test: make issue8606b test more robust

Use actual unmapped memory instead of small integers to make
pointers that will fault when accessed.

Fixes #49562

Change-Id: I2c60c97cf80494dd962a07d10cfeaff6a00f4f8e
Reviewed-on: https://go-review.googlesource.com/c/go/+/364914
Trust: Keith Randall <khr@golang.org>
Run-TryBot: Keith Randall <khr@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>

diff --git a/test/fixedbugs/issue8606b.go b/test/fixedbugs/issue8606b.go
index 448ea566f0bea0ad66b7fc387fa1eb4589380008..41b9a3d00eab60a776f89a867372a1337f052ba8 100644 (file)
--- a/test/fixedbugs/issue8606b.go
+++ b/test/fixedbugs/issue8606b.go
@@ -1,4 +1,5 @@
 // run
+// +build linux darwin
 
 // Copyright 2020 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
@@ -20,20 +21,10 @@ package main
 import (
        "fmt"
        "reflect"
+       "syscall"
        "unsafe"
 )
 
-func bad1() string {
-       s := "foo"
-       (*reflect.StringHeader)(unsafe.Pointer(&s)).Data = 1 // write bad value to data ptr
-       return s
-}
-func bad2() string {
-       s := "foo"
-       (*reflect.StringHeader)(unsafe.Pointer(&s)).Data = 2 // write bad value to data ptr
-       return s
-}
-
 type SI struct {
        s string
        i int
@@ -45,15 +36,31 @@ type SS struct {
 }
 
 func main() {
+       bad1 := "foo"
+       bad2 := "foo"
+
+       p := syscall.Getpagesize()
+       b, err := syscall.Mmap(-1, 0, p, syscall.PROT_READ|syscall.PROT_WRITE, syscall.MAP_ANON|syscall.MAP_PRIVATE)
+       if err != nil {
+               panic(err)
+       }
+       err = syscall.Mprotect(b, syscall.PROT_NONE)
+       if err != nil {
+               panic(err)
+       }
+       // write inaccessible pointers as the data fields of bad1 and bad2.
+       (*reflect.StringHeader)(unsafe.Pointer(&bad1)).Data = uintptr(unsafe.Pointer(&b[0]))
+       (*reflect.StringHeader)(unsafe.Pointer(&bad2)).Data = uintptr(unsafe.Pointer(&b[1]))
+
        for _, test := range []struct {
                a, b interface{}
        }{
-               {SI{s: bad1(), i: 1}, SI{s: bad2(), i: 2}},
-               {SS{s: bad1(), t: "a"}, SS{s: bad2(), t: "aa"}},
-               {SS{s: "a", t: bad1()}, SS{s: "b", t: bad2()}},
+               {SI{s: bad1, i: 1}, SI{s: bad2, i: 2}},
+               {SS{s: bad1, t: "a"}, SS{s: bad2, t: "aa"}},
+               {SS{s: "a", t: bad1}, SS{s: "b", t: bad2}},
                // This one would panic because the length of both strings match, and we check
                // the body of the bad strings before the body of the good strings.
-               //{SS{s: bad1(), t: "a"}, SS{s: bad2(), t: "b"}},
+               //{SS{s: bad1, t: "a"}, SS{s: bad2, t: "b"}},
        } {
                if test.a == test.b {
                        panic(fmt.Sprintf("values %#v and %#v should not be equal", test.a, test.b))