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
  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         return strtobool(buf, &want_page_poisoning);
  17 }
  18 early_param("page_poison", early_page_poison_param);
  19
  20 bool page_poisoning_enabled(void)
  21 {
  22         /*
  23          * Assumes that debug_pagealloc_enabled is set before
  24          * free_all_bootmem.
  25          * Page poisoning is debug page alloc for some arches. If
  26          * either of those options are enabled, enable poisoning.
  27          */
  28         return (want_page_poisoning ||
  29                 (!IS_ENABLED(CONFIG_ARCH_SUPPORTS_DEBUG_PAGEALLOC) &&
  30                 debug_pagealloc_enabled()));
  31 }
  32
  33 static void poison_page(struct page *page)
  34 {
  35         void *addr = kmap_atomic(page);
  36
  37         memset(addr, PAGE_POISON, PAGE_SIZE);
  38         kunmap_atomic(addr);
  39 }
  40
  41 static void poison_pages(struct page *page, int n)
  42 {
  43         int i;
  44
  45         for (i = 0; i < n; i++)
  46                 poison_page(page + i);
  47 }
  48
  49 static bool single_bit_flip(unsigned char a, unsigned char b)
  50 {
  51         unsigned char error = a ^ b;
  52
  53         return error && !(error & (error - 1));
  54 }
  55
  56 static void check_poison_mem(unsigned char *mem, size_t bytes)
  57 {
  58         static DEFINE_RATELIMIT_STATE(ratelimit, 5 * HZ, 10);
  59         unsigned char *start;
  60         unsigned char *end;
  61
  62         if (IS_ENABLED(CONFIG_PAGE_POISONING_NO_SANITY))
  63                 return;
  64
  65         start = memchr_inv(mem, PAGE_POISON, bytes);
  66         if (!start)
  67                 return;
  68
  69         for (end = mem + bytes - 1; end > start; end--) {
  70                 if (*end != PAGE_POISON)
  71                         break;
  72         }
  73
  74         if (!__ratelimit(&ratelimit))
  75                 return;
  76         else if (start == end && single_bit_flip(*start, PAGE_POISON))
  77                 pr_err("pagealloc: single bit error\n");
  78         else
  79                 pr_err("pagealloc: memory corruption\n");
  80
  81         print_hex_dump(KERN_ERR, "", DUMP_PREFIX_ADDRESS, 16, 1, start,
  82                         end - start + 1, 1);
  83         dump_stack();
  84 }
  85
  86 static void unpoison_page(struct page *page)
  87 {
  88         void *addr;
  89
  90         addr = kmap_atomic(page);
  91         /*
  92          * Page poisoning when enabled poisons each and every page
  93          * that is freed to buddy. Thus no extra check is done to
  94          * see if a page was posioned.
  95          */
  96         check_poison_mem(addr, PAGE_SIZE);
  97         kunmap_atomic(addr);
  98 }
  99
 100 static void unpoison_pages(struct page *page, int n)
 101 {
 102         int i;
 103
 104         for (i = 0; i < n; i++)
 105                 unpoison_page(page + i);
 106 }
 107
 108 void kernel_poison_pages(struct page *page, int numpages, int enable)
 109 {
 110         if (!page_poisoning_enabled())
 111                 return;
 112
 113         if (enable)
 114                 unpoison_pages(page, numpages);
 115         else
 116                 poison_pages(page, numpages);
 117 }
 118
 119 #ifndef CONFIG_ARCH_SUPPORTS_DEBUG_PAGEALLOC
 120 void __kernel_map_pages(struct page *page, int numpages, int enable)
 121 {
 122         /* This function does nothing, all work is done via poison pages */
 123 }
 124 #endif