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Date: Thu, 3 Apr 2014 16:14:54 -0700
Message-ID: <CAGXu5jKyzbRR4S0+0daygWcE2-BbFi1X6MFAkPqTNbGiT6huSQ@mail.gmail.com>
Subject: Re: [PATCH] arm: don't allow CONFIG_DEBUG_SET_MODULE_RONX if
 CONFIG_JUMP_LABEL is enabled
From: Kees Cook <keescook@chromium.org>
To: Rabin Vincent <rabin@rab.in>
Cc: Laura Abbott <lauraa@codeaurora.org>,
        Alexander Holler <holler@ahsoftware.de>,
        "linux-arm-kernel@lists.infradead.org" 
	<linux-arm-kernel@lists.infradead.org>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will.deacon@arm.com>, LKML <linux-kernel@vger.kernel.org>,
        Russell King <linux@arm.linux.org.uk>
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Sender: linux-kernel-owner@vger.kernel.org

On Tue, Apr 1, 2014 at 4:08 PM, Rabin Vincent <rabin@rab.in> wrote:
> 2014-04-01 20:36 GMT+02:00 Kees Cook <keescook@chromium.org>:
>> Is there something "sticky" about PMD sections that I'm not aware of?
>> Even after calling set_kernel_text_rw(), any writes to kernel memory
>> fault. :(
>
> section_update() updates init_mm, but each mm has a copy of the first
> level page tables.  So your updates to init_mm won't be visibile to
> currently running processes.  (Have a look at arch/arm/mm/ioremap.c's
> vmalloc_seq stuff for some background on how section support is
> handled on non-SMP; the vmalloc code doesn't use sections on SMP.)

Ah-ha! This is the missing piece of information for me. :)

> Here's a patch (probably whitespace damaged, hence also attached) with
> which dynamic ftrace works for me on top your other paches.  Tested on
> a non-LPAE SMP.

Thanks! I'll incorporate calls to set_all_modules_text_rw/ro and see
what I can make work.

-Kees

-- 
Kees Cook
Chrome OS Security
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