linux-kernel - Re: [PATCH v2] ARM: mm: mark section-aligned portion of rodata NX

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Date:	Thu, 11 Feb 2016 18:00:32 +0000
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Kees Cook <keescook@...omium.org>
Cc:	Ard Biesheuvel <ard.biesheuvel@...aro.org>,
	Laura Abbott <labbott@...oraproject.org>,
	Will Deacon <will.deacon@....com>,
	Nicolas Pitre <nico@...aro.org>,
	Catalin Marinas <catalin.marinas@....com>,
	Vladimir Murzin <vladimir.murzin@....com>,
	Victor Kamensky <victor.kamensky@...aro.org>,
	"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 v2] ARM: mm: mark section-aligned portion of rodata NX

On Fri, Jan 22, 2016 at 01:19:03PM -0800, Kees Cook wrote:
> On Tue, Dec 8, 2015 at 10:38 AM, Kees Cook <keescook@...omium.org> wrote:
> > On Mon, Dec 7, 2015 at 11:47 PM, Ard Biesheuvel
> > <ard.biesheuvel@...aro.org> wrote:
> >> On 7 December 2015 at 23:35, Kees Cook <keescook@...omium.org> wrote:
> >>>  /*
> >>> + * Without CONFIG_DEBUG_ALIGN_RODATA, __start_rodata_section_aligned will
> >>> + * be the first section-aligned location after __start_rodata. Otherwise,
> >>> + * it will be equal to __start_rodata.
> >>> + */
> >>> +__start_rodata_section_aligned = ALIGN(__start_rodata, 1 << SECTION_SHIFT);
...

I'm afraid this causes build errors on two configurations:

./arch/arm/kernel/vmlinux.lds:701: undefined symbol `SECTION_SHIFT' referenced in expression

which I think is down to the new __start_rodata_section_aligned line.

Olof's builder errored out with this for both allnoconfig and
lpc18xx_defconfig builds.  Both probably due to CONFIG_MMU being
unset, and hence no definition for SECTION_SHIFT.

I think you need to make this conditional on CONFIG_MMU.

-- 
RMK's Patch system: http://www.arm.linux.org.uk/developer/patches/
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