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

From: Kees Cook <keescook@chromium.org>
To: Michael Ellerman <mpe@ellerman.id.au>
Cc: "kernel-hardening@lists.openwall.com" 
	<kernel-hardening@lists.openwall.com>,
	Arnd Bergmann <arnd@arndb.de>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	"David S. Miller" <davem@davemloft.net>,
	Mauro Carvalho Chehab <mchehab@osg.samsung.com>,
	Jiri Slaby <jslaby@suse.cz>, Guenter Roeck <linux@roeck-us.net>,
	LKML <linux-kernel@vger.kernel.org>,
	"linuxppc-dev@lists.ozlabs.org" <linuxppc-dev@lists.ozlabs.org>,
	Anton Blanchard <anton@samba.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)
Date: Mon, 1 Aug 2016 12:45:09 -0700	[thread overview]
Message-ID: <CAGXu5jL8UBfs7NjSgKOeqd9toRgtW3gPu53TPLbTMRJiwRUvPg@mail.gmail.com> (raw)
In-Reply-To: <87h9b4oebf.fsf@concordia.ellerman.id.au>

On Mon, Aug 1, 2016 at 5:37 AM, Michael Ellerman <mpe@ellerman.id.au> wrote:
> Kees Cook <keescook@chromium.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@chromium.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