[RFC 02/13] ArmPkg/ArmMmuLib: Introduce region types for RO/XP WB cached memory

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

To prepare for the enablement of booting EFI with the SCTLR.WXN control
enabled, which makes all writeable memory regions non-executable by
default, introduce a memory type that we will use to describe the flash
region that carries the SEC and PEIM modules that execute in place. Even
if these are implicitly read-only due to the ROM nature, they need to be
mapped with read-only attributes in the page tables to be able to
execute from them.

Also add the XP counterpart which will be used for all normal DRAM right
at the outset.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
---
 ArmPkg/Include/Library/ArmLib.h                  |  6 ++++
 ArmPkg/Library/ArmMmuLib/AArch64/ArmMmuLibCore.c | 29 ++++++++++++++++----
 ArmPkg/Library/ArmMmuLib/Arm/ArmMmuLibCore.c     | 16 +++++++++++
 3 files changed, 45 insertions(+), 6 deletions(-)

diff --git a/ArmPkg/Include/Library/ArmLib.h b/ArmPkg/Include/Library/ArmLib.h
index a53f60d98852..fb1ae57b3522 100644
--- a/ArmPkg/Include/Library/ArmLib.h
+++ b/ArmPkg/Include/Library/ArmLib.h
@@ -35,6 +35,12 @@ typedef enum {
   // Do NOT use below two attributes if you are not sure.
   ARM_MEMORY_REGION_ATTRIBUTE_WRITE_BACK_NONSHAREABLE,
 
+  // Special region types for memory that must be mapped with read-only or
+  // non-execute permissions from the very start, e.g., to support the use
+  // of the WXN virtual memory control.
+  ARM_MEMORY_REGION_ATTRIBUTE_WRITE_BACK_RO,
+  ARM_MEMORY_REGION_ATTRIBUTE_WRITE_BACK_XP,
+
   ARM_MEMORY_REGION_ATTRIBUTE_WRITE_THROUGH,
   ARM_MEMORY_REGION_ATTRIBUTE_DEVICE,
 } ARM_MEMORY_REGION_ATTRIBUTES;
diff --git a/ArmPkg/Library/ArmMmuLib/AArch64/ArmMmuLibCore.c b/ArmPkg/Library/ArmMmuLib/AArch64/ArmMmuLibCore.c
index ee4c5c995ce8..9cdaa8b32c62 100644
--- a/ArmPkg/Library/ArmMmuLib/AArch64/ArmMmuLibCore.c
+++ b/ArmPkg/Library/ArmMmuLib/AArch64/ArmMmuLibCore.c
@@ -37,12 +37,33 @@ ArmMemoryAttributeToPageAttribute (
   IN ARM_MEMORY_REGION_ATTRIBUTES  Attributes
   )
 {
+  UINT64  Permissions = 0;
+
+  switch (Attributes) {
+    case ARM_MEMORY_REGION_ATTRIBUTE_WRITE_BACK_RO:
+      Permissions = TT_AP_NO_RO;
+      break;
+
+    case ARM_MEMORY_REGION_ATTRIBUTE_WRITE_BACK_XP:
+    case ARM_MEMORY_REGION_ATTRIBUTE_DEVICE:
+      if (ArmReadCurrentEL () == AARCH64_EL2) {
+        Permissions = TT_XN_MASK;
+      } else {
+        Permissions = TT_UXN_MASK | TT_PXN_MASK;
+      }
+      break;
+    default:
+      break;
+  }
+
   switch (Attributes) {
     case ARM_MEMORY_REGION_ATTRIBUTE_WRITE_BACK_NONSHAREABLE:
       return TT_ATTR_INDX_MEMORY_WRITE_BACK;
 
     case ARM_MEMORY_REGION_ATTRIBUTE_WRITE_BACK:
-      return TT_ATTR_INDX_MEMORY_WRITE_BACK | TT_SH_INNER_SHAREABLE;
+    case ARM_MEMORY_REGION_ATTRIBUTE_WRITE_BACK_RO:
+    case ARM_MEMORY_REGION_ATTRIBUTE_WRITE_BACK_XP:
+      return TT_ATTR_INDX_MEMORY_WRITE_BACK | TT_SH_INNER_SHAREABLE | Permissions;
 
     case ARM_MEMORY_REGION_ATTRIBUTE_WRITE_THROUGH:
       return TT_ATTR_INDX_MEMORY_WRITE_THROUGH | TT_SH_INNER_SHAREABLE;
@@ -54,11 +75,7 @@ ArmMemoryAttributeToPageAttribute (
     default:
       ASSERT (0);
     case ARM_MEMORY_REGION_ATTRIBUTE_DEVICE:
-      if (ArmReadCurrentEL () == AARCH64_EL2) {
-        return TT_ATTR_INDX_DEVICE_MEMORY | TT_XN_MASK;
-      } else {
-        return TT_ATTR_INDX_DEVICE_MEMORY | TT_UXN_MASK | TT_PXN_MASK;
-      }
+      return TT_ATTR_INDX_DEVICE_MEMORY | Permissions;
   }
 }
 
diff --git a/ArmPkg/Library/ArmMmuLib/Arm/ArmMmuLibCore.c b/ArmPkg/Library/ArmMmuLib/Arm/ArmMmuLibCore.c
index 154298357460..00c5f42cd91a 100644
--- a/ArmPkg/Library/ArmMmuLib/Arm/ArmMmuLibCore.c
+++ b/ArmPkg/Library/ArmMmuLib/Arm/ArmMmuLibCore.c
@@ -106,6 +106,14 @@ PopulateLevel2PageTable (
       PageAttributes  = TT_DESCRIPTOR_PAGE_WRITE_BACK;
       PageAttributes &= ~TT_DESCRIPTOR_PAGE_S_SHARED;
       break;
+    case ARM_MEMORY_REGION_ATTRIBUTE_WRITE_BACK_RO:
+      PageAttributes  = TT_DESCRIPTOR_PAGE_WRITE_BACK;
+      PageAttributes |= TT_DESCRIPTOR_PAGE_AP_NO_RO;
+      break;
+    case ARM_MEMORY_REGION_ATTRIBUTE_WRITE_BACK_XP:
+      PageAttributes  = TT_DESCRIPTOR_PAGE_WRITE_BACK;
+      PageAttributes |= TT_DESCRIPTOR_PAGE_XN_MASK;
+      break;
     case ARM_MEMORY_REGION_ATTRIBUTE_WRITE_THROUGH:
       PageAttributes = TT_DESCRIPTOR_PAGE_WRITE_THROUGH;
       break;
@@ -240,6 +248,14 @@ FillTranslationTable (
       Attributes  = TT_DESCRIPTOR_SECTION_WRITE_BACK;
       Attributes &= ~TT_DESCRIPTOR_SECTION_S_SHARED;
       break;
+    case ARM_MEMORY_REGION_ATTRIBUTE_WRITE_BACK_RO:
+      Attributes  = TT_DESCRIPTOR_SECTION_WRITE_BACK;
+      Attributes |= TT_DESCRIPTOR_SECTION_AP_NO_RO;
+      break;
+    case ARM_MEMORY_REGION_ATTRIBUTE_WRITE_BACK_XP:
+      Attributes  = TT_DESCRIPTOR_SECTION_WRITE_BACK;
+      Attributes |= TT_DESCRIPTOR_SECTION_XN_MASK;
+      break;
     case ARM_MEMORY_REGION_ATTRIBUTE_WRITE_THROUGH:
       Attributes = TT_DESCRIPTOR_SECTION_WRITE_THROUGH;
       break;
-- 
2.39.1