linux-kernel - Re: [kernel-hardening] Re: [PATCH] video: constify geode ops structures

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Message-ID: <CAGXu5jJ7HvAKEs0YynnLQH9xJPgb7LKEvuaQtDY=3K9J4xawjQ@mail.gmail.com>
Date:	Mon, 9 Nov 2015 13:24:27 -0800
From:	Kees Cook <keescook@...omium.org>
To:	Julia Lawall <julia.lawall@...6.fr>
Cc:	Emese Revfy <re.emese@...il.com>,
	"kernel-hardening@...ts.openwall.com" 
	<kernel-hardening@...ts.openwall.com>,
	Dan Carpenter <dan.carpenter@...cle.com>,
	Joe Perches <joe@...ches.com>, kernel-janitors@...r.kernel.org,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [kernel-hardening] Re: [PATCH] video: constify geode ops structures

On Mon, Nov 9, 2015 at 9:48 AM, Julia Lawall <julia.lawall@...6.fr> wrote:
> On Mon, 9 Nov 2015, Emese Revfy wrote:
>
>> On Mon, 9 Nov 2015 14:50:47 +0000 (GMT)
>> Julia Lawall <julia.lawall@...6.fr> wrote:
>> > > Actually, it looks like Emese Revfy is going to merge the GCC plugin
>> > > constify stuff sooner rather than later so maybe adding all these consts
>> > > isn't going to be needed.
>> >
>> > Is there any advantage of const over the plugin?  The consts are easy to
>> > add.
>>
>> Hi,
>>
>> I think it's a very good advantage that the plugin constifies automatically
>> without regular maintenance (e.g., generate patches with coccinelle,
>> send patches to the maintainers every new kernel version). ;)
>> But if it doesn't convince you, I did constification by hand (with a coccinelle
>> script) some years ago.
>> There are too many types that can be const and it took too long to prepare and
>> get the maintainers to accept the patches.
>> And it never ends as there are always new types that can be const.
>
> What happens if some structures cannot be made const because there is a
> reassignment somewhere?  Is there any feedback about the problem?

AIUI, for now, we can't make those const (though I would be happy to
be corrected). My hope would be to allow reassignment using something
like PaX's kernel_open/kernel_close inlines to allow for temporary
modification of read-only things (as part of the KERNEXEC feature).

-Kees

>
> julia
>
>>
>> > Does the plugin help for structures that have non-function fields?
>> Yes, it does. See __do_const here:
>> http://www.openwall.com/lists/kernel-hardening/2015/11/06/11
>> or more about the constify plugin:
>> https://pax.grsecurity.net/docs/PaXTeam-H2HC13-PaX-gcc-plugins.pdf
>>
>> --
>> Emese
>>



-- 
Kees Cook
Chrome OS Security
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