Re: [PATCH] mm/migrate: fix do_pages_move for compat pointers

[Arnd Bergmann]

On Tue, Oct 3, 2023, at 18:49, Andrew Morton wrote:
> On Tue,  3 Oct 2023 10:48:56 -0400 Gregory Price 
> <gourry.memverge@xxxxxxxxx> wrote:
>
>> do_pages_move does not handle compat pointers for the page list.
>> correctly.  Add in_compat_syscall check and appropriate get_user
>> fetch when iterating the page list.
>
> What are the userspace visible effects of this change?

It makes the syscall in compat mode (32-bit userspace, 64-bit kernel)
work the same way as the native 32-bit syscall again, restoring the
behavior before my broken commit 5b1b561ba73c ("mm: simplify
compat_sys_move_pages").

       Arnd