[PATCH v2 12/16] KVM: Do not partially reinitialize gfn=>pfn cache during activation

[Sean Christopherson <seanjc@google.com>]

Don't partially reinitialize a gfn=>pfn cache when activating the cache,
and instead assert that the cache is not valid during activation.  Bug
the VM if the assertion fails, as use-after-free and/or data corruption
is all but guaranteed if KVM ends up with a valid-but-inactive cache.

Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 virt/kvm/pfncache.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/virt/kvm/pfncache.c b/virt/kvm/pfncache.c
index 62b47feed36c..2d5b417e50ac 100644
--- a/virt/kvm/pfncache.c
+++ b/virt/kvm/pfncache.c
@@ -342,6 +342,9 @@ void kvm_gpc_init(struct gfn_to_pfn_cache *gpc, struct kvm *kvm,
 	gpc->vcpu = vcpu;
 	gpc->usage = usage;
 	gpc->len = len;
+	gpc->pfn = KVM_PFN_ERR_FAULT;
+	gpc->uhva = KVM_HVA_ERR_BAD;
+
 }
 EXPORT_SYMBOL_GPL(kvm_gpc_init);
 
@@ -350,10 +353,8 @@ int kvm_gpc_activate(struct gfn_to_pfn_cache *gpc, gpa_t gpa)
 	struct kvm *kvm = gpc->kvm;
 
 	if (!gpc->active) {
-		gpc->khva = NULL;
-		gpc->pfn = KVM_PFN_ERR_FAULT;
-		gpc->uhva = KVM_HVA_ERR_BAD;
-		gpc->valid = false;
+		if (KVM_BUG_ON(gpc->valid, kvm))
+			return -EIO;
 
 		spin_lock(&kvm->gpc_lock);
 		list_add(&gpc->list, &kvm->gpc_list);
-- 
2.38.0.413.g74048e4d9e-goog