lsmod | grep cd
Shows nothing for me in a Qubes VM.
lsmod | grep cd
Shows nothing for me in a Qubes VM.
How could an attacker make the kernel load such a module?
Similar as above:
No module load → no exploitation attempt using that module possible.
Or are there other ways a non-root user may cause loading such a module?
Live mode does not use squashfs, but the host/iso does which will fail if the module is not loaded.
Instead of blacklisting you could also skip compiling them into the custom kernel. I guess the cloud kernel from the debian repo won’t have most of those and other stuff. But I also could not get it to work.
Why just stick to non-root?
Because root access means game over if malware gained root. The attacker has way too many ways to compromise the system in persistent ways. Root should be allowed to load the module / mount any disk.
Modprobing stuff would be one of the options for a kernel exploit. Certainly not the only one but at least one options less for the attacker.
Edit: We also have apparmor which limits what a user, including root, can do.
It’s there for me in Virtualbox. Virtualbox might add CD-ROM support by default while Qubes only adds the bare minimum. If so, is there a way to disable it in the Virtualbox ovas by default?
An attacker could attempt to mount something containing the filesystem which will load the module.
Things like thunar-volman and udisks allow unprivileged mounting.
Root can just remove the file that blacklists these modules anyway.
Ubuntu’s default blacklisted modules: modprobe.d\debian - ubuntu/+source/kmod - [no description]
As per linux - Methods root can use to elevate itself to kernel mode - Information Security Stack Exchange, we should disable CPU MSRs.
MSRs are only exposed when the msr
module is loaded so we can blacklist that module to prevent them from being abused.
Does this break virt-detect?
Good point but even if it does, that is only required by two features.
Non-essential features. [1] could be implemented in another way.
Kicksecure has both, VM and host packages:
Whonix doesn’t have that yet and it’s difficult to make the conversion for existing users. (Since this is the “top level” meta package.)
[2] might be lost but I guess that is a feature reduction we can endure.
No. MSRs have nothing to do with that.
I’m pretty sure they do because when i blocked access to them using libvirt it broke hypervisor detection, but @Patrick explained it’s not a big deal.
No, you can even test it yourself by running systemd-detect-virt
and seeing the msr
module isn’t even loaded.
Good to know. Then go for it
Merged.
W: security-misc: obsolete-command-in-modprobe.d-file etc/modprobe.d/30_security-misc.conf install
N:
W: obsolete-command-in-modprobe.d-file
N:
N: Use of 'install' and 'remove' commands in module files in
N: /etc/modprobe.d and /etc/modules-load.d is deprecated and should be
N: replaced with 'softdep' commands.
N:
N: Severity: warning
N:
N: Check: modprobe
N:
I don’t think softdep
would replace security-misc use case of install msr /bin/false
etc.