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Message-Id: <FAEFA506-D7DB-4D92-A773-3A6EA966FE4A@gmail.com> Date: Tue, 21 Feb 2017 15:10:45 +0900 From: Ho-Eun Ryu <hoeun.ryu@...il.com> To: Mark Rutland <mark.rutland@....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 20 Feb 2017, at 7:02 PM, Mark Rutland <mark.rutland@....com> wrote: > > 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? > __ro_mostly_after_init is for kernel builtin core subsystems, not for modules themselves. The section can be writable only during kernel init and module_init/exit. Some hooks (or array of hooks) of a core subsystem can be marked as __ro_mostly_after_init similar to that way of __ro_after_init. After that some modules that may write to those hooks of the subsystem to register/deregister something to the subsystem can safely access those section. Please see RFC 3/7 that makes this section writable. In addition, some subsystems may use this marker for their (array of) hooks and make them writable only at some point of time via set_ro_mostly_after_init_rw/ro pair. please read RFC 4/7 for selinux. > Which specific subsystems whish to modify data structures that are > __ro_after_init? I’m not intending to make writable __ro_after_init section but introducing new section marker that works mostly like __ro_after_init but can be written to at some points. please see RFC 5/7 for cpuhotplug. > > 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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