[PATCH 1/2] KVM: SEV: Free have_run_cpus during VM destruction even if VM is no longer SEV

[Sean Christopherson <seanjc@google.com>]

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.

Fixes: 6f38f8c57464 ("KVM: SVM: Flush cache only on CPUs running SEV guest")
Cc: stable@vger.kernel.org
Reported-by: Stefan Teodorescu <fane@google.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 arch/x86/kvm/svm/sev.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
index 63e8cfa9bf55..c9242c936a40 100644
--- a/arch/x86/kvm/svm/sev.c
+++ b/arch/x86/kvm/svm/sev.c
@@ -2981,13 +2981,17 @@ void sev_vm_destroy(struct kvm *kvm)
 	struct list_head *head = &sev->regions_list;
 	struct list_head *pos, *q;
 
+	/*
+	 * Free the mask even if the VM is not *currently* an SEV VM, as it may
+	 * have been an SEV VM prior to intra-host migration.
+	 */
+	free_cpumask_var(sev->have_run_cpus);
+
 	if (!sev_guest(kvm))
 		return;
 
 	WARN_ON(!list_empty(&sev->mirror_vms));
 
-	free_cpumask_var(sev->have_run_cpus);
-
 	/*
 	 * If this is a mirror VM, remove it from the owner's list of a mirrors
 	 * and skip ASID cleanup (the ASID is tied to the lifetime of the owner).
-- 
2.55.0.1082.g2b9226bbc0-goog