CVE-2026-98472: KVM: SEV: Free have_run_cpus during VM destruction even if VM is no longer SEV

CVE-2026-98472: KVM: SEV: Free have_run_cpus during VM destruction even if VM is no longer SEV

[Greg Kroah-Hartman]

From: Greg Kroah-Hartman <gregkh@kernel.org>

Description
===========

In the Linux kernel, the following vulnerability has been resolved:

KVM: SEV: Free have_run_cpus during VM destruction even if VM is no longer SEV

Unconditionally free SEV's "have run CPUs" cpumask in the VM destroy path,
i.e. even for what appear to be non-SEV VMs, as an SEV VM becomes a non-SEV
VM if its state is intra-host migrated.  Alternatively, the mask could be
freed in sev_migrate_from() when "converting" the source VM, but that gets
annoying because ideally KVM would nullify the mask to guard against UAF,
and nullifying the mask would need be conditioned on CPUMASK_OFFSTACK=y.

Freeing the mask during sev_migrate_from() is also not robust against other
KVM bugs, though that's kind of a moot point since any such bugs would show
up even if sev->active is never set.  I.e. KVM must get that side of things
correct.  But, that's not a great reason to add more code just to make
things marginally less robust.

The Linux kernel CVE team has assigned CVE-2026-98472 to this issue.


Affected and fixed versions
===========================

	Issue introduced in 6.17 with commit 6f38f8c574642a822f2e85f079fa29a49176c49c and fixed in 6.18.55 with commit 6aef7cf800098749ff5d660222efaf6e01e98c09
	Issue introduced in 6.17 with commit 6f38f8c574642a822f2e85f079fa29a49176c49c and fixed in 7.2.9 with commit 9784e5ca91b37b387f3f414af4340c54f7a63566
	Issue introduced in 6.17 with commit 6f38f8c574642a822f2e85f079fa29a49176c49c and fixed in 7.3-rc5 with commit 12c1f6e03f944e399bd2c88441dca5dc702b95a5

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2026-98472
will be updated if fixes are backported, please check that for the most
up to date information about this issue.


Affected files
==============

The file(s) affected by this issue are:
	arch/x86/kvm/svm/sev.c


Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/6aef7cf800098749ff5d660222efaf6e01e98c09
	https://git.kernel.org/stable/c/9784e5ca91b37b387f3f414af4340c54f7a63566
	https://git.kernel.org/stable/c/12c1f6e03f944e399bd2c88441dca5dc702b95a5