mm/page_poison.c

   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
   9 static bool __page_poisoning_enabled __read_mostly;
  10 static bool want_page_poisoning __read_mostly;
  11
  12 static int early_page_poison_param(char *buf)
  13 {
  14         if (!buf)
  15                 return -EINVAL;
  16
  17         if (strcmp(buf, "on") == 0)
  18                 want_page_poisoning = true;
  19         else if (strcmp(buf, "off") == 0)
  20                 want_page_poisoning = false;
  21
  22         return 0;
  23 }
  24 early_param("page_poison", early_page_poison_param);
  25
  26 bool page_poisoning_enabled(void)
  27 {
  28         return __page_poisoning_enabled;
  29 }
  30
  31 static bool need_page_poisoning(void)
  32 {
  33         return want_page_poisoning;
  34 }
  35
  36 static void init_page_poisoning(void)
  37 {
  38         /*
  39          * page poisoning is debug page alloc for some arches. If either
  40          * of those options are enabled, enable poisoning
  41          */
  42         if (!IS_ENABLED(CONFIG_ARCH_SUPPORTS_DEBUG_PAGEALLOC)) {
  43                 if (!want_page_poisoning && !debug_pagealloc_enabled())
  44                         return;
  45         } else {
  46                 if (!want_page_poisoning)
  47                         return;
  48         }
  49
  50         __page_poisoning_enabled = true;
  51 }
  52
  53 struct page_ext_operations page_poisoning_ops = {
  54         .need = need_page_poisoning,
  55         .init = init_page_poisoning,
  56 };
  57
  58 static inline void set_page_poison(struct page *page)
  59 {
  60         struct page_ext *page_ext;
  61
  62         page_ext = lookup_page_ext(page);
  63         __set_bit(PAGE_EXT_DEBUG_POISON, &page_ext->flags);
  64 }
  65
  66 static inline void clear_page_poison(struct page *page)
  67 {
  68         struct page_ext *page_ext;
  69
  70         page_ext = lookup_page_ext(page);
  71         __clear_bit(PAGE_EXT_DEBUG_POISON, &page_ext->flags);
  72 }
  73
  74 bool page_is_poisoned(struct page *page)
  75 {
  76         struct page_ext *page_ext;
  77
  78         page_ext = lookup_page_ext(page);
  79         if (!page_ext)
  80                 return false;
  81
  82         return test_bit(PAGE_EXT_DEBUG_POISON, &page_ext->flags);
  83 }
  84
  85 static void poison_page(struct page *page)
  86 {
  87         void *addr = kmap_atomic(page);
  88
  89         set_page_poison(page);
  90         memset(addr, PAGE_POISON, PAGE_SIZE);
  91         kunmap_atomic(addr);
  92 }
  93
  94 static void poison_pages(struct page *page, int n)
  95 {
  96         int i;
  97
  98         for (i = 0; i < n; i++)
  99                 poison_page(page + i);
 100 }
 101
 102 static bool single_bit_flip(unsigned char a, unsigned char b)
 103 {
 104         unsigned char error = a ^ b;
 105
 106         return error && !(error & (error - 1));
 107 }
 108
 109 static void check_poison_mem(unsigned char *mem, size_t bytes)
 110 {
 111         static DEFINE_RATELIMIT_STATE(ratelimit, 5 * HZ, 10);
 112         unsigned char *start;
 113         unsigned char *end;
 114
 115         if (IS_ENABLED(CONFIG_PAGE_POISONING_NO_SANITY))
 116                 return;
 117
 118         start = memchr_inv(mem, PAGE_POISON, bytes);
 119         if (!start)
 120                 return;
 121
 122         for (end = mem + bytes - 1; end > start; end--) {
 123                 if (*end != PAGE_POISON)
 124                         break;
 125         }
 126
 127         if (!__ratelimit(&ratelimit))
 128                 return;
 129         else if (start == end && single_bit_flip(*start, PAGE_POISON))
 130                 pr_err("pagealloc: single bit error\n");
 131         else
 132                 pr_err("pagealloc: memory corruption\n");
 133
 134         print_hex_dump(KERN_ERR, "", DUMP_PREFIX_ADDRESS, 16, 1, start,
 135                         end - start + 1, 1);
 136         dump_stack();
 137 }
 138
 139 static void unpoison_page(struct page *page)
 140 {
 141         void *addr;
 142
 143         if (!page_is_poisoned(page))
 144                 return;
 145
 146         addr = kmap_atomic(page);
 147         check_poison_mem(addr, PAGE_SIZE);
 148         clear_page_poison(page);
 149         kunmap_atomic(addr);
 150 }
 151
 152 static void unpoison_pages(struct page *page, int n)
 153 {
 154         int i;
 155
 156         for (i = 0; i < n; i++)
 157                 unpoison_page(page + i);
 158 }
 159
 160 void kernel_poison_pages(struct page *page, int numpages, int enable)
 161 {
 162         if (!page_poisoning_enabled())
 163                 return;
 164
 165         if (enable)
 166                 unpoison_pages(page, numpages);
 167         else
 168                 poison_pages(page, numpages);
 169 }
 170
 171 #ifndef CONFIG_ARCH_SUPPORTS_DEBUG_PAGEALLOC
 172 void __kernel_map_pages(struct page *page, int numpages, int enable)
 173 {
 174         /* This function does nothing, all work is done via poison pages */
 175 }
 176 #endif