linux-kernel - Re: [PATCH 2/2] ARM: mm: keep rodata non-executable

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Date:	Tue, 01 Apr 2014 15:54:42 -0700
From:	Laura Abbott <lauraa@...eaurora.org>
To:	Kees Cook <keescook@...omium.org>,
	"Jon Medhurst (Tixy)" <tixy@...aro.org>
CC:	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will.deacon@....com>,
	Larry Bassel <lbassel@...eaurora.org>,
	Stephen Rothwell <sfr@...b.auug.org.au>,
	Russell King <linux@....linux.org.uk>,
	Nicolas Pitre <nico@...aro.org>,
	Ben Dooks <ben.dooks@...ethink.co.uk>,
	Uwe Kleine-König 
	<u.kleine-koenig@...gutronix.de>,
	Grant Likely <grant.likely@...aro.org>,
	Dave Martin <Dave.Martin@....com>,
	Jiang Liu <liuj97@...il.com>,
	Christoffer Dall <cdall@...columbia.edu>,
	Marc Zyngier <marc.zyngier@....com>,
	Rob Herring <rob.herring@...xeda.com>,
	Vitaly Andrianov <vitalya@...com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Simon Baatz <gmbnomis@...il.com>,
	Jonathan Austin <jonathan.austin@....com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Santosh Shilimkar <santosh.shilimkar@...com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 2/2] ARM: mm: keep rodata non-executable

On 4/1/2014 3:34 PM, Kees Cook wrote:
> On Mon, Mar 24, 2014 at 3:47 AM, Jon Medhurst (Tixy) <tixy@...aro.org> wrote:
>> On Sun, 2014-03-23 at 16:21 -0600, Kees Cook wrote:
>>> For this stage, how about I make this "depends on KEXEC=n &&
>>> KPROBES=n"?
>>
>> There's also ftrace (CONFIG_DYNAMIC_FTRACE I believe) which modifies
>> kernel code with a call to probe_kernel_write(), which GDB uses as well.
>>
>> And grepping for the patch_text() function also shows
>> __arch_jump_label_transform() modifies kernel code. Not sure how and
>> when that gets used.
> 
> Right, so, I'm trying to fix ftrace now, and I've hit a wall. It is as
> if changes to the kernel text PMD aren't being noticed after the
> kernel is running. Does anyone know why this might be happening?
> 
> Code and details here:
> https://lkml.org/lkml/2014/4/1/674
> 
> -Kees
> 

We had a flush_tlb_kernel_page after the pmd_flush in our out of tree code
which makes the text writeable in __patch_text.

Laura

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