linux-kernel - Re: [PATCH] lkdtm: Fix targets for objcopy usage

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Date:	Tue, 2 Aug 2016 08:18:25 -0700
From:	Kees Cook <keescook@...omium.org>
To:	Mark Rutland <mark.rutland@....com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Arnd Bergmann <arnd@...db.de>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] lkdtm: Fix targets for objcopy usage

On Tue, Aug 2, 2016 at 2:50 AM, Mark Rutland <mark.rutland@....com> wrote:
> On Mon, Aug 01, 2016 at 02:25:48PM -0700, Kees Cook wrote:
>> On Fri, Jul 29, 2016 at 2:37 AM, Mark Rutland <mark.rutland@....com> wrote:
>> > Hi,
>> >
>> > On Thu, Jul 28, 2016 at 07:30:39PM -0700, Kees Cook wrote:
>> >> The targets for lkdtm's objcopy were missing which caused them to always
>> >> be rebuilt. This corrects the problem.
>> >>
>> >> Additionally, commit f8fa70f392fa ("arm64: localise Image objcopy flags")
>> >> has landed now, so this removes the work-around for the global OBJCOPY
>> >> flag setting.
>> >>
>> >> Reported-by: Linus Torvalds <torvalds@...ux-foundation.org>
>> >> Signed-off-by: Kees Cook <keescook@...omium.org>
>> >
>> > With this applied, LKDTM builds fine for me on arm64, the redundant
>> > rebuilds are gone, and the result appears to work. So FWIW:
>> >
>> > Tested-by: Mark Rutland <mark.rutland@....com>
>>
>> Argh, it looks like ARM suffers the same global OBJCOPY problem, so
>> I'm going to leave that change out. :(
>
> :(
>
> FWIW, I dropped a patch for ARM [1] in Russell's patch system [2]. Hopefully
> that will be picked up during the v4.9 merge window.
>
> Looking again, it appears a number of other arches might be affected:
>
> [mark@...erpostej:~/src/linux]% git grep 'OBJCOPYFLAGS\s\+:=' -- arch/*/Makefile
> arch/arm/Makefile:OBJCOPYFLAGS  :=-O binary -R .comment -S
> arch/blackfin/Makefile:OBJCOPYFLAGS     := -O binary -R .note -R .comment -S
> arch/cris/Makefile:OBJCOPYFLAGS := -O binary -R .note -R .comment -S
> arch/ia64/Makefile:OBJCOPYFLAGS := --strip-all
> arch/m32r/Makefile:OBJCOPYFLAGS := -O binary -R .note -R .comment -S
> arch/metag/Makefile:OBJCOPYFLAGS                                := -O binary -R .note -R .comment -S
> arch/mn10300/Makefile:OBJCOPYFLAGS      := -O binary -R .note -R .comment -R .GCC-command-line -R .note.gnu.build-id -S
> arch/openrisc/Makefile:OBJCOPYFLAGS    := -O binary -R .note -R .comment -S
> arch/s390/Makefile:OBJCOPYFLAGS := -O binary
> arch/sh/Makefile:OBJCOPYFLAGS   := -O binary -R .note -R .note.gnu.build-id -R .comment \
> arch/unicore32/Makefile:OBJCOPYFLAGS            := -O binary -R .note -R .note.gnu.build-id -R .comment -S
>
> ... so we probably need to fix up these first, regardless.

Oof, yeah. I'll add this to the "weird little things to fix" TODO list. :)

>
> In the mean time, can we add the targets dependency, but leave the flags
> work-around intact?

Yeah, done. I've sent a pull request to Greg for that now.

-Kees

>
> Thanks,
> Mark.
>
> [1] http://lists.infradead.org/pipermail/linux-arm-kernel/2016-July/442974.html
> [2] http://www.armlinux.org.uk/developer/patches/viewpatch.php?id=8588/1



-- 
Kees Cook
Chrome OS & Brillo Security