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Message-ID: <CAKv+Gu9umycZm_UP99ZUifLUBb8MuOZHXgU9nB6XioVMa4eeVw@mail.gmail.com> Date: Sun, 19 Feb 2017 11:35:51 +0000 From: Ard Biesheuvel <ard.biesheuvel@...aro.org> To: Hoeun Ryu <hoeun.ryu@...il.com>, Kees Cook <keescook@...omium.org> Cc: kernel-hardening@...ts.openwall.com, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, Catalin Marinas <catalin.marinas@....com>, Will Deacon <will.deacon@....com>, Mark Rutland <mark.rutland@....com>, Laura Abbott <labbott@...hat.com>, Kefeng Wang <wangkefeng.wang@...wei.com>, Jeremy Linton <jeremy.linton@....com>, "linux-arm-kernel@...ts.infradead.org" <linux-arm-kernel@...ts.infradead.org> Subject: Re: [RFC 7/7] arm64: map seperately rodata sections for __ro_mostly_after_init section On 19 February 2017 at 10:04, Hoeun Ryu <hoeun.ryu@...il.com> wrote: > Map rodata sections seperately for the new __ro_mostly_after_init section. > Attribute of memory for __ro_mostly_after_init section can be changed later > so we need a dedicated vmalloced region for set_memory_rw/ro api. > > Signed-off-by: Hoeun Ryu <hoeun.ryu@...il.com> > --- > arch/arm64/mm/mmu.c | 30 ++++++++++++++++++++++++++---- > 1 file changed, 26 insertions(+), 4 deletions(-) > > diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c > index 91271b1..4a89a2e 100644 > --- a/arch/arm64/mm/mmu.c > +++ b/arch/arm64/mm/mmu.c > @@ -434,8 +434,22 @@ void mark_rodata_ro(void) > * mark .rodata as read only. Use __init_begin rather than __end_rodata > * to cover NOTES and EXCEPTION_TABLE. > */ > - section_size = (unsigned long)__init_begin - (unsigned long)__start_rodata; > - create_mapping_late(__pa_symbol(__start_rodata), (unsigned long)__start_rodata, > + section_size = (unsigned long)__start_data_ro_mostly_after_init - > + (unsigned long)__start_rodata; > + create_mapping_late(__pa_symbol(__start_rodata), > + (unsigned long)__start_rodata, > + section_size, PAGE_KERNEL_RO); > + > + section_size = (unsigned long)__end_data_ro_mostly_after_init - > + (unsigned long)__start_data_ro_mostly_after_init; > + create_mapping_late(__pa_symbol(__start_data_ro_mostly_after_init), > + (unsigned long)__start_data_ro_mostly_after_init, > + section_size, PAGE_KERNEL_RO); > + > + section_size = (unsigned long)__init_begin - > + (unsigned long)__end_data_ro_mostly_after_init; > + create_mapping_late(__pa_symbol(__end_data_ro_mostly_after_init), > + (unsigned long)__end_data_ro_mostly_after_init, > section_size, PAGE_KERNEL_RO); > > /* flush the TLBs after updating live kernel mappings */ > @@ -478,10 +492,18 @@ static void __init map_kernel_segment(pgd_t *pgd, void *va_start, void *va_end, > */ > static void __init map_kernel(pgd_t *pgd) > { > - static struct vm_struct vmlinux_text, vmlinux_rodata, vmlinux_init, vmlinux_data; > + static struct vm_struct vmlinux_text, vmlinux_rodata1, vmlinux_rodata2, vmlinux_ro_mostly_after_init, vmlinux_init, vmlinux_data; > > map_kernel_segment(pgd, _text, _etext, PAGE_KERNEL_EXEC, &vmlinux_text); > - map_kernel_segment(pgd, __start_rodata, __init_begin, PAGE_KERNEL, &vmlinux_rodata); > + map_kernel_segment(pgd, __start_rodata, __start_data_ro_mostly_after_init, PAGE_KERNEL, &vmlinux_rodata1); > + __map_kernel_segment(pgd, > + __start_data_ro_mostly_after_init, > + __end_data_ro_mostly_after_init, > + PAGE_KERNEL, > + &vmlinux_ro_mostly_after_init, > + VM_MAP | VM_ALLOC); > + map_kernel_segment(pgd, __end_data_ro_mostly_after_init, __init_begin, PAGE_KERNEL, &vmlinux_rodata2); > + > map_kernel_segment(pgd, __init_begin, __init_end, PAGE_KERNEL_EXEC, > &vmlinux_init); > map_kernel_segment(pgd, _data, _end, PAGE_KERNEL, &vmlinux_data); > -- > 2.7.4 > While it is correct that you are splitting this into three separate segments (otherwise we would not be able to change the permissions later without risking splitting to occur), I think this leads to unnecessary fragmentation. If there is demand for this feature (but you still need to make the argument for that), I wonder if it wouldn't be sufficient, and much more straightforward, to redefine the __ro_after_init semantics to include the kind of subsystem registration and module init context you are targeting, and implement some hooks to temporarily lift the __ro_after_init r/o permission restrictions in a controlled manner. Kees: any thoughts?
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