linux-kernel - Re: [kernel-hardening] [PATCH 0/7] introduce __ro_mostly_after

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Date:   Sun, 19 Feb 2017 11:14:18 +0000
From:   Ard Biesheuvel <ard.biesheuvel@...aro.org>
To:     Hoeun Ryu <hoeun.ryu@...il.com>
Cc:     kernel-hardening@...ts.openwall.com,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [kernel-hardening] [PATCH 0/7] introduce __ro_mostly_after_init
 section marker

Hi Hoeun,

On 19 February 2017 at 10:03, Hoeun Ryu <hoeun.ryu@...il.com> wrote:
>  After `__ro_after_init` marker is included in kernel, many kernel data
> objects can be read-only-after-init. But there are many other places that
> would be good to read-only-after-init but `__ro_after_init` can not be simply
> applicable to them because they should be writable at some points, which are
> during module_init/exit or dynamic de/registration for a specific subsystem.

The argument sounds reasonable, but it would really help if you could
describe some use cases in more detail.

>  `__ro_mostly_after_init` is basically the same to `__ro_after_init`. The
> section is mapped as read-only after kernel init. The different thing is
> this section is temporarily mapped as read-write during module_init/exit and
> de/registration of a subsystem using set_ro_mostly_after_init_rw/ro pair.
>
> - Tested only on arm64.
>
> Description:
>   0001 patch is `__ro_mostly_after_init` itself.
>   0002 patch is to add set_ro_mostly_after_init_rw/ro pair using
>     set_memory_rw/ro.
>   0003 patch is to make the section read-write in module_init/exit.
>   0004 patch is an example for dynamic init/deinit of a subsystem.
>   0005 patch is an example for __ro_mostly_after_init section modified during
>     module_init/exit.
>   0006/0007 patches are fixes for arm64 kernel mapping.
>
> Hoeun Ryu (7):
>   arch: add __ro_mostly_after_init section marker
>   init: add set_ro_mostly_after_init_rw/ro function
>   module: modify memory attrs for __ro_mostly_after_init during
>     module_init/exit
>   selinux: mark __ro_mostly_after_init for selinux_hooks/selinux_nf_ops
>   cpu: mark ro_mostly_after_init for cpuhp_ap/bp_states
>   arm64: add __map_kernel_segment to accept additional vm flags
>   arm64: map seperately rodata sections for __ro_mostly_after_init
>     section
>
>  arch/arm64/mm/mmu.c               | 44 ++++++++++++++++++++++++++++++++-------
>  include/asm-generic/sections.h    |  1 +
>  include/asm-generic/vmlinux.lds.h | 10 +++++++++
>  include/linux/cache.h             | 11 ++++++++++
>  include/linux/init.h              |  6 ++++++
>  init/main.c                       | 24 +++++++++++++++++++++
>  kernel/cpu.c                      |  4 ++--
>  kernel/module.c                   | 10 +++++++--
>  security/selinux/hooks.c          |  8 +++++--
>  9 files changed, 105 insertions(+), 13 deletions(-)
>
> --
> 2.7.4
>