The patch titled
Subject: mm/page_poisoning.c: allow for zero poisoning
has been added to the -mm tree. Its filename is
mm-page_poisoningc-allow-for-zero-poisoning.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/mm-page_poisoningc-allow-for-zero-poisoning.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/mm-page_poisoningc-allow-for-zero-poisoning.patch
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------------------------------------------------------
From: Laura Abbott <labbott@xxxxxxxxxxxxxxxxx>
Subject: mm/page_poisoning.c: allow for zero poisoning
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 Mathias Krause and grsecurity for original work
Signed-off-by: Laura Abbott <labbott@xxxxxxxxxxxxxxxxx>
Cc: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxx>
Cc: Kees Cook <keescook@xxxxxxxxxxxx>
Cc: Mathias Krause <minipli@xxxxxxxxxxxxxx>
Cc: Dave Hansen <dave.hansen@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/poison.h | 4 ++++
mm/Kconfig.debug | 13 +++++++++++++
mm/page_alloc.c | 8 +++++++-
3 files changed, 24 insertions(+), 1 deletion(-)
diff -puN include/linux/poison.h~mm-page_poisoningc-allow-for-zero-poisoning include/linux/poison.h
--- a/include/linux/poison.h~mm-page_poisoningc-allow-for-zero-poisoning
+++ a/include/linux/poison.h
@@ -30,7 +30,11 @@
#define TIMER_ENTRY_STATIC ((void *) 0x300 + POISON_POINTER_DELTA)
/********** mm/debug-pagealloc.c **********/
+#ifdef CONFIG_PAGE_POISONING_ZERO
+#define PAGE_POISON 0x00
+#else
#define PAGE_POISON 0xaa
+#endif
/********** mm/page_alloc.c ************/
diff -puN mm/Kconfig.debug~mm-page_poisoningc-allow-for-zero-poisoning mm/Kconfig.debug
--- a/mm/Kconfig.debug~mm-page_poisoningc-allow-for-zero-poisoning
+++ a/mm/Kconfig.debug
@@ -64,3 +64,16 @@ config PAGE_POISONING_NO_SANITY
If you are only interested in sanitization, say Y. Otherwise
say N.
+
+config PAGE_POISONING_ZERO
+ bool "Use zero for poisoning instead of random data"
+ depends on !HIBERNATION
+ depends on PAGE_POISONING
+ ---help---
+ Instead of using the existing poison value, fill the pages with
+ zeros. This makes it harder to detect when errors are occuring
+ due to sanitization but the zeroing at free means that it is
+ no longer necessary to write zeros when GFP_ZERO is used on
+ allocation.
+
+ If unsure, say N
diff -puN mm/page_alloc.c~mm-page_poisoningc-allow-for-zero-poisoning mm/page_alloc.c
--- a/mm/page_alloc.c~mm-page_poisoningc-allow-for-zero-poisoning
+++ a/mm/page_alloc.c
@@ -1387,6 +1387,12 @@ static inline int check_new_page(struct
return 0;
}
+static inline bool should_zero(void)
+{
+ return !IS_ENABLED(CONFIG_PAGE_POISONING_ZERO) ||
+ !page_poisoning_enabled();
+}
+
static int prep_new_page(struct page *page, unsigned int order, gfp_t gfp_flags,
int alloc_flags)
{
@@ -1406,7 +1412,7 @@ static int prep_new_page(struct page *pa
kernel_map_pages(page, 1 << order, 1);
kasan_alloc_pages(page, order);
- if (gfp_flags & __GFP_ZERO)
+ if (should_zero() && gfp_flags & __GFP_ZERO)
for (i = 0; i < (1 << order); i++)
clear_highpage(page + i);
_
Patches currently in -mm which might be from labbott@xxxxxxxxxxxxxxxxx are
mm-debug-pageallocc-split-out-page-poisoning-from-debug-page_alloc.patch
mm-page_poisonc-enable-page_poisoning-as-a-separate-option.patch
mm-page_poisoningc-allow-for-zero-poisoning.patch
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