linux-kernel - Re: [PATCH v4 0/3] kallsyms base relative series

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Date:	Mon, 25 Jan 2016 10:53:34 -0800
From:	Kees Cook <keescook@...omium.org>
To:	Ard Biesheuvel <ard.biesheuvel@...aro.org>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	"linux-s390@...r.kernel.org" <linux-s390@...r.kernel.org>,
	"linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
	"x86@...nel.org" <x86@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...nel.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	"benh@...nel.crashing.org" <benh@...nel.crashing.org>,
	Michael Ellerman <mpe@...erman.id.au>,
	Michal Marek <mmarek@...e.cz>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Arnd Bergmann <arnd@...db.de>,
	linux-arch <linux-arch@...r.kernel.org>,
	Guenter Roeck <linux@...ck-us.net>
Subject: Re: [PATCH v4 0/3] kallsyms base relative series

On Mon, Jan 25, 2016 at 6:19 AM, Ard Biesheuvel
<ard.biesheuvel@...aro.org> wrote:
> This v4 of my kallsyms base relative implementation is now a 3 piece series,
> since it caused some problems due to the way absolute symbols are handled
> by the absolute per cpu code. As it turns out, that code was probably wrong
> in the sense that it caused non-relocated symbol addresses to be emitted
> for values that are in fact relative to the address of the kernel text.
>
> Patch #1 fixes the scripts/kallsyms invocation to only pass the x86_64
> specific --absolute-percpu option if CONFIG_SMP is also set.
>
> Patch #2 reworks the absolute percpu code to only emit those percpu symbols
> as absolute, and not symbols that have been classified as 'A' (absolute) by
> the linker, since that does not mean quite the same thing.
>
> Patch #3 is the original kallsyms base relative patch, with some
> modifications:
> - folded the s/ULLONG_MAX/-1ULL? change made by Andrew
> - ensured that the kallsyms_relative_base value itself is relocated as
>   required.
> - dropped all of the acks and other tags, as they have become outdated with
>   the recent changes to this patch.
>
> Ard Biesheuvel (3):
>   x86: kallsyms: disable absolute percpu symbols on !SMP
>   kallsyms: don't overload absolute symbol type for percpu symbols
>   kallsyms: add support for relative offsets in kallsyms address table

Still works for me!

Reviewed-by: Kees Cook <keescook@...omium.org>
Tested-by: Kees Cook <keescook@...omium.org>

-Kees

>
>  init/Kconfig            |  16 +++
>  kernel/kallsyms.c       |  38 ++++++--
>  scripts/kallsyms.c      | 102 +++++++++++++++++---
>  scripts/link-vmlinux.sh |   6 +-
>  scripts/namespace.pl    |   2 +
>  5 files changed, 142 insertions(+), 22 deletions(-)
>
> --
> 2.5.0
>



-- 
Kees Cook
Chrome OS & Brillo Security