Re: [PATCH] killswitch: add per-function short-circuit mitigation primitive

[Sasha Levin <sashal@kernel.org>]

On Mon, May 18, 2026 at 07:57:37PM -0400, Paul Moore wrote:
>On Mon, May 18, 2026 at 7:23 PM Song Liu <song@kernel.org> wrote:
>> On Mon, May 18, 2026 at 2:29 PM Paul Moore <paul@paul-moore.com> wrote:
>> [...]
>> > In my opinion, making killswitch an LSM is more of a procedural item
>> > that deals with how we view a capability like killswitch.  I
>> > personally view killswitch as somewhat similar to Lockdown, which is
>> > why I made the suggestion.
>> >
>> > The use of kprobes, while an interesting idea, presents problems as
>> > allowing any kernel symbol to be killed introduces the potential for
>> > security regressions.  As a reminder, some LSMs, as well as other
>> > kernel subsystems, have mechanisms in place to restrict root and/or
>> > enforce one-way configuration locks; while many people equate "root"
>> > with full control, in many cases today that is not strictly correct.
>> >
>> > Yes, kprobes have been around for some time, this is not a new
>> > problem, but killswitch makes it far more convenient and accessible to
>> > do dangerous things with kprobes.  If killswitch makes it past the RFC
>> > stage without any significant changes to its kill mechanism, we may
>> > need to start considering more liberal usage of NOKPROBE_SYMBOL()
>> > which I think would be an unfortunate casualty.
>>
>> I don't think we can use NOKPROBE_SYMBOL(). There are functions
>> that we don't want to killswitch, but still want to trace.
>
>That was exactly my point, but we need to figure something out so
>killswitch doesn't make it easier to cause a regression.

At this point it sounds like you're trying to stop root from shooting itself in
the foot, which we always avoided doing.

killswitch doesn't add any new functionality in that regard: rood can always
load a module, write to /dev/mem, etc which would allow it to do the same
thing. It's just a more convenient way to do it.

-- 
Thanks,
Sasha