mm/page_poison.c

   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 bool want_page_poisoning __read_mostly;
  12
  13 static int __init early_page_poison_param(char *buf)
  14 {
  15         if (!buf)
  16                 return -EINVAL;
  17         return strtobool(buf, &want_page_poisoning);
  18 }
  19 early_param("page_poison", early_page_poison_param);
  20
  21 /**
  22  * page_poisoning_enabled - check if page poisoning is enabled
  23  *
  24  * Return true if page poisoning is enabled, or false if not.
  25  */
  26 bool page_poisoning_enabled(void)
  27 {
  28         /*
  29          * Assumes that debug_pagealloc_enabled is set before
  30          * memblock_free_all.
  31          * Page poisoning is debug page alloc for some arches. If
  32          * either of those options are enabled, enable poisoning.
  33          */
  34         return (want_page_poisoning ||
  35                 (!IS_ENABLED(CONFIG_ARCH_SUPPORTS_DEBUG_PAGEALLOC) &&
  36                 debug_pagealloc_enabled()));
  37 }
  38 EXPORT_SYMBOL_GPL(page_poisoning_enabled);
  39
  40 static void poison_page(struct page *page)
  41 {
  42         void *addr = kmap_atomic(page);
  43
  44         /* KASAN still think the page is in-use, so skip it. */
  45         kasan_disable_current();
  46         memset(addr, PAGE_POISON, PAGE_SIZE);
  47         kasan_enable_current();
  48         kunmap_atomic(addr);
  49 }
  50
  51 static void poison_pages(struct page *page, int n)
  52 {
  53         int i;
  54
  55         for (i = 0; i < n; i++)
  56                 poison_page(page + i);
  57 }
  58
  59 static bool single_bit_flip(unsigned char a, unsigned char b)
  60 {
  61         unsigned char error = a ^ b;
  62
  63         return error && !(error & (error - 1));
  64 }
  65
  66 static void check_poison_mem(unsigned char *mem, size_t bytes)
  67 {
  68         static DEFINE_RATELIMIT_STATE(ratelimit, 5 * HZ, 10);
  69         unsigned char *start;
  70         unsigned char *end;
  71
  72         if (IS_ENABLED(CONFIG_PAGE_POISONING_NO_SANITY))
  73                 return;
  74
  75         start = memchr_inv(mem, PAGE_POISON, bytes);
  76         if (!start)
  77                 return;
  78
  79         for (end = mem + bytes - 1; end > start; end--) {
  80                 if (*end != PAGE_POISON)
  81                         break;
  82         }
  83
  84         if (!__ratelimit(&ratelimit))
  85                 return;
  86         else if (start == end && single_bit_flip(*start, PAGE_POISON))
  87                 pr_err("pagealloc: single bit error\n");
  88         else
  89                 pr_err("pagealloc: memory corruption\n");
  90
  91         print_hex_dump(KERN_ERR, "", DUMP_PREFIX_ADDRESS, 16, 1, start,
  92                         end - start + 1, 1);
  93         dump_stack();
  94 }
  95
  96 static void unpoison_page(struct page *page)
  97 {
  98         void *addr;
  99
 100         addr = kmap_atomic(page);
 101         /*
 102          * Page poisoning when enabled poisons each and every page
 103          * that is freed to buddy. Thus no extra check is done to
 104          * see if a page was posioned.
 105          */
 106         check_poison_mem(addr, PAGE_SIZE);
 107         kunmap_atomic(addr);
 108 }
 109
 110 static void unpoison_pages(struct page *page, int n)
 111 {
 112         int i;
 113
 114         for (i = 0; i < n; i++)
 115                 unpoison_page(page + i);
 116 }
 117
 118 void kernel_poison_pages(struct page *page, int numpages, int enable)
 119 {
 120         if (!page_poisoning_enabled())
 121                 return;
 122
 123         if (enable)
 124                 unpoison_pages(page, numpages);
 125         else
 126                 poison_pages(page, numpages);
 127 }
 128
 129 #ifndef CONFIG_ARCH_SUPPORTS_DEBUG_PAGEALLOC
 130 void __kernel_map_pages(struct page *page, int numpages, int enable)
 131 {
 132         /* This function does nothing, all work is done via poison pages */
 133 }
 134 #endif