UBUNTU: [Config] Disable the hardened usercopy fallback
BugLink: TODO
CONFIG_HARDENED_USERCOPY_FALLBACK has been enabled for a while now and
the only instances of the emitted warning found in Launchpad have been
fixed in Eoan. Lets disable this fallback to strictly enforce hardened
usercopy.
Enable CONFIG_REFCOUNT_FULL on the remaining non-x86 architectures to
ensure that we have refcount_t validation rather than using unchecked
atomic_t implementations.
This change means that armhf, arm64, ppc64el, and s390x kernels will
have stronger validation of refcount_t than i386 and amd64 at the
expense of some performance.
Enable CONFIG_DEBUG_NOTIFIERS to ensure that notifier functions are
present in the core kernel text or module text sections before calling
those functions.
UBUNTU: [Config] Enable linked list manipulation checks
BugLink: TODO
Turn on CONFIG_DEBUG_LIST which does some sanity checking on the
surrounding linked list elements when adding or removing an element. If
the sanity check fails, the list manipulation operation is not performed
and a loud warning is printed to the logs.
This may prevent some attacks that involving a linked list.
