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Date:   Fri, 5 May 2023 17:16:58 +0200
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Subject: Re: [PATCH] sysctl: add config to make randomize_va_space RO
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From:   David Hildenbrand <david@redhat.com>
To:     Sam James <sam@gentoo.org>
Cc:     Michael McCracken <michael.mccracken@gmail.com>,
        linux-kernel@vger.kernel.org, serge@hallyn.com, tycho@tycho.pizza,
        Luis Chamberlain <mcgrof@kernel.org>,
        Kees Cook <keescook@chromium.org>,
        Iurii Zaikin <yzaikin@google.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        linux-fsdevel@vger.kernel.org, linux-mm@kvack.org,
        kernel-hardening@lists.openwall.com
References: <20230504213002.56803-1-michael.mccracken@gmail.com>
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 <c50ac5e4-3f84-c52a-561d-de6530e617d7@redhat.com>
Organization: Red Hat
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On 05.05.23 17:15, David Hildenbrand wrote:
> On 05.05.23 09:46, Sam James wrote:
>>
>> David Hildenbrand <david@redhat.com> writes:
>>
>>> On 04.05.23 23:30, Michael McCracken wrote:
>>>> Add config RO_RANDMAP_SYSCTL to set the mode of the randomize_va_space
>>>> sysctl to 0444 to disallow all runtime changes. This will prevent
>>>> accidental changing of this value by a root service.
>>>> The config is disabled by default to avoid surprises.
>>>
>>> Can you elaborate why we care about "accidental changing of this value
>>> by a root service"?
>>>
>>> We cannot really stop root from doing a lot of stupid things (e.g.,
>>> erase the root fs), so why do we particularly care here?
>>
>> (I'm really not defending the utility of this, fwiw).
>>
>> In the past, I've seen fuzzing tools and other debuggers try to set
>> it, and it might be that an admin doesn't realise that. But they could
>> easily set other dangerous settings unsuitable for production, so...
> 
> At least fuzzing tools randomly toggling it could actually find real
> problems. Debugging tools ... makes sense that they might be using it.
> 
> What I understand is, that it's more of a problem that the system
> continues running and the disabled randomization isn't revealed to an
> admin easily.
> 
> If we really care, not sure what's better: maybe we want to disallow
> disabling it only in a security lockdown kernel? Or at least warn the
> user when disabling it? (WARN_TAINT?)

Sorry, not WARN_TAINT. pr_warn() maybe. Tainting the kernel is probably 
a bit too much as well.

-- 
Thanks,

David / dhildenb