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Subject: [PATCH 18/22] KEYS: asym_tpm: Implement tpm_unbind
From:   David Howells <dhowells@redhat.com>
To:     jmorris@namei.org
Cc:     denkenz@gmail.com, keyrings@vger.kernel.org,
        linux-security-module@vger.kernel.org, linux-kernel@vger.kernel.org
Date:   Wed, 05 Sep 2018 22:56:16 +0100
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From: Denis Kenzior <denkenz@gmail.com>

Signed-off-by: Denis Kenzior <denkenz@gmail.com>
Reviewed-by: James Morris <james.morris@microsoft.com>
Signed-off-by: David Howells <dhowells@redhat.com>
---

 crypto/asymmetric_keys/asym_tpm.c |   82 +++++++++++++++++++++++++++++++++++++
 1 file changed, 82 insertions(+)

diff --git a/crypto/asymmetric_keys/asym_tpm.c b/crypto/asymmetric_keys/asym_tpm.c
index 6a2d33014ecc..e893b5212222 100644
--- a/crypto/asymmetric_keys/asym_tpm.c
+++ b/crypto/asymmetric_keys/asym_tpm.c
@@ -18,8 +18,10 @@
 
 #define TPM_ORD_FLUSHSPECIFIC	186
 #define TPM_ORD_LOADKEY2	65
+#define TPM_ORD_UNBIND		30
 #define TPM_LOADKEY2_SIZE		59
 #define TPM_FLUSHSPECIFIC_SIZE		18
+#define TPM_UNBIND_SIZE			63
 
 #define TPM_RT_KEY                      0x00000001
 
@@ -106,6 +108,86 @@ static int tpm_flushspecific(struct tpm_buf *tb, uint32_t handle)
 	return trusted_tpm_send(tb->data, MAX_BUF_SIZE);
 }
 
+/*
+ * Decrypt a blob provided by userspace using a specific key handle.
+ * The handle is a well known handle or previously loaded by e.g. LoadKey2
+ */
+static int tpm_unbind(struct tpm_buf *tb,
+			uint32_t keyhandle, unsigned char *keyauth,
+			const unsigned char *blob, uint32_t bloblen,
+			void *out, uint32_t outlen)
+{
+	unsigned char nonceodd[TPM_NONCE_SIZE];
+	unsigned char enonce[TPM_NONCE_SIZE];
+	unsigned char authdata[SHA1_DIGEST_SIZE];
+	uint32_t authhandle = 0;
+	unsigned char cont = 0;
+	uint32_t ordinal;
+	uint32_t datalen;
+	int ret;
+
+	ordinal = htonl(TPM_ORD_UNBIND);
+	datalen = htonl(bloblen);
+
+	/* session for loading the key */
+	ret = oiap(tb, &authhandle, enonce);
+	if (ret < 0) {
+		pr_info("oiap failed (%d)\n", ret);
+		return ret;
+	}
+
+	/* generate odd nonce */
+	ret = tpm_get_random(NULL, nonceodd, TPM_NONCE_SIZE);
+	if (ret < 0) {
+		pr_info("tpm_get_random failed (%d)\n", ret);
+		return ret;
+	}
+
+	/* calculate authorization HMAC value */
+	ret = TSS_authhmac(authdata, keyauth, SHA1_DIGEST_SIZE, enonce,
+			   nonceodd, cont, sizeof(uint32_t), &ordinal,
+			   sizeof(uint32_t), &datalen,
+			   bloblen, blob, 0, 0);
+	if (ret < 0)
+		return ret;
+
+	/* build the request buffer */
+	INIT_BUF(tb);
+	store16(tb, TPM_TAG_RQU_AUTH1_COMMAND);
+	store32(tb, TPM_UNBIND_SIZE + bloblen);
+	store32(tb, TPM_ORD_UNBIND);
+	store32(tb, keyhandle);
+	store32(tb, bloblen);
+	storebytes(tb, blob, bloblen);
+	store32(tb, authhandle);
+	storebytes(tb, nonceodd, TPM_NONCE_SIZE);
+	store8(tb, cont);
+	storebytes(tb, authdata, SHA1_DIGEST_SIZE);
+
+	ret = trusted_tpm_send(tb->data, MAX_BUF_SIZE);
+	if (ret < 0) {
+		pr_info("authhmac failed (%d)\n", ret);
+		return ret;
+	}
+
+	datalen = LOAD32(tb->data, TPM_DATA_OFFSET);
+
+	ret = TSS_checkhmac1(tb->data, ordinal, nonceodd,
+			     keyauth, SHA1_DIGEST_SIZE,
+			     sizeof(uint32_t), TPM_DATA_OFFSET,
+			     datalen, TPM_DATA_OFFSET + sizeof(uint32_t),
+			     0, 0);
+	if (ret < 0) {
+		pr_info("TSS_checkhmac1 failed (%d)\n", ret);
+		return ret;
+	}
+
+	memcpy(out, tb->data + TPM_DATA_OFFSET + sizeof(uint32_t),
+	       min(outlen, datalen));
+
+	return datalen;
+}
+
 /*
  * 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