[PATCH v4 0/3] Randomize free memory

[PATCH v4 0/3] Randomize free memory

[Dan Williams]

Changes since v3 [1]:
* Replace runtime 'shuffle_page_order' parameter with a compile-time
  CONFIG_SHUFFLE_PAGE_ALLOCATOR on/off switch and a
  CONFIG_SHUFFLE_PAGE_ORDER if a distro decides that the default 4MB
  shuffling boundary is not sufficient. Administrators will not be
  burdened with making this decision. (Michal)

* Move shuffle related code into a new mm/shuffle.c file.

[1]: https://www.mail-archive.com/linux-kernel@vger.kernel.org/msg1783262.html

---

Some data exfiltration and return-oriented-programming attacks rely on
the ability to infer the location of sensitive data objects. The kernel
page allocator, especially early in system boot, has predictable
first-in-first out behavior for physical pages. Pages are freed in
physical address order when first onlined.

Quoting Kees:
    "While we already have a base-address randomization
     (CONFIG_RANDOMIZE_MEMORY), attacks against the same hardware and
     memory layouts would certainly be using the predictability of
     allocation ordering (i.e. for attacks where the base address isn't
     important: only the relative positions between allocated memory).
     This is common in lots of heap-style attacks. They try to gain
     control over ordering by spraying allocations, etc.

     I'd really like to see this because it gives us something similar
     to CONFIG_SLAB_FREELIST_RANDOM but for the page allocator."

Another motivation for this change is performance in the presence of a
memory-side cache. In the future, memory-side-cache technology will be
available on generally available server platforms. The proposed
randomization approach has been measured to improve the cache conflict
rate by a factor of 2.5X on a well-known Java benchmark. It avoids
performance peaks and valleys to provide more predictable performance.

The initial randomization in patch1 can be undone over time so patch3 is
introduced to inject entropy on page free decisions. It is reasonable to
ask if the page free entropy is sufficient, but it is not enough due to
the in-order initial freeing of pages. At the start of that process
putting page1 in front or behind page0 still keeps them close together,
page2 is still near page1 and has a high chance of being adjacent. As
more pages are added ordering diversity improves, but there is still
high page locality for the low address pages and this leads to no
significant impact to the cache conflict rate.

More details in the patch1 commit message.

---

Dan Williams (3):
      mm: Shuffle initial free memory
      mm: Move buddy list manipulations into helpers
      mm: Maintain randomization of page free lists


 include/linux/list.h     |   17 ++++
 include/linux/mm.h       |   30 +++++++
 include/linux/mm_types.h |    3 +
 include/linux/mmzone.h   |   65 ++++++++++++++++
 init/Kconfig             |   32 ++++++++
 mm/Makefile              |    1 
 mm/compaction.c          |    4 -
 mm/memblock.c            |    9 ++
 mm/memory_hotplug.c      |    2 
 mm/page_alloc.c          |   81 +++++++++-----------
 mm/shuffle.c             |  186 ++++++++++++++++++++++++++++++++++++++++++++++
 11 files changed, 381 insertions(+), 49 deletions(-)
 create mode 100644 mm/shuffle.c

[PATCH v4 1/3] mm: Shuffle initial free memory

[Dan Williams]

Some data exfiltration and return-oriented-programming attacks rely on
the ability to infer the location of sensitive data objects. The kernel
page allocator, especially early in system boot, has predictable
first-in-first out behavior for physical pages. Pages are freed in
physical address order when first onlined.

Introduce shuffle_free_memory(), and its helper shuffle_zone(), to
perform a Fisher-Yates shuffle of the page allocator 'free_area' lists
when they are initially populated with free memory at boot and at
hotplug time.

Quoting Kees:
    "While we already have a base-address randomization
     (CONFIG_RANDOMIZE_MEMORY), attacks against the same hardware and
     memory layouts would certainly be using the predictability of
     allocation ordering (i.e. for attacks where the base address isn't
     important: only the relative positions between allocated memory).
     This is common in lots of heap-style attacks. They try to gain
     control over ordering by spraying allocations, etc.

     I'd really like to see this because it gives us something similar
     to CONFIG_SLAB_FREELIST_RANDOM but for the page allocator."

Another motivation for this change is performance in the presence of a
memory-side cache. In the future, memory-side-cache technology will be
available on generally available server platforms. The proposed
randomization approach has been measured to improve the cache conflict
rate by a factor of 2.5X on a well-known Java benchmark. It avoids
performance peaks and valleys to provide more predictable performance.

While SLAB_FREELIST_RANDOM reduces the predictability of some local slab
caches it leaves vast bulk of memory to be predictably in order
allocated. That ordering can be detected by a memory side-cache.

The shuffling is done in terms of CONFIG_SHUFFLE_PAGE_ORDER sized free
pages where the default CONFIG_SHUFFLE_PAGE_ORDER is MAX_ORDER-1 i.e.
10, 4MB this trades off randomization granularity for time spent
shuffling.  MAX_ORDER-1 was chosen to be minimally invasive to the page
allocator while still showing memory-side cache behavior improvements,
and the expectation that the security implications of finer granularity
randomization is mitigated by CONFIG_SLAB_FREELIST_RANDOM.

The performance impact of the shuffling appears to be in the noise
compared to other memory initialization work. Also the bulk of the work
is done in the background as a part of deferred_init_memmap().

This initial randomization can be undone over time so a follow-on patch
is introduced to inject entropy on page free decisions. It is reasonable
to ask if the page free entropy is sufficient, but it is not enough due
to the in-order initial freeing of pages. At the start of that process
putting page1 in front or behind page0 still keeps them close together,
page2 is still near page1 and has a high chance of being adjacent. As
more pages are added ordering diversity improves, but there is still
high page locality for the low address pages and this leads to no
significant impact to the cache conflict rate.

Cc: Michal Hocko <mhocko@suse.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
---
 include/linux/list.h   |   17 +++++
 include/linux/mm.h     |   17 +++++
 include/linux/mmzone.h |    4 +
 init/Kconfig           |   32 +++++++++
 mm/Makefile            |    1 
 mm/memblock.c          |    9 ++-
 mm/memory_hotplug.c    |    2 +
 mm/page_alloc.c        |    2 +
 mm/shuffle.c           |  170 ++++++++++++++++++++++++++++++++++++++++++++++++
 9 files changed, 253 insertions(+), 1 deletion(-)
 create mode 100644 mm/shuffle.c

diff --git a/include/linux/list.h b/include/linux/list.h
index de04cc5ed536..43f963328d7c 100644
--- a/include/linux/list.h
+++ b/include/linux/list.h
@@ -150,6 +150,23 @@ static inline void list_replace_init(struct list_head *old,
 	INIT_LIST_HEAD(old);
 }
 
+/**
+ * list_swap - replace entry1 with entry2 and re-add entry1 at entry2's position
+ * @entry1: the location to place entry2
+ * @entry2: the location to place entry1
+ */
+static inline void list_swap(struct list_head *entry1,
+			     struct list_head *entry2)
+{
+	struct list_head *pos = entry2->prev;
+
+	list_del(entry2);
+	list_replace(entry1, entry2);
+	if (pos == entry1)
+		pos = entry2;
+	list_add(entry1, pos);
+}
+
 /**
  * list_del_init - deletes entry from list and reinitialize it.
  * @entry: the element to delete from the list.
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 273d4dbd3883..5891bd4e5d29 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -2043,6 +2043,23 @@ extern void mem_init_print_info(const char *str);
 
 extern void reserve_bootmem_region(phys_addr_t start, phys_addr_t end);
 
+#ifdef CONFIG_SHUFFLE_PAGE_ALLOCATOR
+extern void shuffle_free_memory(pg_data_t *pgdat, unsigned long start_pfn,
+		unsigned long end_pfn);
+extern void shuffle_zone(struct zone *z, unsigned long start_pfn,
+		unsigned long end_pfn);
+#else
+static inline void shuffle_free_memory(pg_data_t *pgdat, unsigned long start_pfn,
+		unsigned long end_pfn)
+{
+}
+
+static inline void shuffle_zone(struct zone *z, unsigned long start_pfn,
+		unsigned long end_pfn)
+{
+}
+#endif
+
 /* Free the reserved page into the buddy system, so it gets managed. */
 static inline void __free_reserved_page(struct page *page)
 {
diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index ea29f7081f9d..15029fedbfe6 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -1273,6 +1273,10 @@ void sparse_init(void);
 #else
 #define sparse_init()	do {} while (0)
 #define sparse_index_init(_sec, _nid)  do {} while (0)
+static inline int pfn_present(unsigned long pfn)
+{
+	return 1;
+}
 #endif /* CONFIG_SPARSEMEM */
 
 /*
diff --git a/init/Kconfig b/init/Kconfig
index 1f1bbf7540f8..64123c28eeca 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -1701,6 +1701,38 @@ config SLAB_FREELIST_HARDENED
 	  sacrifies to harden the kernel slab allocator against common
 	  freelist exploit methods.
 
+config SHUFFLE_PAGE_ALLOCATOR
+	bool "Page allocator randomization"
+	default SLAB_FREELIST_RANDOM
+	help
+	  Randomization of the page allocator is both a security feature
+	  and a performance feature on platforms that have a
+	  direct-mapped memory side cache. See section 5.2.27
+	  Heterogeneous Memory Attribute Table (HMAT) in the ACPI 6.2a
+	  specification for an example of how a platform advertises the
+	  presence of a memory side cache. For the security
+	  benefits of this capability it is expected to be paired with
+	  SLAB_FREELIST_RANDOM as that adds local randomization for
+	  small objects while SHUFFLE_PAGE_ALLOCATOR adds randomization at
+	  SHUFFLE_PAGE_ORDER granularities. The runtime impact of the
+	  shuffling is negligible. The performance implications of not
+	  shuffling are significant on platforms with a direct-mapped
+	  memory-side cache.
+
+	  Say Y if unsure.
+
+config SHUFFLE_PAGE_ORDER
+	depends on SHUFFLE_PAGE_ALLOCATOR
+	int "Page allocator shuffle order"
+	range 0 10
+	default 10
+	help
+	  Specify the granularity at which shuffling (randomization) is
+	  performed. By default this is set to MAX_ORDER-1 to minimize
+	  runtime impact of randomization and with the expectation that
+	  SLAB_FREELIST_RANDOM mitigates heap attacks on smaller
+	  object granularities.
+
 config SLUB_CPU_PARTIAL
 	default y
 	depends on SLUB && SMP
diff --git a/mm/Makefile b/mm/Makefile
index d210cc9d6f80..1ffbc67f7395 100644
--- a/mm/Makefile
+++ b/mm/Makefile
@@ -65,6 +65,7 @@ obj-$(CONFIG_SLUB) += slub.o
 obj-$(CONFIG_KASAN)	+= kasan/
 obj-$(CONFIG_FAILSLAB) += failslab.o
 obj-$(CONFIG_MEMORY_HOTPLUG) += memory_hotplug.o
+obj-$(CONFIG_SHUFFLE_PAGE_ALLOCATOR) += shuffle.o
 obj-$(CONFIG_MEMTEST)		+= memtest.o
 obj-$(CONFIG_MIGRATION) += migrate.o
 obj-$(CONFIG_QUICKLIST) += quicklist.o
diff --git a/mm/memblock.c b/mm/memblock.c
index b0ebca546ba1..5b57964352a4 100644
--- a/mm/memblock.c
+++ b/mm/memblock.c
@@ -1985,9 +1985,16 @@ static unsigned long __init free_low_memory_core_early(void)
 	 *  low ram will be on Node1
 	 */
 	for_each_free_mem_range(i, NUMA_NO_NODE, MEMBLOCK_NONE, &start, &end,
-				NULL)
+				NULL) {
+		pg_data_t *pgdat;
+
 		count += __free_memory_core(start, end);
 
+		for_each_online_pgdat(pgdat)
+			shuffle_free_memory(pgdat, PHYS_PFN(start),
+					PHYS_PFN(end));
+	}
+
 	return count;
 }
 
diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 61972da38d93..34c9b6eb3159 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -894,6 +894,8 @@ int __ref online_pages(unsigned long pfn, unsigned long nr_pages, int online_typ
 	zone->zone_pgdat->node_present_pages += onlined_pages;
 	pgdat_resize_unlock(zone->zone_pgdat, &flags);
 
+	shuffle_zone(zone, pfn, zone_end_pfn(zone));
+
 	if (onlined_pages) {
 		node_states_set_node(nid, &arg);
 		if (need_zonelists_rebuild)
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index a02ce11c49f2..9b295b2287da 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1595,6 +1595,8 @@ static int __init deferred_init_memmap(void *data)
 	}
 	pgdat_resize_unlock(pgdat, &flags);
 
+	shuffle_zone(zone, first_init_pfn, zone_end_pfn(zone));
+
 	/* Sanity check that the next zone really is unpopulated */
 	WARN_ON(++zid < MAX_NR_ZONES && populated_zone(++zone));
 
diff --git a/mm/shuffle.c b/mm/shuffle.c
new file mode 100644
index 000000000000..5ed91b5b8441
--- /dev/null
+++ b/mm/shuffle.c
@@ -0,0 +1,170 @@
+// SPDX-License-Identifier: GPL-2.0
+// Copyright(c) 2018 Intel Corporation. All rights reserved.
+
+#include <linux/mm.h>
+#include <linux/init.h>
+#include <linux/mmzone.h>
+#include <linux/random.h>
+#include "internal.h"
+
+/*
+ * For two pages to be swapped in the shuffle, they must be free (on a
+ * 'free_area' lru), have the same order, and have the same migratetype.
+ */
+static struct page * __meminit shuffle_valid_page(unsigned long pfn, int order)
+{
+	struct page *page;
+
+	/*
+	 * Given we're dealing with randomly selected pfns in a zone we
+	 * need to ask questions like...
+	 */
+
+	/* ...is the pfn even in the memmap? */
+	if (!pfn_valid_within(pfn))
+		return NULL;
+
+	/* ...is the pfn in a present section or a hole? */
+	if (!pfn_present(pfn))
+		return NULL;
+
+	/* ...is the page free and currently on a free_area list? */
+	page = pfn_to_page(pfn);
+	if (!PageBuddy(page))
+		return NULL;
+
+	/*
+	 * ...is the page on the same list as the page we will
+	 * shuffle it with?
+	 */
+	if (page_order(page) != order)
+		return NULL;
+
+	return page;
+}
+
+/*
+ * Fisher-Yates shuffle the freelist which prescribes iterating through
+ * an array, pfns in this case, and randomly swapping each entry with
+ * another in the span, end_pfn - start_pfn.
+ *
+ * To keep the implementation simple it does not attempt to correct for
+ * sources of bias in the distribution, like modulo bias or
+ * pseudo-random number generator bias. I.e. the expectation is that
+ * this shuffling raises the bar for attacks that exploit the
+ * predictability of page allocations, but need not be a perfect
+ * shuffle.
+ *
+ * Note that we don't use @z->zone_start_pfn and zone_end_pfn(@z)
+ * directly since the caller may be aware of holes in the zone and can
+ * improve the accuracy of the random pfn selection.
+ */
+#define SHUFFLE_RETRY 10
+static void __meminit shuffle_zone_order(struct zone *z, unsigned long start_pfn,
+		unsigned long end_pfn, const int order)
+{
+	unsigned long i, flags;
+	const int order_pages = 1 << order;
+
+	if (start_pfn < z->zone_start_pfn)
+		start_pfn = z->zone_start_pfn;
+	if (end_pfn > zone_end_pfn(z))
+		end_pfn = zone_end_pfn(z);
+
+	/* probably means that start/end were outside the zone */
+	if (end_pfn <= start_pfn)
+		return;
+	spin_lock_irqsave(&z->lock, flags);
+	start_pfn = ALIGN(start_pfn, order_pages);
+	for (i = start_pfn; i < end_pfn; i += order_pages) {
+		unsigned long j;
+		int migratetype, retry;
+		struct page *page_i, *page_j;
+
+		/*
+		 * We expect page_i, in the sub-range of a zone being
+		 * added (@start_pfn to @end_pfn), to more likely be
+		 * valid compared to page_j randomly selected in the
+		 * span @zone_start_pfn to @spanned_pages.
+		 */
+		page_i = shuffle_valid_page(i, order);
+		if (!page_i)
+			continue;
+
+		for (retry = 0; retry < SHUFFLE_RETRY; retry++) {
+			/*
+			 * Pick a random order aligned page from the
+			 * start of the zone. Use the *whole* zone here
+			 * so that if it is freed in tiny pieces that we
+			 * randomize in the whole zone, not just within
+			 * those fragments.
+			 *
+			 * Since page_j comes from a potentially sparse
+			 * address range we want to try a bit harder to
+			 * find a shuffle point for page_i.
+			 */
+			j = z->zone_start_pfn +
+				ALIGN_DOWN(get_random_long() % z->spanned_pages,
+						order_pages);
+			page_j = shuffle_valid_page(j, order);
+			if (page_j && page_j != page_i)
+				break;
+		}
+		if (retry >= SHUFFLE_RETRY) {
+			pr_debug("%s: failed to swap %#lx\n", __func__, i);
+			continue;
+		}
+
+		/*
+		 * Each migratetype corresponds to its own list, make
+		 * sure the types match otherwise we're moving pages to
+		 * lists where they do not belong.
+		 */
+		migratetype = get_pageblock_migratetype(page_i);
+		if (get_pageblock_migratetype(page_j) != migratetype) {
+			pr_debug("%s: migratetype mismatch %#lx\n", __func__, i);
+			continue;
+		}
+
+		list_swap(&page_i->lru, &page_j->lru);
+
+		pr_debug("%s: swap: %#lx -> %#lx\n", __func__, i, j);
+
+		/* take it easy on the zone lock */
+		if ((i % (100 * order_pages)) == 0) {
+			spin_unlock_irqrestore(&z->lock, flags);
+			cond_resched();
+			spin_lock_irqsave(&z->lock, flags);
+		}
+	}
+	spin_unlock_irqrestore(&z->lock, flags);
+}
+
+void __meminit shuffle_zone(struct zone *z, unsigned long start_pfn,
+               unsigned long end_pfn)
+{
+       int i;
+
+       /* shuffle all the orders at the specified order and higher */
+       for (i = CONFIG_SHUFFLE_PAGE_ORDER; i < MAX_ORDER; i++)
+               shuffle_zone_order(z, start_pfn, end_pfn, i);
+}
+
+/**
+ * shuffle_free_memory - reduce the predictability of the page allocator
+ * @pgdat: node page data
+ * @start_pfn: Limit the shuffle to the greater of this value or zone start
+ * @end_pfn: Limit the shuffle to the less of this value or zone end
+ *
+ * While shuffle_zone() attempts to avoid holes with pfn_valid() and
+ * pfn_present() they can not report sub-section sized holes. @start_pfn
+ * and @end_pfn limit the shuffle to the exact memory pages being freed.
+ */
+void __meminit shuffle_free_memory(pg_data_t *pgdat, unsigned long start_pfn,
+		unsigned long end_pfn)
+{
+	struct zone *z;
+
+	for (z = pgdat->node_zones; z < pgdat->node_zones + MAX_NR_ZONES; z++)
+		shuffle_zone(z, start_pfn, end_pfn);
+}

Re: [PATCH v4 1/3] mm: Shuffle initial free memory

[Kees Cook]

On Wed, Oct 10, 2018 at 6:36 PM, Dan Williams <dan.j.williams@intel.com> wrote:
> While SLAB_FREELIST_RANDOM reduces the predictability of some local slab
> caches it leaves vast bulk of memory to be predictably in order
> allocated. That ordering can be detected by a memory side-cache.
>
> The shuffling is done in terms of CONFIG_SHUFFLE_PAGE_ORDER sized free
> pages where the default CONFIG_SHUFFLE_PAGE_ORDER is MAX_ORDER-1 i.e.
> 10, 4MB this trades off randomization granularity for time spent
> shuffling.  MAX_ORDER-1 was chosen to be minimally invasive to the page
> allocator while still showing memory-side cache behavior improvements,
> and the expectation that the security implications of finer granularity
> randomization is mitigated by CONFIG_SLAB_FREELIST_RANDOM.

Perhaps it would help some of the detractors of this feature to make
this a runtime choice? Some benchmarks show improvements, some show
regressions. It could just be up to the admin to turn this on/off
given their paranoia levels? (i.e. the shuffling could become a no-op
with a given specific boot param?)

-Kees

-- 
Kees Cook
Pixel Security

Re: [PATCH v4 1/3] mm: Shuffle initial free memory

[Dan Williams]

On Mon, Oct 15, 2018 at 3:25 PM Kees Cook <keescook@chromium.org> wrote:
>
> On Wed, Oct 10, 2018 at 6:36 PM, Dan Williams <dan.j.williams@intel.com> wrote:
> > While SLAB_FREELIST_RANDOM reduces the predictability of some local slab
> > caches it leaves vast bulk of memory to be predictably in order
> > allocated. That ordering can be detected by a memory side-cache.
> >
> > The shuffling is done in terms of CONFIG_SHUFFLE_PAGE_ORDER sized free
> > pages where the default CONFIG_SHUFFLE_PAGE_ORDER is MAX_ORDER-1 i.e.
> > 10, 4MB this trades off randomization granularity for time spent
> > shuffling.  MAX_ORDER-1 was chosen to be minimally invasive to the page
> > allocator while still showing memory-side cache behavior improvements,
> > and the expectation that the security implications of finer granularity
> > randomization is mitigated by CONFIG_SLAB_FREELIST_RANDOM.
>
> Perhaps it would help some of the detractors of this feature to make
> this a runtime choice? Some benchmarks show improvements, some show
> regressions. It could just be up to the admin to turn this on/off
> given their paranoia levels? (i.e. the shuffling could become a no-op
> with a given specific boot param?)

Yes, I think it's a valid concern to not turn this on for everybody
given the potential for performance regression. For the next version
I'll add some runtime detection for a memory-side-cache to set the
default on/off, and include a command line override for the paranoid
that want in on regardless of the presence of such a cache.

Re: [PATCH v4 1/3] mm: Shuffle initial free memory

[Michal Hocko]

On Mon 15-10-18 15:25:47, Kees Cook wrote:
> On Wed, Oct 10, 2018 at 6:36 PM, Dan Williams <dan.j.williams@intel.com> wrote:
> > While SLAB_FREELIST_RANDOM reduces the predictability of some local slab
> > caches it leaves vast bulk of memory to be predictably in order
> > allocated. That ordering can be detected by a memory side-cache.
> >
> > The shuffling is done in terms of CONFIG_SHUFFLE_PAGE_ORDER sized free
> > pages where the default CONFIG_SHUFFLE_PAGE_ORDER is MAX_ORDER-1 i.e.
> > 10, 4MB this trades off randomization granularity for time spent
> > shuffling.  MAX_ORDER-1 was chosen to be minimally invasive to the page
> > allocator while still showing memory-side cache behavior improvements,
> > and the expectation that the security implications of finer granularity
> > randomization is mitigated by CONFIG_SLAB_FREELIST_RANDOM.
> 
> Perhaps it would help some of the detractors of this feature to make
> this a runtime choice? Some benchmarks show improvements, some show
> regressions. It could just be up to the admin to turn this on/off
> given their paranoia levels? (i.e. the shuffling could become a no-op
> with a given specific boot param?)

Sure, making this a opt-in is really necessary but it would be even
_better_ to actually evaluate how much security relevance it has as
well. If for nothing else then to allow an educated decision rather than
a fear driven one. And that pretty much involves evaluation on how hard
it is to bypass the randomness. If I am going to pay some overhead I
would like to know how much hardening I get in return, right? Something
completely missing in the current evaluation so far.
-- 
Michal Hocko
SUSE Labs

[PATCH v4 2/3] mm: Move buddy list manipulations into helpers

[Dan Williams]

In preparation for runtime randomization of the zone lists, take all
(well, most of) the list_*() functions in the buddy allocator and put
them in helper functions. Provide a common control point for injecting
additional behavior when freeing pages.

Cc: Michal Hocko <mhocko@suse.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
---
 include/linux/mm.h       |    3 --
 include/linux/mm_types.h |    3 ++
 include/linux/mmzone.h   |   51 ++++++++++++++++++++++++++++++++++
 mm/compaction.c          |    4 +--
 mm/page_alloc.c          |   70 ++++++++++++++++++----------------------------
 5 files changed, 84 insertions(+), 47 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 5891bd4e5d29..856b0530c55d 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -473,9 +473,6 @@ static inline void vma_set_anonymous(struct vm_area_struct *vma)
 struct mmu_gather;
 struct inode;
 
-#define page_private(page)		((page)->private)
-#define set_page_private(page, v)	((page)->private = (v))
-
 #if !defined(__HAVE_ARCH_PTE_DEVMAP) || !defined(CONFIG_TRANSPARENT_HUGEPAGE)
 static inline int pmd_devmap(pmd_t pmd)
 {
diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index 5ed8f6292a53..72f37ea6dedb 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -209,6 +209,9 @@ struct page {
 #define PAGE_FRAG_CACHE_MAX_SIZE	__ALIGN_MASK(32768, ~PAGE_MASK)
 #define PAGE_FRAG_CACHE_MAX_ORDER	get_order(PAGE_FRAG_CACHE_MAX_SIZE)
 
+#define page_private(page)		((page)->private)
+#define set_page_private(page, v)	((page)->private = (v))
+
 struct page_frag_cache {
 	void * va;
 #if (PAGE_SIZE < PAGE_FRAG_CACHE_MAX_SIZE)
diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index 15029fedbfe6..0b91ce871895 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -18,6 +18,8 @@
 #include <linux/pageblock-flags.h>
 #include <linux/page-flags-layout.h>
 #include <linux/atomic.h>
+#include <linux/mm_types.h>
+#include <linux/page-flags.h>
 #include <asm/page.h>
 
 /* Free memory management - zoned buddy allocator.  */
@@ -98,6 +100,55 @@ struct free_area {
 	unsigned long		nr_free;
 };
 
+/* Used for pages not on another list */
+static inline void add_to_free_area(struct page *page, struct free_area *area,
+			     int migratetype)
+{
+	list_add(&page->lru, &area->free_list[migratetype]);
+	area->nr_free++;
+}
+
+/* Used for pages not on another list */
+static inline void add_to_free_area_tail(struct page *page, struct free_area *area,
+				  int migratetype)
+{
+	list_add_tail(&page->lru, &area->free_list[migratetype]);
+	area->nr_free++;
+}
+
+/* Used for pages which are on another list */
+static inline void move_to_free_area(struct page *page, struct free_area *area,
+			     int migratetype)
+{
+	list_move(&page->lru, &area->free_list[migratetype]);
+}
+
+static inline struct page *get_page_from_free_area(struct free_area *area,
+					    int migratetype)
+{
+	return list_first_entry_or_null(&area->free_list[migratetype],
+					struct page, lru);
+}
+
+static inline void rmv_page_order(struct page *page)
+{
+	__ClearPageBuddy(page);
+	set_page_private(page, 0);
+}
+
+static inline void del_page_from_free_area(struct page *page,
+		struct free_area *area, int migratetype)
+{
+	list_del(&page->lru);
+	rmv_page_order(page);
+	area->nr_free--;
+}
+
+static inline bool free_area_empty(struct free_area *area, int migratetype)
+{
+	return list_empty(&area->free_list[migratetype]);
+}
+
 struct pglist_data;
 
 /*
diff --git a/mm/compaction.c b/mm/compaction.c
index 7c607479de4a..44adbfa073b3 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -1359,13 +1359,13 @@ static enum compact_result __compact_finished(struct zone *zone,
 		bool can_steal;
 
 		/* Job done if page is free of the right migratetype */
-		if (!list_empty(&area->free_list[migratetype]))
+		if (!free_area_empty(area, migratetype))
 			return COMPACT_SUCCESS;
 
 #ifdef CONFIG_CMA
 		/* MIGRATE_MOVABLE can fallback on MIGRATE_CMA */
 		if (migratetype == MIGRATE_MOVABLE &&
-			!list_empty(&area->free_list[MIGRATE_CMA]))
+			!free_area_empty(area, MIGRATE_CMA))
 			return COMPACT_SUCCESS;
 #endif
 		/*
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 9b295b2287da..e1e0b54423f0 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -704,12 +704,6 @@ static inline void set_page_order(struct page *page, unsigned int order)
 	__SetPageBuddy(page);
 }
 
-static inline void rmv_page_order(struct page *page)
-{
-	__ClearPageBuddy(page);
-	set_page_private(page, 0);
-}
-
 /*
  * This function checks whether a page is free && is the buddy
  * we can coalesce a page and its buddy if
@@ -810,13 +804,11 @@ static inline void __free_one_page(struct page *page,
 		 * Our buddy is free or it is CONFIG_DEBUG_PAGEALLOC guard page,
 		 * merge with it and move up one order.
 		 */
-		if (page_is_guard(buddy)) {
+		if (page_is_guard(buddy))
 			clear_page_guard(zone, buddy, order, migratetype);
-		} else {
-			list_del(&buddy->lru);
-			zone->free_area[order].nr_free--;
-			rmv_page_order(buddy);
-		}
+		else
+			del_page_from_free_area(buddy, &zone->free_area[order],
+					migratetype);
 		combined_pfn = buddy_pfn & pfn;
 		page = page + (combined_pfn - pfn);
 		pfn = combined_pfn;
@@ -866,15 +858,13 @@ static inline void __free_one_page(struct page *page,
 		higher_buddy = higher_page + (buddy_pfn - combined_pfn);
 		if (pfn_valid_within(buddy_pfn) &&
 		    page_is_buddy(higher_page, higher_buddy, order + 1)) {
-			list_add_tail(&page->lru,
-				&zone->free_area[order].free_list[migratetype]);
-			goto out;
+			add_to_free_area_tail(page, &zone->free_area[order],
+					      migratetype);
+			return;
 		}
 	}
 
-	list_add(&page->lru, &zone->free_area[order].free_list[migratetype]);
-out:
-	zone->free_area[order].nr_free++;
+	add_to_free_area(page, &zone->free_area[order], migratetype);
 }
 
 /*
@@ -1819,7 +1809,7 @@ static inline void expand(struct zone *zone, struct page *page,
 		if (set_page_guard(zone, &page[size], high, migratetype))
 			continue;
 
-		list_add(&page[size].lru, &area->free_list[migratetype]);
+		add_to_free_area(&page[size], area, migratetype);
 		area->nr_free++;
 		set_page_order(&page[size], high);
 	}
@@ -1961,13 +1951,10 @@ struct page *__rmqueue_smallest(struct zone *zone, unsigned int order,
 	/* Find a page of the appropriate size in the preferred list */
 	for (current_order = order; current_order < MAX_ORDER; ++current_order) {
 		area = &(zone->free_area[current_order]);
-		page = list_first_entry_or_null(&area->free_list[migratetype],
-							struct page, lru);
+		page = get_page_from_free_area(area, migratetype);
 		if (!page)
 			continue;
-		list_del(&page->lru);
-		rmv_page_order(page);
-		area->nr_free--;
+		del_page_from_free_area(page, area, migratetype);
 		expand(zone, page, order, current_order, area, migratetype);
 		set_pcppage_migratetype(page, migratetype);
 		return page;
@@ -2057,8 +2044,7 @@ static int move_freepages(struct zone *zone,
 		}
 
 		order = page_order(page);
-		list_move(&page->lru,
-			  &zone->free_area[order].free_list[migratetype]);
+		move_to_free_area(page, &zone->free_area[order], migratetype);
 		page += 1 << order;
 		pages_moved += 1 << order;
 	}
@@ -2207,7 +2193,7 @@ static void steal_suitable_fallback(struct zone *zone, struct page *page,
 
 single_page:
 	area = &zone->free_area[current_order];
-	list_move(&page->lru, &area->free_list[start_type]);
+	move_to_free_area(page, area, start_type);
 }
 
 /*
@@ -2231,7 +2217,7 @@ int find_suitable_fallback(struct free_area *area, unsigned int order,
 		if (fallback_mt == MIGRATE_TYPES)
 			break;
 
-		if (list_empty(&area->free_list[fallback_mt]))
+		if (free_area_empty(area, fallback_mt))
 			continue;
 
 		if (can_steal_fallback(order, migratetype))
@@ -2318,9 +2304,7 @@ static bool unreserve_highatomic_pageblock(const struct alloc_context *ac,
 		for (order = 0; order < MAX_ORDER; order++) {
 			struct free_area *area = &(zone->free_area[order]);
 
-			page = list_first_entry_or_null(
-					&area->free_list[MIGRATE_HIGHATOMIC],
-					struct page, lru);
+			page = get_page_from_free_area(area, MIGRATE_HIGHATOMIC);
 			if (!page)
 				continue;
 
@@ -2433,8 +2417,7 @@ __rmqueue_fallback(struct zone *zone, int order, int start_migratetype)
 	VM_BUG_ON(current_order == MAX_ORDER);
 
 do_steal:
-	page = list_first_entry(&area->free_list[fallback_mt],
-							struct page, lru);
+	page = get_page_from_free_area(area, fallback_mt);
 
 	steal_suitable_fallback(zone, page, start_migratetype, can_steal);
 
@@ -2861,6 +2844,7 @@ EXPORT_SYMBOL_GPL(split_page);
 
 int __isolate_free_page(struct page *page, unsigned int order)
 {
+	struct free_area *area = &page_zone(page)->free_area[order];
 	unsigned long watermark;
 	struct zone *zone;
 	int mt;
@@ -2885,9 +2869,8 @@ int __isolate_free_page(struct page *page, unsigned int order)
 	}
 
 	/* Remove page from free list */
-	list_del(&page->lru);
-	zone->free_area[order].nr_free--;
-	rmv_page_order(page);
+
+	del_page_from_free_area(page, area, mt);
 
 	/*
 	 * Set the pageblock if the isolated page is at least half of a
@@ -3181,13 +3164,13 @@ bool __zone_watermark_ok(struct zone *z, unsigned int order, unsigned long mark,
 			continue;
 
 		for (mt = 0; mt < MIGRATE_PCPTYPES; mt++) {
-			if (!list_empty(&area->free_list[mt]))
+			if (!free_area_empty(area, mt))
 				return true;
 		}
 
 #ifdef CONFIG_CMA
 		if ((alloc_flags & ALLOC_CMA) &&
-		    !list_empty(&area->free_list[MIGRATE_CMA])) {
+		    !free_area_empty(area, MIGRATE_CMA)) {
 			return true;
 		}
 #endif
@@ -5022,7 +5005,7 @@ void show_free_areas(unsigned int filter, nodemask_t *nodemask)
 
 			types[order] = 0;
 			for (type = 0; type < MIGRATE_TYPES; type++) {
-				if (!list_empty(&area->free_list[type]))
+				if (!free_area_empty(area, type))
 					types[order] |= 1 << type;
 			}
 		}
@@ -8128,6 +8111,9 @@ __offline_isolated_pages(unsigned long start_pfn, unsigned long end_pfn)
 	spin_lock_irqsave(&zone->lock, flags);
 	pfn = start_pfn;
 	while (pfn < end_pfn) {
+		struct free_area *area;
+		int mt;
+
 		if (!pfn_valid(pfn)) {
 			pfn++;
 			continue;
@@ -8146,13 +8132,13 @@ __offline_isolated_pages(unsigned long start_pfn, unsigned long end_pfn)
 		BUG_ON(page_count(page));
 		BUG_ON(!PageBuddy(page));
 		order = page_order(page);
+		area = &zone->free_area[order];
 #ifdef CONFIG_DEBUG_VM
 		pr_info("remove from free list %lx %d %lx\n",
 			pfn, 1 << order, end_pfn);
 #endif
-		list_del(&page->lru);
-		rmv_page_order(page);
-		zone->free_area[order].nr_free--;
+		mt = get_pageblock_migratetype(page);
+		del_page_from_free_area(page, area, mt);
 		for (i = 0; i < (1 << order); i++)
 			SetPageReserved((page+i));
 		pfn += (1 << order);

[PATCH v4 3/3] mm: Maintain randomization of page free lists

[Dan Williams]

When freeing a page with an order >= shuffle_page_order randomly select
the front or back of the list for insertion.

While the mm tries to defragment physical pages into huge pages this can
tend to make the page allocator more predictable over time. Inject the
front-back randomness to preserve the initial randomness established by
shuffle_free_memory() when the kernel was booted.

The overhead of this manipulation is constrained by only being applied
for MAX_ORDER sized pages by default.

Cc: Michal Hocko <mhocko@suse.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
---
 include/linux/mm.h     |   10 ++++++++++
 include/linux/mmzone.h |   10 ++++++++++
 mm/page_alloc.c        |   11 +++++++++--
 mm/shuffle.c           |   16 ++++++++++++++++
 4 files changed, 45 insertions(+), 2 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 856b0530c55d..91a1e7fb465a 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -2045,6 +2045,11 @@ extern void shuffle_free_memory(pg_data_t *pgdat, unsigned long start_pfn,
 		unsigned long end_pfn);
 extern void shuffle_zone(struct zone *z, unsigned long start_pfn,
 		unsigned long end_pfn);
+
+static inline bool is_shuffle_order(int order)
+{
+	return order >= CONFIG_SHUFFLE_PAGE_ORDER;
+}
 #else
 static inline void shuffle_free_memory(pg_data_t *pgdat, unsigned long start_pfn,
 		unsigned long end_pfn)
@@ -2055,6 +2060,11 @@ static inline void shuffle_zone(struct zone *z, unsigned long start_pfn,
 		unsigned long end_pfn)
 {
 }
+
+static inline bool is_shuffle_order(int order)
+{
+	return false;
+}
 #endif
 
 /* Free the reserved page into the buddy system, so it gets managed. */
diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index 0b91ce871895..c7abf21ed9f4 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -98,6 +98,8 @@ extern int page_group_by_mobility_disabled;
 struct free_area {
 	struct list_head	free_list[MIGRATE_TYPES];
 	unsigned long		nr_free;
+	u64			rand;
+	u8			rand_bits;
 };
 
 /* Used for pages not on another list */
@@ -116,6 +118,14 @@ static inline void add_to_free_area_tail(struct page *page, struct free_area *ar
 	area->nr_free++;
 }
 
+#ifdef CONFIG_SHUFFLE_PAGE_ALLOCATOR
+/* Used to preserve page allocation order entropy */
+void add_to_free_area_random(struct page *page, struct free_area *area,
+		int migratetype);
+#else
+#define add_to_free_area_random add_to_free_area
+#endif
+
 /* Used for pages which are on another list */
 static inline void move_to_free_area(struct page *page, struct free_area *area,
 			     int migratetype)
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index e1e0b54423f0..eef241ceb2c4 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -42,6 +42,7 @@
 #include <linux/mempolicy.h>
 #include <linux/memremap.h>
 #include <linux/stop_machine.h>
+#include <linux/random.h>
 #include <linux/sort.h>
 #include <linux/pfn.h>
 #include <linux/backing-dev.h>
@@ -850,7 +851,8 @@ static inline void __free_one_page(struct page *page,
 	 * so it's less likely to be used soon and more likely to be merged
 	 * as a higher order page
 	 */
-	if ((order < MAX_ORDER-2) && pfn_valid_within(buddy_pfn)) {
+	if ((order < MAX_ORDER-2) && pfn_valid_within(buddy_pfn)
+			&& !is_shuffle_order(order)) {
 		struct page *higher_page, *higher_buddy;
 		combined_pfn = buddy_pfn & pfn;
 		higher_page = page + (combined_pfn - pfn);
@@ -864,7 +866,12 @@ static inline void __free_one_page(struct page *page,
 		}
 	}
 
-	add_to_free_area(page, &zone->free_area[order], migratetype);
+	if (is_shuffle_order(order))
+		add_to_free_area_random(page, &zone->free_area[order],
+				migratetype);
+	else
+		add_to_free_area(page, &zone->free_area[order], migratetype);
+
 }
 
 /*
diff --git a/mm/shuffle.c b/mm/shuffle.c
index 5ed91b5b8441..3937d0bc3670 100644
--- a/mm/shuffle.c
+++ b/mm/shuffle.c
@@ -168,3 +168,19 @@ void __meminit shuffle_free_memory(pg_data_t *pgdat, unsigned long start_pfn,
 	for (z = pgdat->node_zones; z < pgdat->node_zones + MAX_NR_ZONES; z++)
 		shuffle_zone(z, start_pfn, end_pfn);
 }
+
+void add_to_free_area_random(struct page *page, struct free_area *area,
+		int migratetype)
+{
+	if (area->rand_bits == 0) {
+		area->rand_bits = 64;
+		area->rand = get_random_u64();
+	}
+
+	if (area->rand & 1)
+		add_to_free_area(page, area, migratetype);
+	else
+		add_to_free_area_tail(page, area, migratetype);
+	area->rand_bits--;
+	area->rand >>= 1;
+}