runtime: fix integer overflow in amd64 memmove.

Fixes #4981.

R=bradfitz, fullung, rsc, minux.ma
CC=golang-dev
https://golang.org/cl/7474047

src/pkg/runtime/memmove_amd64.s

@@ -23,11 +23,12 @@
 // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 // THE SOFTWARE.
 
+// void runtime·memmove(void*, void*, uintptr)
 TEXT runtime·memmove(SB), 7, $0
 
 	MOVQ	to+0(FP), DI
 	MOVQ	fr+8(FP), SI
-	MOVLQSX	n+16(FP), BX
+	MOVQ	n+16(FP), BX
 
 /*
  * check and set for backwards
@@ -38,7 +39,7 @@ TEXT runtime·memmove(SB), 7, $0
 /*
  * forward copy loop
  */
-forward:	
+forward:
 	MOVQ	BX, CX
 	SHRQ	$3, CX
 	ANDQ	$7, BX

src/pkg/runtime/memmove_linux_amd64_test.go

+// Copyright 2013 The Go Authors.  All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package runtime_test
+
+import (
+	"io/ioutil"
+	"os"
+	"reflect"
+	"syscall"
+	"testing"
+	"unsafe"
+)
+
+// TestMemmoveOverflow maps 3GB of memory and calls memmove on
+// the corresponding slice.
+func TestMemmoveOverflow(t *testing.T) {
+	// Create a temporary file.
+	tmp, err := ioutil.TempFile("", "go-memmovetest")
+	if err != nil {
+		t.Fatal(err)
+	}
+	_, err = tmp.Write(make([]byte, 65536))
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer os.Remove(tmp.Name())
+	defer tmp.Close()
+
+	// Set up mappings.
+	base, _, errno := syscall.Syscall6(syscall.SYS_MMAP,
+		0xa0<<32, 3<<30, syscall.PROT_READ|syscall.PROT_WRITE, syscall.MAP_PRIVATE|syscall.MAP_ANONYMOUS, ^uintptr(0), 0)
+	if errno != 0 {
+		t.Skipf("could not create memory mapping: %s", errno)
+	}
+	syscall.Syscall(syscall.SYS_MUNMAP, base, 3<<30, 0)
+
+	for off := uintptr(0); off < 3<<30; off += 65536 {
+		_, _, errno := syscall.Syscall6(syscall.SYS_MMAP,
+			base+off, 65536, syscall.PROT_READ|syscall.PROT_WRITE, syscall.MAP_SHARED|syscall.MAP_FIXED, tmp.Fd(), 0)
+		if errno != 0 {
+			t.Fatalf("could not map a page at requested 0x%x: %s", base+off, errno)
+		}
+		defer syscall.Syscall(syscall.SYS_MUNMAP, base+off, 65536, 0)
+	}
+
+	var s []byte
+	sp := (*reflect.SliceHeader)(unsafe.Pointer(&s))
+	sp.Data = base
+	sp.Len, sp.Cap = 3<<30, 3<<30
+
+	n := copy(s[1:], s)
+	if n != 3<<30-1 {
+		t.Fatalf("copied %d bytes, expected %d", n, 3<<30-1)
+	}
+	n = copy(s, s[1:])
+	if n != 3<<30-1 {
+		t.Fatalf("copied %d bytes, expected %d", n, 3<<30-1)
+	}
+}

src/pkg/runtime/runtime.h

@@ -668,7 +668,7 @@ void	runtime·prints(int8*);
 void	runtime·printf(int8*, ...);
 byte*	runtime·mchr(byte*, byte, byte*);
 int32	runtime·mcmp(byte*, byte*, uint32);
-void	runtime·memmove(void*, void*, uint32);
+void	runtime·memmove(void*, void*, uintptr);
 void*	runtime·mal(uintptr);
 String	runtime·catstring(String, String);
 String	runtime·gostring(byte*);