[PATCH v5 21/38] ArmPkg: Implement ArmSetMemoryOverrideLib

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

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@kernel.org>
---
 ArmPkg/ArmPkg.dsc                                                  |  1 +
 ArmPkg/Library/ArmSetMemoryOverrideLib/ArmSetMemoryOverrideLib.c   | 78 ++++++++++++++++++++
 ArmPkg/Library/ArmSetMemoryOverrideLib/ArmSetMemoryOverrideLib.inf | 28 +++++++
 3 files changed, 107 insertions(+)

diff --git a/ArmPkg/ArmPkg.dsc b/ArmPkg/ArmPkg.dsc
index 3fb95d1951a9..43eb0f4f463e 100644
--- a/ArmPkg/ArmPkg.dsc
+++ b/ArmPkg/ArmPkg.dsc
@@ -119,6 +119,7 @@ [Components.common]
   ArmPkg/Library/ArmPsciResetSystemLib/ArmPsciResetSystemLib.inf
   ArmPkg/Library/ArmExceptionLib/ArmExceptionLib.inf
   ArmPkg/Library/ArmExceptionLib/ArmRelocateExceptionLib.inf
+  ArmPkg/Library/ArmSetMemoryOverrideLib/ArmSetMemoryOverrideLib.inf
 
   ArmPkg/Drivers/CpuDxe/CpuDxe.inf
   ArmPkg/Drivers/CpuPei/CpuPei.inf
diff --git a/ArmPkg/Library/ArmSetMemoryOverrideLib/ArmSetMemoryOverrideLib.c b/ArmPkg/Library/ArmSetMemoryOverrideLib/ArmSetMemoryOverrideLib.c
new file mode 100644
index 000000000000..866dbbdaa7d5
--- /dev/null
+++ b/ArmPkg/Library/ArmSetMemoryOverrideLib/ArmSetMemoryOverrideLib.c
@@ -0,0 +1,78 @@
+/** @file
+  Overlay implementation of DXE core gCpuSetMemoryAttributes for ARM.
+
+  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;
+
+/**
+  Clone of CPU_ARCH_PROTOCOL::SetMemoryAttributes() which is made available to
+  the DXE core by NULL library class resolution, so that it can manage page
+  permissions right from the start.
+
+  @param  This                  CPU arch protocol pointer, should be NULL.
+  @param  BaseAddress           Start address of the region.
+  @param  Length                Size of the region, in bytes.
+  @param  Attributes            Attributes to set on the region.
+
+  @retval EFI_SUCCESS           Operation completed successfully.
+  @retval EFI_OUT_OF_RESOURCES  Operation failed due to lack of memory.
+
+**/
+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;
+}
+
+/**
+  Library constructor.
+
+  @retval RETURN_SUCCESS   Operation successful.
+
+**/
+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..2dc9d42d09bd
--- /dev/null
+++ b/ArmPkg/Library/ArmSetMemoryOverrideLib/ArmSetMemoryOverrideLib.inf
@@ -0,0 +1,28 @@
+## @file
+#  Overlay implementation of DXE core gCpuSetMemoryAttributes for ARM.
+#
+#  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
-- 
2.39.2