linux-kernel - Re: [PATCH] mm/migrate: fix do_pages

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Message-Id: <325de88f-1237-4910-aa2a-97707bedae26@app.fastmail.com>
Date:   Tue, 03 Oct 2023 18:57:37 +0200
From:   "Arnd Bergmann" <arnd@...db.de>
To:     "Andrew Morton" <akpm@...ux-foundation.org>,
        "Gregory Price" <gourry.memverge@...il.com>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        "Gregory Price" <gregory.price@...verge.com>
Subject: Re: [PATCH] mm/migrate: fix do_pages_move for compat pointers

On Tue, Oct 3, 2023, at 18:49, Andrew Morton wrote:
> On Tue,  3 Oct 2023 10:48:56 -0400 Gregory Price 
> <gourry.memverge@...il.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").

       Arnd