KVM: x86: 32-bit wraparound read/write not emulated correctly

If we got a wraparound of 32-bit operand, and the limit is 0xffffffff, read and
writes should be successful. It just needs to be done in two segments.
Signed-off-by: Nadav Amit <namit@cs.technion.ac.il>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/emulate.c

@@ -684,9 +684,13 @@ static __always_inline int __linearize(struct x86_emulate_ctxt *ctxt,
 		}
 		if (addr.ea > lim)
 			goto bad;
-		*max_size = min_t(u64, ~0u, (u64)lim + 1 - addr.ea);
-		if (size > *max_size)
-			goto bad;
+		if (lim == 0xffffffff)
+			*max_size = ~0u;
+		else {
+			*max_size = (u64)lim + 1 - addr.ea;
+			if (size > *max_size)
+				goto bad;
+		}
 		la &= (u32)-1;
 		break;
 	}

arch/x86/kvm/x86.c

@@ -4495,6 +4495,8 @@ int emulator_read_write(struct x86_emulate_ctxt *ctxt, unsigned long addr,
 		if (rc != X86EMUL_CONTINUE)
 			return rc;
 		addr += now;
+		if (ctxt->mode != X86EMUL_MODE_PROT64)
+			addr = (u32)addr;
 		val += now;
 		bytes -= now;
 	}