KVM: x86/mmu: Use MMU's role to detect CR4.SMEP value in nested NPT walk

Use the MMU's role to get its effective SMEP value when injecting a fault
into the guest.  When walking L1's (nested) NPT while L2 is active, vCPU
state will reflect L2, whereas NPT uses the host's (L1 in this case) CR0,
CR4, EFER, etc...  If L1 and L2 have different settings for SMEP and
L1 does not have EFER.NX=1, this can result in an incorrect PFEC.FETCH
when injecting #NPF.

Fixes: e57d4a356ad3 ("KVM: Add instruction fetch checking when walking guest page table")
Cc: stable@vger.kernel.org
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20210622175739.3610207-5-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/arch/x86/kvm/mmu/paging_tmpl.h b/arch/x86/kvm/mmu/paging_tmpl.h
index 823a5919f9fa01fb85562bff4ed23d88c0c8285f..52fffd68b52299c913f63a0127e5e09f12df6f0f 100644 (file)
--- a/arch/x86/kvm/mmu/paging_tmpl.h
+++ b/arch/x86/kvm/mmu/paging_tmpl.h
@@ -471,8 +471,7 @@ retry_walk:
 
 error:
        errcode |= write_fault | user_fault;
-       if (fetch_fault && (mmu->nx ||
-                           kvm_read_cr4_bits(vcpu, X86_CR4_SMEP)))
+       if (fetch_fault && (mmu->nx || mmu->mmu_role.ext.cr4_smep))
                errcode |= PFERR_FETCH_MASK;
 
        walker->fault.vector = PF_VECTOR;