linux-kernel - Re: next-20170515: WARNING: CPU: 0 PID: 1 at arch/x86/mm/dump_pagetables.c:236 note

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Message-ID: <CAGXu5jLuccswsUnr_ABC7FyNgGttJ8s54bLndRsoNR44tBvQTw@mail.gmail.com>
Date:   Fri, 19 May 2017 12:16:27 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Andy Lutomirski <luto@...nel.org>
Cc:     Catalin Marinas <catalin.marinas@....com>,
        "Luis R. Rodriguez" <mcgrof@...nel.org>,
        Steven Rostedt <srostedt@...hat.com>,
        Stephen Smalley <sds@...ho.nsa.gov>,
        Ingo Molnar <mingo@...nel.org>,
        Michal Hocko <mhocko@...nel.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Mateusz Guzik <mguzik@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: next-20170515: WARNING: CPU: 0 PID: 1 at arch/x86/mm/dump_pagetables.c:236
 note_page+0x630/0x7e0

On Fri, May 19, 2017 at 11:27 AM, Andy Lutomirski <luto@...nel.org> wrote:
> One thing I've pondered: can we make some debugging mode (kmemleak,
> perhaps?) check that freed memory is RW at the time it's freed?  I
> once wrote some buggy code that freed an R page and caused an OOPS
> much later, and this bug here seems likely to be some code that frees
> RWX memory.

Which begs for even more checks: nothing should ever make a page RWX.
Either R, RW, or RX only... (or X too I guess, in the future).

-Kees

-- 
Kees Cook
Pixel Security