Add lesson 55

Signed-off-by: Konstantin Aladyshev <aladyshev22@gmail.com>

9 files changed, 593 insertions, 0 deletions

diff --git a/Lessons/Lesson_55/README.md b/Lessons/Lesson_55/README.md
new file mode 100644
index 0000000..123f439
--- /dev/null
+++ b/Lessons/Lesson_55/README.md
@@ -0,0 +1,272 @@
+We know how to add font for the new language, and we now how to populate strings for some of the existing languages in the system dynamically.
+Let's see if it is possible to create another language option dynamically.
+
+`Select Language` menu gets all possible language options from the value of the `PlatformLangCodes` EFI variable. And the current language option is reflected by the `PlatformLang` EFI option.
+
+Initially the values for these options are set with a help of PCD in the https://github.com/tianocore/edk2/blob/master/MdePkg/MdePkg.dec:
+```
+  ## Default platform supported RFC 4646 languages: (American) English & French.
+  # @Prompt Default Value of PlatformLangCodes Variable.
+  gEfiMdePkgTokenSpaceGuid.PcdUefiVariableDefaultPlatformLangCodes|"en;fr;en-US;fr-FR"|VOID*|0x0000001e
+
+  ## Default current RFC 4646 language: (American) English.
+  # @Prompt Default Value of PlatformLang Variable.
+  gEfiMdePkgTokenSpaceGuid.PcdUefiVariableDefaultPlatformLang|"en-US"|VOID*|0x0000001f
+```
+You can look at the actual code in the `UiCreateLanguageMenu` function from the https://github.com/tianocore/edk2/blob/master/MdeModulePkg/Application/UiApp/FrontPageCustomizedUiSupport.c.
+
+Let's see if it is possible to modify `PlatformLangCodes` and add another language into it.
+
+First create an app that would print the value for the `PlatformLangCodes` option:
+```
+#include <Library/UefiBootServicesTableLib.h>
+#include <Library/UefiLib.h>
+
+EFI_STATUS
+EFIAPI
+UefiMain (
+  IN EFI_HANDLE        ImageHandle,
+  IN EFI_SYSTEM_TABLE  *SystemTable
+  )
+{
+  EFI_STATUS Status;
+
+  CHAR8* LanguageString;
+  Status = GetEfiGlobalVariable2(L"PlatformLangCodes", (VOID**)&LanguageString, NULL);
+  if (EFI_ERROR(Status)) {
+    Print(L"Error! Can't perform GetEfiGlobalVariable2, status=%r\n", Status);
+    return Status;
+  }
+  Print(L"Current value of the 'PlatformLangCodes' variable is '%a'\n", LanguageString);
+
+  return EFI_SUCCESS;
+}
+```
+We've already used `gRT->GetVariable` protocol function directly before, so here we use `GetEfiGlobalVariable2` library function to the simplify code. This function is defined in the https://github.com/tianocore/edk2/blob/master/MdePkg/Library/UefiLib/UefiLib.c:
+```
+**
+  Returns a pointer to an allocated buffer that contains the contents of a
+  variable retrieved through the UEFI Runtime Service GetVariable().  This
+  function always uses the EFI_GLOBAL_VARIABLE GUID to retrieve variables.
+  The returned buffer is allocated using AllocatePool().  The caller is
+  responsible for freeing this buffer with FreePool().
+  If Name is NULL, then ASSERT().
+  If Value is NULL, then ASSERT().
+  @param[in]  Name  The pointer to a Null-terminated Unicode string.
+  @param[out] Value The buffer point saved the variable info.
+  @param[out] Size  The buffer size of the variable.
+  @return EFI_OUT_OF_RESOURCES      Allocate buffer failed.
+  @return EFI_SUCCESS               Find the specified variable.
+  @return Others Errors             Return errors from call to gRT->GetVariable.
+**/
+EFI_STATUS
+EFIAPI
+GetEfiGlobalVariable2 (
+  IN CONST CHAR16    *Name,
+  OUT VOID           **Value,
+  OUT UINTN          *Size OPTIONAL
+  )
+```
+
+If you build and run our application now, you would get the value from the PCD:
+```
+FS0:\> AddNewLanguage.efi
+Current value of the 'PlatformLangCodes' variable is 'en;fr;en-US;fr-FR'
+```
+
+Now let's try to add `;ru-RU` to the end of the variable and write it back.
+
+First construct new string and fill it with the necessary data:
+```
+CHAR8* NewLanguageString = AllocatePool(AsciiStrLen(LanguageString) + AsciiStrSize(";ru-RU"));
+if (NewLanguageString == NULL) {
+  Print(L"Error! Can't allocate size for new PlatformLangCodes variable\n");
+  FreePool(LanguageString);
+  return EFI_OUT_OF_RESOURCES;
+}
+
+CopyMem(NewLanguageString, LanguageString, AsciiStrLen(LanguageString));
+CopyMem(&NewLanguageString[AsciiStrLen(LanguageString)], ";ru-RU", AsciiStrSize(";ru-RU"));
+
+Print(L"Set 'PlatformLangCodes' variable to '%a'\n", NewLanguageString);
+```
+Just in case ASCII string functions are defined in the https://github.com/tianocore/edk2/blob/master/MdePkg/Library/BaseLib/String.c.
+Also don't forget to include `Library/MemoryAllocationLib.h` header for the `AllocatePool` function and `Library/BaseMemoryLib.h` header for the `CopyMem` function.
+
+Now use `SetVariable` call to update variable:
+```
+Status = gRT->SetVariable (
+              L"PlatformLangCodes",
+              &gEfiGlobalVariableGuid,
+              EFI_VARIABLE_BOOTSERVICE_ACCESS | EFI_VARIABLE_RUNTIME_ACCESS,
+              AsciiStrSize(NewLanguageString),
+              NewLanguageString
+              );
+if (EFI_ERROR(Status)) {
+  Print(L"Error! Can't set 'PlatformLangCodes' variable, status=%r\n", Status);
+}
+```
+`SetVariable` is a Runtime Service, you can find its definition in the UEFI specification:
+```
+SetVariable()
+
+Summary:
+Sets the value of a variable.
+
+Prototype:
+typedef
+EFI_STATUS
+SetVariable (
+ IN CHAR16 *VariableName,
+ IN EFI_GUID *VendorGuid,
+ IN UINT32 Attributes,
+ IN UINTN DataSize,
+ IN VOID *Data
+ );
+
+Parameters:
+VariableName 	A Null-terminated string that is the name of the vendor’s variable. Each VariableName is unique for each VendorGuid.
+VendorGuid 	A unique identifier for the vendor.
+Attributes 	Attributes bitmask to set for the variable.
+DataSize 	The size in bytes of the Data buffer.
+Data 		The contents for the variable.
+```
+In case you forgot `gRT` is a shortcut for the `SystemTable->RuntimeServices` from the `UefiRuntimeServicesTableLib` library. So don't forget to include its library header `<Library/UefiRuntimeServicesTableLib.h>`.
+
+If you build and run our application now you would get:
+```
+FS0:\> AddNewLanguage.efi
+Current value of the 'PlatformLangCodes' variable is 'en;fr;en-US;fr-FR'
+Set 'PlatformLangCodes' variable to 'en;fr;en-US;fr-FR;ru-RU'
+Error! Can't set 'PlatformLangCodes' variable, status=Write Protected
+```
+
+Unfortunately it is not possible to add new language at runtime as 'PlatformLangCodes' EFI variable is write protected. Therefore it is not possible to add another localization language at runtime.
+
+If you look at the UEFI spec you'll see:
+```
+The PlatformLangCodes variable contains a null- terminated ASCII string representing the language
+codes that the firmware can support. At initialization time the firmware computes the supported
+languages and creates this data variable. Since the firmware creates this value on each initialization, its
+contents are not stored in nonvolatile memory. This value is considered read-only. 
+```
+
+# EDKII_VARIABLE_POLICY_PROTOCOL
+
+The `PlatformLangCodes` is locked for modifications with a help of a `gEdkiiVariablePolicyProtocolGuid` protocol. This is a custom EDKII protocol for setting different policies on variables.
+
+You can read more about the UEFI Variable Policy protocol in the https://github.com/tianocore/edk2/tree/master/MdeModulePkg/Library/VariablePolicyLib/ReadMe.md
+
+The header file is placed under https://github.com/tianocore/edk2/blob/master/MdeModulePkg/Include/Protocol/VariablePolicy.h
+
+The policy for the `PlatformLangCodes` EFI variable is set in the https://github.com/tianocore/edk2/blob/master/MdeModulePkg/Universal/BdsDxe/BdsEntry.c along with couple of other variables:
+```
+///
+/// The read-only variables defined in UEFI Spec.
+///
+CHAR16  *mReadOnlyVariables[] = {
+  EFI_PLATFORM_LANG_CODES_VARIABLE_NAME,             // L"PlatformLangCodes"  The language codes that the firmware supports
+  EFI_LANG_CODES_VARIABLE_NAME,
+  EFI_BOOT_OPTION_SUPPORT_VARIABLE_NAME,
+  EFI_HW_ERR_REC_SUPPORT_VARIABLE_NAME,
+  EFI_OS_INDICATIONS_SUPPORT_VARIABLE_NAME
+  };
+
+...
+
+  // Mark the read-only variables if the Variable Lock protocol exists
+  //
+  Status = gBS->LocateProtocol(&gEdkiiVariablePolicyProtocolGuid,
+NULL, (VOID**)&VariablePolicy);
+  DEBUG((DEBUG_INFO, "[BdsDxe] Locate Variable Policy protocol -
+%r\n", Status));
+  if (!EFI_ERROR (Status)) {
+    for (Index = 0; Index < ARRAY_SIZE (mReadOnlyVariables); Index++) {
+      Status = RegisterBasicVariablePolicy(
+                 VariablePolicy,
+                 &gEfiGlobalVariableGuid,
+                 mReadOnlyVariables[Index],
+                 VARIABLE_POLICY_NO_MIN_SIZE,
+                 VARIABLE_POLICY_NO_MAX_SIZE,
+                 VARIABLE_POLICY_NO_MUST_ATTR,
+                 VARIABLE_POLICY_NO_CANT_ATTR,
+                 VARIABLE_POLICY_TYPE_LOCK_NOW
+                 );
+      ASSERT_EFI_ERROR(Status);
+    }
+  }
+```
+
+# Try to execute DisableVariablePolicy()
+
+We can try to perform `DisableVariablePolicy()` to disable `VariablePolicyProtocol`.
+
+UefiLessonsPkg/AddNewLanguage/AddNewLanguage.c
+```
+...
+#include <Protocol/VariablePolicy.h>
+
+EFI_STATUS
+EFIAPI
+UefiMain (
+  IN EFI_HANDLE        ImageHandle,
+  IN EFI_SYSTEM_TABLE  *SystemTable
+  )
+{
+  ...
+
+  EDKII_VARIABLE_POLICY_PROTOCOL* VariablePolicyProtocol;
+  Status = gBS->LocateProtocol(&gEdkiiVariablePolicyProtocolGuid,
+                               NULL, 
+                               (VOID**)&VariablePolicyProtocol);
+  if (EFI_ERROR(Status)) {
+    Print(L"Error! Could not find Variable Policy protocol: %r\n", Status);
+    return Status;
+  }  
+  Status = VariablePolicyProtocol->DisableVariablePolicy();
+  if (EFI_ERROR(Status)) {
+    Print(L"Error! Can't disable VariablePolicy: %r\n", Status);
+    return Status;
+  }
+}
+```
+
+UefiLessonsPkg/AddNewLanguage/AddNewLanguage.inf:
+```
+....
+[Packages]
+  ...
+  MdeModulePkg/MdeModulePkg.dec
+...
+
+[Protocols]
+  gEdkiiVariablePolicyProtocolGuid
+```
+
+But unfortunately this call would fail:
+```
+FS0:\> AddNewLanguage.efi
+Current value of the 'PlatformLangCodes' variable is 'en;fr;en-US;fr-FR'
+Set 'PlatformLangCodes' variable to 'en;fr;en-US;fr-FR;ru-RU'
+Error! Can't set PlatformLangCodes variable, status=Write Protected
+Error! Can't disable VariablePolicy: Write Protected
+```
+
+This happend because in the end of the DXE UEFI stage variable policy is locked in the MdeModulePkg/Universal/Variable/RuntimeDxe/VariableDxe.c:
+```
+VOID
+EFIAPI
+OnEndOfDxe (
+  EFI_EVENT Event,
+  VOID *Context
+)
+{
+  EFI_STATUS Status;
+  DEBUG ((EFI_D_INFO, "[Variable]END_OF_DXE is signaled\n"));
+   ...
+  Status = LockVariablePolicy ();
+   ...
+}
+```
+Locking means that is no longer possible to change or disable policy for variables. Therefore there is no way to change `PlatformLangCodes` at runtime.
+
diff --git a/Lessons/Lesson_55/UefiLessonsPkg/AddNewLanguage/AddNewLanguage.c b/Lessons/Lesson_55/UefiLessonsPkg/AddNewLanguage/AddNewLanguage.c
new file mode 100644
index 0000000..cd4920d
--- /dev/null
+++ b/Lessons/Lesson_55/UefiLessonsPkg/AddNewLanguage/AddNewLanguage.c
@@ -0,0 +1,71 @@
+/*
+ * Copyright (c) 2021, Konstantin Aladyshev <aladyshev22@gmail.com>
+ *
+ * SPDX-License-Identifier: MIT
+ */
+
+#include <Library/UefiBootServicesTableLib.h>
+#include <Library/UefiLib.h>
+
+#include <Library/MemoryAllocationLib.h>
+#include <Library/BaseMemoryLib.h>
+#include <Library/UefiRuntimeServicesTableLib.h>
+#include <Protocol/VariablePolicy.h>
+
+
+EFI_STATUS
+EFIAPI
+UefiMain (
+  IN EFI_HANDLE        ImageHandle,
+  IN EFI_SYSTEM_TABLE  *SystemTable
+  )
+{
+  EFI_STATUS Status;
+
+  CHAR8* LanguageString;
+  Status = GetEfiGlobalVariable2(L"PlatformLangCodes", (VOID**)&LanguageString, NULL);
+  if (EFI_ERROR(Status)) {
+    Print(L"Error! Can't perform GetEfiGlobalVariable2, status=%r\n", Status);
+    return Status;
+  }
+  Print(L"Current value of the 'PlatformLangCodes' variable is '%a'\n", LanguageString);
+
+  CHAR8* NewLanguageString = AllocatePool(AsciiStrLen(LanguageString) + AsciiStrSize(";ru-RU"));
+  if (NewLanguageString == NULL) {
+    Print(L"Error! Can't allocate size for new PlatformLangCodes variable\n");
+    FreePool(LanguageString);
+    return EFI_OUT_OF_RESOURCES;
+  }
+
+  CopyMem(NewLanguageString, LanguageString, AsciiStrLen(LanguageString));
+  CopyMem(&NewLanguageString[AsciiStrLen(LanguageString)], ";ru-RU", AsciiStrSize(";ru-RU"));
+
+  Print(L"Set 'PlatformLangCodes' variable to '%a'\n", NewLanguageString);
+
+  Status = gRT->SetVariable (
+                L"PlatformLangCodes",
+                &gEfiGlobalVariableGuid,
+                EFI_VARIABLE_BOOTSERVICE_ACCESS | EFI_VARIABLE_RUNTIME_ACCESS,
+                AsciiStrSize(NewLanguageString),
+                NewLanguageString
+                );
+  if (EFI_ERROR(Status)) {
+    Print(L"Error! Can't set PlatformLangCodes variable, status=%r\n", Status);
+  }
+
+  EDKII_VARIABLE_POLICY_PROTOCOL* VariablePolicyProtocol;
+  Status = gBS->LocateProtocol(&gEdkiiVariablePolicyProtocolGuid,
+                               NULL,
+                               (VOID**)&VariablePolicyProtocol);
+  if (EFI_ERROR(Status)) {
+    Print(L"Error! Could not find Variable Policy protocol: %r\n", Status);
+    return Status;
+  }
+  Status = VariablePolicyProtocol->DisableVariablePolicy();
+  if (EFI_ERROR(Status)) {
+    Print(L"Error! Can't disable VariablePolicy: %r\n", Status);
+    return Status;
+  }
+
+  return EFI_SUCCESS;
+}
diff --git a/Lessons/Lesson_55/UefiLessonsPkg/AddNewLanguage/AddNewLanguage.inf b/Lessons/Lesson_55/UefiLessonsPkg/AddNewLanguage/AddNewLanguage.inf
new file mode 100644
index 0000000..1a34438
--- /dev/null
+++ b/Lessons/Lesson_55/UefiLessonsPkg/AddNewLanguage/AddNewLanguage.inf
@@ -0,0 +1,27 @@
+##
+# Copyright (c) 2021, Konstantin Aladyshev <aladyshev22@gmail.com>
+#
+# SPDX-License-Identifier: MIT
+##
+
+[Defines]
+  INF_VERSION                    = 1.25
+  BASE_NAME                      = AddNewLanguage
+  FILE_GUID                      = 6790e268-0762-4ce8-8999-2ff2131e6512
+  MODULE_TYPE                    = UEFI_APPLICATION
+  VERSION_STRING                 = 1.0
+  ENTRY_POINT                    = UefiMain
+
+[Sources]
+  AddNewLanguage.c
+
+[Packages]
+  MdePkg/MdePkg.dec
+  MdeModulePkg/MdeModulePkg.dec
+
+[LibraryClasses]
+  UefiApplicationEntryPoint
+  UefiLib
+
+[Protocols]
+  gEdkiiVariablePolicyProtocolGuid
diff --git a/Lessons/Lesson_55/UefiLessonsPkg/UefiLessonsPkg.dec b/Lessons/Lesson_55/UefiLessonsPkg/UefiLessonsPkg.dec
new file mode 100644
index 0000000..40b351c
--- /dev/null
+++ b/Lessons/Lesson_55/UefiLessonsPkg/UefiLessonsPkg.dec
@@ -0,0 +1,45 @@
+##
+# Copyright (c) 2021, Konstantin Aladyshev <aladyshev22@gmail.com>
+#
+# SPDX-License-Identifier: MIT
+##
+
+[Defines]

+  DEC_SPECIFICATION              = 0x00010005

+  PACKAGE_NAME                   = UefiLessonsPkg

+  PACKAGE_GUID                   = 7e7edbba-ca2c-4177-a3f0-d3371358773a

+  PACKAGE_VERSION                = 1.01

+

+[Includes]

+  Include

+

+[Guids]

+  # FILE_GUID as defined in UefiLessonsPkg/HelloWorld/HelloWorld.inf

+  gHelloWorldFileGuid            = {0x2e55fa38, 0xf148, 0x42d3, {0xaf, 0x90, 0x1b, 0xe2, 0x47, 0x32, 0x3e, 0x30}}

+  gUefiLessonsPkgTokenSpaceGuid = {0x150cab53, 0xad47, 0x4385, {0xb5, 0xdd, 0xbc, 0xfc, 0x76, 0xba, 0xca, 0xf0}}

+  gHIIStringsCGuid = { 0x8e0b8ed3, 0x14f7, 0x499d, { 0xa2, 0x24, 0xae, 0xe8, 0x9d, 0xc9, 0x7f, 0xa3 }}

+  gHIIStringsUNIGuid = { 0x6ee19058, 0x0fe2, 0x44ed, { 0x89, 0x1c, 0xa5, 0xd7, 0xe1, 0x08, 0xee, 0x1a }}

+  gHIIStringsUNIRCGuid = { 0x785693b4, 0x623e, 0x40fa, { 0x9a, 0x45, 0x68, 0xda, 0x38, 0x30, 0x89, 0xdd }}

+  gHIIAddRussianFontGuid = { 0x9fe2f616, 0x323c, 0x45a7, { 0x87, 0xa2, 0xdf, 0xef, 0xf5, 0x17, 0xcc, 0x66 }}

+

+[Protocols]

+  gSimpleClassProtocolGuid = { 0xb5510eea, 0x6f11, 0x4e4b, { 0xad, 0x0f, 0x35, 0xce, 0x17, 0xbd, 0x7a, 0x67 }}

+

+[PcdsFixedAtBuild]

+  gUefiLessonsPkgTokenSpaceGuid.PcdMyVar32|42|UINT32|0x00000001

+  gUefiLessonsPkgTokenSpaceGuid.PcdMyVar32_1|42|UINT32|0x00000002

+  gUefiLessonsPkgTokenSpaceGuid.PcdMyVar32_2|42|UINT32|0x00000003

+  gUefiLessonsPkgTokenSpaceGuid.PcdMyVarBool|FALSE|BOOLEAN|0x00000004

+

+[PcdsPatchableInModule]

+  gUefiLessonsPkgTokenSpaceGuid.PcdMyPatchableVar32|0x31313131|UINT32|0x10000001

+

+[PcdsFeatureFlag]

+  gUefiLessonsPkgTokenSpaceGuid.PcdMyFeatureFlagVar|FALSE|BOOLEAN|0x20000001

+

+[PcdsDynamic]

+  gUefiLessonsPkgTokenSpaceGuid.PcdMyDynamicVar32|0x38323232|UINT32|0x30000001

+  gUefiLessonsPkgTokenSpaceGuid.PcdMyDynamicVar32_1|42|UINT32|0x30000002

+

+[PcdsDynamicEx]

+  gUefiLessonsPkgTokenSpaceGuid.PcdMyDynamicExVar32|0x38333333|UINT32|0x40000001

diff --git a/Lessons/Lesson_55/UefiLessonsPkg/UefiLessonsPkg.dsc b/Lessons/Lesson_55/UefiLessonsPkg/UefiLessonsPkg.dsc
new file mode 100644
index 0000000..85ea19a
--- /dev/null
+++ b/Lessons/Lesson_55/UefiLessonsPkg/UefiLessonsPkg.dsc
@@ -0,0 +1,78 @@
+##
+# Copyright (c) 2021, Konstantin Aladyshev <aladyshev22@gmail.com>
+#
+# SPDX-License-Identifier: MIT
+##
+
+[Defines]
+  DSC_SPECIFICATION              = 0x0001001C
+  PLATFORM_GUID                  = 3db7270f-ffac-4139-90a4-0ae68f3f8167
+  PLATFORM_VERSION               = 0.01
+  PLATFORM_NAME                  = UefiLessonsPkg
+  SKUID_IDENTIFIER               = DEFAULT
+  SUPPORTED_ARCHITECTURES        = X64
+  BUILD_TARGETS                  = RELEASE
+
+
+[LibraryClasses]
+  UefiApplicationEntryPoint|MdePkg/Library/UefiApplicationEntryPoint/UefiApplicationEntryPoint.inf
+  UefiBootServicesTableLib|MdePkg/Library/UefiBootServicesTableLib/UefiBootServicesTableLib.inf
+  DebugLib|MdePkg/Library/UefiDebugLibConOut/UefiDebugLibConOut.inf
+  BaseLib|MdePkg/Library/BaseLib/BaseLib.inf
+  #PcdLib|MdePkg/Library/BasePcdLibNull/BasePcdLibNull.inf
+  PcdLib|MdePkg/Library/DxePcdLib/DxePcdLib.inf
+  BaseMemoryLib|MdePkg/Library/BaseMemoryLib/BaseMemoryLib.inf
+  RegisterFilterLib|MdePkg/Library/RegisterFilterLibNull/RegisterFilterLibNull.inf
+  PrintLib|MdePkg/Library/BasePrintLib/BasePrintLib.inf
+  DebugPrintErrorLevelLib|MdePkg/Library/BaseDebugPrintErrorLevelLib/BaseDebugPrintErrorLevelLib.inf
+  UefiLib|MdePkg/Library/UefiLib/UefiLib.inf
+  MemoryAllocationLib|MdePkg/Library/UefiMemoryAllocationLib/UefiMemoryAllocationLib.inf
+  DevicePathLib|MdePkg/Library/UefiDevicePathLib/UefiDevicePathLib.inf
+  UefiRuntimeServicesTableLib|MdePkg/Library/UefiRuntimeServicesTableLib/UefiRuntimeServicesTableLib.inf
+  ShellCEntryLib|ShellPkg/Library/UefiShellCEntryLib/UefiShellCEntryLib.inf
+  ShellLib|ShellPkg/Library/UefiShellLib/UefiShellLib.inf
+  FileHandleLib|MdePkg/Library/UefiFileHandleLib/UefiFileHandleLib.inf  
+  HiiLib|MdeModulePkg/Library/UefiHiiLib/UefiHiiLib.inf
+  SortLib|MdeModulePkg/Library/UefiSortLib/UefiSortLib.inf
+  UefiHiiServicesLib|MdeModulePkg/Library/UefiHiiServicesLib/UefiHiiServicesLib.inf
+  UefiDriverEntryPoint|MdePkg/Library/UefiDriverEntryPoint/UefiDriverEntryPoint.inf
+  #SimpleLibrary|UefiLessonsPkg/Library/SimpleLibrary/SimpleLibrary.inf
+  #SimpleLibrary|UefiLessonsPkg/Library/SimpleLibraryWithConstructor/SimpleLibraryWithConstructor.inf
+  SimpleLibrary|UefiLessonsPkg/Library/SimpleLibraryWithConstructorAndDestructor/SimpleLibraryWithConstructorAndDestructor.inf
+
+[Components]
+  UefiLessonsPkg/SimplestApp/SimplestApp.inf
+  UefiLessonsPkg/HelloWorld/HelloWorld.inf
+  UefiLessonsPkg/ImageHandle/ImageHandle.inf
+  UefiLessonsPkg/ImageInfo/ImageInfo.inf
+  UefiLessonsPkg/MemoryInfo/MemoryInfo.inf
+  UefiLessonsPkg/SimpleShellApp/SimpleShellApp.inf
+  UefiLessonsPkg/ListVariables/ListVariables.inf
+  UefiLessonsPkg/ShowBootVariables/ShowBootVariables.inf
+  UefiLessonsPkg/InteractiveApp/InteractiveApp.inf
+  UefiLessonsPkg/PCDLesson/PCDLesson.inf
+  UefiLessonsPkg/SmbiosInfo/SmbiosInfo.inf
+  UefiLessonsPkg/ShowTables/ShowTables.inf
+  UefiLessonsPkg/AcpiInfo/AcpiInfo.inf
+  UefiLessonsPkg/SaveBGRT/SaveBGRT.inf
+  UefiLessonsPkg/ListPCI/ListPCI.inf
+  UefiLessonsPkg/SimpleDriver/SimpleDriver.inf
+  UefiLessonsPkg/PCIRomInfo/PCIRomInfo.inf
+  UefiLessonsPkg/Library/SimpleLibrary/SimpleLibrary.inf
+  UefiLessonsPkg/Library/SimpleLibraryWithConstructor/SimpleLibraryWithConstructor.inf
+  UefiLessonsPkg/SimpleLibraryUser/SimpleLibraryUser.inf
+  UefiLessonsPkg/SimpleClassProtocol/SimpleClassProtocol.inf
+  UefiLessonsPkg/SimpleClassUser/SimpleClassUser.inf
+  UefiLessonsPkg/HotKeyDriver/HotKeyDriver.inf
+  UefiLessonsPkg/ShowHII/ShowHII.inf
+  UefiLessonsPkg/HIIStringsC/HIIStringsC.inf
+  UefiLessonsPkg/HIIStringsUNI/HIIStringsUNI.inf
+  UefiLessonsPkg/HIIStringsUNIRC/HIIStringsUNIRC.inf
+  UefiLessonsPkg/HIIStringsMan/HIIStringsMan.inf
+  UefiLessonsPkg/HIIAddRussianFont/HIIAddRussianFont.inf
+  UefiLessonsPkg/HIIAddLocalization/HIIAddLocalization.inf
+  UefiLessonsPkg/AddNewLanguage/AddNewLanguage.inf
+
+[PcdsFixedAtBuild]
+  gUefiLessonsPkgTokenSpaceGuid.PcdMyVar32_2|44
+
diff --git a/README.md b/README.md
index 81df75b..e39595d 100644
--- a/README.md
+++ b/README.md
@@ -58,6 +58,7 @@ These series of lessons are intendend to get you started with UEFI programming i
 - [Lesson 52](Lessons/Lesson_52): Add Russian font - Part 1: investigate `EFI_NARROW_GLYPH`/`EFI_WIDE_GLYPH` format, construct glyph array from the *.woff font file
 - [Lesson 53](Lessons/Lesson_53): Add Russian font - Part 2: construct `EFI_HII_SIMPLE_FONT_PACKAGE` and populate it to the HII database 
 - [Lesson 54](Lessons/Lesson_54): Use `NewString` and `SetString` functions from the `EFI_HII_STRING_PROTOCOL` to add String Package for another language dynamically 
+- [Lesson 55](Lessons/Lesson_55): Try to modify `PlatformLangCodes` EFI variable and add another language dynamically. Variable protection with a help of `EDKII_VARIABLE_POLICY_PROTOCOL`
 
 
 _____
diff --git a/UefiLessonsPkg/AddNewLanguage/AddNewLanguage.c b/UefiLessonsPkg/AddNewLanguage/AddNewLanguage.c
new file mode 100644
index 0000000..cd4920d
--- /dev/null
+++ b/UefiLessonsPkg/AddNewLanguage/AddNewLanguage.c
@@ -0,0 +1,71 @@
+/*
+ * Copyright (c) 2021, Konstantin Aladyshev <aladyshev22@gmail.com>
+ *
+ * SPDX-License-Identifier: MIT
+ */
+
+#include <Library/UefiBootServicesTableLib.h>
+#include <Library/UefiLib.h>
+
+#include <Library/MemoryAllocationLib.h>
+#include <Library/BaseMemoryLib.h>
+#include <Library/UefiRuntimeServicesTableLib.h>
+#include <Protocol/VariablePolicy.h>
+
+
+EFI_STATUS
+EFIAPI
+UefiMain (
+  IN EFI_HANDLE        ImageHandle,
+  IN EFI_SYSTEM_TABLE  *SystemTable
+  )
+{
+  EFI_STATUS Status;
+
+  CHAR8* LanguageString;
+  Status = GetEfiGlobalVariable2(L"PlatformLangCodes", (VOID**)&LanguageString, NULL);
+  if (EFI_ERROR(Status)) {
+    Print(L"Error! Can't perform GetEfiGlobalVariable2, status=%r\n", Status);
+    return Status;
+  }
+  Print(L"Current value of the 'PlatformLangCodes' variable is '%a'\n", LanguageString);
+
+  CHAR8* NewLanguageString = AllocatePool(AsciiStrLen(LanguageString) + AsciiStrSize(";ru-RU"));
+  if (NewLanguageString == NULL) {
+    Print(L"Error! Can't allocate size for new PlatformLangCodes variable\n");
+    FreePool(LanguageString);
+    return EFI_OUT_OF_RESOURCES;
+  }
+
+  CopyMem(NewLanguageString, LanguageString, AsciiStrLen(LanguageString));
+  CopyMem(&NewLanguageString[AsciiStrLen(LanguageString)], ";ru-RU", AsciiStrSize(";ru-RU"));
+
+  Print(L"Set 'PlatformLangCodes' variable to '%a'\n", NewLanguageString);
+
+  Status = gRT->SetVariable (
+                L"PlatformLangCodes",
+                &gEfiGlobalVariableGuid,
+                EFI_VARIABLE_BOOTSERVICE_ACCESS | EFI_VARIABLE_RUNTIME_ACCESS,
+                AsciiStrSize(NewLanguageString),
+                NewLanguageString
+                );
+  if (EFI_ERROR(Status)) {
+    Print(L"Error! Can't set PlatformLangCodes variable, status=%r\n", Status);
+  }
+
+  EDKII_VARIABLE_POLICY_PROTOCOL* VariablePolicyProtocol;
+  Status = gBS->LocateProtocol(&gEdkiiVariablePolicyProtocolGuid,
+                               NULL,
+                               (VOID**)&VariablePolicyProtocol);
+  if (EFI_ERROR(Status)) {
+    Print(L"Error! Could not find Variable Policy protocol: %r\n", Status);
+    return Status;
+  }
+  Status = VariablePolicyProtocol->DisableVariablePolicy();
+  if (EFI_ERROR(Status)) {
+    Print(L"Error! Can't disable VariablePolicy: %r\n", Status);
+    return Status;
+  }
+
+  return EFI_SUCCESS;
+}
diff --git a/UefiLessonsPkg/AddNewLanguage/AddNewLanguage.inf b/UefiLessonsPkg/AddNewLanguage/AddNewLanguage.inf
new file mode 100644
index 0000000..1a34438
--- /dev/null
+++ b/UefiLessonsPkg/AddNewLanguage/AddNewLanguage.inf
@@ -0,0 +1,27 @@
+##
+# Copyright (c) 2021, Konstantin Aladyshev <aladyshev22@gmail.com>
+#
+# SPDX-License-Identifier: MIT
+##
+
+[Defines]
+  INF_VERSION                    = 1.25
+  BASE_NAME                      = AddNewLanguage
+  FILE_GUID                      = 6790e268-0762-4ce8-8999-2ff2131e6512
+  MODULE_TYPE                    = UEFI_APPLICATION
+  VERSION_STRING                 = 1.0
+  ENTRY_POINT                    = UefiMain
+
+[Sources]
+  AddNewLanguage.c
+
+[Packages]
+  MdePkg/MdePkg.dec
+  MdeModulePkg/MdeModulePkg.dec
+
+[LibraryClasses]
+  UefiApplicationEntryPoint
+  UefiLib
+
+[Protocols]
+  gEdkiiVariablePolicyProtocolGuid
diff --git a/UefiLessonsPkg/UefiLessonsPkg.dsc b/UefiLessonsPkg/UefiLessonsPkg.dsc
index 48b78ca..85ea19a 100644
--- a/UefiLessonsPkg/UefiLessonsPkg.dsc
+++ b/UefiLessonsPkg/UefiLessonsPkg.dsc
@@ -71,6 +71,7 @@
   UefiLessonsPkg/HIIStringsMan/HIIStringsMan.inf
   UefiLessonsPkg/HIIAddRussianFont/HIIAddRussianFont.inf
   UefiLessonsPkg/HIIAddLocalization/HIIAddLocalization.inf
+  UefiLessonsPkg/AddNewLanguage/AddNewLanguage.inf
 
 [PcdsFixedAtBuild]
   gUefiLessonsPkgTokenSpaceGuid.PcdMyVar32_2|44