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Re: [PATCH] Allow userspace control of runtime disabling/enabling of driver probing

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On Tue, Jan 3, 2017 at 3:34 PM, Rafael J. Wysocki <rafael@kernel.org> wrote:
> On Tue, Jan 3, 2017 at 11:58 PM, Kees Cook <keescook@chromium.org> wrote:
>> From: Matthew Garrett <mjg59@coreos.com>
>>
>> Various attacks are made possible due to the large attack surface of
>> kernel drivers and the easy availability of hotpluggable hardware that can
>> be programmed to mimic arbitrary devices. This allows attackers to find a
>> single vulnerable driver and then produce a device that can exploit it by
>> plugging into a hotpluggable bus (such as PCI or USB). This violates user
>> assumptions about unattended systems being secure as long as the screen
>> is locked.
>>
>> The kernel already has support for deferring driver binding in order
>> to avoid problems over suspend/resume. By exposing this to userspace we
>> can disable probing when the screen is locked and simply reenable it on
>> unlock.
>>
>> This is not a complete solution - since this still permits device
>> creation and simply blocks driver binding, it won't stop userspace
>> drivers from attaching to devices and it won't protect against any kernel
>> vulnerabilities in the core bus code. However, it should be sufficient to
>> block attacks like Poisontap (https://samy.pl/poisontap/).
>
> It also looks like this may be worked around by tricking the user to
> unlock the screen while the malicious device is still attached to the
> system.

It certainly changes the temporal aspect of the attack (i.e. there is
a delay and must be "silent" in that the local user cannot notice it).

> If that really is the case, I wonder if it's worth the extra complexity.

I think so, since it's not that much more complexity (it uses the
existing deferral mechanism).

-Kees

-- 
Kees Cook
Nexus Security

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Thread

[PATCH] Allow userspace control of runtime disabling/enabling of  driver probing Kees Cook <keescook@chromium.org> - 2017-01-04 00:00 +0100
  Re: [PATCH] Allow userspace control of runtime disabling/enabling of  driver probing "Rafael J. Wysocki" <rafael@kernel.org> - 2017-01-04 00:40 +0100
    Re: [PATCH] Allow userspace control of runtime disabling/enabling of  driver probing Kees Cook <keescook@chromium.org> - 2017-01-04 00:50 +0100
      Re: [PATCH] Allow userspace control of runtime disabling/enabling of  driver probing "Rafael J. Wysocki" <rafael@kernel.org> - 2017-01-04 02:50 +0100
  Re: [PATCH] Allow userspace control of runtime disabling/enabling of  driver probing Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-01-04 10:40 +0100
    Re: [PATCH] Allow userspace control of runtime disabling/enabling of  driver probing Matthew Garrett <mjg59@coreos.com> - 2017-01-04 19:20 +0100
      Re: [PATCH] Allow userspace control of runtime disabling/enabling of  driver probing Matthew Garrett <mjg59@coreos.com> - 2017-01-04 19:40 +0100
        Re: [PATCH] Allow userspace control of runtime disabling/enabling of  driver probing Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-01-04 20:50 +0100
          Re: [PATCH] Allow userspace control of runtime disabling/enabling of  driver probing Matthew Garrett <mjg59@coreos.com> - 2017-01-04 21:10 +0100
            Re: [PATCH] Allow userspace control of runtime disabling/enabling of  driver probing Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-01-04 21:50 +0100
              Re: [PATCH] Allow userspace control of runtime disabling/enabling of  driver probing Matthew Garrett <mjg59@coreos.com> - 2017-01-04 23:00 +0100
                Re: [PATCH] Allow userspace control of runtime disabling/enabling of  driver probing Matthew Garrett <mjg59@coreos.com> - 2017-01-04 23:40 +0100
      Re: [PATCH] Allow userspace control of runtime disabling/enabling of  driver probing Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-01-04 20:50 +0100
        Re: [PATCH] Allow userspace control of runtime disabling/enabling of  driver probing Matthew Garrett <mjg59@coreos.com> - 2017-01-04 21:10 +0100
          Re: [PATCH] Allow userspace control of runtime disabling/enabling of  driver probing Tomeu Vizoso <tomeu.vizoso@collabora.com> - 2017-01-05 09:20 +0100

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