[PATCH 3/4] KVM: x86/mmu: Bug the VM if KVM calcs a CPU role with EFER.LMA=1 && CR4.PAE=0

[Sean Christopherson <seanjc@google.com>]

Bug the VM if KVM attempts to construct a CPU role with the should-be-
impossible combination of long mode being active without PAE paging being
enabled.  KVM's MMU construction assumes that EFER.LMA can be set if and
only CR4.PAE is set, and will create a completely invalid MMU if that
assumption fails.  FNAME(walk_addr_generic) already has sanity checks to
try and mitigate the fallout, but attempt to catch such bugs earlier, as
this is (at least) the second time KVM has had bugs that escaped into
FNAME(walk_addr_generic), and it's entirely possible the bad state could
cause problems elsewhere.

Cc: stable@vger.kernel.org
Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 arch/x86/kvm/mmu/mmu.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 064ecc33b926..81c30e2c74f3 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -5910,6 +5910,9 @@ static union kvm_cpu_role kvm_calc_cpu_role(struct kvm_vcpu *vcpu,
 		return role;
 	}
 
+	if (KVM_BUG_ON(____is_efer_lma(regs) && !____is_cr4_pae(regs), vcpu->kvm))
+		*(u64 *)&regs->efer &= ~EFER_LMA;
+
 	role.base.efer_nx = ____is_efer_nx(regs);
 	role.base.cr0_wp = ____is_cr0_wp(regs);
 	role.base.cr4_smep = ____is_cr4_smep(regs);
-- 
2.55.0.887.g758fc8c411-goog