linux-kernel - Re: [PATCH] kconfig: Add kernel config option for fuzz testing.

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Date:   Tue, 18 Feb 2020 19:54:40 +0900
From:   Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
To:     Matthew Garrett <mjg59@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>
Cc:     Andi Kleen <ak@...ux.intel.com>,
        "Theodore Y. Ts'o" <tytso@....edu>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Petr Mladek <pmladek@...e.com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Arnd Bergmann <arnd@...db.de>, Jiri Slaby <jslaby@...e.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] kconfig: Add kernel config option for fuzz testing.

On 2020/01/03 4:57, Matthew Garrett wrote:
> On Tue, Dec 17, 2019 at 12:53 AM Dmitry Vyukov <dvyukov@...gle.com> wrote:
>> +Matthew for a lockdown question
>> We are considering [ab]using lockdown (you knew this will happen!) for
>> fuzzing kernel. LOCKDOWN_DEBUGFS is a no-go for us and we may want a
>> few other things that may be fuzzing-specific.
>> The current inflexibility comes from the global ordering of levels:
>>
>> if (kernel_locked_down >= level)
>> if (kernel_locked_down >= what) {
>>
>> Is it done for performance? Or for simplicity?
> 
> Simplicity. Based on discussion, we didn't want the lockdown LSM to
> enable arbitrary combinations of lockdown primitives, both because
> that would make it extremely difficult for userland developers and
> because it would make it extremely easy for local admins to
> accidentally configure policies that didn't achieve the desired
> outcome. There's no inherent problem in adding new options, but really
> right now they should fall into cases where they're protecting either
> the integrity of the kernel or preventing leakage of confidential
> information from the kernel.
> 

Can we resume this topic?

I think build-time lockdown (i.e. kernel config option) is more reliable
and easier to use.