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Commit 8823b1db authored by Laura Abbott's avatar Laura Abbott Committed by Linus Torvalds
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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 <labbott@fedoraproject.org>
Cc: 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: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent ff8e8116

Documentation/kernel-parameters.txt

+5 −0
Original line number Diff line number Diff line
@@ -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

include/linux/mm.h

+9 −0
Original line number Diff line number Diff line
@@ -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);





#ifdef CONFIG_PAGE_POISONING

extern bool page_poisoning_enabled(void);

extern void kernel_poison_pages(struct page *page, int numpages, int enable);

#else

static inline bool page_poisoning_enabled(void) { return false; }

static inline void kernel_poison_pages(struct page *page, int numpages,

					int enable) { }

#endif



#ifdef CONFIG_DEBUG_PAGEALLOC

extern bool _debug_pagealloc_enabled;

extern void __kernel_map_pages(struct page *page, int numpages, int enable);

mm/Kconfig.debug

+24 −1
Original line number Diff line number Diff line
@@ -41,4 +41,27 @@ config DEBUG_PAGEALLOC_ENABLE_DEFAULT 
	  can be overridden by debug_pagealloc=off|on.



config PAGE_POISONING

	bool
 
	bool "Poison pages after freeing"

	select PAGE_EXTENSION

	select PAGE_POISONING_NO_SANITY if HIBERNATION

	---help---

	  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



config PAGE_POISONING_NO_SANITY

	depends on PAGE_POISONING

	bool "Only poison, don't sanity check"

	---help---

	   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.

mm/Makefile

+1 −1
Original line number Diff line number Diff line
@@ -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

mm/page_alloc.c

+2 −0
Original line number Diff line number Diff line
@@ -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)