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Date:   Tue, 3 Oct 2023 10:17:17 -0700
From:   Andrew Morton <akpm@linux-foundation.org>
To:     "Arnd Bergmann" <arnd@arndb.de>
Cc:     "Gregory Price" <gourry.memverge@gmail.com>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org,
        "Gregory Price" <gregory.price@memverge.com>
Subject: Re: [PATCH] mm/migrate: fix do_pages_move for compat pointers
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On Tue, 03 Oct 2023 19:01:45 +0200 "Arnd Bergmann" <arnd@arndb.de> wrote:

> On Tue, Oct 3, 2023, at 18:57, Arnd Bergmann wrote:
> > On Tue, Oct 3, 2023, at 18:49, Andrew Morton wrote:
> >> On Tue,  3 Oct 2023 10:48:56 -0400 Gregory Price 
> >> <gourry.memverge@gmail.com> 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").
> 
> More specifically, my patch moved the parsing of the 'pages'
> array from the main entry point into do_pages_stat(), which left
> the syscall working correctly for the 'stat' operation (nodes = NULL),
> while the 'move' operation (nodes != NULL) is now missing
> the conversion and interprets 'pages' as an array of 64-bit
> pointers instead of the intended 32-bit userspace pointers.
> 

Thanks.  So is a cc:stable warranted?