>
> > +     }
> >
> >       return work1 - payload->blob;
> > +err:
> > +     kfree(scratch);
> > +     return rc;
> >  }
> >
> >  struct tpm2_key_context {
> > @@ -91,15 +169,21 @@ 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 +192,57 @@ 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 +305,42 @@ 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;
> > +}
>
> What is hdrlen here? Or rather, what kinds of bounds checking is needed
> here?

The prototype of asn1_action_t looks like this:

typedef int (*asn1_action_t)(void *context,
     size_t hdrlen, /* In case of ANY type */
     unsigned char tag, /* In case of ANY type */
     const void *value, size_t vlen);

I'm not an ASN.1 expert, but from studying asn1_ber_decoder(), it
looks like the core unit of an ASN.1 thing is a TLV, and hdrlen
represents the number of bytes in the datastream that make up the {TL}
portion. Based on the ANY comment above this seems to maybe be useful
for certain generic/undefined object types, but I think it's not
relevant to the types we're using. The vlen arg is the L value of the
TLV, which is what we save away in tpm2_key_context. In
asn1_ber_decoder(), I do see checks that what they pass for vlen stays
within the bounds of the source data buffer (since I knew you'd ask
:)).


>
> > +
> > +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 +385,7 @@ 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 +474,14 @@ 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 +528,11 @@ 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 +589,6 @@ 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)
> > --
> > 2.31.0
> >
>
> Otherwise looks good!

Thank you for reviewing it!
-Evan

Re: [PATCH v2 05/10] security: keys: trusted: Verify creation data

[Evan Green]

On Tue, Sep 20, 2022 at 4:07 PM Kees Cook <keescook@chromium.org> wrote:
>
> On Tue, Aug 23, 2022 at 03:25:21PM -0700, Evan Green wrote:
> > If a loaded key contains creation data, ask the TPM to verify that
> > creation data. This allows users like encrypted hibernate to know that
> > the loaded and parsed creation data has not been tampered with.
> >
> > Partially-sourced-from: Matthew Garrett <mjg59@google.com>
> > Signed-off-by: Evan Green <evgreen@chromium.org>
> >
> > ---
> > Source material for this change is at:
> > https://patchwork.kernel.org/project/linux-pm/patch/20210220013255.1083202-9-matthewgarrett@google.com/
> >
> > Changes in v2:
> >  - Adjust hash len by 2 due to new ASN.1 storage, and add underflow
> >    check.
> >
> >  include/linux/tpm.h                       |  1 +
> >  security/keys/trusted-keys/trusted_tpm2.c | 77 ++++++++++++++++++++++-
> >  2 files changed, 77 insertions(+), 1 deletion(-)
> >
> > diff --git a/include/linux/tpm.h b/include/linux/tpm.h
> > index 8320cbac6f4009..438f8bc0a50582 100644
> > --- a/include/linux/tpm.h
> > +++ b/include/linux/tpm.h
> > @@ -224,6 +224,7 @@ enum tpm2_command_codes {
> >       TPM2_CC_SELF_TEST               = 0x0143,
> >       TPM2_CC_STARTUP                 = 0x0144,
> >       TPM2_CC_SHUTDOWN                = 0x0145,
> > +     TPM2_CC_CERTIFYCREATION         = 0x014A,
> >       TPM2_CC_NV_READ                 = 0x014E,
> >       TPM2_CC_CREATE                  = 0x0153,
> >       TPM2_CC_LOAD                    = 0x0157,
> > diff --git a/security/keys/trusted-keys/trusted_tpm2.c b/security/keys/trusted-keys/trusted_tpm2.c
> > index 1d1470b880ca01..f81c6578c7f783 100644
> > --- a/security/keys/trusted-keys/trusted_tpm2.c
> > +++ b/security/keys/trusted-keys/trusted_tpm2.c
> > @@ -691,6 +691,74 @@ static int tpm2_unseal_cmd(struct tpm_chip *chip,
> >       return rc;
> >  }
> >
> > +/**
> > + * tpm2_certify_creation() - execute a TPM2_CertifyCreation command
> > + *
> > + * @chip: TPM chip to use
> > + * @payload: the key data in clear and encrypted form
> > + * @blob_handle: the loaded TPM handle of the key
> > + *
> > + * Return: 0 on success
> > + *         -EINVAL on tpm error status
> > + *         < 0 error from tpm_send or tpm_buf_init
> > + */
> > +static int tpm2_certify_creation(struct tpm_chip *chip,
> > +                              struct trusted_key_payload *payload,
> > +                              u32 blob_handle)
> > +{
> > +     struct tpm_header *head;
> > +     struct tpm_buf buf;
> > +     int rc;
> > +
> > +     rc = tpm_buf_init(&buf, TPM2_ST_SESSIONS, TPM2_CC_CERTIFYCREATION);
> > +     if (rc)
> > +             return rc;
> > +
> > +     /* Use TPM_RH_NULL for signHandle */
> > +     tpm_buf_append_u32(&buf, 0x40000007);
> > +
> > +     /* Object handle */
> > +     tpm_buf_append_u32(&buf, blob_handle);
> > +
> > +     /* Auth */
> > +     tpm_buf_append_u32(&buf, 9);
> > +     tpm_buf_append_u32(&buf, TPM2_RS_PW);
> > +     tpm_buf_append_u16(&buf, 0);
> > +     tpm_buf_append_u8(&buf, 0);
> > +     tpm_buf_append_u16(&buf, 0);
> > +
> > +     /* Qualifying data */
> > +     tpm_buf_append_u16(&buf, 0);
> > +
> > +     /* Creation data hash */
> > +     if (payload->creation_hash_len < 2) {
> > +             rc = -EINVAL;
> > +             goto out;
> > +     }
> > +
> > +     tpm_buf_append_u16(&buf, payload->creation_hash_len - 2);
> > +     tpm_buf_append(&buf, payload->creation_hash + 2,
> > +                    payload->creation_hash_len - 2);
> > +
> > +     /* signature scheme */
> > +     tpm_buf_append_u16(&buf, TPM_ALG_NULL);
> > +
> > +     /* creation ticket */
> > +     tpm_buf_append(&buf, payload->tk, payload->tk_len);
> > +
> > +     rc = tpm_transmit_cmd(chip, &buf, 6, "certifying creation data");
> > +     if (rc)
> > +             goto out;
> > +
> > +     head = (struct tpm_header *)buf.data;
> > +
> > +     if (head->return_code != 0)
> > +             rc = -EINVAL;
>
> Do you have a reference to this TPM command spec? I have a dim memory of
> some of these commands having success/failure listed separately from
> other things in the reply. Is that true here? (i.e. is the return_code
> only about "yes I replied" and there is a missing "but the answer is no"
> check?)

Here's the link to the volumes:
https://trustedcomputinggroup.org/resource/tpm-library-specification/

The description for TPM2_CertifyCreation in part 3 says this:
```
This command is used to prove the association between an object and
its creation data. The TPM will
validate that the ticket was produced by the TPM and that the ticket
validates the association between a
loaded public area and the provided hash of the creation data (creationHash).
NOTE 1 See 18.1 for description of how the signing scheme is selected.
The TPM will create a test ticket using the Name associated with
objectHandle and creationHash as:
HMAC(proof, (TPM_ST_CREATION || objectHandle→Name || creationHash)) (4)
This ticket is then compared to creation ticket. If the tickets are
not the same, the TPM shall return
TPM_RC_TICKET.
If the ticket is valid, then the TPM will create a TPMS_ATTEST
structure and place creationHash of the
command in the creationHash field of the structure. The Name
associated with objectHandle will be
included in the attestation data that is then signed using the key
associated with signHandle.
```

So my aim there was to check responseCode in the response, and as long
as it's success and not RC_TICKET I should be ok. Though I see now
from other examples I should have used
(be32_to_cpu(header->return_code) != TPM2_RC_SUCCESS). I will change
that.


>
> > +out:
> > +     tpm_buf_destroy(&buf);
> > +     return rc;
> > +}
> > +
> >  /**
> >   * tpm2_unseal_trusted() - unseal the payload of a trusted key
> >   *
> > @@ -716,8 +784,15 @@ int tpm2_unseal_trusted(struct tpm_chip *chip,
> >               goto out;
> >
> >       rc = tpm2_unseal_cmd(chip, payload, options, blob_handle);
> > -     tpm2_flush_context(chip, blob_handle);
> > +     if (rc)
> > +             goto flush;
> > +
> > +     if (payload->creation_len)
> > +             rc = tpm2_certify_creation(chip, payload, blob_handle);
> >
> > +
> > +flush:
> > +     tpm2_flush_context(chip, blob_handle);
> >  out:
> >       tpm_put_ops(chip);
> >
> > --
> > 2.31.0
> >
>
> Otherwise looks good to me. :)
>
> --
> Kees Cook