KVM: x86: Inject #GP if guest attempts to toggle CR4.LA57 in 64-bit mode

commit d74fcfc1f0ff4b6c26ecef1f9e48d8089ab4eaac upstream.

Inject a #GP on MOV CR4 if CR4.LA57 is toggled in 64-bit mode, which is
illegal per Intel's SDM:

  CR4.LA57
    57-bit linear addresses (bit 12 of CR4) ... blah blah blah ...
    This bit cannot be modified in IA-32e mode.

Note, the pseudocode for MOV CR doesn't call out the fault condition,
which is likely why the check was missed during initial development.
This is arguably an SDM bug and will hopefully be fixed in future
release of the SDM.

Fixes: fd8cb433734ee ("KVM: MMU: Expose the LA57 feature to VM.")
Cc: stable@vger.kernel.org
Reported-by: Sebastien Boeuf <sebastien.boeuf@intel.com>
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Message-Id: <20200703021714.5549-1-sean.j.christopherson@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 0db7f5cd9c720f117292ccc6d864c56aad368736..09f47c837c2587994e971f39966a468d1c7495bc 100644 (file)
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -806,6 +806,8 @@ int kvm_set_cr4(struct kvm_vcpu *vcpu, unsigned long cr4)
        if (is_long_mode(vcpu)) {
                if (!(cr4 & X86_CR4_PAE))
                        return 1;
+               if ((cr4 ^ old_cr4) & X86_CR4_LA57)
+                       return 1;
        } else if (is_paging(vcpu) && (cr4 & X86_CR4_PAE)
                   && ((cr4 ^ old_cr4) & pdptr_bits)
                   && !load_pdptrs(vcpu, vcpu->arch.walk_mmu,