Live › vulnerability › CVE-2026-98719
Go to dashboardThe Linux kernel's KVM SEV code could free the have-run-CPUs mask twice when guest initialization failed, because the pointer was not cleared after freeing. The fix nullifies the pointer when the mask is freed and routes allocation and freeing through helpers.
Summary written from the sources below. Check the originals before acting.
First seen by InfraStack 2026-10-23 21:57 UTC. All times on this page are UTC.
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In the Linux kernel, the following vulnerability has been resolved:
KVM: SEV: Nullify "have run CPUs" mask pointer when freeing it
Nullify have_run_cpus when freeing the mask, particularly in the error path of __sev_guest_init(), so that KVM doesn't have to subtly use sev->active to track whether or not the mask has been freed. As pointed out by Sashiko, blindly freeing the mask in sev_vm_destroy() results in a double-free if the mask is freed if __sev_guest_init() fails.
Throw the logic in a helper as nullifying the pointer is frustratingly difficult and weird due to have_run_cpus being a single-entry array when CPUMASK_OFFSTACK=n. Deliberately don't use CPUMASK_VAR_NULL, as it's not directly assignable when the cpumask is on-stack, e.g. requires using a local variable and a memcpy(), which is beyond ridiculous. Furthermore, while clearing the on-stack bitmask is an unnecessary and arguably unwanted side effect, KVM absolutely relies on '0' being the "null" value given that the struct is zero-allocated.
Opportunistically add an alloc() helper to pair with free(); there are just enough call sites to make doing so worthwhile.
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