[edk2-devel] [RFC 08/13] ArmPkg: Implement ArmSetMemoryOverrideLib

[Ard Biesheuvel]

Implement the ARM version of a NULL class library that can be overlaid
on top of the DXE core to equip it right from its launch with an
implementation of the CPU arch protocol member that sets type and
permission attributes on memory regions.

This bridges the gap between dispatch of DXE core and dispatch of the
DXE driver that implements the CPU arch protocol, removing the need to
rely on memory mappings that are writable and executable at the same
time.

Signed-off-by: Ard Biesheuvel <ardb at kernel.org>
---
 ArmPkg/Library/ArmSetMemoryOverrideLib/ArmSetMemoryOverrideLib.c   | 56 ++++++++++++++++++++
 ArmPkg/Library/ArmSetMemoryOverrideLib/ArmSetMemoryOverrideLib.inf | 25 +++++++++
 2 files changed, 81 insertions(+)

diff --git a/ArmPkg/Library/ArmSetMemoryOverrideLib/ArmSetMemoryOverrideLib.c b/ArmPkg/Library/ArmSetMemoryOverrideLib/ArmSetMemoryOverrideLib.c
new file mode 100644
index 000000000000..d2a9bc96be35
--- /dev/null
+++ b/ArmPkg/Library/ArmSetMemoryOverrideLib/ArmSetMemoryOverrideLib.c
@@ -0,0 +1,56 @@
+/** @file
+  Copyright (c) 2023, Google LLC. All rights reserved.
+
+  SPDX-License-Identifier: BSD-2-Clause-Patent
+**/
+
+#include <PiDxe.h>
+
+#include <Library/ArmMmuLib.h>
+#include <Library/DebugLib.h>
+#include <Protocol/Cpu.h>
+
+extern EFI_CPU_SET_MEMORY_ATTRIBUTES  gCpuSetMemoryAttributes;
+
+STATIC UINTN  mRecursionLevel;
+
+STATIC
+EFI_STATUS
+EFIAPI
+EarlyArmSetMemoryAttributes (
+  IN  EFI_CPU_ARCH_PROTOCOL  *This,
+  IN  EFI_PHYSICAL_ADDRESS   BaseAddress,
+  IN  UINT64                 Length,
+  IN  UINT64                 Attributes
+  )
+{
+  EFI_STATUS  Status;
+
+  // There are cases where the use of strict memory permissions may trigger
+  // unbounded recursion in the page table code. This happens when setting
+  // memory permissions results in a page table split and therefore a page
+  // allocation, which could trigger a recursive invocation of this function.
+  ASSERT (mRecursionLevel < 2);
+
+  mRecursionLevel++;
+
+  Status = ArmSetMemoryAttributes (
+             BaseAddress,
+             Length,
+             Attributes
+             );
+
+  mRecursionLevel--;
+  return Status;
+}
+
+RETURN_STATUS
+EFIAPI
+ArmSetMemoryOverrideLibConstructor (
+  VOID
+  )
+{
+  gCpuSetMemoryAttributes = EarlyArmSetMemoryAttributes;
+
+  return RETURN_SUCCESS;
+}
diff --git a/ArmPkg/Library/ArmSetMemoryOverrideLib/ArmSetMemoryOverrideLib.inf b/ArmPkg/Library/ArmSetMemoryOverrideLib/ArmSetMemoryOverrideLib.inf
new file mode 100644
index 000000000000..f07da3dd2d15
--- /dev/null
+++ b/ArmPkg/Library/ArmSetMemoryOverrideLib/ArmSetMemoryOverrideLib.inf
@@ -0,0 +1,25 @@
+#/** @file
+#  Copyright (c) 2023, Google LLC. All rights reserved.
+#
+#  SPDX-License-Identifier: BSD-2-Clause-Patent
+#**/
+
+[Defines]
+  INF_VERSION                    = 1.29
+  BASE_NAME                      = ArmSetMemoryOverrideLib
+  FILE_GUID                      = 849a43c0-6ad9-428e-8a5a-e090f7853bd3
+  MODULE_TYPE                    = BASE
+  VERSION_STRING                 = 1.0
+  LIBRARY_CLASS                  = NULL|DXE_CORE
+  CONSTRUCTOR                    = ArmSetMemoryOverrideLibConstructor
+
+[Sources.common]
+  ArmSetMemoryOverrideLib.c
+
+[Packages]
+  ArmPkg/ArmPkg.dec
+  MdePkg/MdePkg.dec
+
+[LibraryClasses]
+  ArmMmuLib
+  DebugLib
-- 
2.39.1



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