diff options
| -rw-r--r-- | crypto/asymmetric_keys/asym_tpm.c | 135 |
1 files changed, 135 insertions, 0 deletions
diff --git a/crypto/asymmetric_keys/asym_tpm.c b/crypto/asymmetric_keys/asym_tpm.c index 308c51e055a4..837472d107d5 100644 --- a/crypto/asymmetric_keys/asym_tpm.c +++ b/crypto/asymmetric_keys/asym_tpm.c @@ -7,11 +7,25 @@ #include <linux/seq_file.h> #include <linux/scatterlist.h> #include <linux/tpm.h> +#include <crypto/akcipher.h> #include <asm/unaligned.h> #include <keys/asymmetric-subtype.h> #include <crypto/asym_tpm_subtype.h> /* + * Maximum buffer size for the BER/DER encoded public key. The public key + * is of the form SEQUENCE { INTEGER n, INTEGER e } where n is a maximum 2048 + * bit key and e is usually 65537 + * The encoding overhead is: + * - max 4 bytes for SEQUENCE + * - max 4 bytes for INTEGER n type/length + * - 257 bytes of n + * - max 2 bytes for INTEGER e type/length + * - 3 bytes of e + */ +#define PUB_KEY_BUF_SIZE (4 + 4 + 257 + 2 + 3) + +/* * Provide a part of a description of the key for /proc/keys. */ static void asym_tpm_describe(const struct key *asymmetric_key, @@ -38,6 +52,126 @@ static void asym_tpm_destroy(void *payload0, void *payload3) kfree(tk); } +/* How many bytes will it take to encode the length */ +static inline uint32_t definite_length(uint32_t len) +{ + if (len <= 127) + return 1; + if (len <= 255) + return 2; + return 3; +} + +static inline uint8_t *encode_tag_length(uint8_t *buf, uint8_t tag, + uint32_t len) +{ + *buf++ = tag; + + if (len <= 127) { + buf[0] = len; + return buf + 1; + } + + if (len <= 255) { + buf[0] = 0x81; + buf[1] = len; + return buf + 2; + } + + buf[0] = 0x82; + put_unaligned_be16(len, buf + 1); + return buf + 3; +} + +static uint32_t derive_pub_key(const void *pub_key, uint32_t len, uint8_t *buf) +{ + uint8_t *cur = buf; + uint32_t n_len = definite_length(len) + 1 + len + 1; + uint32_t e_len = definite_length(3) + 1 + 3; + uint8_t e[3] = { 0x01, 0x00, 0x01 }; + + /* SEQUENCE */ + cur = encode_tag_length(cur, 0x30, n_len + e_len); + /* INTEGER n */ + cur = encode_tag_length(cur, 0x02, len + 1); + cur[0] = 0x00; + memcpy(cur + 1, pub_key, len); + cur += len + 1; + cur = encode_tag_length(cur, 0x02, sizeof(e)); + memcpy(cur, e, sizeof(e)); + cur += sizeof(e); + + return cur - buf; +} + +/* + * Determine the crypto algorithm name. + */ +static int determine_akcipher(const char *encoding, const char *hash_algo, + char alg_name[CRYPTO_MAX_ALG_NAME]) +{ + /* TODO: We don't support hashing yet */ + if (hash_algo) + return -ENOPKG; + + if (strcmp(encoding, "pkcs1") == 0) { + strcpy(alg_name, "pkcs1pad(rsa)"); + return 0; + } + + if (strcmp(encoding, "raw") == 0) { + strcpy(alg_name, "rsa"); + return 0; + } + + return -ENOPKG; +} + +/* + * Query information about a key. + */ +static int tpm_key_query(const struct kernel_pkey_params *params, + struct kernel_pkey_query *info) +{ + struct tpm_key *tk = params->key->payload.data[asym_crypto]; + int ret; + char alg_name[CRYPTO_MAX_ALG_NAME]; + struct crypto_akcipher *tfm; + uint8_t der_pub_key[PUB_KEY_BUF_SIZE]; + uint32_t der_pub_key_len; + int len; + + /* TPM only works on private keys, public keys still done in software */ + ret = determine_akcipher(params->encoding, params->hash_algo, alg_name); + if (ret < 0) + return ret; + + tfm = crypto_alloc_akcipher(alg_name, 0, 0); + if (IS_ERR(tfm)) + return PTR_ERR(tfm); + + der_pub_key_len = derive_pub_key(tk->pub_key, tk->pub_key_len, + der_pub_key); + + ret = crypto_akcipher_set_pub_key(tfm, der_pub_key, der_pub_key_len); + if (ret < 0) + goto error_free_tfm; + + len = crypto_akcipher_maxsize(tfm); + + info->key_size = tk->key_len; + info->max_data_size = tk->key_len / 8; + info->max_sig_size = len; + info->max_enc_size = len; + info->max_dec_size = tk->key_len / 8; + + ret = 0; +error_free_tfm: + crypto_free_akcipher(tfm); + pr_devel("<==%s() = %d\n", __func__, ret); + return ret; +} + /* * Parse enough information out of TPM_KEY structure: * TPM_STRUCT_VER -> 4 bytes @@ -194,6 +328,7 @@ struct asymmetric_key_subtype asym_tpm_subtype = { .name_len = sizeof("asym_tpm") - 1, .describe = asym_tpm_describe, .destroy = asym_tpm_destroy, + .query = tpm_key_query, }; EXPORT_SYMBOL_GPL(asym_tpm_subtype); |