Re: [PATCH v19 10/25] x86/mm: Update pte_modify for _PAGE_COW

Kees Cook
2021-02-04T20:20:22Z

On Wed, Feb 03, 2021 at 02:55:32PM -0800, Yu-cheng Yu wrote:
> The read-only and Dirty PTE has been used to indicate copy-on-write pages.
> However, newer x86 processors also regard a read-only and Dirty PTE as a
> shadow stack page. In order to separate the two, the software-defined
> _PAGE_COW is created to replace _PAGE_DIRTY for the copy-on-write case, and
> pte_*() are updated.
>
> Pte_modify() changes a PTE to 'newprot', but it doesn't use the pte_*().
> Introduce fixup_dirty_pte(), which sets a dirty PTE, based on _PAGE_RW,
> to either _PAGE_DIRTY or _PAGE_COW.
>
> Apply the same changes to pmd_modify().
>
> Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com>

Reviewed-by: Kees Cook <keescook@chromium.org>

--
Kees Cook