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Date: Mon, 20 Feb 2017 10:02:13 +0000
From: Mark Rutland <mark.rutland@....com>
To: Hoeun Ryu <hoeun.ryu@...il.com>
Cc: kernel-hardening@...ts.openwall.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/7] introduce __ro_mostly_after_init
section marker
On Sun, Feb 19, 2017 at 07:03:38PM +0900, Hoeun Ryu 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.
Could you elaborate on this?
For modules, I assume that the __ro_after_init data structures are part
of the module, and not part of the "real" kernel image. Is that the case?
Which specific subsystems whish to modify data structures that are
__ro_after_init?
This sounds like the proposed mostly-ro/rarely-rw stuff would be a
better fit for that case.
Thanks,
Mark.
> `__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
>
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