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Date: Wed, 05 Sep 2018 22:56:29 +0100
From: David Howells <dhowells@...hat.com>
To: jmorris@...ei.org
Cc: denkenz@...il.com, keyrings@...r.kernel.org,
linux-security-module@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH 20/22] KEYS: asym_tpm: Implement signature verification
From: Denis Kenzior <denkenz@...il.com>
This patch implements the verify_signature operation. The public key
portion extracted from the TPM key blob is used. The operation is
performed entirely in software using the crypto API.
Signed-off-by: Denis Kenzior <denkenz@...il.com>
Signed-off-by: David Howells <dhowells@...hat.com>
---
crypto/asymmetric_keys/asym_tpm.c | 106 +++++++++++++++++++++++++++++++++++--
1 file changed, 100 insertions(+), 6 deletions(-)
diff --git a/crypto/asymmetric_keys/asym_tpm.c b/crypto/asymmetric_keys/asym_tpm.c
index 6f5d5cf98910..a38ba375675e 100644
--- a/crypto/asymmetric_keys/asym_tpm.c
+++ b/crypto/asymmetric_keys/asym_tpm.c
@@ -15,6 +15,7 @@
#include <keys/asymmetric-subtype.h>
#include <keys/trusted.h>
#include <crypto/asym_tpm_subtype.h>
+#include <crypto/public_key.h>
#define TPM_ORD_FLUSHSPECIFIC 186
#define TPM_ORD_LOADKEY2 65
@@ -286,12 +287,16 @@ static uint32_t derive_pub_key(const void *pub_key, uint32_t len, uint8_t *buf)
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)");
+ if (!hash_algo) {
+ strcpy(alg_name, "pkcs1pad(rsa)");
+ return 0;
+ }
+
+ if (snprintf(alg_name, CRYPTO_MAX_ALG_NAME, "pkcs1pad(rsa,%s)",
+ hash_algo) >= CRYPTO_MAX_ALG_NAME)
+ return -EINVAL;
+
return 0;
}
@@ -342,7 +347,8 @@ static int tpm_key_query(const struct kernel_pkey_params *params,
info->max_dec_size = tk->key_len / 8;
info->supported_ops = KEYCTL_SUPPORTS_ENCRYPT |
- KEYCTL_SUPPORTS_DECRYPT;
+ KEYCTL_SUPPORTS_DECRYPT |
+ KEYCTL_SUPPORTS_VERIFY;
ret = 0;
error_free_tfm:
@@ -487,6 +493,93 @@ static int tpm_key_eds_op(struct kernel_pkey_params *params,
return ret;
}
+/*
+ * Verify a signature using a public key.
+ */
+static int tpm_key_verify_signature(const struct key *key,
+ const struct public_key_signature *sig)
+{
+ const struct tpm_key *tk = key->payload.data[asym_crypto];
+ struct crypto_wait cwait;
+ struct crypto_akcipher *tfm;
+ struct akcipher_request *req;
+ struct scatterlist sig_sg, digest_sg;
+ char alg_name[CRYPTO_MAX_ALG_NAME];
+ uint8_t der_pub_key[PUB_KEY_BUF_SIZE];
+ uint32_t der_pub_key_len;
+ void *output;
+ unsigned int outlen;
+ int ret;
+
+ pr_devel("==>%s()\n", __func__);
+
+ BUG_ON(!tk);
+ BUG_ON(!sig);
+ BUG_ON(!sig->s);
+
+ if (!sig->digest)
+ return -ENOPKG;
+
+ ret = determine_akcipher(sig->encoding, sig->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;
+
+ ret = -ENOMEM;
+ req = akcipher_request_alloc(tfm, GFP_KERNEL);
+ if (!req)
+ goto error_free_tfm;
+
+ ret = -ENOMEM;
+ outlen = crypto_akcipher_maxsize(tfm);
+ output = kmalloc(outlen, GFP_KERNEL);
+ if (!output)
+ goto error_free_req;
+
+ sg_init_one(&sig_sg, sig->s, sig->s_size);
+ sg_init_one(&digest_sg, output, outlen);
+ akcipher_request_set_crypt(req, &sig_sg, &digest_sg, sig->s_size,
+ outlen);
+ crypto_init_wait(&cwait);
+ akcipher_request_set_callback(req, CRYPTO_TFM_REQ_MAY_BACKLOG |
+ CRYPTO_TFM_REQ_MAY_SLEEP,
+ crypto_req_done, &cwait);
+
+ /* Perform the verification calculation. This doesn't actually do the
+ * verification, but rather calculates the hash expected by the
+ * signature and returns that to us.
+ */
+ ret = crypto_wait_req(crypto_akcipher_verify(req), &cwait);
+ if (ret)
+ goto out_free_output;
+
+ /* Do the actual verification step. */
+ if (req->dst_len != sig->digest_size ||
+ memcmp(sig->digest, output, sig->digest_size) != 0)
+ ret = -EKEYREJECTED;
+
+out_free_output:
+ kfree(output);
+error_free_req:
+ akcipher_request_free(req);
+error_free_tfm:
+ crypto_free_akcipher(tfm);
+ pr_devel("<==%s() = %d\n", __func__, ret);
+ if (WARN_ON_ONCE(ret > 0))
+ ret = -EINVAL;
+ return ret;
+}
+
/*
* Parse enough information out of TPM_KEY structure:
* TPM_STRUCT_VER -> 4 bytes
@@ -645,6 +738,7 @@ struct asymmetric_key_subtype asym_tpm_subtype = {
.destroy = asym_tpm_destroy,
.query = tpm_key_query,
.eds_op = tpm_key_eds_op,
+ .verify_signature = tpm_key_verify_signature,
};
EXPORT_SYMBOL_GPL(asym_tpm_subtype);
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