Re: [PATCH v23 16/28] mm: Fixup places that call pte_mkwrite() directly

Borislav Petkov
2021-03-18T09:48:32Z

On Tue, Mar 16, 2021 at 08:10:42AM -0700, 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

s/effect the same result/have the same result/

> 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()

You can simply say "was writable" instead of trying to hint at the
variable there.

> 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>
> ---
> mm/memory.c | 5 ++---
> mm/migrate.c | 3 +--
> mm/mprotect.c | 2 +-
> 3 files changed, 4 insertions(+), 6 deletions(-)

As with the previous one, I guess this one needs a mm person ACK. I
mean, it is pretty obvious but still...

Thx.

--
Regards/Gruss,
Boris.