[PATCH v7 3/5] crypto: tpm2_key: Introduce a TPM2 key type

Jarkko Sakkinen
2024-05-28T21:08:44Z

TPM2 ASN.1 format is required for trusted keys and asymmetric keys. Move it
to crypto in order to make it available for both. Implement validation with
coverage of all TPMT_PUBLIC shared fields. Key type specific fields must be
covered by the different subsystems using this.

A Kconfig option CRYPTO_TPM2_KEY can be used to select the feature, which
depends only crypto subsystem itself and ASN.1 parser.

Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org>
---
v6:
* Relocate to crypto. Validate the shared part and provide
accessor functions. Use a fixed buffer size.
v2:
* Do not allocate blob twice. Use the one inside struct tpm2_key.
---
crypto/Kconfig | 7 ++
crypto/Makefile | 6 +
crypto/tpm2_key.asn1 | 11 ++
crypto/tpm2_key.c | 134 ++++++++++++++++++++
include/crypto/tpm2_key.h | 46 +++++++
security/keys/trusted-keys/Kconfig | 2 +-
security/keys/trusted-keys/Makefile | 2 -
security/keys/trusted-keys/tpm2key.asn1 | 11 --
security/keys/trusted-keys/trusted_tpm2.c | 141 +++++-----------------
9 files changed, 235 insertions(+), 125 deletions(-)
create mode 100644 crypto/tpm2_key.asn1
create mode 100644 crypto/tpm2_key.c
create mode 100644 include/crypto/tpm2_key.h
delete mode 100644 security/keys/trusted-keys/tpm2key.asn1

diff --git a/crypto/Kconfig b/crypto/Kconfig
index 5688d42a59c2..c8989bc71f57 100644
--- a/crypto/Kconfig
+++ b/crypto/Kconfig
@@ -5,6 +5,13 @@
config XOR_BLOCKS
tristate

+config CRYPTO_TPM2_KEY
+ bool
+ depends on CRYPTO
+ select ASN1
+ select OID_REGISTRY
+ default n
+
#
# async_tx api: hardware offloaded memory transfer/transform support
#
diff --git a/crypto/Makefile b/crypto/Makefile
index edbbaa3ffef5..d932fdb72319 100644
--- a/crypto/Makefile
+++ b/crypto/Makefile
@@ -216,3 +216,9 @@ obj-$(CONFIG_CRYPTO_SIMD) += crypto_simd.o
# Key derivation function
#
obj-$(CONFIG_CRYPTO_KDF800108_CTR) += kdf_sp800108.o
+
+ifdef CONFIG_CRYPTO_TPM2_KEY
+$(obj)/tpm2_key.asn1.o: $(obj)/tpm2_key.asn1.h $(obj)/tpm2_key.asn1.c
+$(obj)/tpm2_key.o: $(obj)/tpm2_key.asn1.h
+obj-y += tpm2_key.o tpm2_key.asn1.o
+endif
diff --git a/crypto/tpm2_key.asn1 b/crypto/tpm2_key.asn1
new file mode 100644
index 000000000000..b235d02ab78e
--- /dev/null
+++ b/crypto/tpm2_key.asn1
@@ -0,0 +1,11 @@
+---
+--- ASN.1 for TPM 2.0 keys
+---
+
+TPMKey ::= SEQUENCE {
+ type OBJECT IDENTIFIER ({tpm2_key_get_type}),
+ emptyAuth [0] EXPLICIT BOOLEAN OPTIONAL,
+ parent INTEGER ({tpm2_key_get_parent}),
+ pubkey OCTET STRING ({tpm2_get_public}),
+ privkey OCTET STRING ({tpm2_get_private})
+ }
diff --git a/crypto/tpm2_key.c b/crypto/tpm2_key.c
new file mode 100644
index 000000000000..78f55478d046
--- /dev/null
+++ b/crypto/tpm2_key.c
@@ -0,0 +1,134 @@
+// SPDX-License-Identifier: GPL-2.0-only
+
+#include <crypto/tpm2_key.h>
+#include <linux/oid_registry.h>
+#include <linux/slab.h>
+#include <linux/types.h>
+#include <asm/unaligned.h>
+#include "tpm2_key.asn1.h"
+
+#undef pr_fmt
+#define pr_fmt(fmt) "tpm2_key: "fmt
+
+struct tpm2_key_decoder_context {
+ u32 parent;
+ const u8 *pub;
+ u32 pub_len;
+ const u8 *priv;
+ u32 priv_len;
+ enum OID oid;
+};
+
+int tpm2_key_get_parent(void *context, size_t hdrlen,
+ unsigned char tag,
+ const void *value, size_t vlen)
+{
+ struct tpm2_key_decoder_context *decoder = context;
+ const u8 *v = value;
+ int i;
+
+ decoder->parent = 0;
+ for (i = 0; i < vlen; i++) {
+ decoder->parent <<= 8;
+ decoder->parent |= v[i];
+ }
+
+ return 0;
+}
+
+int tpm2_key_get_type(void *context, size_t hdrlen,
+ unsigned char tag,
+ const void *value, size_t vlen)
+{
+ struct tpm2_key_decoder_context *decoder = context;
+
+ decoder->oid = look_up_OID(value, vlen);
+ return 0;
+}
+
+static inline bool tpm2_key_is_valid(const void *value, size_t vlen)
+{
+ if (vlen < 2 || vlen > TPM2_KEY_BYTES_MAX)
+ return false;
+
+ if (get_unaligned_be16(value) != vlen - 2)
+ return false;
+
+ return true;
+}
+
+int tpm2_get_public(void *context, size_t hdrlen, unsigned char tag,
+ const void *value, size_t vlen)
+{
+ struct tpm2_key_decoder_context *decoder = context;
+
+ if (!tpm2_key_is_valid(value, vlen))
+ return -EBADMSG;
+
+ if (sizeof(struct tpm2_key_desc) > vlen - 2)
+ return -EBADMSG;
+
+ decoder->pub = value;
+ decoder->pub_len = vlen;
+ return 0;
+}
+
+int tpm2_get_private(void *context, size_t hdrlen, unsigned char tag,
+ const void *value, size_t vlen)
+{
+ struct tpm2_key_decoder_context *decoder = context;
+
+ if (!tpm2_key_is_valid(value, vlen))
+ return -EBADMSG;
+
+ decoder->priv = value;
+ decoder->priv_len = vlen;
+ return 0;
+}
+
+/**
+ * tpm_key_decode() - Decode TPM2 ASN.1 key
+ * @src: ASN.1 source.
+ * @src_len: ASN.1 source length.
+ *
+ * Decodes the TPM2 ASN.1 key and validates that the public key data has all
+ * the shared fields of TPMT_PUBLIC. This is full coverage of the memory that
+ * can be validated before doing any key type specific validation.
+ *
+ * Return:
+ * - TPM2 ASN.1 key on success.
+ * - -EBADMSG when decoding fails.
+ * - -ENOMEM when OOM while allocating struct tpm2_key.
+ */
+struct tpm2_key *tpm2_key_decode(const u8 *src, u32 src_len)
+{
+ struct tpm2_key_decoder_context decoder;
+ struct tpm2_key *key;
+ u8 *data;
+ int ret;
+
+ memset(&decoder, 0, sizeof(decoder));
+ ret = asn1_ber_decoder(&tpm2_key_decoder, &decoder, src, src_len);
+ if (ret < 0) {
+ if (ret != -EBADMSG)
+ pr_info("Decoder error %d\n", ret);
+
+ return ERR_PTR(-EBADMSG);
+ }
+
+ key = kzalloc(sizeof(*key), GFP_KERNEL);
+ if (!key)
+ return ERR_PTR(-ENOMEM);
+
+ data = &key->data[0];
+ memcpy(&data[0], decoder.priv, decoder.priv_len);
+ memcpy(&data[decoder.priv_len], decoder.pub, decoder.pub_len);
+
+ key->oid = decoder.oid;
+ key->priv_len = decoder.priv_len;
+ key->pub_len = decoder.pub_len;
+ key->parent = decoder.parent;
+ key->desc = (struct tpm2_key_desc *)&data[decoder.priv_len + 2];
+ return key;
+}
+EXPORT_SYMBOL_GPL(tpm2_key_decode);
diff --git a/include/crypto/tpm2_key.h b/include/crypto/tpm2_key.h
new file mode 100644
index 000000000000..74debaf707bf
--- /dev/null
+++ b/include/crypto/tpm2_key.h
@@ -0,0 +1,46 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+#ifndef __LINUX_TPM2_KEY_H__
+#define __LINUX_TPM2_KEY_H__
+
+#include <linux/oid_registry.h>
+#include <linux/slab.h>
+
+#define TPM2_KEY_BYTES_MAX 1024
+
+/* TPM2 Structures 12.2.4: TPMT_PUBLIC */
+struct tpm2_key_desc {
+ __be16 type;
+ __be16 name_alg;
+ __be32 object_attributes;
+ __be16 policy_size;
+} __packed;
+
+/* Decoded TPM2 ASN.1 key. */
+struct tpm2_key {
+ u8 data[2 * TPM2_KEY_BYTES_MAX];
+ struct tpm2_key_desc *desc;
+ u16 priv_len;
+ u16 pub_len;
+ u32 parent;
+ enum OID oid;
+ char oid_str[64];
+};
+
+struct tpm2_key *tpm2_key_decode(const u8 *src, u32 src_len);
+
+static inline const void *tpm2_key_data(const struct tpm2_key *key)
+{
+ return &key->data[0];
+}
+
+static inline u16 tpm2_key_type(const struct tpm2_key *key)
+{
+ return be16_to_cpu(key->desc->type);
+}
+
+static inline int tpm2_key_policy_size(const struct tpm2_key *key)
+{
+ return be16_to_cpu(key->desc->policy_size);
+}
+
+#endif /* __LINUX_TPM2_KEY_H__ */
diff --git a/security/keys/trusted-keys/Kconfig b/security/keys/trusted-keys/Kconfig
index 1fb8aa001995..00d9489384ac 100644
--- a/security/keys/trusted-keys/Kconfig
+++ b/security/keys/trusted-keys/Kconfig
@@ -9,9 +9,9 @@ config TRUSTED_KEYS_TPM
select CRYPTO_HMAC
select CRYPTO_SHA1
select CRYPTO_HASH_INFO
+ select CRYPTO_TPM2_KEY
select ASN1_ENCODER
select OID_REGISTRY
- select ASN1
select HAVE_TRUSTED_KEYS
help
Enable use of the Trusted Platform Module (TPM) as trusted key
diff --git a/security/keys/trusted-keys/Makefile b/security/keys/trusted-keys/Makefile
index f0f3b27f688b..2674d5c10fc9 100644
--- a/security/keys/trusted-keys/Makefile
+++ b/security/keys/trusted-keys/Makefile
@@ -7,9 +7,7 @@ obj-$(CONFIG_TRUSTED_KEYS) += trusted.o
trusted-y += trusted_core.o
trusted-$(CONFIG_TRUSTED_KEYS_TPM) += trusted_tpm1.o

-$(obj)/trusted_tpm2.o: $(obj)/tpm2key.asn1.h
trusted-$(CONFIG_TRUSTED_KEYS_TPM) += trusted_tpm2.o
-trusted-$(CONFIG_TRUSTED_KEYS_TPM) += tpm2key.asn1.o

trusted-$(CONFIG_TRUSTED_KEYS_TEE) += trusted_tee.o

diff --git a/security/keys/trusted-keys/tpm2key.asn1 b/security/keys/trusted-keys/tpm2key.asn1
deleted file mode 100644
index f57f869ad600..000000000000
--- a/security/keys/trusted-keys/tpm2key.asn1
+++ /dev/null
@@ -1,11 +0,0 @@
----
---- ASN.1 for TPM 2.0 keys
----
-
-TPMKey ::= SEQUENCE {
- type OBJECT IDENTIFIER ({tpm2_key_type}),
- emptyAuth [0] EXPLICIT BOOLEAN OPTIONAL,
- parent INTEGER ({tpm2_key_parent}),
- pubkey OCTET STRING ({tpm2_key_pub}),
- privkey OCTET STRING ({tpm2_key_priv})
- }
diff --git a/security/keys/trusted-keys/trusted_tpm2.c b/security/keys/trusted-keys/trusted_tpm2.c
index 06c8fa7b21ae..b9e505e99e8c 100644
--- a/security/keys/trusted-keys/trusted_tpm2.c
+++ b/security/keys/trusted-keys/trusted_tpm2.c
@@ -13,11 +13,10 @@

#include <keys/trusted-type.h>
#include <keys/trusted_tpm.h>
+#include <crypto/tpm2_key.h>

#include <asm/unaligned.h>

-#include "tpm2key.asn1.h"
-
static struct tpm2_hash tpm2_hash_map[] = {
{HASH_ALGO_SHA1, TPM_ALG_SHA1},
{HASH_ALGO_SHA256, TPM_ALG_SHA256},
@@ -98,106 +97,6 @@ static int tpm2_key_encode(struct trusted_key_payload *payload,
return ret;
}

-struct tpm2_key_context {
- u32 parent;
- const u8 *pub;
- u32 pub_len;
- const u8 *priv;
- u32 priv_len;
-};
-
-static int tpm2_key_decode(struct trusted_key_payload *payload,
- struct trusted_key_options *options,
- u8 **buf)
-{
- int ret;
- struct tpm2_key_context ctx;
- u8 *blob;
-
- memset(&ctx, 0, sizeof(ctx));
-
- ret = asn1_ber_decoder(&tpm2key_decoder, &ctx, payload->blob,
- payload->blob_len);
- if (ret < 0)
- return ret;
-
- if (ctx.priv_len + ctx.pub_len > MAX_BLOB_SIZE)
- return -E2BIG;
-
- blob = kmalloc(ctx.priv_len + ctx.pub_len + 4, GFP_KERNEL);
- if (!blob)
- return -ENOMEM;
-
- *buf = blob;
- options->keyhandle = ctx.parent;
-
- memcpy(blob, ctx.priv, ctx.priv_len);
- blob += ctx.priv_len;
-
- memcpy(blob, ctx.pub, ctx.pub_len);
-
- return 0;
-}
-
-int tpm2_key_parent(void *context, size_t hdrlen,
- unsigned char tag,
- const void *value, size_t vlen)
-{
- struct tpm2_key_context *ctx = context;
- const u8 *v = value;
- int i;
-
- ctx->parent = 0;
- for (i = 0; i < vlen; i++) {
- ctx->parent <<= 8;
- ctx->parent |= v[i];
- }
-
- return 0;
-}
-
-int tpm2_key_type(void *context, size_t hdrlen,
- unsigned char tag,
- const void *value, size_t vlen)
-{
- enum OID oid = look_up_OID(value, vlen);
-
- if (oid != OID_TPMSealedData) {
- char buffer[50];
-
- sprint_oid(value, vlen, buffer, sizeof(buffer));
- pr_debug("OID is \"%s\" which is not TPMSealedData\n",
- buffer);
- return -EINVAL;
- }
-
- return 0;
-}
-
-int tpm2_key_pub(void *context, size_t hdrlen,
- unsigned char tag,
- const void *value, size_t vlen)
-{
- struct tpm2_key_context *ctx = context;
-
- ctx->pub = value;
- ctx->pub_len = vlen;
-
- return 0;
-}
-
-int tpm2_key_priv(void *context, size_t hdrlen,
- unsigned char tag,
- const void *value, size_t vlen)
-{
- struct tpm2_key_context *ctx = context;
-
- ctx->priv = value;
- ctx->priv_len = vlen;
-
- return 0;
-}
-
/**
* tpm2_buf_append_auth() - append TPMS_AUTH_COMMAND to the buffer.
*
@@ -387,22 +286,43 @@ static int tpm2_load_cmd(struct tpm_chip *chip,
struct trusted_key_options *options,
u32 *blob_handle)
{
- struct tpm_buf buf;
unsigned int private_len;
unsigned int public_len;
unsigned int blob_len;
- u8 *blob, *pub;
- int rc;
+ struct tpm2_key *key;
+ const u8 *blob, *pub;
+ struct tpm_buf buf;
u32 attrs;
+ int rc;

- rc = tpm2_key_decode(payload, options, &blob);
- if (rc) {
- /* old form */
+ key = tpm2_key_decode(payload->blob, payload->blob_len);
+ if (IS_ERR(key)) {
+ /* Get the error code and reset the pointer to the key: */
+ rc = PTR_ERR(key);
+ key = NULL;
+
+ if (rc == -ENOMEM)
+ return -ENOMEM;
+
+ /* A sanity check, as only -EBADMSG or -ENOMEM are expected: */
+ if (rc != -EBADMSG)
+ pr_err("tpm2_key_decode(): spurious error code %d\n", rc);
+
+ /* Fallback to the legacy format: */
blob = payload->blob;
payload->old_format = 1;
+ } else {
+ blob = tpm2_key_data(key);
+ if (key->oid != OID_TPMSealedData) {
+ kfree(key);
+ return -EBADMSG;
+ }
}

- /* new format carries keyhandle but old format doesn't */
+ /*
+ * Must be non-zero here, either extracted from the ASN.1 for the new
+ * format or specified on the command line for the old.
+ */
if (!options->keyhandle)
return -EINVAL;

@@ -464,8 +384,7 @@ static int tpm2_load_cmd(struct tpm_chip *chip,
(__be32 *) &buf.data[TPM_HEADER_SIZE]);

out:
- if (blob != payload->blob)
- kfree(blob);
+ kfree(key);
tpm_buf_destroy(&buf);

if (rc > 0)
--
2.45.1