KVM: nVMX: Truncate base/index GPR value on address calc in !64-bit

Drop bits 63:32 of the base and/or index GPRs when calculating the
effective address of a VMX instruction memory operand.  Outside of 64-bit
mode, memory encodings are strictly limited to E*X and below.

Fixes: 064aea77 ("KVM: nVMX: Decoding memory operands of VMX instructions")
Cc: stable@vger.kernel.org
Signed-off-by: NSean Christopherson <seanjc@google.com>
Message-Id: <20210422022128.3464144-7-seanjc@google.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/vmx/nested.c

@@ -4619,9 +4619,9 @@ int get_vmx_mem_address(struct kvm_vcpu *vcpu, unsigned long exit_qualification,
 	else if (addr_size == 0)
 		off = (gva_t)sign_extend64(off, 15);
 	if (base_is_valid)
-		off += kvm_register_read(vcpu, base_reg);
+		off += kvm_register_readl(vcpu, base_reg);
 	if (index_is_valid)
-		off += kvm_register_read(vcpu, index_reg) << scaling;
+		off += kvm_register_readl(vcpu, index_reg) << scaling;
 	vmx_get_segment(vcpu, &s, seg_reg);
 
 	/*