linux-kernel - Re: [PATCHv2 1/4] arm64: dump: Make ptdump debugfs a separate option

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Date:   Wed, 12 Oct 2016 15:57:46 -0700
From:   Laura Abbott <labbott@...hat.com>
To:     Kees Cook <keescook@...omium.org>
Cc:     AKASHI Takahiro <takahiro.akashi@...aro.org>,
        Mark Rutland <mark.rutland@....com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        David Brown <david.brown@...aro.org>,
        Will Deacon <will.deacon@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        LKML <linux-kernel@...r.kernel.org>,
        "kernel-hardening@...ts.openwall.com" 
        <kernel-hardening@...ts.openwall.com>
Subject: Re: [PATCHv2 1/4] arm64: dump: Make ptdump debugfs a separate option

On 10/12/2016 03:45 PM, Kees Cook wrote:
> On Wed, Oct 12, 2016 at 3:31 PM, Laura Abbott <labbott@...hat.com> wrote:
>>
>> ptdump_register currently initializes a set of page table information and
>> registers debugfs. There are uses for the ptdump option without wanting the
>> debugfs options. Split this out to make it a separate option.
>>
>> Signed-off-by: Laura Abbott <labbott@...hat.com>
>> ---
>> v2: Minor style fixups per Mark Rutland, intialization is now separate from
>>     register since it never needed to be combined in the first place, EFI
>>     page table registration.
>> ---
>>  arch/arm64/Kconfig.debug           |  6 +++++-
>>  arch/arm64/include/asm/ptdump.h    | 13 ++++++++-----
>>  arch/arm64/mm/Makefile             |  3 ++-
>>  arch/arm64/mm/dump.c               | 26 +++++---------------------
>>  arch/arm64/mm/ptdump_debugfs.c     | 31 +++++++++++++++++++++++++++++++
>>  drivers/firmware/efi/arm-runtime.c |  5 ++---
>>  6 files changed, 53 insertions(+), 31 deletions(-)
>>  create mode 100644 arch/arm64/mm/ptdump_debugfs.c
>>
>> diff --git a/arch/arm64/Kconfig.debug b/arch/arm64/Kconfig.debug
>> index b661fe7..21a5b74 100644
>> --- a/arch/arm64/Kconfig.debug
>> +++ b/arch/arm64/Kconfig.debug
>> @@ -2,9 +2,13 @@ menu "Kernel hacking"
>>
>>  source "lib/Kconfig.debug"
>>
>> -config ARM64_PTDUMP
>> +config ARM64_PTDUMP_CORE
>> +       def_bool n
>> +
>> +config ARM64_PTDUMP_DEBUGFS
>>         bool "Export kernel pagetable layout to userspace via debugfs"
>
> I think this can be a tristate now, yes? (I did this on x86 so I could
> load ptdump as a module for Chrome OS image testing but then leave the
> module off the read-only partition for release images...)
>
> https://git.kernel.org/linus/8609d1b5daa36350e020e737946c40887af1743a
>
> -Kees
>

I saw the module for x86. arm64 works slightly differently since there
are multiple debugfs dumping sources, the init_mm and EFI page tables.
These are built in and can call register but then have no way to
actually register the debugfs entry when the module is inserted since
the current config covers both/all of the exporters. I
decided against trying to add the infrastructure to make modularity
work because I was spending more time on that than the actual W^X checks.

Thanks,
Laura

>>         depends on DEBUG_KERNEL
>> +       select ARM64_PTDUMP_CORE
>>         select DEBUG_FS
>>          help
>>           Say Y here if you want to show the kernel pagetable layout in a
>
>
>