1#include <linux/kernel.h>
2#include <linux/string.h>
3#include <linux/mm.h>
4#include <linux/highmem.h>
5#include <linux/page_ext.h>
6#include <linux/poison.h>
7#include <linux/ratelimit.h>
8
9static bool page_poisoning_enabled __read_mostly;
10
11static bool need_page_poisoning(void)
12{
13	if (!debug_pagealloc_enabled())
14		return false;
15
16	return true;
17}
18
19static void init_page_poisoning(void)
20{
21	if (!debug_pagealloc_enabled())
22		return;
23
24	page_poisoning_enabled = true;
25}
26
27struct page_ext_operations page_poisoning_ops = {
28	.need = need_page_poisoning,
29	.init = init_page_poisoning,
30};
31
32static inline void set_page_poison(struct page *page)
33{
34	struct page_ext *page_ext;
35
36	page_ext = lookup_page_ext(page);
37	__set_bit(PAGE_EXT_DEBUG_POISON, &page_ext->flags);
38}
39
40static inline void clear_page_poison(struct page *page)
41{
42	struct page_ext *page_ext;
43
44	page_ext = lookup_page_ext(page);
45	__clear_bit(PAGE_EXT_DEBUG_POISON, &page_ext->flags);
46}
47
48static inline bool page_poison(struct page *page)
49{
50	struct page_ext *page_ext;
51
52	page_ext = lookup_page_ext(page);
53	return test_bit(PAGE_EXT_DEBUG_POISON, &page_ext->flags);
54}
55
56static void poison_page(struct page *page)
57{
58	void *addr = kmap_atomic(page);
59
60	set_page_poison(page);
61	memset(addr, PAGE_POISON, PAGE_SIZE);
62	kunmap_atomic(addr);
63}
64
65static void poison_pages(struct page *page, int n)
66{
67	int i;
68
69	for (i = 0; i < n; i++)
70		poison_page(page + i);
71}
72
73static bool single_bit_flip(unsigned char a, unsigned char b)
74{
75	unsigned char error = a ^ b;
76
77	return error && !(error & (error - 1));
78}
79
80static void check_poison_mem(unsigned char *mem, size_t bytes)
81{
82	static DEFINE_RATELIMIT_STATE(ratelimit, 5 * HZ, 10);
83	unsigned char *start;
84	unsigned char *end;
85
86	start = memchr_inv(mem, PAGE_POISON, bytes);
87	if (!start)
88		return;
89
90	for (end = mem + bytes - 1; end > start; end--) {
91		if (*end != PAGE_POISON)
92			break;
93	}
94
95	if (!__ratelimit(&ratelimit))
96		return;
97	else if (start == end && single_bit_flip(*start, PAGE_POISON))
98		printk(KERN_ERR "pagealloc: single bit error\n");
99	else
100		printk(KERN_ERR "pagealloc: memory corruption\n");
101
102	print_hex_dump(KERN_ERR, "", DUMP_PREFIX_ADDRESS, 16, 1, start,
103			end - start + 1, 1);
104	dump_stack();
105}
106
107static void unpoison_page(struct page *page)
108{
109	void *addr;
110
111	if (!page_poison(page))
112		return;
113
114	addr = kmap_atomic(page);
115	check_poison_mem(addr, PAGE_SIZE);
116	clear_page_poison(page);
117	kunmap_atomic(addr);
118}
119
120static void unpoison_pages(struct page *page, int n)
121{
122	int i;
123
124	for (i = 0; i < n; i++)
125		unpoison_page(page + i);
126}
127
128void __kernel_map_pages(struct page *page, int numpages, int enable)
129{
130	if (!page_poisoning_enabled)
131		return;
132
133	if (enable)
134		unpoison_pages(page, numpages);
135	else
136		poison_pages(page, numpages);
137}
138