linux-kernel - Re: [PATCH] arm: don't allow CONFIG_DEBUG_SET_MODULE_RONX if CONFIG_JUMP

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Date:	Thu, 3 Apr 2014 16:14:54 -0700
From:	Kees Cook <keescook@...omium.org>
To:	Rabin Vincent <rabin@....in>
Cc:	Laura Abbott <lauraa@...eaurora.org>,
	Alexander Holler <holler@...oftware.de>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will.deacon@....com>,
	LKML <linux-kernel@...r.kernel.org>,
	Russell King <linux@....linux.org.uk>
Subject: Re: [PATCH] arm: don't allow CONFIG_DEBUG_SET_MODULE_RONX if
 CONFIG_JUMP_LABEL is enabled

On Tue, Apr 1, 2014 at 4:08 PM, Rabin Vincent <rabin@....in> wrote:
> 2014-04-01 20:36 GMT+02:00 Kees Cook <keescook@...omium.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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