linux-kernel - Re: [PATCH] lkdtm: add test for executing .rodata

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Message-ID: <CAKv+Gu8_FHVwmerw1aMkNGGn=7NtuWnuSBCXHBsSZXCNRRU7KA@mail.gmail.com>
Date:	Thu, 18 Feb 2016 13:46:38 +0100
From:	Ard Biesheuvel <ard.biesheuvel@...aro.org>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	PaX Team <pageexec@...email.hu>, Laura Abbott <labbott@...hat.com>,
	Kees Cook <keescook@...omium.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Mark Rutland <mark.rutland@....com>,
	Jeremy Linton <jeremy.linton@....com>,
	"kernel-hardening@...ts.openwall.com" 
	<kernel-hardening@...ts.openwall.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] lkdtm: add test for executing .rodata

On 18 February 2016 at 13:07, Arnd Bergmann <arnd@...db.de> wrote:
> On Thursday 18 February 2016 12:34:50 Ard Biesheuvel wrote:
>>
>> We have __section() as an alias for __attribute__((__section__())), so
>> we could use that instead.
>>
>> However, that does not fix the issue Kees is trying to solve, where a
>> .rodata section is emitted with the "x" bit set, which causes the
>> linker to complain:
>>
>> /tmp/cc50ffWw.s: Assembler messages:
>> /tmp/cc50ffWw.s:2: Warning: setting incorrect section attributes for
>> .rodata.text
>>
>> I wonder if we could get away with doing something like
>>
>> AFLAGS_lkdtm.o += -Wa,-W
>>
>> here? This just hides the warnings, but may result in the .rodata
>> section in the vmlinux file to have X permissions as well. I don't
>> think anyone uses an ELF loader to load their kernel, but who knows
>> ...
>
> Don't we also get a warning when we link objects with conflicting
> section attributes?
>

I didn't see one

> Maybe a solution would be to define a separate section for this one
> function, and then use a linker script to move it into .rodata?
> Or maybe "objcopy --set-section-flags  --rename-section"?
>

I think objcopy is the easiest.