Reviewed-by: Ashish Singhal Tested-by: Ashish Singhal ________________________________ From: Ard Biesheuvel Sent: Wednesday, March 25, 2020 9:29 AM To: devel@edk2.groups.io Cc: Ard Biesheuvel ; Laszlo Ersek ; Leif Lindholm ; Ashish Singhal Subject: [PATCH v3 1/3] ArmPkg/ArmMmuLib AARCH64: limit recursion when freeing page tables External email: Use caution opening links or attachments FreePageTablesRecursive () traverses the page table tree depth first to free all pages that it finds, without taking into account the level at which it is operating. Since TT_TYPE_TABLE_ENTRY aliases TT_TYPE_BLOCK_ENTRY_LEVEL3, we cannot distinguish table entries from block entries unless we take the level into account, and so we may be dereferencing garbage if we happen to try and free a hierarchy of page tables that has level 3 pages in it. Let's fix this by passing the level into FreePageTablesRecursive (), and limit the recursion to levels < 3. Signed-off-by: Ard Biesheuvel --- ArmPkg/Library/ArmMmuLib/AArch64/ArmMmuLibCore.c | 18 ++++++++++++------ 1 file changed, 12 insertions(+), 6 deletions(-) diff --git a/ArmPkg/Library/ArmMmuLib/AArch64/ArmMmuLibCore.c b/ArmPkg/Library/ArmMmuLib/AArch64/ArmMmuLibCore.c index a43d468b73ca..d78918cf7ba8 100644 --- a/ArmPkg/Library/ArmMmuLib/AArch64/ArmMmuLibCore.c +++ b/ArmPkg/Library/ArmMmuLib/AArch64/ArmMmuLibCore.c @@ -142,15 +142,21 @@ ReplaceTableEntry ( STATIC VOID FreePageTablesRecursive ( - IN UINT64 *TranslationTable + IN UINT64 *TranslationTable, + IN UINTN Level ) { UINTN Index; - for (Index = 0; Index < TT_ENTRY_COUNT; Index++) { - if ((TranslationTable[Index] & TT_TYPE_MASK) == TT_TYPE_TABLE_ENTRY) { - FreePageTablesRecursive ((VOID *)(UINTN)(TranslationTable[Index] & - TT_ADDRESS_MASK_BLOCK_ENTRY)); + ASSERT (Level <= 3); + + if (Level < 3) { + for (Index = 0; Index < TT_ENTRY_COUNT; Index++) { + if ((TranslationTable[Index] & TT_TYPE_MASK) == TT_TYPE_TABLE_ENTRY) { + FreePageTablesRecursive ((VOID *)(UINTN)(TranslationTable[Index] & + TT_ADDRESS_MASK_BLOCK_ENTRY), + Level + 1); + } } } FreePages (TranslationTable, 1); @@ -254,7 +260,7 @@ UpdateRegionMappingRecursive ( // possible for existing table entries, since we cannot revert the // modifications we made to the subhierarchy it represents.) // - FreePageTablesRecursive (TranslationTable); + FreePageTablesRecursive (TranslationTable, Level + 1); } return Status; } -- 2.17.1 ----------------------------------------------------------------------------------- This email message is for the sole use of the intended recipient(s) and may contain confidential information. Any unauthorized review, use, disclosure or distribution is prohibited. If you are not the intended recipient, please contact the sender by reply email and destroy all copies of the original message. -----------------------------------------------------------------------------------