1 // SPDX-License-Identifier: GPL-2.0
2 #include <linux/kernel.h>
3 #include <linux/string.h>
4 #include <linux/mm.h>
5 #include <linux/highmem.h>
6 #include <linux/page_ext.h>
7 #include <linux/poison.h>
8 #include <linux/ratelimit.h>
9 #include <linux/kasan.h>
10
11 static DEFINE_STATIC_KEY_FALSE_RO(want_page_poisoning);
12
early_page_poison_param(char * buf)13 static int __init early_page_poison_param(char *buf)
14 {
15 int ret;
16 bool tmp;
17
18 ret = strtobool(buf, &tmp);
19 if (ret)
20 return ret;
21
22 if (tmp)
23 static_branch_enable(&want_page_poisoning);
24 else
25 static_branch_disable(&want_page_poisoning);
26
27 return 0;
28 }
29 early_param("page_poison", early_page_poison_param);
30
31 /**
32 * page_poisoning_enabled - check if page poisoning is enabled
33 *
34 * Return true if page poisoning is enabled, or false if not.
35 */
page_poisoning_enabled(void)36 bool page_poisoning_enabled(void)
37 {
38 /*
39 * Assumes that debug_pagealloc_enabled is set before
40 * memblock_free_all.
41 * Page poisoning is debug page alloc for some arches. If
42 * either of those options are enabled, enable poisoning.
43 */
44 return (static_branch_unlikely(&want_page_poisoning) ||
45 (!IS_ENABLED(CONFIG_ARCH_SUPPORTS_DEBUG_PAGEALLOC) &&
46 debug_pagealloc_enabled()));
47 }
48 EXPORT_SYMBOL_GPL(page_poisoning_enabled);
49
poison_page(struct page * page)50 static void poison_page(struct page *page)
51 {
52 void *addr = kmap_atomic(page);
53
54 /* KASAN still think the page is in-use, so skip it. */
55 kasan_disable_current();
56 memset(addr, PAGE_POISON, PAGE_SIZE);
57 kasan_enable_current();
58 kunmap_atomic(addr);
59 }
60
poison_pages(struct page * page,int n)61 static void poison_pages(struct page *page, int n)
62 {
63 int i;
64
65 for (i = 0; i < n; i++)
66 poison_page(page + i);
67 }
68
single_bit_flip(unsigned char a,unsigned char b)69 static bool single_bit_flip(unsigned char a, unsigned char b)
70 {
71 unsigned char error = a ^ b;
72
73 return error && !(error & (error - 1));
74 }
75
check_poison_mem(unsigned char * mem,size_t bytes)76 static void check_poison_mem(unsigned char *mem, size_t bytes)
77 {
78 static DEFINE_RATELIMIT_STATE(ratelimit, 5 * HZ, 10);
79 unsigned char *start;
80 unsigned char *end;
81
82 if (IS_ENABLED(CONFIG_PAGE_POISONING_NO_SANITY))
83 return;
84
85 start = memchr_inv(mem, PAGE_POISON, bytes);
86 if (!start)
87 return;
88
89 for (end = mem + bytes - 1; end > start; end--) {
90 if (*end != PAGE_POISON)
91 break;
92 }
93
94 if (!__ratelimit(&ratelimit))
95 return;
96 else if (start == end && single_bit_flip(*start, PAGE_POISON))
97 pr_err("pagealloc: single bit error\n");
98 else
99 pr_err("pagealloc: memory corruption\n");
100
101 print_hex_dump(KERN_ERR, "", DUMP_PREFIX_ADDRESS, 16, 1, start,
102 end - start + 1, 1);
103 dump_stack();
104 }
105
unpoison_page(struct page * page)106 static void unpoison_page(struct page *page)
107 {
108 void *addr;
109
110 addr = kmap_atomic(page);
111 /*
112 * Page poisoning when enabled poisons each and every page
113 * that is freed to buddy. Thus no extra check is done to
114 * see if a page was poisoned.
115 */
116 check_poison_mem(addr, PAGE_SIZE);
117 kunmap_atomic(addr);
118 }
119
unpoison_pages(struct page * page,int n)120 static 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
kernel_poison_pages(struct page * page,int numpages,int enable)128 void kernel_poison_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
139 #ifndef CONFIG_ARCH_SUPPORTS_DEBUG_PAGEALLOC
__kernel_map_pages(struct page * page,int numpages,int enable)140 void __kernel_map_pages(struct page *page, int numpages, int enable)
141 {
142 /* This function does nothing, all work is done via poison pages */
143 }
144 #endif
145
