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

[Borislav Petkov <bp@alien8.de>]

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.

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