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Message-ID: <CAKv+Gu8J03Hr1xZ3Q7+z9RV1o4bZOZ83hTTeX=QdQN0rXrMYSQ@mail.gmail.com> Date: Sun, 19 Feb 2017 11:24:08 +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>, Arnd Bergmann <arnd@...db.de>, Kees Cook <keescook@...omium.org>, Ingo Molnar <mingo@...nel.org>, "linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org> Subject: Re: [RFC 1/7] arch: add __ro_mostly_after_init section marker On 19 February 2017 at 10:04, 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. > `__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. > Use `__ro_mostly_after_init` as a way to mark such memory instead when > `__ro_after_init` is not applicable because the memory should be writable > at the described points of time. They are read-only right after kernel init > and writable temporarily only during module_init/exit and dynamic > de/registration for a subsystem. > > Signed-off-by: Hoeun Ryu <hoeun.ryu@...il.com> > --- > include/asm-generic/sections.h | 1 + > include/asm-generic/vmlinux.lds.h | 10 ++++++++++ > include/linux/cache.h | 11 +++++++++++ > 3 files changed, 22 insertions(+) > > diff --git a/include/asm-generic/sections.h b/include/asm-generic/sections.h > index 4df64a1..16a6f21 100644 > --- a/include/asm-generic/sections.h > +++ b/include/asm-generic/sections.h > @@ -34,6 +34,7 @@ extern char __bss_start[], __bss_stop[]; > extern char __init_begin[], __init_end[]; > extern char _sinittext[], _einittext[]; > extern char __start_data_ro_after_init[], __end_data_ro_after_init[]; > +extern char __start_data_ro_mostly_after_init[], __end_data_ro_mostly_after_init[]; > extern char _end[]; > extern char __per_cpu_load[], __per_cpu_start[], __per_cpu_end[]; > extern char __kprobes_text_start[], __kprobes_text_end[]; > diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h > index 4e09b28..cc5f44e 100644 > --- a/include/asm-generic/vmlinux.lds.h > +++ b/include/asm-generic/vmlinux.lds.h > @@ -265,6 +265,15 @@ > __end_data_ro_after_init = .; > #endif > > +#ifndef RO_MOSTLY_AFTER_INIT_DATA > +#define RO_MOSTLY_AFTER_INIT_DATA(align) \ > + . = ALIGN(align); \ > + VMLINUX_SYMBOL(__start_data_ro_mostly_after_init) = .; \ > + *(.data..ro_mostly_after_init) \ > + . = ALIGN(align); \ > + VMLINUX_SYMBOL(__end_data_ro_mostly_after_init) = .; > +#endif > + > /* > * Read only Data > */ > @@ -275,6 +284,7 @@ > *(.rodata) *(.rodata.*) \ > RO_AFTER_INIT_DATA /* Read only after init */ \ > KEEP(*(__vermagic)) /* Kernel version magic */ \ > + RO_MOSTLY_AFTER_INIT_DATA(align) \ You can't really drop this in the middle of a section like this. On arm64, we try very hard to use a minimal segment alignment of 64 KB (of 2 MB if DEBUG_ALIGN_RODATA=y), to ensure that the TLB footprint of the kernel image is minimized. So this should be a separate section in the arm64 linker script. > . = ALIGN(8); \ > VMLINUX_SYMBOL(__start___tracepoints_ptrs) = .; \ > KEEP(*(__tracepoints_ptrs)) /* Tracepoints: pointer array */ \ > diff --git a/include/linux/cache.h b/include/linux/cache.h > index 1be04f8..fd1cb9b 100644 > --- a/include/linux/cache.h > +++ b/include/linux/cache.h > @@ -30,6 +30,17 @@ > #define __ro_after_init __attribute__((__section__(".data..ro_after_init"))) > #endif > > +/* > + * __ro_mostly_after_init is almost like __ro_after_init. > + * but __ro_mostly_after_init section is temporarily writable only during > + * module_init/exit or dynamic de/registeration of a subsystem using > + * set_ro_mostly_after_init_rw/ro pair. > + */ > +#ifndef __ro_mostly_after_init > +#define __ro_mostly_after_init \ > + __attribute__((__section__(".data..ro_mostly_after_init"))) > +#endif > + > #ifndef ____cacheline_aligned > #define ____cacheline_aligned __attribute__((__aligned__(SMP_CACHE_BYTES))) > #endif > -- > 2.7.4 >
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