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Subject[PATCH 19/22] KEYS: asym_tpm: Implement the decrypt operation
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From: Denis Kenzior <denkenz@gmail.com>

This patch implements the pkey_decrypt operation using the private key
blob. The blob is first loaded into the TPM via tpm_loadkey2. Once the
handle is obtained, tpm_unbind operation is used to decrypt the data on
the TPM and the result is returned. The key loaded by tpm_loadkey2 is
then evicted via tpm_flushspecific operation.

This patch assumes that the SRK authorization is a well known 20-byte of
zeros and the same holds for the key authorization of the provided key.

Signed-off-by: Denis Kenzior <denkenz@gmail.com>
Signed-off-by: David Howells <dhowells@redhat.com>
---

crypto/asymmetric_keys/asym_tpm.c | 58 ++++++++++++++++++++++++++++++++++++-
1 file changed, 57 insertions(+), 1 deletion(-)

diff --git a/crypto/asymmetric_keys/asym_tpm.c b/crypto/asymmetric_keys/asym_tpm.c
index e893b5212222..6f5d5cf98910 100644
--- a/crypto/asymmetric_keys/asym_tpm.c
+++ b/crypto/asymmetric_keys/asym_tpm.c
@@ -341,7 +341,8 @@ static int tpm_key_query(const struct kernel_pkey_params *params,
info->max_enc_size = len;
info->max_dec_size = tk->key_len / 8;

- info->supported_ops = KEYCTL_SUPPORTS_ENCRYPT;
+ info->supported_ops = KEYCTL_SUPPORTS_ENCRYPT |
+ KEYCTL_SUPPORTS_DECRYPT;

ret = 0;
error_free_tfm:
@@ -410,6 +411,58 @@ static int tpm_key_encrypt(struct tpm_key *tk,
return ret;
}

+/*
+ * Decryption operation is performed with the private key in the TPM.
+ */
+static int tpm_key_decrypt(struct tpm_key *tk,
+ struct kernel_pkey_params *params,
+ const void *in, void *out)
+{
+ struct tpm_buf *tb;
+ uint32_t keyhandle;
+ uint8_t srkauth[SHA1_DIGEST_SIZE];
+ uint8_t keyauth[SHA1_DIGEST_SIZE];
+ int r;
+
+ pr_devel("==>%s()\n", __func__);
+
+ if (params->hash_algo)
+ return -ENOPKG;
+
+ if (strcmp(params->encoding, "pkcs1"))
+ return -ENOPKG;
+
+ tb = kzalloc(sizeof(*tb), GFP_KERNEL);
+ if (!tb)
+ return -ENOMEM;
+
+ /* TODO: Handle a non-all zero SRK authorization */
+ memset(srkauth, 0, sizeof(srkauth));
+
+ r = tpm_loadkey2(tb, SRKHANDLE, srkauth,
+ tk->blob, tk->blob_len, &keyhandle);
+ if (r < 0) {
+ pr_devel("loadkey2 failed (%d)\n", r);
+ goto error;
+ }
+
+ /* TODO: Handle a non-all zero key authorization */
+ memset(keyauth, 0, sizeof(keyauth));
+
+ r = tpm_unbind(tb, keyhandle, keyauth,
+ in, params->in_len, out, params->out_len);
+ if (r < 0)
+ pr_devel("tpm_unbind failed (%d)\n", r);
+
+ if (tpm_flushspecific(tb, keyhandle) < 0)
+ pr_devel("flushspecific failed (%d)\n", r);
+
+error:
+ kzfree(tb);
+ pr_devel("<==%s() = %d\n", __func__, r);
+ return r;
+}
+
/*
* Do encryption, decryption and signing ops.
*/
@@ -424,6 +477,9 @@ static int tpm_key_eds_op(struct kernel_pkey_params *params,
case kernel_pkey_encrypt:
ret = tpm_key_encrypt(tk, params, in, out);
break;
+ case kernel_pkey_decrypt:
+ ret = tpm_key_decrypt(tk, params, in, out);
+ break;
default:
BUG();
}
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