Re: [PATCH v19 15/25] mm: Fixup places that call pte_mkwrite() directly

Kees Cook
2021-02-04T20:22:58Z

On Wed, Feb 03, 2021 at 02:55:37PM -0800, Yu-cheng Yu wrote:
> When serving a page fault, maybe_mkwrite() makes a PTE writable if it is in
> a writable vma. A shadow stack vma is writable, but its PTEs need
> _PAGE_DIRTY to be set to become writable. For this reason, maybe_mkwrite()
> has been updated.
>
> There are a few places that call pte_mkwrite() directly, but effect the
> same result as from maybe_mkwrite(). These sites need to be updated for
> shadow stack as well. Thus, change them to maybe_mkwrite():
>
> - do_anonymous_page() and migrate_vma_insert_page() check VM_WRITE directly
> and call pte_mkwrite(), which is the same as maybe_mkwrite(). Change
> them to maybe_mkwrite().
>
> - In do_numa_page(), if the numa entry 'was-writable', then pte_mkwrite()
> is called directly. Fix it by doing maybe_mkwrite().
>
> - In change_pte_range(), pte_mkwrite() is called directly. Replace it with
> maybe_mkwrite().
>
> A shadow stack vma is writable but has different vma
> flags, and handled accordingly in maybe_mkwrite().
>
> Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com>

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

--
Kees Cook