Re: [PATCH v7 5/5] keys: asymmetric: Add tpm2_key_ecdsa
From: Stefan Berger
Date: Tue May 28 2024 - 19:16:15 EST
On 5/28/24 17:08, Jarkko Sakkinen wrote:
* Asymmetric TPM2 ECDSA key with signing and verification.
* Enabled with CONFIG_ASYMMETRIC_TPM2_KEY_ECDSA_SUBTYPE.
Cc: Stefan Berger <stefanb@xxxxxxxxxxxxx>
Signed-off-by: Jarkko Sakkinen <jarkko@xxxxxxxxxx>
---
v7:
* Rewrote the signature encoder.
* Added the missing sha256() call to the signature verifier.
v6:
* The very first version.
* Stefan: any idea why the signature give -EKEYREJECTED?
---
crypto/asymmetric_keys/Kconfig | 15 +
crypto/asymmetric_keys/Makefile | 1 +
crypto/asymmetric_keys/tpm2_key_ecdsa.c | 462 ++++++++++++++++++++++++
crypto/ecdsa.c | 1 -
drivers/char/tpm/tpm-buf.c | 2 +-
include/linux/tpm.h | 7 +
6 files changed, 486 insertions(+), 2 deletions(-)
create mode 100644 crypto/asymmetric_keys/tpm2_key_ecdsa.c
diff --git a/crypto/asymmetric_keys/Kconfig b/crypto/asymmetric_keys/Kconfig
index 9d88c1190621..c97f11e0340c 100644
--- a/crypto/asymmetric_keys/Kconfig
+++ b/crypto/asymmetric_keys/Kconfig
@@ -24,6 +24,21 @@ config ASYMMETRIC_PUBLIC_KEY_SUBTYPE
appropriate hash algorithms (such as SHA-1) must be available.
ENOPKG will be reported if the requisite algorithm is unavailable.
+config ASYMMETRIC_TPM2_KEY_ECDSA_SUBTYPE
+ tristate "Asymmetric TPM2 ECDSA crypto algorithm subtype"
+ depends on TCG_TPM
+ select CRYPTO_ECDSA
+ select CRYPTO_SHA256
+ select CRYPTO_HASH_INFO
+ select CRYPTO_TPM2_KEY
+ select ASN1
+ select ASN1_ENCODER
+ help
+ This option provides support for asymmetric TPM2 key type handling.
+ If signature generation and/or verification are to be used,
+ appropriate hash algorithms (such as SHA-256) must be available.
+ ENOPKG will be reported if the requisite algorithm is unavailable.
+
config ASYMMETRIC_TPM2_KEY_RSA_SUBTYPE
tristate "Asymmetric TPM2 RSA crypto algorithm subtype"
depends on TCG_TPM
diff --git a/crypto/asymmetric_keys/Makefile b/crypto/asymmetric_keys/Makefile
index c6da84607824..0843d2268a69 100644
--- a/crypto/asymmetric_keys/Makefile
+++ b/crypto/asymmetric_keys/Makefile
@@ -11,6 +11,7 @@ asymmetric_keys-y := \
signature.o
obj-$(CONFIG_ASYMMETRIC_PUBLIC_KEY_SUBTYPE) += public_key.o
+obj-$(CONFIG_ASYMMETRIC_TPM2_KEY_ECDSA_SUBTYPE) += tpm2_key_ecdsa.o
obj-$(CONFIG_ASYMMETRIC_TPM2_KEY_RSA_SUBTYPE) += tpm2_key_rsa.o
#
diff --git a/crypto/asymmetric_keys/tpm2_key_ecdsa.c b/crypto/asymmetric_keys/tpm2_key_ecdsa.c
new file mode 100644
index 000000000000..e2f599a0ffe0
--- /dev/null
+++ b/crypto/asymmetric_keys/tpm2_key_ecdsa.c
@@ -0,0 +1,462 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/* Asymmetric TPM2 ECDSA key subtype.
+ *
+ * See Documentation/crypto/asymmetric-keys.rst
+ */
+
+#include <asm/unaligned.h>
+#include <crypto/internal/ecc.h>
+#include <crypto/akcipher.h>
+#include <crypto/sha2.h>
+#include <crypto/public_key.h>
+#include <crypto/tpm2_key.h>
+#include <keys/asymmetric-parser.h>
+#include <keys/asymmetric-subtype.h>
+#include <linux/asn1_encoder.h>
+#include <linux/keyctl.h>
+#include <linux/module.h>
+#include <linux/scatterlist.h>
+#include <linux/slab.h>
+#include <linux/tpm.h>
+
+#undef pr_fmt
+#define pr_fmt(fmt) "tpm2_key_ecdsa: "fmt
+
+struct tpm2_ecc_parms {
+ __be16 symmetric;
+ __be16 scheme;
+ __be16 ecc;
+ __be16 kdf;
+};
+
+static const u8 *tpm2_key_ecdsa_ecc_x(const struct tpm2_key *key)
+{
+ const off_t o = key->priv_len + 2 + sizeof(*key->desc);
+
+ return &key->data[o + sizeof(struct tpm2_ecc_parms)];
+}
+
+static const u8 *tpm2_key_ecdsa_ecc_y(const struct tpm2_key *key)
+{
+ const u8 *x = tpm2_key_ecdsa_ecc_x(key);
+ u16 x_size = get_unaligned_be16(&x[0]);
+
+ /* +2 from the size field: */
+ return &x[2 + x_size];
+}
+
+static void tpm2_key_ecdsa_describe(const struct key *asymmetric_key,
+ struct seq_file *m)
+{
+ struct tpm2_key *key = asymmetric_key->payload.data[asym_crypto];
+
+ if (!key) {
+ pr_err("key missing");
+ return;
+ }
+
+ seq_puts(m, "TPM2/ECDSA");
+}
+
+static void tpm2_key_ecdsa_destroy(void *payload0, void *payload3)
+{
+ struct tpm2_key *key = payload0;
+
+ if (!key)
+ return;
+
+ kfree(key);
+}
+
+static const char *tpm2_ecc_name(u16 ecc)
+{
+ const char *name;
+
+ switch (ecc) {
+ case TPM2_ECC_NIST_P521:
+ name = "ecdsa-nist-p521";
+ break;
+ case TPM2_ECC_NIST_P384:
+ name = "ecdsa-nist-p384";
+ break;
+ default:
+ name = "ecdsa-nist-p256";
+ break;
+ }
+
+ return name;
+}
+
+static int tpm2_key_ecdsa_query(const struct kernel_pkey_params *params,
+ struct kernel_pkey_query *info)
+{
+ const struct tpm2_key *key = params->key->payload.data[asym_crypto];
+ const off_t o = key->priv_len + 2 + sizeof(*key->desc);
+ const struct tpm2_ecc_parms *p =
+ (const struct tpm2_ecc_parms *)&key->data[o];
+ u16 ecc = be16_to_cpu(p->ecc);
+ const char *ecc_name = tpm2_ecc_name(ecc);
+ const u8 *x = tpm2_key_ecdsa_ecc_x(key);
+ u16 x_size = get_unaligned_be16(&x[0]);
+ struct crypto_akcipher *tfm;
+ char data[256];
Due to NIST p521 1 + 2 * 66 = 133 should be enough.
If x_size exceeeds 66 then something is wrong.
+ u8 *ptr;
+ int ret;
+
+ memset(data, 0, sizeof(data));
+
+ tfm = crypto_alloc_akcipher(ecc_name, 0, 0);
+ if (IS_ERR(tfm))
+ return PTR_ERR(tfm);
+
+ /* Probe for ecdsa_set_pub_key(): */
+ ptr = &data[0];
+ *ptr++ = 0x04; /* uncompressed */
+ memcpy(&ptr[0], &x[2], x_size);
+ memcpy(&ptr[x_size], &x[2 + x_size + 2], x_size);
+ ret = crypto_akcipher_set_pub_key(tfm, data, 2 * x_size + 1);
+ crypto_free_akcipher(tfm);
+ if (ret < 0)
+ return ret;
+
+ info->max_sig_size = 256;
+ info->key_size = 256;
+ info->max_data_size = 256;
+ info->supported_ops = KEYCTL_SUPPORTS_SIGN | KEYCTL_SUPPORTS_VERIFY;
+ return ret;
+}
+
+static int tpm2_key_ecdsa_sign(struct tpm_chip *chip, struct tpm2_key *key,
+ struct kernel_pkey_params *params,
+ const void *in, void *out)
+{
+ u8 r[SHA256_DIGEST_SIZE], s[SHA256_DIGEST_SIZE];
+ u32 in_len = params->in_len;
+ bool r_0, s_0;
+ struct tpm_header *head;
+ struct tpm_buf buf;
+ u32 key_handle;
+ u8 *ptr = out;
+ off_t offset;
+ int ret;
+
+
+ /* Require explicit hash algorithm: */
+ if (!params->hash_algo)
+ return -EINVAL;
+
+ /* Currently only support SHA256: */
+ if (!!strcmp(params->hash_algo, "sha256"))
+ return -EINVAL;
+
+ ret = tpm_try_get_ops(chip);
+ if (ret)
+ return ret;
+
+ ret = tpm2_start_auth_session(chip);
+ if (ret)
+ goto err_ops;
+
+ ret = tpm_buf_init(&buf, TPM2_ST_SESSIONS, TPM2_CC_LOAD);
+ if (ret < 0) {
+ tpm2_end_auth_session(chip);
+ goto err_ops;
+ }
+
+ tpm_buf_append_name(chip, &buf, key->parent, NULL);
+ tpm_buf_append_hmac_session(chip, &buf, TPM2_SA_CONTINUE_SESSION |
+ TPM2_SA_ENCRYPT, NULL, 0);
+ tpm_buf_append(&buf, &key->data[0], key->priv_len + key->pub_len);
+ if (buf.flags & TPM_BUF_OVERFLOW) {
+ tpm2_end_auth_session(chip);
+ ret = -E2BIG;
+ goto err_buf;
+ }
+ tpm_buf_fill_hmac_session(chip, &buf);
+ ret = tpm_transmit_cmd(chip, &buf, 4, "ECDSA loading");
+ ret = tpm_buf_check_hmac_response(chip, &buf, ret);
+ if (ret) {
+ tpm2_end_auth_session(chip);
+ ret = -EIO;
+ goto err_buf;
+ }
+
+ key_handle = be32_to_cpup((__be32 *)&buf.data[TPM_HEADER_SIZE]);
+
+ tpm_buf_reset(&buf, TPM2_ST_SESSIONS, TPM2_CC_SIGN);
+ tpm_buf_append_name(chip, &buf, key_handle, NULL);
+ tpm_buf_append_hmac_session(chip, &buf, TPM2_SA_DECRYPT, NULL, 0);
+
+ sha256(in, in_len, r);
+ tpm_buf_append_u16(&buf, SHA256_DIGEST_SIZE);
+ tpm_buf_append(&buf, r, SHA256_DIGEST_SIZE);
+ tpm_buf_append_u16(&buf, TPM_ALG_ECDSA);
+ tpm_buf_append_u16(&buf, TPM_ALG_SHA256);
+
+ /* 10.7.2 A NULL Ticket */
+ tpm_buf_append_u16(&buf, TPM2_ST_HASHCHECK);
+ tpm_buf_append_u32(&buf, TPM2_RH_NULL);
+ tpm_buf_append_u16(&buf, 0);
+
+ tpm_buf_fill_hmac_session(chip, &buf);
+ ret = tpm_transmit_cmd(chip, &buf, 4, "ECDSA signing");
+ ret = tpm_buf_check_hmac_response(chip, &buf, ret);
+ if (ret) {
+ tpm2_end_auth_session(chip);
+ ret = -EIO;
+ goto err_key_handle;
+ }
+
+ /* Move to parameters: */
+ head = (struct tpm_header *)buf.data;
+ offset = sizeof(*head);
+ if (be16_to_cpu(head->tag) == TPM2_ST_SESSIONS)
+ offset += 4;
+
+ ret = -EIO;
+
+ /* Copy R: */
+ if (tpm_buf_read_u16(&buf, &offset) != TPM_ALG_ECDSA ||
+ tpm_buf_read_u16(&buf, &offset) != TPM_ALG_SHA256 ||
+ tpm_buf_read_u16(&buf, &offset) != SHA256_DIGEST_SIZE) {
+ pr_warn("offset=%u\n", offset);
+ goto err_key_handle;
+ }
+
+ tpm_buf_read(&buf, &offset, SHA256_DIGEST_SIZE, r);
+ r_0 = (r[0] & 0x80) != 0;
+ pr_info("r_0=%d\n", r_0);
+
+ /* Copy S: */
+ if (tpm_buf_read_u16(&buf, &offset) != SHA256_DIGEST_SIZE) {
+ pr_warn("offset=%u\n", offset);
+ goto err_key_handle;
+ }
+
+ tpm_buf_read(&buf, &offset, SHA256_DIGEST_SIZE, s);
+ s_0 = (r[0] & 0x80) != 0;
+ pr_info("s_0=%d\n", r_0);
+
+ /* Encode the ASN.1 signature: */
+#define TPM2_KEY_ECDSA_SIG_SIZE (2 + 2 * (2 + SHA256_DIGEST_SIZE) + r_0 + s_0)
+ pr_info("sig_size=%d\n", TPM2_KEY_ECDSA_SIG_SIZE);
+ ptr[0] = 0x30; /* SEQUENCE */
+ ptr[1] = TPM2_KEY_ECDSA_SIG_SIZE - 2;
+#define TPM2_KEY_ECDSA_SIG_R_TAG 2
+#define TPM2_KEY_ECDSA_SIG_R_SIZE 3
+#define TPM2_KEY_ECDSA_SIG_R_BODY 4
+ ptr[TPM2_KEY_ECDSA_SIG_R_TAG] = 0x02; /* INTEGER */
+ ptr[TPM2_KEY_ECDSA_SIG_R_SIZE] = SHA256_DIGEST_SIZE + r_0;
The size of the signature has nothing to do with the size of the hash.
SHA256_DIGEST_SIZE (32) happens to match the number of bytes of a
coordinate of prime256v1 / NIST p256 but should fail when you use
secp521r1 / NIST p521 since then r or s may then be 66 or 67 bytes (if
most sign. bit is set) long.
+ ptr[TPM2_KEY_ECDSA_SIG_R_BODY] = 0x00; /* maybe dummy write */
+ memcpy(&ptr[TPM2_KEY_ECDSA_SIG_R_BODY + r_0], r, SHA256_DIGEST_SIZE);
+#define TPM2_KEY_ECDSA_SIG_S_TAG (4 + r_0 + SHA256_DIGEST_SIZE)
+#define TPM2_KEY_ECDSA_SIG_S_SIZE (5 + r_0 + SHA256_DIGEST_SIZE)
+#define TPM2_KEY_ECDSA_SIG_S_BODY (6 + r_0 + SHA256_DIGEST_SIZE)
+ ptr[TPM2_KEY_ECDSA_SIG_S_TAG] = 0x02; /* INTEGER */
+ ptr[TPM2_KEY_ECDSA_SIG_S_SIZE] = SHA256_DIGEST_SIZE + s_0;
+ ptr[TPM2_KEY_ECDSA_SIG_S_BODY] = 0x00; /* maybe dummy write */
+ memcpy(&ptr[TPM2_KEY_ECDSA_SIG_S_BODY + s_0], s, SHA256_DIGEST_SIZE);
+ ret = TPM2_KEY_ECDSA_SIG_SIZE;
+
+err_key_handle:
+ tpm2_flush_context(chip, key_handle);
+
+err_buf:
+ tpm_buf_destroy(&buf);
+
+err_ops:
+ tpm_put_ops(chip);
+ return ret;
+}
+