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![Laura Abbott](/assets/img/avatar_default.png)
By default, page poisoning uses a poison value (0xaa) on free. If this is changed to 0, the page is not only sanitized but zeroing on alloc with __GFP_ZERO can be skipped as well. The tradeoff is that detecting corruption from the poisoning is harder to detect. This feature also cannot be used with hibernation since pages are not guaranteed to be zeroed after hibernation. Credit to Grsecurity/PaX team for inspiring this work Signed-off-by: Laura Abbott <labbott@fedoraproject.org> Acked-by: Rafael J. Wysocki <rjw@rjwysocki.net> Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> Cc: Vlastimil Babka <vbabka@suse.cz> Cc: Michal Hocko <mhocko@suse.com> Cc: Kees Cook <keescook@chromium.org> Cc: Mathias Krause <minipli@googlemail.com> Cc: Dave Hansen <dave.hansen@intel.com> Cc: Jianyu Zhan <nasa4836@gmail.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
176 lines
3.5 KiB
C
176 lines
3.5 KiB
C
#include <linux/kernel.h>
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#include <linux/string.h>
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#include <linux/mm.h>
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#include <linux/highmem.h>
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#include <linux/page_ext.h>
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#include <linux/poison.h>
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#include <linux/ratelimit.h>
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static bool __page_poisoning_enabled __read_mostly;
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static bool want_page_poisoning __read_mostly;
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static int early_page_poison_param(char *buf)
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{
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if (!buf)
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return -EINVAL;
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if (strcmp(buf, "on") == 0)
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want_page_poisoning = true;
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else if (strcmp(buf, "off") == 0)
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want_page_poisoning = false;
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return 0;
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}
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early_param("page_poison", early_page_poison_param);
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bool page_poisoning_enabled(void)
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{
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return __page_poisoning_enabled;
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}
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static bool need_page_poisoning(void)
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{
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return want_page_poisoning;
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}
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static void init_page_poisoning(void)
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{
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/*
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* page poisoning is debug page alloc for some arches. If either
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* of those options are enabled, enable poisoning
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*/
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if (!IS_ENABLED(CONFIG_ARCH_SUPPORTS_DEBUG_PAGEALLOC)) {
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if (!want_page_poisoning && !debug_pagealloc_enabled())
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return;
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} else {
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if (!want_page_poisoning)
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return;
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}
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__page_poisoning_enabled = true;
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}
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struct page_ext_operations page_poisoning_ops = {
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.need = need_page_poisoning,
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.init = init_page_poisoning,
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};
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static inline void set_page_poison(struct page *page)
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{
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struct page_ext *page_ext;
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page_ext = lookup_page_ext(page);
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__set_bit(PAGE_EXT_DEBUG_POISON, &page_ext->flags);
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}
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static inline void clear_page_poison(struct page *page)
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{
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struct page_ext *page_ext;
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page_ext = lookup_page_ext(page);
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__clear_bit(PAGE_EXT_DEBUG_POISON, &page_ext->flags);
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}
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bool page_is_poisoned(struct page *page)
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{
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struct page_ext *page_ext;
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page_ext = lookup_page_ext(page);
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if (!page_ext)
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return false;
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return test_bit(PAGE_EXT_DEBUG_POISON, &page_ext->flags);
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}
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static void poison_page(struct page *page)
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{
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void *addr = kmap_atomic(page);
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set_page_poison(page);
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memset(addr, PAGE_POISON, PAGE_SIZE);
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kunmap_atomic(addr);
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}
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static void poison_pages(struct page *page, int n)
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{
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int i;
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for (i = 0; i < n; i++)
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poison_page(page + i);
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}
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static bool single_bit_flip(unsigned char a, unsigned char b)
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{
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unsigned char error = a ^ b;
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return error && !(error & (error - 1));
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}
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static void check_poison_mem(unsigned char *mem, size_t bytes)
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{
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static DEFINE_RATELIMIT_STATE(ratelimit, 5 * HZ, 10);
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unsigned char *start;
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unsigned char *end;
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if (IS_ENABLED(CONFIG_PAGE_POISONING_NO_SANITY))
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return;
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start = memchr_inv(mem, PAGE_POISON, bytes);
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if (!start)
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return;
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for (end = mem + bytes - 1; end > start; end--) {
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if (*end != PAGE_POISON)
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break;
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}
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if (!__ratelimit(&ratelimit))
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return;
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else if (start == end && single_bit_flip(*start, PAGE_POISON))
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pr_err("pagealloc: single bit error\n");
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else
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pr_err("pagealloc: memory corruption\n");
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print_hex_dump(KERN_ERR, "", DUMP_PREFIX_ADDRESS, 16, 1, start,
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end - start + 1, 1);
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dump_stack();
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}
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static void unpoison_page(struct page *page)
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{
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void *addr;
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if (!page_is_poisoned(page))
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return;
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addr = kmap_atomic(page);
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check_poison_mem(addr, PAGE_SIZE);
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clear_page_poison(page);
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kunmap_atomic(addr);
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}
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static void unpoison_pages(struct page *page, int n)
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{
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int i;
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for (i = 0; i < n; i++)
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unpoison_page(page + i);
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}
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void kernel_poison_pages(struct page *page, int numpages, int enable)
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{
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if (!page_poisoning_enabled())
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return;
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if (enable)
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unpoison_pages(page, numpages);
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else
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poison_pages(page, numpages);
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}
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#ifndef CONFIG_ARCH_SUPPORTS_DEBUG_PAGEALLOC
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void __kernel_map_pages(struct page *page, int numpages, int enable)
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{
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/* This function does nothing, all work is done via poison pages */
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}
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#endif
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