[edk2-devel] [Patch V6 06/22] UefiCpuPkg/CpuPageTableLib: Fix issue when splitting leaf entry

[duntan]

When splitting leaf parent entry to smaller granularity, create
child page table before modifing parent entry. In previous code
logic, when splitting a leaf parent entry, parent entry will
point to a null 4k memory before child page table is created in
this 4k memory. When the page table to be modified is the page
table in CR3, if the executed CpuPageTableLib code is in the
range mapped by the modified leaf parent entry, then issue will
happen.

Signed-off-by: Dun Tan <dun.tan at intel.com>
Cc: Eric Dong <eric.dong at intel.com>
Cc: Ray Ni <ray.ni at intel.com>
Cc: Rahul Kumar <rahul1.kumar at intel.com>
Tested-by: Gerd Hoffmann <kraxel at redhat.com>
Acked-by: Gerd Hoffmann <kraxel at redhat.com>
---
 UefiCpuPkg/Library/CpuPageTableLib/CpuPageTableMap.c | 19 +++++++++++--------
 1 file changed, 11 insertions(+), 8 deletions(-)

diff --git a/UefiCpuPkg/Library/CpuPageTableLib/CpuPageTableMap.c b/UefiCpuPkg/Library/CpuPageTableLib/CpuPageTableMap.c
index 57f1db203b..f09bb63ad1 100644
--- a/UefiCpuPkg/Library/CpuPageTableLib/CpuPageTableMap.c
+++ b/UefiCpuPkg/Library/CpuPageTableLib/CpuPageTableMap.c
@@ -363,21 +363,24 @@ PageTableLibMapInLevel (
       //
       // Create 512 child-level entries that map to 2M/4K.
       //
-      ParentPagingEntry->Uintn = (UINTN)Buffer + *BufferSize;
-      ZeroMem ((VOID *)ParentPagingEntry->Uintn, SIZE_4KB);
+      PagingEntry = (IA32_PAGING_ENTRY *)((UINTN)Buffer + *BufferSize);
+      ZeroMem (PagingEntry, SIZE_4KB);
+
+      for (SubOffset = 0, Index = 0; Index < 512; Index++) {
+        PagingEntry[Index].Uint64 = OneOfPagingEntry.Uint64 + SubOffset;
+        SubOffset                += RegionLength;
+      }
 
       //
       // Set NOP attributes
       // Note: Should NOT inherit the attributes from the original entry because a zero RW bit
       //       will make the entire region read-only even the child entries set the RW bit.
       //
+      // Non-leaf entry doesn't have PAT bit. So use ~IA32_PE_BASE_ADDRESS_MASK_40 is to make sure PAT bit
+      // (bit12) in original big-leaf entry is not assigned to PageTableBaseAddress field of non-leaf entry.
+      //
       PageTableLibSetPnle (&ParentPagingEntry->Pnle, &NopAttribute, &AllOneMask);
-
-      PagingEntry = (IA32_PAGING_ENTRY *)(UINTN)IA32_PNLE_PAGE_TABLE_BASE_ADDRESS (&ParentPagingEntry->Pnle);
-      for (SubOffset = 0, Index = 0; Index < 512; Index++) {
-        PagingEntry[Index].Uint64 = OneOfPagingEntry.Uint64 + SubOffset;
-        SubOffset                += RegionLength;
-      }
+      ParentPagingEntry->Uint64 = ((UINTN)(VOID *)PagingEntry) | (ParentPagingEntry->Uint64 & (~IA32_PE_BASE_ADDRESS_MASK_40));
     }
   } else {
     //
-- 
2.31.1.windows.1



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