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Date: Wed, 8 Jun 2016 08:46:02 -0700
From: Kees Cook <keescook@...omium.org>
To: Laura Abbott <labbott@...hat.com>
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>
Subject: Re: [PATCH 3/5] lkdtm: add function for testing .rodata section
On Tue, Jun 7, 2016 at 6:02 PM, Laura Abbott <labbott@...hat.com> wrote:
> On 06/07/2016 02:57 PM, Kees Cook wrote:
>>
>> 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.
>>
>
> Permit me to be the bearer of bad architecture news once again. With
> arm64 cross compiler (both Fedora 6.1.1 and Linaro 5.1)
>
> CC drivers/misc/lkdtm_rodata.o
> OBJCOPY drivers/misc/lkdtm_rodata_objcopy.o
> LD drivers/misc/lkdtm.o
> drivers/misc/lkdtm_rodata_objcopy.o: file not recognized: File format not
> recognized
> scripts/Makefile.build:423: recipe for target 'drivers/misc/lkdtm.o' failed
> make[2]: *** [drivers/misc/lkdtm.o] Error 1
> scripts/Makefile.build:440: recipe for target 'drivers/misc' failed
> make[1]: *** [drivers/misc] Error 2
> Makefile:985: recipe for target 'drivers' failed
> make: *** [drivers] Error 2
>
>
> As far as I can tell this is because arm64 defines OBJCOPYFLAGS and they get
> propagated to objcopy
>
> aarch64-linux-gnu-objcopy -O binary -R .note -R .note.gnu.build-id -R
> .comment
> -S --set-section-flags .text=alloc,readonly
> --rename-section .text=.rodata drivers/misc/lkdtm_rodata.o
> drivers/misc/lkdtm_rodata_objcopy.o
>
> vs x86
>
> objcopy --set-section-flags .text=alloc,readonly --rename-section
> .text=.rodata
> drivers/misc/lkdtm_rodata.o drivers/misc/lkdtm_rodata_objcopy.o
>
>
> specifically it's the -O binary that seems to break things, the same failure
> happens on x86 as well with the the same commands. It works if I clear out
> the OBJCOPYFLAGS variable first but I don't think that's the correct way to
> fix this.
>
> Thanks,
> Laura
>
>
>> 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
>>
>> diff --git a/drivers/misc/Makefile b/drivers/misc/Makefile
>> index c3cb6ad8cc37..b2d3d68dfa22 100644
>> --- a/drivers/misc/Makefile
>> +++ b/drivers/misc/Makefile
>> @@ -59,3 +59,10 @@ obj-$(CONFIG_CXL_BASE) += cxl/
>> obj-$(CONFIG_PANEL) += panel.o
>>
>> lkdtm-$(CONFIG_LKDTM) += lkdtm_core.o
>> +lkdtm-$(CONFIG_LKDTM) += lkdtm_rodata_objcopy.o
>> +
>> +OBJCOPYFLAGS_lkdtm_rodata_objcopy.o := \
>> + --set-section-flags .text=alloc,readonly \
>> + --rename-section .text=.rodata
>> +$(obj)/lkdtm_rodata_objcopy.o: $(obj)/lkdtm_rodata.o
>> + $(call if_changed,objcopy)
Uhhhh... How is arm64 injecting those extra flags? OBJCOPYFLAGS is
being set with := here?
In related news I need to figure out how to get my cross-compiler
builds more well scripted...
-Kees
--
Kees Cook
Chrome OS & Brillo Security
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