cpuctl(formely devcpu) patch test request

Stanislav Sedov stas at FreeBSD.org
Mon Jun 16 16:44:46 UTC 2008

On Sun, 15 Jun 2008 15:26:39 -0400
Coleman Kane <cokane at FreeBSD.org> mentioned:

> I think the anti-foot-shooting measures referred to above were also
> taking into consideration for security reasons. It might be valuable for
> someone to be able to configure this feature to be rdmsr-only, thereby
> limiting potential harm vectors in the event that an attacker is likely
> to crack access to the system for supervisory privileges. This would be
> a legitimate consideration to make, especially so that the module could
> at least provide a sane "safe operating mode" to those that would
> benefit from read-only access.
> So, for example, I would consider most crackers to be skilled enough to
> inject an ioctl call somewhere, even if the primary user of the system
> is not so skilled., but they want to use software written by others that
> makes use of this interface.

On the other hand, providing extra security levels via sysctl looks
slightly overkill to me, as if the attacker would be able to issue
a ioctl call somewhere it would be easy to him to make a sysctl
call as well. Priv(9) checks and/or securelevels could be used
to limit the usage of this functionality. Furthermore, there're
a lot of other possible ways to execure an msr instructions,
including loading your own simple kernel object.

Stanislav Sedov
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