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

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Message-ID: <CAGXu5jK+eYwiEPRGqfF3Ai=cGUkGAGU3o3fwDWCB6RJtHPA-bw@mail.gmail.com>
Date:   Wed, 12 Oct 2016 16:13:41 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Laura Abbott <labbott@...hat.com>
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 Wed, Oct 12, 2016 at 3:57 PM, Laura Abbott <labbott@...hat.com> wrote:
> 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.

Okay, sounds fine. I'll see if I can take a look at this in the future
if no one else beats me to it.

In the meantime, this whole series looks good to me. :)

Reviewed-by: Kees Cook <keescook@...omium.org>

-Kees

-- 
Kees Cook
Nexus Security