KVM: x86: Emulator does not calculate address correctly

In long-mode, when the address size is 4 bytes, the linear address is not
truncated as the emulator mistakenly does.  Instead, the offset within the
segment (the ea field) should be truncated according to the address size.

As Intel SDM says: "In 64-bit mode, the effective address components are added
and the effective address is truncated ... before adding the full 64-bit
segment base."
Signed-off-by: Nadav Amit <namit@cs.technion.ac.il>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/emulate.c

@@ -655,7 +655,8 @@ static __always_inline int __linearize(struct x86_emulate_ctxt *ctxt,
 	u16 sel;
 	unsigned cpl;
 
-	la = seg_base(ctxt, addr.seg) + addr.ea;
+	la = seg_base(ctxt, addr.seg) +
+	    (fetch || ctxt->ad_bytes == 8 ? addr.ea : (u32)addr.ea);
 	*max_size = 0;
 	switch (ctxt->mode) {
 	case X86EMUL_MODE_PROT64:
@@ -717,7 +718,7 @@ static __always_inline int __linearize(struct x86_emulate_ctxt *ctxt,
 		}
 		break;
 	}
-	if (fetch ? ctxt->mode != X86EMUL_MODE_PROT64 : ctxt->ad_bytes != 8)
+	if (ctxt->mode != X86EMUL_MODE_PROT64)
 		la &= (u32)-1;
 	if (insn_aligned(ctxt, size) && ((la & (size - 1)) != 0))
 		return emulate_gp(ctxt, 0);