Commit 8823b1db authored by Laura Abbott's avatar Laura Abbott Committed by Linus Torvalds
Browse files

mm/page_poison.c: enable PAGE_POISONING as a separate option

Page poisoning is currently set up as a feature if architectures don't
have architecture debug page_alloc to allow unmapping of pages.  It has
uses apart from that though.  Clearing of the pages on free provides an
increase in security as it helps to limit the risk of information leaks.
Allow page poisoning to be enabled as a separate option independent of
kernel_map pages since the two features do separate work.  Because of
how hiberanation is implemented, the checks on alloc cannot occur if
hibernation is enabled.  The runtime alloc checks can also be enabled
with an option when !HIBERNATION.

Credit to Grsecurity/PaX team for inspiring this work
Signed-off-by: default avatarLaura Abbott <>
Cc: Rafael J. Wysocki <>
Cc: "Kirill A. Shutemov" <>
Cc: Vlastimil Babka <>
Cc: Michal Hocko <>
Cc: Kees Cook <>
Cc: Mathias Krause <>
Cc: Dave Hansen <>
Cc: Jianyu Zhan <>
Signed-off-by: default avatarAndrew Morton <>
Signed-off-by: default avatarLinus Torvalds <>
parent ff8e8116
......@@ -2731,6 +2731,11 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
we can turn it on.
on: enable the feature
page_poison= [KNL] Boot-time parameter changing the state of
poisoning on the buddy allocator.
off: turn off poisoning
on: turn on poisoning
panic= [KNL] Kernel behaviour on panic: delay <timeout>
timeout > 0: seconds before rebooting
timeout = 0: wait forever
......@@ -2176,6 +2176,15 @@ extern int apply_to_page_range(struct mm_struct *mm, unsigned long address,
unsigned long size, pte_fn_t fn, void *data);
extern bool page_poisoning_enabled(void);
extern void kernel_poison_pages(struct page *page, int numpages, int enable);
static inline bool page_poisoning_enabled(void) { return false; }
static inline void kernel_poison_pages(struct page *page, int numpages,
int enable) { }
extern bool _debug_pagealloc_enabled;
extern void __kernel_map_pages(struct page *page, int numpages, int enable);
......@@ -41,4 +41,27 @@ config DEBUG_PAGEALLOC_ENABLE_DEFAULT
can be overridden by debug_pagealloc=off|on.
bool "Poison pages after freeing"
Fill the pages with poison patterns after free_pages() and verify
the patterns before alloc_pages. The filling of the memory helps
reduce the risk of information leaks from freed data. This does
have a potential performance impact.
Note that "poison" here is not the same thing as the "HWPoison"
for CONFIG_MEMORY_FAILURE. This is software poisoning only.
If unsure, say N
bool "Only poison, don't sanity check"
Skip the sanity checking on alloc, only fill the pages with
poison on free. This reduces some of the overhead of the
poisoning feature.
If you are only interested in sanitization, say Y. Otherwise
say N.
......@@ -48,7 +48,7 @@ obj-$(CONFIG_SPARSEMEM_VMEMMAP) += sparse-vmemmap.o
obj-$(CONFIG_SLOB) += slob.o
obj-$(CONFIG_MMU_NOTIFIER) += mmu_notifier.o
obj-$(CONFIG_KSM) += ksm.o
obj-$(CONFIG_PAGE_POISONING) += debug-pagealloc.o
obj-$(CONFIG_PAGE_POISONING) += page_poison.o
obj-$(CONFIG_SLAB) += slab.o
obj-$(CONFIG_SLUB) += slub.o
obj-$(CONFIG_KMEMCHECK) += kmemcheck.o
......@@ -1025,6 +1025,7 @@ static bool free_pages_prepare(struct page *page, unsigned int order)
PAGE_SIZE << order);
arch_free_page(page, order);
kernel_poison_pages(page, 1 << order, 0);
kernel_map_pages(page, 1 << order, 0);
return true;
......@@ -1420,6 +1421,7 @@ static int prep_new_page(struct page *page, unsigned int order, gfp_t gfp_flags,
arch_alloc_page(page, order);
kernel_map_pages(page, 1 << order, 1);
kernel_poison_pages(page, 1 << order, 1);
kasan_alloc_pages(page, order);
if (gfp_flags & __GFP_ZERO)
......@@ -6,22 +6,48 @@
#include <linux/poison.h>
#include <linux/ratelimit.h>
static bool page_poisoning_enabled __read_mostly;
static bool __page_poisoning_enabled __read_mostly;
static bool want_page_poisoning __read_mostly;
static bool need_page_poisoning(void)
static int early_page_poison_param(char *buf)
if (!debug_pagealloc_enabled())
return false;
if (!buf)
return -EINVAL;
if (strcmp(buf, "on") == 0)
want_page_poisoning = true;
else if (strcmp(buf, "off") == 0)
want_page_poisoning = false;
return true;
return 0;
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)
if (!debug_pagealloc_enabled())
* page poisoning is debug page alloc for some arches. If either
* of those options are enabled, enable poisoning
if (!want_page_poisoning && !debug_pagealloc_enabled())
} else {
if (!want_page_poisoning)
page_poisoning_enabled = true;
__page_poisoning_enabled = true;
struct page_ext_operations page_poisoning_ops = {
......@@ -83,6 +109,9 @@ static void check_poison_mem(unsigned char *mem, size_t bytes)
unsigned char *start;
unsigned char *end;
start = memchr_inv(mem, PAGE_POISON, bytes);
if (!start)
......@@ -95,9 +124,9 @@ static void check_poison_mem(unsigned char *mem, size_t bytes)
if (!__ratelimit(&ratelimit))
else if (start == end && single_bit_flip(*start, PAGE_POISON))
printk(KERN_ERR "pagealloc: single bit error\n");
pr_err("pagealloc: single bit error\n");
printk(KERN_ERR "pagealloc: memory corruption\n");
pr_err("pagealloc: memory corruption\n");
print_hex_dump(KERN_ERR, "", DUMP_PREFIX_ADDRESS, 16, 1, start,
end - start + 1, 1);
......@@ -125,9 +154,9 @@ static void unpoison_pages(struct page *page, int n)
unpoison_page(page + i);
void __kernel_map_pages(struct page *page, int numpages, int enable)
void kernel_poison_pages(struct page *page, int numpages, int enable)
if (!page_poisoning_enabled)
if (!page_poisoning_enabled())
if (enable)
......@@ -135,3 +164,10 @@ void __kernel_map_pages(struct page *page, int numpages, int enable)
poison_pages(page, numpages);
void __kernel_map_pages(struct page *page, int numpages, int enable)
/* This function does nothing, all work is done via poison pages */
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