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Message-Id: <BAB6E3DA-D1D2-4016-AFE3-03E49F0BF672@gmail.com> Date: Tue, 21 Feb 2017 15:21:51 +0900 From: Ho-Eun Ryu <hoeun.ryu@...il.com> To: Ard Biesheuvel <ard.biesheuvel@...aro.org> Cc: kernel-hardening@...ts.openwall.com, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org> Subject: Re: [PATCH 0/7] introduce __ro_mostly_after_init section marker > On 19 Feb 2017, at 8:14 PM, Ard Biesheuvel <ard.biesheuvel@...aro.org> wrote: > > 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. Please see RFC 4/7 [1] and RFC 5/7 [2]. RFC 4 shows that cpu_ap/bp_states are marked as __ro_mostly_after_init. cpu_ap/bp_states can not be marked as __ro_after_init because some modules can write to those objects using cpuhp_setup/remove_state api during module_init/exit. RFC 5 shows that selinux_hooks and selinux_nf_hooks are marked as __ro_mostly_after_init. those hooks can not be marked as __ro_after_init because selinux_disable() function. Those hooks should be writable during selinux_disable to deregister the hooks. [1] https://lkml.org/lkml/2017/2/19/37 [2] https://lkml.org/lkml/2017/2/19/35 > >> `__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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