tpm: add TPM2_GetRandom command support

Add support for TPM2 GetRandom command

Signed-off-by: Dhananjay Phadke <dphadke@linux.microsoft.com>
Reviewed-by: Simon Glass <sjg@chromium.org>

lib/tpm-v2.c

@@ -422,3 +422,47 @@ u32 tpm2_pcr_setauthvalue(struct udevice *dev, const char *pw,
 
 	return tpm_sendrecv_command(dev, command_v2, NULL, NULL);
 }
+
+u32 tpm2_get_random(struct udevice *dev, void *data, u32 count)
+{
+	const u8 command_v2[10] = {
+		tpm_u16(TPM2_ST_NO_SESSIONS),
+		tpm_u32(12),
+		tpm_u32(TPM2_CC_GET_RANDOM),
+	};
+	u8 buf[COMMAND_BUFFER_SIZE], response[COMMAND_BUFFER_SIZE];
+
+	const size_t data_size_offset = 10;
+	const size_t data_offset = 12;
+	size_t response_length = sizeof(response);
+	u32 data_size;
+	u8 *out = data;
+
+	while (count > 0) {
+		u32 this_bytes = min((size_t)count,
+				     sizeof(response) - data_offset);
+		u32 err;
+
+		if (pack_byte_string(buf, sizeof(buf), "sw",
+				     0, command_v2, sizeof(command_v2),
+				     sizeof(command_v2), this_bytes))
+			return TPM_LIB_ERROR;
+		err = tpm_sendrecv_command(dev, buf, response,
+					   &response_length);
+		if (err)
+			return err;
+		if (unpack_byte_string(response, response_length, "w",
+				       data_size_offset, &data_size))
+			return TPM_LIB_ERROR;
+		if (data_size > this_bytes)
+			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;
+}