linux-kernel - Re: [PATCH 0/2] Proper ro_after

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Message-ID: <CAGXu5j+LOL=wD7djNJrz-iAFRhuKxuZdjKhVCPWfzC_O=DmfxA@mail.gmail.com>
Date:	Tue, 7 Jun 2016 08:49:14 -0700
From:	Kees Cook <keescook@...omium.org>
To:	Heiko Carstens <heiko.carstens@...ibm.com>
Cc:	Ingo Molnar <mingo@...nel.org>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 0/2] Proper ro_after_init implementation on s390

On Tue, Jun 7, 2016 at 5:06 AM, Heiko Carstens
<heiko.carstens@...ibm.com> wrote:
> These two patches allow a proper ro_after_init implementation on s390.
>
> The current implementation maps __ro_after_init to __read_mostly,
> which means that ro_after_init data won't be write protected at all.
>
> Reason for this is that s390 write protects rodata very early (before
> init calls) and therefore adding ro_after_init data to rodata would
> lead to crashes.
>
> Since I don't want to mark the page table entries much later read-only
> on s390 just to make this work, allow an architecture specific
> handling which can be used to move the ro_after_init data to a
> different place which can be marked read-only later when
> mark_rodata_ro gets executed.
>
> Note: these patches require the s390 kernel page table splitting
> support which currently is only available at
>
> git://git.kernel.org/pub/scm/linux/kernel/git/s390/linux.git features
>
> (included in linux-next)
>
> Therefore, if we can agree on this solution I'd like to add these
> patches to the s390 tree, so it can be merged during the next merge
> window.
>
> Heiko Carstens (2):
>   vmlinux.lds.h: allow arch specific handling of ro_after_init data section
>   s390/mm: add proper __ro_after_init support
>
>  arch/s390/include/asm/cache.h     |  3 ---
>  arch/s390/include/asm/sections.h  |  1 +
>  arch/s390/kernel/vmlinux.lds.S    | 12 +++++++++++-
>  arch/s390/mm/init.c               |  7 ++++---
>  arch/s390/mm/vmem.c               |  7 +++----
>  include/asm-generic/vmlinux.lds.h | 10 +++++++++-
>  6 files changed, 28 insertions(+), 12 deletions(-)

Awesome! This looks great to me! Have you had a chance to look through
any of the arch/s390/ __init code for variables that should be marked
__ro_after_init?

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

-Kees


-- 
Kees Cook
Chrome OS & Brillo Security