Commit 1414c7f4 authored by Laura Abbott's avatar Laura Abbott Committed by Linus Torvalds
Browse files

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 Grsecurity/PaX team for inspiring this work

Signed-off-by: default avatarLaura Abbott <labbott@fedoraproject.org>
Acked-by: default avatarRafael 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 8823b1db

include/linux/mm.h

+2 −0
Original line number Diff line number Diff line
@@ -2179,10 +2179,12 @@ extern int apply_to_page_range(struct mm_struct *mm, unsigned long address, 
#ifdef CONFIG_PAGE_POISONING

extern bool page_poisoning_enabled(void);

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

extern bool page_is_poisoned(struct page *page);

#else

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

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

					int enable) { }

static inline bool page_is_poisoned(struct page *page) { return false; }

#endif



#ifdef CONFIG_DEBUG_PAGEALLOC

include/linux/poison.h

+4 −0
Original line number Diff line number Diff line
@@ -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 ************/

kernel/power/hibernate.c

+17 −0
Original line number Diff line number Diff line
@@ -1158,6 +1158,22 @@ static int __init kaslr_nohibernate_setup(char *str) 
	return nohibernate_setup(str);

}



static int __init page_poison_nohibernate_setup(char *str)

{

#ifdef CONFIG_PAGE_POISONING_ZERO

	/*

	 * The zeroing option for page poison skips the checks on alloc.

	 * since hibernation doesn't save free pages there's no way to

	 * guarantee the pages will still be zeroed.

	 */

	if (!strcmp(str, "on")) {

		pr_info("Disabling hibernation due to page poisoning\n");

		return nohibernate_setup(str);

	}

#endif

	return 1;

}



__setup("noresume", noresume_setup);

__setup("resume_offset=", resume_offset_setup);

__setup("resume=", resume_setup);
@@ -1166,3 +1182,4 @@ __setup("resumewait", resumewait_setup); 
__setup("resumedelay=", resumedelay_setup);

__setup("nohibernate", nohibernate_setup);

__setup("kaslr", kaslr_nohibernate_setup);

__setup("page_poison=", page_poison_nohibernate_setup);

mm/Kconfig.debug

+14 −0
Original line number Diff line number Diff line
@@ -65,3 +65,17 @@ 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 PAGE_POISONING

	---help---

	   Instead of using the existing poison value, fill the pages with

	   zeros. This makes it harder to detect when errors are occurring

	   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.



	   Enabling page poisoning with this option will disable hibernation



	   If unsure, say N

mm/page_alloc.c

+10 −1
Original line number Diff line number Diff line
@@ -1405,15 +1405,24 @@ static inline int check_new_page(struct page *page) 
	return 0;

}



static inline bool free_pages_prezeroed(bool poisoned)

{

	return IS_ENABLED(CONFIG_PAGE_POISONING_ZERO) &&

		page_poisoning_enabled() && poisoned;

}



static int prep_new_page(struct page *page, unsigned int order, gfp_t gfp_flags,

								int alloc_flags)

{

	int i;

	bool poisoned = true;



	for (i = 0; i < (1 << order); i++) {

		struct page *p = page + i;

		if (unlikely(check_new_page(p)))

			return 1;

		if (poisoned)

			poisoned &= page_is_poisoned(p);

	}



	set_page_private(page, 0);
@@ -1424,7 +1433,7 @@ static int prep_new_page(struct page *page, unsigned int order, gfp_t gfp_flags, 
	kernel_poison_pages(page, 1 << order, 1);

	kasan_alloc_pages(page, order);



	if (gfp_flags & __GFP_ZERO)

	if (!free_pages_prezeroed(poisoned) && (gfp_flags & __GFP_ZERO))

		for (i = 0; i < (1 << order); i++)

			clear_highpage(page + i);

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