Re: [PATCH v7 5/5] keys: asymmetric: Add tpm2_key_ecdsa

Stefan Berger
2024-05-28T23:16:03Z

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@linux.ibm.com>
> Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org>
> ---
> 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;
> +}
> +