page_poison.c
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#include <linux/kernel.h>
#include <linux/string.h>
#include <linux/mm.h>
#include <linux/highmem.h>
#include <linux/page_ext.h>
#include <linux/poison.h>
#include <linux/ratelimit.h>
static bool __page_poisoning_enabled __read_mostly;
static bool want_page_poisoning __read_mostly;
static int early_page_poison_param(char *buf)
{
if (!buf)
return -EINVAL;
return strtobool(buf, &want_page_poisoning);
}
early_param("page_poison", early_page_poison_param);
bool page_poisoning_enabled(void)
{
return __page_poisoning_enabled;
}
static bool need_page_poisoning(void)
{
return want_page_poisoning;
}
static void init_page_poisoning(void)
{
/*
* page poisoning is debug page alloc for some arches. If either
* of those options are enabled, enable poisoning
*/
if (!IS_ENABLED(CONFIG_ARCH_SUPPORTS_DEBUG_PAGEALLOC)) {
if (!want_page_poisoning && !debug_pagealloc_enabled())
return;
} else {
if (!want_page_poisoning)
return;
}
__page_poisoning_enabled = true;
}
struct page_ext_operations page_poisoning_ops = {
.need = need_page_poisoning,
.init = init_page_poisoning,
};
static inline void set_page_poison(struct page *page)
{
struct page_ext *page_ext;
page_ext = lookup_page_ext(page);
if (unlikely(!page_ext))
return;
__set_bit(PAGE_EXT_DEBUG_POISON, &page_ext->flags);
}
static inline void clear_page_poison(struct page *page)
{
struct page_ext *page_ext;
page_ext = lookup_page_ext(page);
if (unlikely(!page_ext))
return;
__clear_bit(PAGE_EXT_DEBUG_POISON, &page_ext->flags);
}
bool page_is_poisoned(struct page *page)
{
struct page_ext *page_ext;
page_ext = lookup_page_ext(page);
if (unlikely(!page_ext))
return false;
return test_bit(PAGE_EXT_DEBUG_POISON, &page_ext->flags);
}
static void poison_page(struct page *page)
{
void *addr = kmap_atomic(page);
set_page_poison(page);
memset(addr, PAGE_POISON, PAGE_SIZE);
kunmap_atomic(addr);
}
static void poison_pages(struct page *page, int n)
{
int i;
for (i = 0; i < n; i++)
poison_page(page + i);
}
static bool single_bit_flip(unsigned char a, unsigned char b)
{
unsigned char error = a ^ b;
return error && !(error & (error - 1));
}
static void check_poison_mem(unsigned char *mem, size_t bytes)
{
static DEFINE_RATELIMIT_STATE(ratelimit, 5 * HZ, 10);
unsigned char *start;
unsigned char *end;
if (IS_ENABLED(CONFIG_PAGE_POISONING_NO_SANITY))
return;
start = memchr_inv(mem, PAGE_POISON, bytes);
if (!start)
return;
for (end = mem + bytes - 1; end > start; end--) {
if (*end != PAGE_POISON)
break;
}
if (!__ratelimit(&ratelimit))
return;
else if (start == end && single_bit_flip(*start, PAGE_POISON))
pr_err("pagealloc: single bit error\n");
else
pr_err("pagealloc: memory corruption\n");
print_hex_dump(KERN_ERR, "", DUMP_PREFIX_ADDRESS, 16, 1, start,
end - start + 1, 1);
dump_stack();
}
static void unpoison_page(struct page *page)
{
void *addr;
if (!page_is_poisoned(page))
return;
addr = kmap_atomic(page);
check_poison_mem(addr, PAGE_SIZE);
clear_page_poison(page);
kunmap_atomic(addr);
}
static void unpoison_pages(struct page *page, int n)
{
int i;
for (i = 0; i < n; i++)
unpoison_page(page + i);
}
void kernel_poison_pages(struct page *page, int numpages, int enable)
{
if (!page_poisoning_enabled())
return;
if (enable)
unpoison_pages(page, numpages);
else
poison_pages(page, numpages);
}
#ifndef CONFIG_ARCH_SUPPORTS_DEBUG_PAGEALLOC
void __kernel_map_pages(struct page *page, int numpages, int enable)
{
/* This function does nothing, all work is done via poison pages */
}
#endif