[edk2-devel] [PATCH v5 13/38] MdeModulePkg/DxeCore: Unconditionally set memory protections

[Ard Biesheuvel]

Instead of relying on a questionable heuristic that avoids calling into
the SetMemoryAttributes () DXE service when the old memory type and the
new one are subjected to the same NX memory protection policy, make this
call unconditionally. This avoids corner cases where memory region
attributes are out of sync with the policy, either due to the fact that
we are in the middle of ramping up the protections, or due to explicit
invocations of SetMemoryAttributes() by drivers.

This requires the architecture page table code to be able to deal with
this, in particular, it needs to be robust against potential recursion
due to NX policies being applied to newly allocated page tables.

Signed-off-by: Ard Biesheuvel <ardb at kernel.org>
---
 MdeModulePkg/Core/Dxe/Misc/MemoryProtection.c | 12 ------------
 1 file changed, 12 deletions(-)

diff --git a/MdeModulePkg/Core/Dxe/Misc/MemoryProtection.c b/MdeModulePkg/Core/Dxe/Misc/MemoryProtection.c
index b89ab046fa73..5a82eee80781 100644
--- a/MdeModulePkg/Core/Dxe/Misc/MemoryProtection.c
+++ b/MdeModulePkg/Core/Dxe/Misc/MemoryProtection.c
@@ -1246,7 +1246,6 @@ ApplyMemoryProtectionPolicy (
   IN  UINT64                Length
   )
 {
-  UINT64  OldAttributes;
   UINT64  NewAttributes;
 
   //
@@ -1302,16 +1301,5 @@ ApplyMemoryProtectionPolicy (
   //
   NewAttributes = GetPermissionAttributeForMemoryType (NewType);
 
-  if (OldType != EfiMaxMemoryType) {
-    OldAttributes = GetPermissionAttributeForMemoryType (OldType);
-    if (OldAttributes == NewAttributes) {
-      // policy is the same between OldType and NewType
-      return EFI_SUCCESS;
-    }
-  } else if (NewAttributes == 0) {
-    // newly added region of a type that does not require protection
-    return EFI_SUCCESS;
-  }
-
   return gCpu->SetMemoryAttributes (gCpu, Memory, Length, NewAttributes);
 }
-- 
2.39.2



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