januscape-livepatch

A hand-written kernel livepatch for Januscape (CVE-2026-53359), fixing kvm_mmu_get_child_sp and __link_shadow_page without a reboot.

status
PoC since 2026-07
stack
C, Linux livepatch, KVM

Fixes the bugs used by the public Januscape exploit PoC: the gfn mismatch in kvm_mmu_get_child_sp (81ccda30b4e8) and the use-after-free path in __link_shadow_page (0cb2af2ea66ad). Tested on Ubuntu kernels 6.2+. Use at your own risk.

How it was written is explained in Livepatching the Linux kernel: through the eyes of an SRE.

# make && insmod ./januscape-livepatch.ko
# echo 0 > /sys/kernel/livepatch/januscape_livepatch/enabled

Requires linux-source and linux-headers for the running kernel; set the source path in the Makefile.