KVM: nVMX: Account for KVM reserved CR4 bits in consistency checks

Check that the guest (L2) and host (L1) CR4 values that would be loaded
by nested VM-Enter and VM-Exit respectively are valid with respect to
KVM's (L0 host) allowed CR4 bits.  Failure to check KVM reserved bits
would allow L1 to load an illegal CR4 (or trigger hardware VM-Fail or
failed VM-Entry) by massaging guest CPUID to allow features that are not
supported by KVM.  Amusingly, KVM itself is an accomplice in its doom, as
KVM adjusts L1's MSR_IA32_VMX_CR4_FIXED1 to allow L1 to enable bits for
L2 based on L1's CPUID model.

Note, although nested_{guest,host}_cr4_valid() are _currently_ used if
and only if the vCPU is post-VMXON (nested.vmxon == true), that may not
be true in the future, e.g. emulating VMXON has a bug where it doesn't
check the allowed/required CR0/CR4 bits.

Cc: stable@vger.kernel.org
Fixes: 3ce5a61d0f22 ("KVM: nVMX: fix checks on CR{0,4} during virtual VMX operation")
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20220607213604.3346000-3-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/arch/x86/kvm/vmx/nested.h b/arch/x86/kvm/vmx/nested.h
index c92cea0b8cccf6be24c010c30d3f622fdaf00b60..129ae4e01f7c1397dddbb8e684b77f144ad4b40e 100644 (file)
--- a/arch/x86/kvm/vmx/nested.h
+++ b/arch/x86/kvm/vmx/nested.h
@@ -281,7 +281,8 @@ static inline bool nested_cr4_valid(struct kvm_vcpu *vcpu, unsigned long val)
        u64 fixed0 = to_vmx(vcpu)->nested.msrs.cr4_fixed0;
        u64 fixed1 = to_vmx(vcpu)->nested.msrs.cr4_fixed1;
 
-       return fixed_bits_valid(val, fixed0, fixed1);
+       return fixed_bits_valid(val, fixed0, fixed1) &&
+              __kvm_is_valid_cr4(vcpu, val);
 }
 
 /* No difference in the restrictions on guest and host CR4 in VMX operation. */