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