[RFC 05/13] MdeModulePkg/DxeIpl AARCH64: Remap DXE core code section before launch

["Ard Biesheuvel" <ardb@kernel.org>]

To permit the platform to adopt a stricter policy when it comes to
memory protections, and map all memory XP by default, add the necessary
handling to the DXE IPL PEIM to ensure that the DXE core code section is
mapped executable before invoking the DXE core.

It is up to the DXE core itself to manage the executable permissions on
other DXE and UEFI drivers and applications that it dispatches.

Note that this requires that the DXE IPL executes non-shadowed from a FV
that is mapped executable.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
---
 MdeModulePkg/Core/DxeIplPeim/Arm/DxeLoadFunc.c | 69 ++++++++++++++++++++
 MdeModulePkg/Core/DxeIplPeim/DxeIpl.inf        |  1 +
 2 files changed, 70 insertions(+)

diff --git a/MdeModulePkg/Core/DxeIplPeim/Arm/DxeLoadFunc.c b/MdeModulePkg/Core/DxeIplPeim/Arm/DxeLoadFunc.c
index f62b6dcb38a7..21eac2851554 100644
--- a/MdeModulePkg/Core/DxeIplPeim/Arm/DxeLoadFunc.c
+++ b/MdeModulePkg/Core/DxeIplPeim/Arm/DxeLoadFunc.c
@@ -11,6 +11,69 @@ SPDX-License-Identifier: BSD-2-Clause-Patent
 #include "DxeIpl.h"
 
 #include <Library/ArmMmuLib.h>
+#include <Library/PeCoffLib.h>
+
+STATIC
+VOID
+RemapDxeCoreCodeReadOnly (
+  IN EFI_PHYSICAL_ADDRESS  DxeCoreEntryPoint,
+  IN EFI_PEI_HOB_POINTERS  HobList
+  )
+{
+  EFI_PEI_HOB_POINTERS                  Hob;
+  EFI_HOB_MEMORY_ALLOCATION             *ModuleHob;
+  PE_COFF_LOADER_IMAGE_CONTEXT          ImageContext;
+  RETURN_STATUS                         Status;
+  EFI_IMAGE_OPTIONAL_HEADER_PTR_UNION   Hdr;
+  EFI_IMAGE_SECTION_HEADER              *Section;
+  UINTN                                 Index;
+
+  ImageContext.ImageRead = PeCoffLoaderImageReadFromMemory;
+  ImageContext.Handle    = NULL;
+
+  //
+  // Find the module HOB for the DXE core
+  //
+  for (Hob.Raw = HobList.Raw; !END_OF_HOB_LIST (Hob); Hob.Raw = GET_NEXT_HOB (Hob)) {
+    if (GET_HOB_TYPE (Hob) == EFI_HOB_TYPE_MEMORY_ALLOCATION) {
+      ModuleHob = Hob.MemoryAllocation;
+      if ((ModuleHob->AllocDescriptor.MemoryBaseAddress <= DxeCoreEntryPoint &&
+          ((ModuleHob->AllocDescriptor.MemoryBaseAddress + ModuleHob->AllocDescriptor.MemoryLength) > DxeCoreEntryPoint)))
+      {
+        ImageContext.Handle = (VOID *)(UINTN)ModuleHob->AllocDescriptor.MemoryBaseAddress;
+        break;
+      }
+    }
+  }
+
+  ASSERT (ImageContext.Handle != NULL);
+
+  Status = PeCoffLoaderGetImageInfo (&ImageContext);
+  ASSERT_RETURN_ERROR (Status);
+
+  Hdr.Union = (EFI_IMAGE_OPTIONAL_HEADER_UNION *)((UINT8 *)ImageContext.Handle +
+                                                  ImageContext.PeCoffHeaderOffset);
+  ASSERT (Hdr.Pe32->Signature == EFI_IMAGE_NT_SIGNATURE);
+
+  Section = (EFI_IMAGE_SECTION_HEADER *)((UINT8 *)Hdr.Union + sizeof (UINT32) +
+                                         sizeof (EFI_IMAGE_FILE_HEADER) +
+                                         Hdr.Pe32->FileHeader.SizeOfOptionalHeader
+                                         );
+
+  for (Index = 0; Index < Hdr.Pe32->FileHeader.NumberOfSections; Index++) {
+    if ((Section[Index].Characteristics & EFI_IMAGE_SCN_CNT_CODE) != 0) {
+      ArmSetMemoryRegionReadOnly (
+          (UINTN)((UINT8 *)ImageContext.Handle + Section[Index].VirtualAddress),
+          Section[Index].Misc.VirtualSize
+          );
+
+      ArmClearMemoryRegionNoExec (
+          (UINTN)((UINT8 *)ImageContext.Handle + Section[Index].VirtualAddress),
+          Section[Index].Misc.VirtualSize
+          );
+    }
+  }
+}
 
 /**
    Transfers control to DxeCore.
@@ -33,6 +96,12 @@ HandOffToDxeCore (
   VOID        *TopOfStack;
   EFI_STATUS  Status;
 
+  //
+  // DRAM may be mapped with non-executable permissions by default, so
+  // we'll need to map the DXE core code region executable explicitly.
+  //
+  RemapDxeCoreCodeReadOnly (DxeCoreEntryPoint, HobList);
+
   //
   // Allocate 128KB for the Stack
   //
diff --git a/MdeModulePkg/Core/DxeIplPeim/DxeIpl.inf b/MdeModulePkg/Core/DxeIplPeim/DxeIpl.inf
index 62821477d012..d85ca79dc0c3 100644
--- a/MdeModulePkg/Core/DxeIplPeim/DxeIpl.inf
+++ b/MdeModulePkg/Core/DxeIplPeim/DxeIpl.inf
@@ -82,6 +82,7 @@ [LibraryClasses]
 
 [LibraryClasses.ARM, LibraryClasses.AARCH64]
   ArmMmuLib
+  PeCoffLib
 
 [Ppis]
   gEfiDxeIplPpiGuid                      ## PRODUCES
-- 
2.39.1