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Subject[PATCH 11/22] KEYS: asym_tpm: extract key size & public key
From
Date
From: Denis Kenzior <denkenz@gmail.com>

The parsed BER/DER blob obtained from user space contains a TPM_Key
structure. This structure has some information about the key as well as
the public key portion.

This patch extracts this information for future use.

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

crypto/asymmetric_keys/asym_tpm.c | 112 +++++++++++++++++++++++++++++++++++++
include/crypto/asym_tpm_subtype.h | 3 +
2 files changed, 115 insertions(+)

diff --git a/crypto/asymmetric_keys/asym_tpm.c b/crypto/asymmetric_keys/asym_tpm.c
index d0b2b97e8e54..308c51e055a4 100644
--- a/crypto/asymmetric_keys/asym_tpm.c
+++ b/crypto/asymmetric_keys/asym_tpm.c
@@ -7,6 +7,7 @@
#include <linux/seq_file.h>
#include <linux/scatterlist.h>
#include <linux/tpm.h>
+#include <asm/unaligned.h>
#include <keys/asymmetric-subtype.h>
#include <crypto/asym_tpm_subtype.h>

@@ -37,6 +38,110 @@ static void asym_tpm_destroy(void *payload0, void *payload3)
kfree(tk);
}

+/*
+ * Parse enough information out of TPM_KEY structure:
+ * TPM_STRUCT_VER -> 4 bytes
+ * TPM_KEY_USAGE -> 2 bytes
+ * TPM_KEY_FLAGS -> 4 bytes
+ * TPM_AUTH_DATA_USAGE -> 1 byte
+ * TPM_KEY_PARMS -> variable
+ * UINT32 PCRInfoSize -> 4 bytes
+ * BYTE* -> PCRInfoSize bytes
+ * TPM_STORE_PUBKEY
+ * UINT32 encDataSize;
+ * BYTE* -> encDataSize;
+ *
+ * TPM_KEY_PARMS:
+ * TPM_ALGORITHM_ID -> 4 bytes
+ * TPM_ENC_SCHEME -> 2 bytes
+ * TPM_SIG_SCHEME -> 2 bytes
+ * UINT32 parmSize -> 4 bytes
+ * BYTE* -> variable
+ */
+static int extract_key_parameters(struct tpm_key *tk)
+{
+ const void *cur = tk->blob;
+ uint32_t len = tk->blob_len;
+ const void *pub_key;
+ uint32_t sz;
+ uint32_t key_len;
+
+ if (len < 11)
+ return -EBADMSG;
+
+ /* Ensure this is a legacy key */
+ if (get_unaligned_be16(cur + 4) != 0x0015)
+ return -EBADMSG;
+
+ /* Skip to TPM_KEY_PARMS */
+ cur += 11;
+ len -= 11;
+
+ if (len < 12)
+ return -EBADMSG;
+
+ /* Make sure this is an RSA key */
+ if (get_unaligned_be32(cur) != 0x00000001)
+ return -EBADMSG;
+
+ /* Make sure this is TPM_ES_RSAESPKCSv15 encoding scheme */
+ if (get_unaligned_be16(cur + 4) != 0x0002)
+ return -EBADMSG;
+
+ /* Make sure this is TPM_SS_RSASSAPKCS1v15_DER signature scheme */
+ if (get_unaligned_be16(cur + 6) != 0x0003)
+ return -EBADMSG;
+
+ sz = get_unaligned_be32(cur + 8);
+ if (len < sz + 12)
+ return -EBADMSG;
+
+ /* Move to TPM_RSA_KEY_PARMS */
+ len -= 12;
+ cur += 12;
+
+ /* Grab the RSA key length */
+ key_len = get_unaligned_be32(cur);
+
+ switch (key_len) {
+ case 512:
+ case 1024:
+ case 1536:
+ case 2048:
+ break;
+ default:
+ return -EINVAL;
+ }
+
+ /* Move just past TPM_KEY_PARMS */
+ cur += sz;
+ len -= sz;
+
+ if (len < 4)
+ return -EBADMSG;
+
+ sz = get_unaligned_be32(cur);
+ if (len < 4 + sz)
+ return -EBADMSG;
+
+ /* Move to TPM_STORE_PUBKEY */
+ cur += 4 + sz;
+ len -= 4 + sz;
+
+ /* Grab the size of the public key, it should jive with the key size */
+ sz = get_unaligned_be32(cur);
+ if (sz > 256)
+ return -EINVAL;
+
+ pub_key = cur + 4;
+
+ tk->key_len = key_len;
+ tk->pub_key = pub_key;
+ tk->pub_key_len = sz;
+
+ return 0;
+}
+
/* Given the blob, parse it and load it into the TPM */
struct tpm_key *tpm_key_create(const void *blob, uint32_t blob_len)
{
@@ -64,8 +169,15 @@ struct tpm_key *tpm_key_create(const void *blob, uint32_t blob_len)

tk->blob_len = blob_len;

+ r = extract_key_parameters(tk);
+ if (r < 0)
+ goto error_extract;
+
return tk;

+error_extract:
+ kfree(tk->blob);
+ tk->blob_len = 0;
error_memdup:
kfree(tk);
error:
diff --git a/include/crypto/asym_tpm_subtype.h b/include/crypto/asym_tpm_subtype.h
index 03550b850998..48198c36d6b9 100644
--- a/include/crypto/asym_tpm_subtype.h
+++ b/include/crypto/asym_tpm_subtype.h
@@ -7,6 +7,9 @@
struct tpm_key {
void *blob;
u32 blob_len;
+ uint16_t key_len; /* Size in bits of the key */
+ const void *pub_key; /* pointer inside blob to the public key bytes */
+ uint16_t pub_key_len; /* length of the public key */
};

struct tpm_key *tpm_key_create(const void *blob, uint32_t blob_len);
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