Document: Spelling check.

Correct the spelling problem in document.

Change-Id: I461a496c2f9faee3c9e282f457104119963330d5
Signed-off-by: Jianliang Shen <jianliang.shen@arm.com>
diff --git a/docs/security/threat_models/generic_threat_model.rst b/docs/security/threat_models/generic_threat_model.rst
index 5659c24..6356951 100644
--- a/docs/security/threat_models/generic_threat_model.rst
+++ b/docs/security/threat_models/generic_threat_model.rst
@@ -6,8 +6,8 @@
 Introduction
 ************
 
-This document introduces a generic thread model of Trusted Firmware-M (TF-M).
-This generic thread model provides an overall analysis of TF-M implementation
+This document introduces a generic threat model of Trusted Firmware-M (TF-M).
+This generic threat model provides an overall analysis of TF-M implementation
 and identifies general threats and mitigation.
 
 .. note::
@@ -28,7 +28,7 @@
 each RoT service may require a dedicated threat model.
 
 The analysis on specific models, topologies or RoT services may be covered in
-dedicated thread model documents. Those threat models are out of the scope of
+dedicated threat model documents. Those threat models are out of the scope of
 this document.
 
 Methodology
@@ -69,7 +69,7 @@
 running in SPE.
 
 The TOE can vary in different TF-M models, RoT services and usage scenarios.
-Refer to dedicated thread models for the specific TOE definitions.
+Refer to dedicated threat models for the specific TOE definitions.
 
 ********************
 Asset identification
@@ -113,7 +113,7 @@
 in the figure below. Other modules inside SPE stay in the same TOE as TF-M does.
 
 Valid Data flows across the Trust Boundary are also shown in the figure below.
-This thread model only focuses on the data flows related to TF-M.
+This threat model only focuses on the data flows related to TF-M.
 
 .. figure:: overall-DFD.png