[PATCH] ArmPkg/UncachedMemoryAllocationLib: set XP bit via CPU arch protocol

[Ard Biesheuvel <ard.biesheuvel@linaro.org>]

Commit e7b24ec9785d ("ArmPkg/UncachedMemoryAllocationLib: map uncached
allocations non-executable") adds code that manipulates the GCD memory
space attributes of a newly allocated uncached region without checking
whether this region expose these attributes in its capabilities mask.

Given that the intent is to remove executable permissions from the region,
this is a fairly pointless exercise to begin with, regardless of whether
it is correct or not. The reason is that RO/XP memory attributes in the
GCD memory space map or the UEFI memory map are completely disconnected
from the actual mapping permissions used in the page tables.

So instead, invoke the CPU arch protocol directly, and add the non-exec
attributes in the page tables directly.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
---
 ArmPkg/Library/UncachedMemoryAllocationLib/UncachedMemoryAllocationLib.c   | 36 ++++++++++++++++----
 ArmPkg/Library/UncachedMemoryAllocationLib/UncachedMemoryAllocationLib.inf |  8 ++++-
 2 files changed, 36 insertions(+), 8 deletions(-)

diff --git a/ArmPkg/Library/UncachedMemoryAllocationLib/UncachedMemoryAllocationLib.c b/ArmPkg/Library/UncachedMemoryAllocationLib/UncachedMemoryAllocationLib.c
index b4fbfbcb362b..2530175bab7a 100644
--- a/ArmPkg/Library/UncachedMemoryAllocationLib/UncachedMemoryAllocationLib.c
+++ b/ArmPkg/Library/UncachedMemoryAllocationLib/UncachedMemoryAllocationLib.c
@@ -27,6 +27,10 @@
 #include <Library/DxeServicesTableLib.h>
 #include <Library/CacheMaintenanceLib.h>
 
+#include <Protocol/Cpu.h>
+
+STATIC EFI_CPU_ARCH_PROTOCOL    *mCpu;
+
 VOID *
 UncachedInternalAllocatePages (
   IN EFI_MEMORY_TYPE  MemoryType,
@@ -150,15 +154,19 @@ AllocatePagesFromList (
 
   Status = gDS->GetMemorySpaceDescriptor (Memory, &Descriptor);
   if (EFI_ERROR (Status)) {
-    gBS->FreePages (Memory, Pages);
-    return Status;
+    goto FreePages;
   }
 
   Status = gDS->SetMemorySpaceAttributes (Memory, EFI_PAGES_TO_SIZE (Pages),
-                  EFI_MEMORY_WC | EFI_MEMORY_XP);
+                  EFI_MEMORY_WC);
   if (EFI_ERROR (Status)) {
-    gBS->FreePages (Memory, Pages);
-    return Status;
+    goto FreePages;
+  }
+
+  Status = mCpu->SetMemoryAttributes (mCpu, Memory, EFI_PAGES_TO_SIZE (Pages),
+                   EFI_MEMORY_XP);
+  if (EFI_ERROR (Status)) {
+    goto FreePages;
   }
 
   InvalidateDataCacheRange ((VOID *)(UINTN)Memory, EFI_PAGES_TO_SIZE (Pages));
@@ -166,8 +174,8 @@ AllocatePagesFromList (
   NewNode = AllocatePool (sizeof (FREE_PAGE_NODE));
   if (NewNode == NULL) {
     ASSERT (FALSE);
-    gBS->FreePages (Memory, Pages);
-    return EFI_OUT_OF_RESOURCES;
+    Status = EFI_OUT_OF_RESOURCES;
+    goto FreePages;
   }
 
   NewNode->Base       = Memory;
@@ -181,6 +189,10 @@ AllocatePagesFromList (
 
   *Allocation = NewNode->Allocation;
   return EFI_SUCCESS;
+
+FreePages:
+  gBS->FreePages (Memory, Pages);
+  return Status;
 }
 
 /**
@@ -238,6 +250,16 @@ FreePagesFromList (
  */
 EFI_STATUS
 EFIAPI
+UncachedMemoryAllocationLibConstructor (
+  IN EFI_HANDLE        ImageHandle,
+  IN EFI_SYSTEM_TABLE  *SystemTable
+  )
+{
+  return gBS->LocateProtocol (&gEfiCpuArchProtocolGuid, NULL, (VOID **)&mCpu);
+}
+
+EFI_STATUS
+EFIAPI
 UncachedMemoryAllocationLibDestructor (
   IN EFI_HANDLE        ImageHandle,
   IN EFI_SYSTEM_TABLE  *SystemTable
diff --git a/ArmPkg/Library/UncachedMemoryAllocationLib/UncachedMemoryAllocationLib.inf b/ArmPkg/Library/UncachedMemoryAllocationLib/UncachedMemoryAllocationLib.inf
index d7a0f2f792a1..c637430c9020 100644
--- a/ArmPkg/Library/UncachedMemoryAllocationLib/UncachedMemoryAllocationLib.inf
+++ b/ArmPkg/Library/UncachedMemoryAllocationLib/UncachedMemoryAllocationLib.inf
@@ -22,7 +22,7 @@ [Defines]
   MODULE_TYPE                    = DXE_DRIVER
   VERSION_STRING                 = 1.0
   LIBRARY_CLASS                  = UncachedMemoryAllocationLib
-
+  CONSTRUCTOR                    = UncachedMemoryAllocationLibConstructor
   DESTRUCTOR                     = UncachedMemoryAllocationLibDestructor
 
 [Sources.common]
@@ -42,3 +42,9 @@ [LibraryClasses]
 
 [Pcd]
   gArmTokenSpaceGuid.PcdArmFreeUncachedMemorySizeThreshold
+
+[Protocols]
+  gEfiCpuArchProtocolGuid
+
+[Depex]
+  gEfiCpuArchProtocolGuid
-- 
2.7.4