[edk2-devel] [PATCH 3/3] 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 | 29 --------------------
 1 file changed, 29 deletions(-)

diff --git a/MdeModulePkg/Core/Dxe/Misc/MemoryProtection.c b/MdeModulePkg/Core/Dxe/Misc/MemoryProtection.c
index 36987843f142..503feb72b5d0 100644
--- a/MdeModulePkg/Core/Dxe/Misc/MemoryProtection.c
+++ b/MdeModulePkg/Core/Dxe/Misc/MemoryProtection.c
@@ -1263,9 +1263,7 @@ ApplyMemoryProtectionPolicy (
   IN  UINT64                Length
   )
 {
-  UINT64      OldAttributes;
   UINT64      NewAttributes;
-  EFI_STATUS  Status;
 
   //
   // The policy configured in PcdDxeNxMemoryProtectionPolicy
@@ -1320,32 +1318,5 @@ ApplyMemoryProtectionPolicy (
   //
   NewAttributes = GetPermissionAttributeForMemoryType (NewType);
 
-  if (OldType != EfiMaxMemoryType) {
-    OldAttributes = GetPermissionAttributeForMemoryType (OldType);
-    if (!mAfterDxeNxMemoryProtectionInit &&
-        (OldAttributes == NewAttributes)) {
-      return EFI_SUCCESS;
-    }
-
-    //
-    // If available, use the EFI memory attribute protocol to obtain
-    // the current attributes of the region. If the entire region is
-    // covered and the attributes match, we don't have to do anything.
-    //
-    if (mMemoryAttribute != NULL) {
-      Status = mMemoryAttribute->GetMemoryAttributes (mMemoryAttribute,
-                                                      Memory,
-                                                      Length,
-                                                      &OldAttributes
-                                                      );
-      if (!EFI_ERROR (Status) && (OldAttributes == NewAttributes)) {
-        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);
 }
-- 
2.39.1



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