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

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Message-ID: <20160223203131.GA1797@davidb.org>
Date:	Tue, 23 Feb 2016 13:31:31 -0700
From:	David Brown <david.brown@...aro.org>
To:	kernel-hardening@...ts.openwall.com
Cc:	PaX Team <pageexec@...email.hu>,
	Ard Biesheuvel <ard.biesheuvel@...aro.org>,
	Laura Abbott <labbott@...hat.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Mark Rutland <mark.rutland@....com>,
	Jeremy Linton <jeremy.linton@....com>,
	Arnd Bergmann <arnd@...db.de>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [kernel-hardening] Re: [PATCH] lkdtm: add test for executing
 .rodata

On Mon, Feb 22, 2016 at 12:46:28PM -0800, Kees Cook wrote:
>On Thu, Feb 18, 2016 at 1:27 PM, PaX Team <pageexec@...email.hu> wrote:
>> On 18 Feb 2016 at 12:34, Ard Biesheuvel wrote:
>>
>>> 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
>>
>> in that case why not use a top-level asm statement to set the section
>> and its attributes (and compile the file with fno-toplevel-reorder)?
>
>GCC really wants to declare the section. :(

Why not then just use its mechanism to set the section on the code?

static void do_nothing_rodata(void)
	__attribute__((section(".rodata")))
{
	return;
}

David