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 <a...@kernel.org>
---
MdeModulePkg/Core/DxeIplPeim/Arm/DxeLoadFunc.c | 73 ++++++++++++++++++++
MdeModulePkg/Core/DxeIplPeim/DxeIpl.inf | 1 +
2 files changed, 74 insertions(+)
diff --git a/MdeModulePkg/Core/DxeIplPeim/Arm/DxeLoadFunc.c
b/MdeModulePkg/Core/DxeIplPeim/Arm/DxeLoadFunc.c
index f62b6dcb38a7..c57ffa87e30f 100644
--- a/MdeModulePkg/Core/DxeIplPeim/Arm/DxeLoadFunc.c
+++ b/MdeModulePkg/Core/DxeIplPeim/Arm/DxeLoadFunc.c
@@ -11,6 +11,73 @@ SPDX-License-Identifier: BSD-2-Clause-Patent
#include "DxeIpl.h"
#include <Library/ArmMmuLib.h>
+#include <Library/PeCoffLib.h>
+
+/**
+ Discover the code sections of the DXE core, and remap them read-only
+ and executable.
+
+ @param DxeCoreEntryPoint The entrypoint of the DXE core executable.
+ @param HobList The list of HOBs passed to the DXE core from PEI.
+**/
+STATIC
+VOID
+RemapDxeCoreCodeReadOnly (
+ IN EFI_PHYSICAL_ADDRESS DxeCoreEntryPoint,
+ IN EFI_PEI_HOB_POINTERS HobList
+ )
+{
+ EFI_PEI_HOB_POINTERS Hob;
+ 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) &&
+ (CompareGuid (&Hob.MemoryAllocation->AllocDescriptor.Name,
&gEfiHobMemoryAllocModuleGuid)) &&
+ (Hob.MemoryAllocationModule->EntryPoint == DxeCoreEntryPoint))
+ {
+ ImageContext.Handle = (VOID
*)(UINTN)Hob.MemoryAllocation->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 +100,12 @@ 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
--
2.39.2
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