[PATCH] KVM: Make loading cr3 more robust

Prevent the guest's loading of a corrupt cr3 (pointing at no guest phsyical
page) from crashing the host.

Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Avi Kivity <avi@qumranet.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 13 insertions, 1 deletions

diff --git a/drivers/kvm/kvm_main.c b/drivers/kvm/kvm_main.c
index 0675d3e51692..67c1154960f0 100644
--- a/drivers/kvm/kvm_main.c
+++ b/drivers/kvm/kvm_main.c
@@ -463,7 +463,19 @@ void set_cr3(struct kvm_vcpu *vcpu, unsigned long cr3)
 
         vcpu->cr3 = cr3;
         spin_lock(&vcpu->kvm->lock);
-        vcpu->mmu.new_cr3(vcpu);
+        /*
+         * Does the new cr3 value map to physical memory? (Note, we
+         * catch an invalid cr3 even in real-mode, because it would
+         * cause trouble later on when we turn on paging anyway.)
+         *
+         * A real CPU would silently accept an invalid cr3 and would
+         * attempt to use it - with largely undefined (and often hard
+         * to debug) behavior on the guest side.
+         */
+        if (unlikely(!gfn_to_memslot(vcpu->kvm, cr3 >> PAGE_SHIFT)))
+                inject_gp(vcpu);
+        else
+                vcpu->mmu.new_cr3(vcpu);
         spin_unlock(&vcpu->kvm->lock);
 }
 EXPORT_SYMBOL_GPL(set_cr3);