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[134.134.136.24]) by mx.google.com with ESMTPS id l14-v6si25628752pgi.34.2018.10.10.18.49.59 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 10 Oct 2018 18:49:59 -0700 (PDT) Received-SPF: pass (google.com: domain of dan.j.williams@intel.com designates 134.134.136.24 as permitted sender) client-ip=134.134.136.24; Authentication-Results: mx.google.com; spf=pass (google.com: domain of dan.j.williams@intel.com designates 134.134.136.24 as permitted sender) smtp.mailfrom=dan.j.williams@intel.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=intel.com X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga005.jf.intel.com ([10.7.209.41]) by orsmga102.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 10 Oct 2018 18:49:59 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.54,366,1534834800"; d="scan'208";a="264684939" Received: from dwillia2-desk3.jf.intel.com (HELO dwillia2-desk3.amr.corp.intel.com) ([10.54.39.16]) by orsmga005.jf.intel.com with ESMTP; 10 Oct 2018 18:48:34 -0700 Subject: [PATCH v4 1/3] mm: Shuffle initial free memory From: Dan Williams To: akpm@linux-foundation.org Cc: Michal Hocko , Kees Cook , Dave Hansen , linux-mm@kvack.org, linux-kernel@vger.kernel.org, keescook@chromium.org Date: Wed, 10 Oct 2018 18:36:47 -0700 Message-ID: <153922180696.838512.12621709717839260874.stgit@dwillia2-desk3.amr.corp.intel.com> In-Reply-To: <153922180166.838512.8260339805733812034.stgit@dwillia2-desk3.amr.corp.intel.com> References: <153922180166.838512.8260339805733812034.stgit@dwillia2-desk3.amr.corp.intel.com> User-Agent: StGit/0.18-2-gc94f MIME-Version: 1.0 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: X-Virus-Scanned: ClamAV using ClamSMTP 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 Cc: Kees Cook Cc: Dave Hansen Signed-off-by: Dan Williams --- 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 +#include +#include +#include +#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); +}