linux-kernel - Re: Linker segfault on powerpc when CONFIG_LKDTM=y (was Re: [kernel-hardening] [PATCH 3/5] lkdtm: add function for testing .rodata section)

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Date:	Mon, 1 Aug 2016 12:45:09 -0700
From:	Kees Cook <keescook@...omium.org>
To:	Michael Ellerman <mpe@...erman.id.au>
Cc:	"kernel-hardening@...ts.openwall.com" 
	<kernel-hardening@...ts.openwall.com>,
	Arnd Bergmann <arnd@...db.de>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"David S. Miller" <davem@...emloft.net>,
	Mauro Carvalho Chehab <mchehab@....samsung.com>,
	Jiri Slaby <jslaby@...e.cz>,
	Guenter Roeck <linux@...ck-us.net>,
	LKML <linux-kernel@...r.kernel.org>,
	"linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
	Anton Blanchard <anton@...ba.org>
Subject: Re: Linker segfault on powerpc when CONFIG_LKDTM=y (was Re:
 [kernel-hardening] [PATCH 3/5] lkdtm: add function for testing .rodata section)

On Mon, Aug 1, 2016 at 5:37 AM, Michael Ellerman <mpe@...erman.id.au> wrote:
> Kees Cook <keescook@...omium.org> writes:
>
>> This adds a function that lives in the .rodata section. The section
>> flags are corrected using objcopy since there is no way with gcc to
>> declare section flags in an architecture-agnostic way.
>>
>> Signed-off-by: Kees Cook <keescook@...omium.org>
>> ---
>>  drivers/misc/Makefile       |  7 +++++++
>>  drivers/misc/lkdtm.h        |  6 ++++++
>>  drivers/misc/lkdtm_core.c   | 24 +++++++++++++++++-------
>>  drivers/misc/lkdtm_rodata.c | 10 ++++++++++
>>  4 files changed, 40 insertions(+), 7 deletions(-)
>>  create mode 100644 drivers/misc/lkdtm.h
>>  create mode 100644 drivers/misc/lkdtm_rodata.c
>
> This is blowing up my linker :(
>
>   scripts/link-vmlinux.sh: line 52: 36260 Segmentation fault      (core dumped) ${LD} ${LDFLAGS} ${LDFLAGS_vmlinux} -o ${2} -T ${lds} ${KBUILD_VMLINUX_INIT} --start-group ${KBUILD_VMLINUX_MAIN} --end-group ${1}
>
> Haven't had a chance to debug it further.

Argh. Do you want a quick fix for this now? I can add a PPC CONFIG
blacklist for the rodata check, maybe?

Also, what version of gcc? I'll see if I can reproduce this with a
cross compiler...

-Kees

-- 
Kees Cook
Chrome OS & Brillo Security