On Tue, May 23, 2017 at 11:36 AM, Kees Cook [off-list ref] wrote:

On Tue, May 23, 2017 at 12:48 AM, Solar Designer [off-list ref] wrote:

quoted

For modules_autoload_mode=2, we already seem to have the equivalent of
modprobe=/bin/true (or does it differ subtly, maybe in return values?),
which I already use at startup on a GPU box like this (preloading
modules so that the OpenCL backends wouldn't need the autoloading):

nvidia-smi
nvidia-modprobe -u -c=0
#modprobe nvidia_uvm
#modprobe fglrx

sysctl -w kernel.modprobe=/bin/true
sysctl -w kernel.hotplug=/bin/true

but it's good to also have this supported more explicitly and more
consistently through modules_autoload_mode=2 while we're at it.  So I
support having this mode as well.  I just question the need to have it
non-resettable.

I agree it's useful to have the explicit =2 state just to avoid
confusion when more systems start implementing
CONFIG_STATIC_USERMODEHELPER and kernel.modprobe becomes read-only
(though the userspace implementation may allow for some way to disable
it, etc). I just like avoiding the upcall to modprobe at all.

I fully support =2 to mean "no automatic loading at all".  I dislike
making it non-resettable.  If you can write to sysctls, then, most
likely you can either call init_module() directly or the system has
module loading disabled entirely.