linux/mm/page_poison.c
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   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
  11static bool want_page_poisoning __read_mostly;
  12
  13static int __init early_page_poison_param(char *buf)
  14{
  15        if (!buf)
  16                return -EINVAL;
  17        return strtobool(buf, &want_page_poisoning);
  18}
  19early_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 */
  26bool 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}
  38EXPORT_SYMBOL_GPL(page_poisoning_enabled);
  39
  40static 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
  51static 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
  59static 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
  66static 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
  96static 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 poisoned.
 105         */
 106        check_poison_mem(addr, PAGE_SIZE);
 107        kunmap_atomic(addr);
 108}
 109
 110static 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
 118void 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
 130void __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
 135