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

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Message-ID: <CAGXu5jLhZMMS_StwD_2yDPoF1tL1OwfBrfo3n217RYnrHkwMww@mail.gmail.com>
Date:	Tue, 23 Feb 2016 12:53:25 -0800
From:	Kees Cook <keescook@...omium.org>
To:	PaX Team <pageexec@...email.hu>
Cc:	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>,
	"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 Mon, Feb 22, 2016 at 3:21 PM, PaX Team <pageexec@...email.hu> wrote:
> On 22 Feb 2016 at 12:46, Kees Cook wrote:
>
>> GCC really wants to declare the section. :(
>
> hmm, i see, so how about going about it another way. instead of trying
> to do this at compile/link time, do it an load/runtime. one way of doing
> it would be to preserve a page in .rodata then map in a code page underneath
> that holds your empty function (which you can generate from C). it'd be
> somewhat similar to how the vsyscall page on amd64 is mapped (or used to
> be mapped) from the kernel image into its userland visible place.

I prefer using all the "regular" mechanisms so that I really know I'm
exercising the actual case I want to be testing. (i.e. I don't want to
bypass the linker.)

If only there were some way to filter gcc output, like with plugins. ;)

-Kees

-- 
Kees Cook
Chrome OS & Brillo Security