tpm: add tpm_get_random()

Add a function to obtain random data from the TPM. Signed-off-by: André Draszik <adraszik@tycoint.com> Added commit message, add cast to min() Signed-off-by: Simon Glass <sjg@chromium.org> Acked-by: Simon Glass <sjg@chromium.org>

tpm: add tpm_get_random()
Add a function to obtain random data from the TPM. Signed-off-by: André Draszik <adraszik@tycoint.com> Added commit message, add cast to min() Signed-off-by: Simon Glass <sjg@chromium.org> Acked-by: Simon Glass <sjg@chromium.org>
André Draszik · Simon Glass
1 parent e8155dfe33
Showing 2 changed files with 55 additions and 0 deletions Side-by-side Diff
include/tpm.h
lib/tpm.c
@@ -651,5 +651,17 @@
 uint32_t tpm_find_key_sha1(const uint8_t auth[20], const uint8_t
 			   pubkey_digest[20], uint32_t *handle);
 #endif /* CONFIG_TPM_LOAD_KEY_BY_SHA1 */
+
+/**
+ * Read random bytes from the TPM RNG. The implementation deals with the fact
+ * that the TPM may legally return fewer bytes than requested by retrying
+ * until @p count bytes have been received.
+ *
+ * @param data		output buffer for the random bytes
+ * @param count		size of output buffer
+ * @return return code of the operation
+ */
+uint32_t tpm_get_random(void *data, uint32_t count);
+
 #endif /* __TPM_H */
@@ -1049,4 +1049,47 @@
 #endif /* CONFIG_TPM_LOAD_KEY_BY_SHA1 */
  
 #endif /* CONFIG_TPM_AUTH_SESSIONS */
+
+uint32_t tpm_get_random(void *data, uint32_t count)
+{
+	const uint8_t command[14] = {
+		0x0, 0xc1,		/* TPM_TAG */
+		0x0, 0x0, 0x0, 0xe,	/* parameter size */
+		0x0, 0x0, 0x0, 0x46,	/* TPM_COMMAND_CODE */
+	};
+	const size_t length_offset = 10;
+	const size_t data_size_offset = 10;
+	const size_t data_offset = 14;
+	uint8_t buf[COMMAND_BUFFER_SIZE], response[COMMAND_BUFFER_SIZE];
+	size_t response_length = sizeof(response);
+	uint32_t data_size;
+	uint8_t *out = data;
+
+	while (count > 0) {
+		uint32_t this_bytes = min((size_t)count,
+					  sizeof (response) - data_offset);
+		uint32_t err;
+
+		if (pack_byte_string(buf, sizeof(buf), "sd",
+				     0, command, sizeof(command),
+				     length_offset, this_bytes))
+			return TPM_LIB_ERROR;
+		err = tpm_sendrecv_command(buf, response, &response_length);
+		if (err)
+			return err;
+		if (unpack_byte_string(response, response_length, "d",
+				       data_size_offset, &data_size))
+			return TPM_LIB_ERROR;
+		if (data_size > count)
+			return TPM_LIB_ERROR;
+		if (unpack_byte_string(response, response_length, "s",
+				       data_offset, out, data_size))
+			return TPM_LIB_ERROR;
+
+		count -= data_size;
+		out += data_size;
+	}
+
+	return 0;
+}
...	...	@@ -651,5 +651,17 @@
651	651	uint32_t tpm_find_key_sha1(const uint8_t auth[20], const uint8_t
652	652	pubkey_digest[20], uint32_t *handle);
653	653	#endif /* CONFIG_TPM_LOAD_KEY_BY_SHA1 */
	654	+
	655	+/**
	656	+ * Read random bytes from the TPM RNG. The implementation deals with the fact
	657	+ * that the TPM may legally return fewer bytes than requested by retrying
	658	+ * until @p count bytes have been received.
	659	+ *
	660	+ * @param data output buffer for the random bytes
	661	+ * @param count size of output buffer
	662	+ * @return return code of the operation
	663	+ */
	664	+uint32_t tpm_get_random(void *data, uint32_t count);
	665	+
654	666	#endif /* __TPM_H */
...	...	@@ -1049,4 +1049,47 @@
1049	1049	#endif /* CONFIG_TPM_LOAD_KEY_BY_SHA1 */
1050	1050
1051	1051	#endif /* CONFIG_TPM_AUTH_SESSIONS */
	1052	+
	1053	+uint32_t tpm_get_random(void *data, uint32_t count)
	1054	+{
	1055	+ const uint8_t command[14] = {
	1056	+ 0x0, 0xc1, /* TPM_TAG */
	1057	+ 0x0, 0x0, 0x0, 0xe, /* parameter size */
	1058	+ 0x0, 0x0, 0x0, 0x46, /* TPM_COMMAND_CODE */
	1059	+ };
	1060	+ const size_t length_offset = 10;
	1061	+ const size_t data_size_offset = 10;
	1062	+ const size_t data_offset = 14;
	1063	+ uint8_t buf[COMMAND_BUFFER_SIZE], response[COMMAND_BUFFER_SIZE];
	1064	+ size_t response_length = sizeof(response);
	1065	+ uint32_t data_size;
	1066	+ uint8_t *out = data;
	1067	+
	1068	+ while (count > 0) {
	1069	+ uint32_t this_bytes = min((size_t)count,
	1070	+ sizeof (response) - data_offset);
	1071	+ uint32_t err;
	1072	+
	1073	+ if (pack_byte_string(buf, sizeof(buf), "sd",
	1074	+ 0, command, sizeof(command),
	1075	+ length_offset, this_bytes))
	1076	+ return TPM_LIB_ERROR;
	1077	+ err = tpm_sendrecv_command(buf, response, &response_length);
	1078	+ if (err)
	1079	+ return err;
	1080	+ if (unpack_byte_string(response, response_length, "d",
	1081	+ data_size_offset, &data_size))
	1082	+ return TPM_LIB_ERROR;
	1083	+ if (data_size > count)
	1084	+ return TPM_LIB_ERROR;
	1085	+ if (unpack_byte_string(response, response_length, "s",
	1086	+ data_offset, out, data_size))
	1087	+ return TPM_LIB_ERROR;
	1088	+
	1089	+ count -= data_size;
	1090	+ out += data_size;
	1091	+ }
	1092	+
	1093	+ return 0;
	1094	+}