KVM: MMU: Segregate shadow pages with different cr0.wp

When cr0.wp=0, we may shadow a gpte having u/s=1 and r/w=0 with an spte
having u/s=0 and r/w=1.  This allows excessive access if the guest sets
cr0.wp=1 and accesses through this spte.

Fix by making cr0.wp part of the base role; we'll have different sptes for
the two cases and the problem disappears.

Signed-off-by: Avi Kivity <avi@redhat.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

arch/x86/include/asm/kvm_host.h

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 3f0007b..76f5483 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -179,6 +179,7 @@
 		unsigned access:3;
 		unsigned invalid:1;
 		unsigned nxe:1;
+		unsigned cr0_wp:1;
 	};
 };
 

arch/x86/kvm/mmu.c

diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index de99638..81563e7 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -217,7 +217,7 @@
 }
 EXPORT_SYMBOL_GPL(kvm_mmu_set_mask_ptes);
 
-static int is_write_protection(struct kvm_vcpu *vcpu)
+static bool is_write_protection(struct kvm_vcpu *vcpu)
 {
 	return kvm_read_cr0_bits(vcpu, X86_CR0_WP);
 }
@@ -2432,6 +2432,7 @@
 		r = paging32_init_context(vcpu);
 
 	vcpu->arch.mmu.base_role.cr4_pae = !!is_pae(vcpu);
+	vcpu->arch.mmu.base_role.cr0_wp = is_write_protection(vcpu);
 
 	return r;
 }