On Wed, Mar 25, 2020 at 16:29:38 +0100, Ard Biesheuvel wrote:
> 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 <ard.biesheu...@linaro.org>
LGTM
Reviewed-by: Leif Lindholm <l...@nuviainc.com>
One question, which does not require any action on this patch:
Could that 3 be a #define (or Pcd) for future-proofing, or do the
bindings already restrict us in ways that can't reasonably be tweaked?
> ---
> 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
>
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