Re: Are the keys of mounted encrypted disks secured during reboot?

I'm asking about when a regular shutdown/reboot/suspend-to-disk is
issued. In most cases the rootfs volume is not unmounted because that
would require a pivot_root to a special initrd/ramdisk-rootfs just for
powering off.
So that would mean the device isn't deactivated via cryptsetup -
because that would fail.
In that case, when the kernel is preparing to reboot/poweroff, will it
wipe the keys or just leave them there vulnerable to cold boot or
forensics?

On Mon, Dec 26, 2022 at 7:42 PM Milan Broz <[email protected]> wrote:
>
> On 12/26/22 20:13, John Smith wrote:
> > During the course of proper shutdown/reboot/suspend-to-disk, does the
> > kernel securely erase (or at least free memory of - as it pertains to
> > init_on_free=1) encryption keys of all dmcrypt/luks systems which
> > remained mounted?
>
> If the device is properly deactivated, then keys are always wiped.
>
> (Actually, with LUKS2, dm-crypt no longer keeps own copy of the key, it
> is stored in kernel keyring only for activation and then, obviously, in kernel
> crypto where is is directly used for encryption. So if it is not
> deactivated, it is responsibility of these subsystems to wipe it on reboot.)
>
> For suspend to ram, it is more complicated - there is a way how to wipe key
> and freeze device temporarily (see luksSuspend), but I do no think many systems
> actually use it. Debian has cryptsetup-suspend that can do this AFAIK.
>
> For suspend to disk, the memory should be written to encrypted device.
> (And RAM contents disappears after some short time with no power anyway.)
>
> Milan