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-rw-r--r--crypto/asymmetric_keys/asym_tpm.c135
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);