From 6b821be1407c46950a2d334e5a240ea5ba47d416 Mon Sep 17 00:00:00 2001
From: Ard Biesheuvel <ardb@kernel.org>
Date: Tue, 7 Feb 2023 16:09:56 +0100
Subject: ArmPkg/ArmMmuLib: Implement EFI_MEMORY_RP using access flag

Implement support for read-protected memory by wiring it up to the
access flag in the page table descriptor. The resulting mapping is
implicitly non-writable and non-executable as well, but this is good
enough for implementing this attribute, as we never rely on write or
execute permissions without read permissions.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Reviewed-by: Leif Lindholm <quic_llindhol@quicinc.com>
---
 ArmPkg/Library/ArmMmuLib/AArch64/ArmMmuLibCore.c | 58 ++++++++++++++++++++++--
 ArmPkg/Library/ArmMmuLib/Arm/ArmMmuLibUpdate.c   | 48 ++++++++++++++++++++
 2 files changed, 103 insertions(+), 3 deletions(-)

(limited to 'ArmPkg/Library')

diff --git a/ArmPkg/Library/ArmMmuLib/AArch64/ArmMmuLibCore.c b/ArmPkg/Library/ArmMmuLib/AArch64/ArmMmuLibCore.c
index 764c7d3..6d21a2e 100644
--- a/ArmPkg/Library/ArmMmuLib/AArch64/ArmMmuLibCore.c
+++ b/ArmPkg/Library/ArmMmuLib/AArch64/ArmMmuLibCore.c
@@ -438,7 +438,11 @@ GcdAttributeToPageAttribute (
     PageAttributes |= TT_AP_NO_RO;
   }
 
-  return PageAttributes | TT_AF;
+  if ((GcdAttributes & EFI_MEMORY_RP) == 0) {
+    PageAttributes |= TT_AF;
+  }
+
+  return PageAttributes;
 }
 
 EFI_STATUS
@@ -459,9 +463,9 @@ ArmSetMemoryAttributes (
     // No memory type was set in Attributes, so we are going to update the
     // permissions only.
     //
-    PageAttributes   &= TT_AP_MASK | TT_UXN_MASK | TT_PXN_MASK;
+    PageAttributes   &= TT_AP_MASK | TT_UXN_MASK | TT_PXN_MASK | TT_AF;
     PageAttributeMask = ~(TT_ADDRESS_MASK_BLOCK_ENTRY | TT_AP_MASK |
-                          TT_PXN_MASK | TT_XN_MASK);
+                          TT_PXN_MASK | TT_XN_MASK | TT_AF);
   }
 
   return UpdateRegionMapping (
@@ -534,6 +538,54 @@ ArmClearMemoryRegionNoExec (
            );
 }
 
+/**
+  Convert a region of memory to read-protected, by clearing the access flag.
+
+  @param  BaseAddress           The start of the region.
+  @param  Length                The size of the region.
+
+  @retval EFI_SUCCESS           The attributes were set successfully.
+  @retval EFI_OUT_OF_RESOURCES  The operation failed due to insufficient memory.
+
+**/
+EFI_STATUS
+ArmSetMemoryRegionNoAccess (
+  IN  EFI_PHYSICAL_ADDRESS  BaseAddress,
+  IN  UINT64                Length
+  )
+{
+  return SetMemoryRegionAttribute (
+           BaseAddress,
+           Length,
+           0,
+           ~(TT_ADDRESS_MASK_BLOCK_ENTRY | TT_AF)
+           );
+}
+
+/**
+  Convert a region of memory to read-enabled, by setting the access flag.
+
+  @param  BaseAddress           The start of the region.
+  @param  Length                The size of the region.
+
+  @retval EFI_SUCCESS           The attributes were set successfully.
+  @retval EFI_OUT_OF_RESOURCES  The operation failed due to insufficient memory.
+
+**/
+EFI_STATUS
+ArmClearMemoryRegionNoAccess (
+  IN  EFI_PHYSICAL_ADDRESS  BaseAddress,
+  IN  UINT64                Length
+  )
+{
+  return SetMemoryRegionAttribute (
+           BaseAddress,
+           Length,
+           TT_AF,
+           ~TT_ADDRESS_MASK_BLOCK_ENTRY
+           );
+}
+
 EFI_STATUS
 ArmSetMemoryRegionReadOnly (
   IN  EFI_PHYSICAL_ADDRESS  BaseAddress,
diff --git a/ArmPkg/Library/ArmMmuLib/Arm/ArmMmuLibUpdate.c b/ArmPkg/Library/ArmMmuLib/Arm/ArmMmuLibUpdate.c
index 23f613f..247cf87 100644
--- a/ArmPkg/Library/ArmMmuLib/Arm/ArmMmuLibUpdate.c
+++ b/ArmPkg/Library/ArmMmuLib/Arm/ArmMmuLibUpdate.c
@@ -523,3 +523,51 @@ ArmClearMemoryRegionReadOnly (
            TT_DESCRIPTOR_SECTION_AP_MASK
            );
 }
+
+/**
+  Convert a region of memory to read-protected, by clearing the access flag.
+
+  @param  BaseAddress           The start of the region.
+  @param  Length                The size of the region.
+
+  @retval EFI_SUCCESS           The attributes were set successfully.
+  @retval EFI_OUT_OF_RESOURCES  The operation failed due to insufficient memory.
+
+**/
+EFI_STATUS
+ArmSetMemoryRegionNoAccess (
+  IN  EFI_PHYSICAL_ADDRESS  BaseAddress,
+  IN  UINT64                Length
+  )
+{
+  return SetMemoryAttributes (
+           BaseAddress,
+           Length,
+           EFI_MEMORY_RP,
+           TT_DESCRIPTOR_SECTION_AF
+           );
+}
+
+/**
+  Convert a region of memory to read-enabled, by setting the access flag.
+
+  @param  BaseAddress           The start of the region.
+  @param  Length                The size of the region.
+
+  @retval EFI_SUCCESS           The attributes were set successfully.
+  @retval EFI_OUT_OF_RESOURCES  The operation failed due to insufficient memory.
+
+**/
+EFI_STATUS
+ArmClearMemoryRegionNoAccess (
+  IN  EFI_PHYSICAL_ADDRESS  BaseAddress,
+  IN  UINT64                Length
+  )
+{
+  return SetMemoryAttributes (
+           BaseAddress,
+           Length,
+           0,
+           TT_DESCRIPTOR_SECTION_AF
+           );
+}
-- 
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