On Wed, Jul 20, 2016 at 01:45:42PM +1000, Balbir Singh wrote:

quoted

IOW, if your kernel forced signature verification, you should not be
able to do sig_enforce=0. If you kernel did not have
CONFIG_MODULE_SIG_FORCE=y, then sig_enforce should be 0 by default anyway
and you are not making it worse using command line.

OK.. I checked and you are right, but that is an example and there are
other things like security=, thermal.*, nosmep, nosmap that need auditing
for safety and might hurt the system security if used. I still think
think that assuming you can pass any command line without breaking security
is a broken argument.

Quite, and you don't need to run code in a privileged environment to do
any of that.

It's also not trivial to protect against: new kernels gain new arguments
which older kernels may not know about.  No matter how much protection
is built into older kernels, newer kernels can become vulnerable through
the addition of further arguments.

Also, how sure are we that there are no stack overflow issues with kernel
command line parsing?  Can we be sure that there's none?  This is
something which happens early in the kernel boot, before the full memory
protections have been set up.

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