From: Kees Cook <keescook@chromium.org>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Ingo Molnar <mingo@kernel.org>,
Andy Lutomirski <luto@amacapital.net>,
PaX Team <pageexec@freemail.hu>,
"kernel-hardening@lists.openwall.com"
<kernel-hardening@lists.openwall.com>,
Mathias Krause <minipli@googlemail.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
Ingo Molnar <mingo@redhat.com>,
Thomas Gleixner <tglx@linutronix.de>,
"H. Peter Anvin" <hpa@zytor.com>, x86-ml <x86@kernel.org>,
Arnd Bergmann <arnd@arndb.de>,
Michael Ellerman <mpe@ellerman.id.au>,
linux-arch <linux-arch@vger.kernel.org>,
Emese Revfy <re.emese@gmail.com>
Subject: Re: [kernel-hardening] [PATCH 0/2] introduce post-init read-only memory
Date: Fri, 27 Nov 2015 12:03:40 -0800 [thread overview]
Message-ID: <CAGXu5j+mvknX69Kk1S8u54LR4T+KED8zZdkqQWA9KMrOvtVQtQ@mail.gmail.com> (raw)
In-Reply-To: <CA+55aFxH+Gy4U8WbGWXh+ybrvng8tw1=2CrjPnJSju3+c5XpbA@mail.gmail.com>
On Fri, Nov 27, 2015 at 10:00 AM, Linus Torvalds
<torvalds@linux-foundation.org> wrote:
> On Thu, Nov 26, 2015 at 11:59 PM, Ingo Molnar <mingo@kernel.org> wrote:
>>
>> * Andy Lutomirski <luto@amacapital.net> wrote:
>>
>>> > Can you see any fragility in such a technique?
>>>
>>> After Linus shot down my rdmsr/rwmsr decoding patch, good luck...
>>
>> I think that case was entirely different, but I've Cc:-ed Linus to shoot my idea
>> down if it's crap.
>
> Yeah, no, I hate it. I'm with the PaX team on this one - I think there
> are three valid responses, and I think we might want to have a dynamic
> config option (kernel command line or proc or whatever) to pick
> between the two:
>
> - just oops and kill the machine, like for any other unhandled kernel
> page fault. This is probably what you should have on a server
This is how the v2 series works now.
> - print a warning and a backtrace, and just mark the page read-write
> so that the machine survives, but we get notified and can fix whatever
> broken code
This seems very easy to add. Should I basically reverse the effects of
mark_rodata_ro(), or should I only make the new ro-after-init section
as RW? (I think the former would be easier.)
> - have an option to disable the RO data logic.
I added this as "rodata=off" in the v2 series.
> I think that second option is good for debugging. In some places,
> oopses that kill things are just too hard to debug (ie it might be the
> modesetting or early boot or whatever).
>
> In fact, I think we should _start_ with the second option - perhaps
> just during the rc's - and then when we're pretty sure all the silly
> bugs it finds (maybe none, who knows) are handled, we should go to the
> first one.
>
> The third option would be purely for "user that cannot fix things
> directly and has reported the problem can now turn off the distracting
> warning". We should never default to it.
>
> Trying to actually *recover* any other way thanm by turning the area
> read-write is just too damn fragile. You can't just skip over the
> instruction that does the write - there are flags values etc that get
> updated by read-modify-write instructions, but as PaX says, there nmay
> also be subsequent logic that gets confused and actually introduces
> even *more* problems downstream if the write is just discarded.
>
> So maybe we could have some kind of "mark it read-only again later"
> thing that tries to make sure it doesn't stay writable for a long
> time, but quite frankly, I don't think it's worth it. Once the write
> has been done, and the warning has been emitted, there's likely very
> little upside to then trying to close the barn doors after that horse
> has bolted.
>
> Linus
-Kees
--
Kees Cook
Chrome OS & Brillo Security
next prev parent reply other threads:[~2015-11-27 20:03 UTC|newest]
Thread overview: 41+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-11-24 21:38 [kernel-hardening] [PATCH 0/2] introduce post-init read-only memory Kees Cook
2015-11-24 21:38 ` [kernel-hardening] [PATCH 1/2] x86: " Kees Cook
2015-11-25 0:34 ` [kernel-hardening] " Andy Lutomirski
2015-11-25 0:44 ` Kees Cook
2015-11-25 0:54 ` Michael Ellerman
2015-11-25 15:03 ` Kees Cook
2015-11-25 23:05 ` Michael Ellerman
2015-11-25 23:32 ` Kees Cook
2015-11-24 21:38 ` [kernel-hardening] [PATCH 2/2] x86, vdso: mark vDSO read-only after init Kees Cook
2015-11-25 9:13 ` [kernel-hardening] [PATCH 0/2] introduce post-init read-only memory Mathias Krause
2015-11-25 10:06 ` Clemens Ladisch
2015-11-25 11:14 ` PaX Team
2015-11-26 15:23 ` Daniel Micay
2015-11-25 11:05 ` PaX Team
2015-11-26 8:54 ` Ingo Molnar
2015-11-26 9:57 ` PaX Team
2015-11-26 10:42 ` Ingo Molnar
2015-11-26 12:14 ` PaX Team
2015-11-27 8:05 ` Ingo Molnar
2015-11-27 15:29 ` PaX Team
2015-11-27 16:30 ` Andy Lutomirski
2015-11-29 8:08 ` Ingo Molnar
2015-11-29 11:15 ` PaX Team
2015-11-29 15:39 ` Ingo Molnar
2015-11-29 18:05 ` Mathias Krause
2015-11-30 8:01 ` Ingo Molnar
2015-11-26 16:11 ` Andy Lutomirski
2015-11-27 7:59 ` Ingo Molnar
2015-11-27 18:00 ` Linus Torvalds
2015-11-27 18:03 ` Linus Torvalds
2015-11-27 20:03 ` Kees Cook [this message]
2015-11-27 20:09 ` Andy Lutomirski
2015-11-29 8:05 ` Ingo Molnar
2015-11-30 21:14 ` H. Peter Anvin
2015-11-30 21:33 ` Kees Cook
2015-11-30 21:38 ` Andy Lutomirski
2015-11-30 21:43 ` H. Peter Anvin
2015-11-25 17:26 ` Kees Cook
2015-11-25 17:31 ` H. Peter Anvin
2015-11-25 18:54 ` Kees Cook
2015-11-25 19:06 ` H. Peter Anvin
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