Subject: Re: [kernel-hardening] [PATCH 0/2] introduce post-init read-only
 memory
To: Ingo Molnar <mingo@kernel.org>, Andy Lutomirski <luto@amacapital.net>
References: <1448401114-24650-1-git-send-email-keescook@chromium.org>
 <CA+rthh-euk2hGGWjsDqXogWSmzmJNV1aiUVfnTfrzyQhndgbOQ@mail.gmail.com>
 <565595F5.32536.DB9FE75@pageexec.freemail.hu>
 <20151126085425.GA29848@gmail.com>
 <CALCETrXrvAY+mXx+JULw7W+xokcSPFgWm5-McJf9EKhYehPhbA@mail.gmail.com>
 <20151127075959.GA24991@gmail.com>
 <CA+55aFxH+Gy4U8WbGWXh+ybrvng8tw1=2CrjPnJSju3+c5XpbA@mail.gmail.com>
 <CAGXu5j+mvknX69Kk1S8u54LR4T+KED8zZdkqQWA9KMrOvtVQtQ@mail.gmail.com>
 <CALCETrVVYMUgxABoEVfJgLtE+nB44aijqG5saq8dTQSTVWxbMA@mail.gmail.com>
 <20151129080505.GA23721@gmail.com>
Cc: Kees Cook <keescook@chromium.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        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>,
        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>
From: "H. Peter Anvin" <hpa@zytor.com>
Message-ID: <565CBC37.9090106@zytor.com>
Date: Mon, 30 Nov 2015 13:14:31 -0800
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101
 Thunderbird/38.3.0
MIME-Version: 1.0
In-Reply-To: <20151129080505.GA23721@gmail.com>
Content-Type: text/plain; charset=windows-1252
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1448
Lines: 36

On 11/29/15 00:05, Ingo Molnar wrote:
> 
> * Andy Lutomirski <luto@amacapital.net> wrote:
> 
>>>>  - 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.)
>>
>> I'd suggest verifying that the page in question is .data..ro_after_init and, if 
>> so, marking that one page RW.
> 
> Yes, this was PaX's suggestion as well, and I agree: doing that turns a quite 
> possibly unrecoverable boot/shutdown time or suspend/resume time (suspend is 
> really a special category of 'bootup') crasher oops into a more informative stack 
> dump.
> 
> These ro related faults tend to trigger when init/deinit is running, and oopsing 
> in those sequences is typically a lot less survivable than say oopsing in a high 
> level system call while not holding locks.
> 

I think what should do is have a debug option which can be set to "rw",
"log" or "oops"; the latter should probably be the default.

	-hpa


--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/