1// Copyright 2017 The Go Authors. All rights reserved.
2// Use of this source code is governed by a BSD-style
3// license that can be found in the LICENSE file.
4//
5//go:build linux
6
7package bytes_test
8
9import (
10	. "bytes"
11	"syscall"
12	"testing"
13)
14
15// This file tests the situation where byte operations are checking
16// data very near to a page boundary. We want to make sure those
17// operations do not read across the boundary and cause a page
18// fault where they shouldn't.
19
20// These tests run only on linux. The code being tested is
21// not OS-specific, so it does not need to be tested on all
22// operating systems.
23
24// dangerousSlice returns a slice which is immediately
25// preceded and followed by a faulting page.
26func dangerousSlice(t *testing.T) []byte {
27	pagesize := syscall.Getpagesize()
28	b, err := syscall.Mmap(0, 0, 3*pagesize, syscall.PROT_READ|syscall.PROT_WRITE, syscall.MAP_ANONYMOUS|syscall.MAP_PRIVATE)
29	if err != nil {
30		t.Fatalf("mmap failed %s", err)
31	}
32	err = syscall.Mprotect(b[:pagesize], syscall.PROT_NONE)
33	if err != nil {
34		t.Fatalf("mprotect low failed %s\n", err)
35	}
36	err = syscall.Mprotect(b[2*pagesize:], syscall.PROT_NONE)
37	if err != nil {
38		t.Fatalf("mprotect high failed %s\n", err)
39	}
40	return b[pagesize : 2*pagesize]
41}
42
43func TestEqualNearPageBoundary(t *testing.T) {
44	t.Parallel()
45	b := dangerousSlice(t)
46	for i := range b {
47		b[i] = 'A'
48	}
49	for i := 0; i <= len(b); i++ {
50		Equal(b[:i], b[len(b)-i:])
51		Equal(b[len(b)-i:], b[:i])
52	}
53}
54
55func TestIndexByteNearPageBoundary(t *testing.T) {
56	t.Parallel()
57	b := dangerousSlice(t)
58	for i := range b {
59		idx := IndexByte(b[i:], 1)
60		if idx != -1 {
61			t.Fatalf("IndexByte(b[%d:])=%d, want -1\n", i, idx)
62		}
63	}
64}
65
66func TestIndexNearPageBoundary(t *testing.T) {
67	t.Parallel()
68	q := dangerousSlice(t)
69	if len(q) > 64 {
70		// Only worry about when we're near the end of a page.
71		q = q[len(q)-64:]
72	}
73	b := dangerousSlice(t)
74	if len(b) > 256 {
75		// Only worry about when we're near the end of a page.
76		b = b[len(b)-256:]
77	}
78	for j := 1; j < len(q); j++ {
79		q[j-1] = 1 // difference is only found on the last byte
80		for i := range b {
81			idx := Index(b[i:], q[:j])
82			if idx != -1 {
83				t.Fatalf("Index(b[%d:], q[:%d])=%d, want -1\n", i, j, idx)
84			}
85		}
86		q[j-1] = 0
87	}
88
89	// Test differing alignments and sizes of q which always end on a page boundary.
90	q[len(q)-1] = 1 // difference is only found on the last byte
91	for j := 0; j < len(q); j++ {
92		for i := range b {
93			idx := Index(b[i:], q[j:])
94			if idx != -1 {
95				t.Fatalf("Index(b[%d:], q[%d:])=%d, want -1\n", i, j, idx)
96			}
97		}
98	}
99	q[len(q)-1] = 0
100}
101
102func TestCountNearPageBoundary(t *testing.T) {
103	t.Parallel()
104	b := dangerousSlice(t)
105	for i := range b {
106		c := Count(b[i:], []byte{1})
107		if c != 0 {
108			t.Fatalf("Count(b[%d:], {1})=%d, want 0\n", i, c)
109		}
110		c = Count(b[:i], []byte{0})
111		if c != i {
112			t.Fatalf("Count(b[:%d], {0})=%d, want %d\n", i, c, i)
113		}
114	}
115}
116