feat(cozystack): disable KVM nested virtualization in Talos skills (CVE-2026-53359)#17
feat(cozystack): disable KVM nested virtualization in Talos skills (CVE-2026-53359)#17Andrei Kvapil (kvaps) wants to merge 2 commits into
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…VE-2026-53359) Prescribe kvm_intel.nested=0 and kvm_amd.nested=0 via machine.install.extraKernelArgs in the talos-bootstrap node overlay, add a Phase 7 review check and a post-upgrade verification, to mitigate CVE-2026-53359 (Januscape). Placing the args under machine.install makes talm re-apply them on every upgrade so the mitigation survives OS bumps. Signed-off-by: Andrei Kvapil <kvapss@gmail.com> Assisted-By: Claude <noreply@anthropic.com>
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Code Review
This pull request implements mitigations for CVE-2026-53359 by disabling KVM nested virtualization across the Talos bootstrap configuration, manual installation steps, and post-upgrade checks. The feedback correctly identifies an error in the post-upgrade verification command, which incorrectly uses 'talm' instead of 'talosctl' to read /proc/cmdline.
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| # 6. CVE-2026-53359 mitigation survived the OS upgrade (nested virtualization still off). | ||
| # machine.install.extraKernelArgs is re-applied by `talm upgrade`; confirm per node: | ||
| talm -n <node-ip> read /proc/cmdline | grep -o 'kvm_intel.nested=[01]' # expect kvm_intel.nested=0 |
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The command uses talm to read /proc/cmdline, but talm does not have a read command. Direct node file reading is performed using talosctl.
| talm -n <node-ip> read /proc/cmdline | grep -o 'kvm_intel.nested=[01]' # expect kvm_intel.nested=0 | |
| talosctl -n <node-ip> read /proc/cmdline | grep -o 'kvm_intel.nested=[01]' # expect kvm_intel.nested=0 |
…lout (CVE-2026-53359) kvm_intel/kvm_amd are built into the Talos kernel, so nested= is settable only from the kernel command line. Pin grubUseUKICmdline=false (Talos >=1.12) so extraKernelArgs land on the built cmdline, and note the args take effect via talm upgrade, not a plain apply. Signed-off-by: Andrei Kvapil <kvapss@gmail.com> Assisted-By: Claude <noreply@anthropic.com>
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Summary
Prescribes disabling KVM nested virtualization in the
cozystackplugin's Talos skills, to mitigate CVE-2026-53359 ("Januscape"), a guest-to-host escape in the Linux KVM/x86 shadow MMU (a use-after-free inkvm_mmu_get_child_sp()from shadow-page role confusion).The vulnerable code path is only reachable when a guest is allowed to use nested virtualization; disabling it on the host removes the attack surface regardless of the node kernel patch level. Fixed upstream in
81ccda30b4e8/ stable 6.12.95, 6.6.144, 6.1.177, 6.18.38, 7.1.3 (2026-07-04); no released Talos ships the fixed kernel yet.Change
talos-bootstrapskill: the generatednodes/<name>.yamloverlay now setskvm_intel.nested=0andkvm_amd.nested=0undermachine.install.extraKernelArgs, and Phase 7 review verifies they are present.talos-bootstrapreference (manual-steps.md): the node-config example documents the same.cluster-upgradereference (post-upgrade-checks.md): adds a post-upgrade check that the args are still on the kernel command line.Placing the args under
machine.installis deliberate:talmre-applies that section on everytalm upgrade, so the mitigation survives OS image bumps (and each apply/upgrade reboots the node). Both args are set so one config covers Intel and AMD.The canonical source is the cozystack
talmpreset (linked below); this repo makes the skills prescribe and verify it.Part of a coordinated set of PRs (see Related PRs below).
Related PRs
Coordinated CVE-2026-53359 (Januscape) nested-virtualization mitigation across Cozystack repos:
cozystack/genericpresets (canonical source)