linux-kernel - Re: [PATCH] ARM: mm: mark section-aligned portion of rodata NX

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Message-ID: <CAGXu5jKOn7S-GVu4bZU+B3QbrJZxen4mPzK7-TyzcFf7YiKDNA@mail.gmail.com>
Date:	Mon, 7 Dec 2015 13:56:02 -0800
From:	Kees Cook <keescook@...omium.org>
To:	Ard Biesheuvel <ard.biesheuvel@...aro.org>
Cc:	Laura Abbott <labbott@...oraproject.org>,
	Russell King <linux@....linux.org.uk>,
	Will Deacon <will.deacon@....com>,
	Catalin Marinas <catalin.marinas@....com>,
	Victor Kamensky <victor.kamensky@...aro.org>,
	Vladimir Murzin <vladimir.murzin@....com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] ARM: mm: mark section-aligned portion of rodata NX

On Mon, Dec 7, 2015 at 1:52 PM, Ard Biesheuvel
<ard.biesheuvel@...aro.org> wrote:
> On 7 December 2015 at 21:54, Kees Cook <keescook@...omium.org> wrote:
>> When rodata is large enough that it crosses a section boundary after the
>> kernel text, mark the rest NX. This is as close to full NX of rodata as
>> we can get without splitting page tables or doing section alignment via
>> CONFIG_DEBUG_ALIGN_RODATA.
>>
>> Signed-off-by: Kees Cook <keescook@...omium.org>
>> ---
>> I am baffled why I can't put the ALIGN in the ".start = " initializer.
>> GCC seems to think it's non-static, but only because of the "&" operator.
>> Does anyone see a way to do this that doesn't require the runtime ALIGN?
>
> Yes, but you need to move the ALIGN() expression to the linker script
> as the value of a new symbol

I didn't see a way to do this without actually bumping the alignment
(CONFIG_DEBUG_ALIGN_RODATA already does that, I want the other case).
Do you have an example anywhere I could look at?

-Kees

-- 
Kees Cook
Chrome OS & Brillo Security
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