On Fri, Nov 4, 2016 at 7:45 AM, Juerg Haefliger <juerg.haefliger@xxxxxxx> wrote: > This patch adds support for XPFO which protects against 'ret2dir' kernel > attacks. The basic idea is to enforce exclusive ownership of page frames > by either the kernel or userspace, unless explicitly requested by the > kernel. Whenever a page destined for userspace is allocated, it is > unmapped from physmap (the kernel's page table). When such a page is > reclaimed from userspace, it is mapped back to physmap. > > Additional fields in the page_ext struct are used for XPFO housekeeping. > Specifically two flags to distinguish user vs. kernel pages and to tag > unmapped pages and a reference counter to balance kmap/kunmap operations > and a lock to serialize access to the XPFO fields. > > Known issues/limitations: > - Only supports x86-64 (for now) > - Only supports 4k pages (for now) > - There are most likely some legitimate uses cases where the kernel needs > to access userspace which need to be made XPFO-aware > - Performance penalty > > Reference paper by the original patch authors: > http://www.cs.columbia.edu/~vpk/papers/ret2dir.sec14.pdf Would it be possible to create an lkdtm test that can exercise this protection? > Suggested-by: Vasileios P. Kemerlis <vpk@xxxxxxxxxxxxxxx> > Signed-off-by: Juerg Haefliger <juerg.haefliger@xxxxxxx> > --- > arch/x86/Kconfig | 3 +- > arch/x86/mm/init.c | 2 +- > drivers/ata/libata-sff.c | 4 +- > include/linux/highmem.h | 15 +++- > include/linux/page_ext.h | 7 ++ > include/linux/xpfo.h | 39 +++++++++ > lib/swiotlb.c | 3 +- > mm/Makefile | 1 + > mm/page_alloc.c | 2 + > mm/page_ext.c | 4 + > mm/xpfo.c | 206 +++++++++++++++++++++++++++++++++++++++++++++++ > security/Kconfig | 19 +++++ > 12 files changed, 298 insertions(+), 7 deletions(-) > create mode 100644 include/linux/xpfo.h > create mode 100644 mm/xpfo.c > > diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig > index bada636d1065..38b334f8fde5 100644 > --- a/arch/x86/Kconfig > +++ b/arch/x86/Kconfig > @@ -165,6 +165,7 @@ config X86 > select HAVE_STACK_VALIDATION if X86_64 > select ARCH_USES_HIGH_VMA_FLAGS if X86_INTEL_MEMORY_PROTECTION_KEYS > select ARCH_HAS_PKEYS if X86_INTEL_MEMORY_PROTECTION_KEYS > + select ARCH_SUPPORTS_XPFO if X86_64 > > config INSTRUCTION_DECODER > def_bool y > @@ -1361,7 +1362,7 @@ config ARCH_DMA_ADDR_T_64BIT > > config X86_DIRECT_GBPAGES > def_bool y > - depends on X86_64 && !DEBUG_PAGEALLOC && !KMEMCHECK > + depends on X86_64 && !DEBUG_PAGEALLOC && !KMEMCHECK && !XPFO > ---help--- > Certain kernel features effectively disable kernel > linear 1 GB mappings (even if the CPU otherwise > diff --git a/arch/x86/mm/init.c b/arch/x86/mm/init.c > index 22af912d66d2..a6fafbae02bb 100644 > --- a/arch/x86/mm/init.c > +++ b/arch/x86/mm/init.c > @@ -161,7 +161,7 @@ static int page_size_mask; > > static void __init probe_page_size_mask(void) > { > -#if !defined(CONFIG_KMEMCHECK) > +#if !defined(CONFIG_KMEMCHECK) && !defined(CONFIG_XPFO) > /* > * For CONFIG_KMEMCHECK or pagealloc debugging, identity mapping will > * use small pages. > diff --git a/drivers/ata/libata-sff.c b/drivers/ata/libata-sff.c > index 051b6158d1b7..58af734be25d 100644 > --- a/drivers/ata/libata-sff.c > +++ b/drivers/ata/libata-sff.c > @@ -715,7 +715,7 @@ static void ata_pio_sector(struct ata_queued_cmd *qc) > > DPRINTK("data %s\n", qc->tf.flags & ATA_TFLAG_WRITE ? "write" : "read"); > > - if (PageHighMem(page)) { > + if (PageHighMem(page) || xpfo_page_is_unmapped(page)) { > unsigned long flags; > > /* FIXME: use a bounce buffer */ > @@ -860,7 +860,7 @@ static int __atapi_pio_bytes(struct ata_queued_cmd *qc, unsigned int bytes) > > DPRINTK("data %s\n", qc->tf.flags & ATA_TFLAG_WRITE ? "write" : "read"); > > - if (PageHighMem(page)) { > + if (PageHighMem(page) || xpfo_page_is_unmapped(page)) { > unsigned long flags; > > /* FIXME: use bounce buffer */ > diff --git a/include/linux/highmem.h b/include/linux/highmem.h > index bb3f3297062a..7a17c166532f 100644 > --- a/include/linux/highmem.h > +++ b/include/linux/highmem.h > @@ -7,6 +7,7 @@ > #include <linux/mm.h> > #include <linux/uaccess.h> > #include <linux/hardirq.h> > +#include <linux/xpfo.h> > > #include <asm/cacheflush.h> > > @@ -55,24 +56,34 @@ static inline struct page *kmap_to_page(void *addr) > #ifndef ARCH_HAS_KMAP > static inline void *kmap(struct page *page) > { > + void *kaddr; > + > might_sleep(); > - return page_address(page); > + kaddr = page_address(page); > + xpfo_kmap(kaddr, page); > + return kaddr; > } > > static inline void kunmap(struct page *page) > { > + xpfo_kunmap(page_address(page), page); > } > > static inline void *kmap_atomic(struct page *page) > { > + void *kaddr; > + > preempt_disable(); > pagefault_disable(); > - return page_address(page); > + kaddr = page_address(page); > + xpfo_kmap(kaddr, page); > + return kaddr; > } > #define kmap_atomic_prot(page, prot) kmap_atomic(page) > > static inline void __kunmap_atomic(void *addr) > { > + xpfo_kunmap(addr, virt_to_page(addr)); > pagefault_enable(); > preempt_enable(); > } > diff --git a/include/linux/page_ext.h b/include/linux/page_ext.h > index 9298c393ddaa..0e451a42e5a3 100644 > --- a/include/linux/page_ext.h > +++ b/include/linux/page_ext.h > @@ -29,6 +29,8 @@ enum page_ext_flags { > PAGE_EXT_DEBUG_POISON, /* Page is poisoned */ > PAGE_EXT_DEBUG_GUARD, > PAGE_EXT_OWNER, > + PAGE_EXT_XPFO_KERNEL, /* Page is a kernel page */ > + PAGE_EXT_XPFO_UNMAPPED, /* Page is unmapped */ > #if defined(CONFIG_IDLE_PAGE_TRACKING) && !defined(CONFIG_64BIT) > PAGE_EXT_YOUNG, > PAGE_EXT_IDLE, > @@ -44,6 +46,11 @@ enum page_ext_flags { > */ > struct page_ext { > unsigned long flags; > +#ifdef CONFIG_XPFO > + int inited; /* Map counter and lock initialized */ > + atomic_t mapcount; /* Counter for balancing map/unmap requests */ > + spinlock_t maplock; /* Lock to serialize map/unmap requests */ > +#endif > }; > > extern void pgdat_page_ext_init(struct pglist_data *pgdat); > diff --git a/include/linux/xpfo.h b/include/linux/xpfo.h > new file mode 100644 > index 000000000000..77187578ca33 > --- /dev/null > +++ b/include/linux/xpfo.h > @@ -0,0 +1,39 @@ > +/* > + * Copyright (C) 2016 Hewlett Packard Enterprise Development, L.P. > + * Copyright (C) 2016 Brown University. All rights reserved. > + * > + * Authors: > + * Juerg Haefliger <juerg.haefliger@xxxxxxx> > + * Vasileios P. Kemerlis <vpk@xxxxxxxxxxxx> > + * > + * This program is free software; you can redistribute it and/or modify it > + * under the terms of the GNU General Public License version 2 as published by > + * the Free Software Foundation. > + */ > + > +#ifndef _LINUX_XPFO_H > +#define _LINUX_XPFO_H > + > +#ifdef CONFIG_XPFO > + > +extern struct page_ext_operations page_xpfo_ops; > + > +extern void xpfo_kmap(void *kaddr, struct page *page); > +extern void xpfo_kunmap(void *kaddr, struct page *page); > +extern void xpfo_alloc_page(struct page *page, int order, gfp_t gfp); > +extern void xpfo_free_page(struct page *page, int order); > + > +extern bool xpfo_page_is_unmapped(struct page *page); > + > +#else /* !CONFIG_XPFO */ > + > +static inline void xpfo_kmap(void *kaddr, struct page *page) { } > +static inline void xpfo_kunmap(void *kaddr, struct page *page) { } > +static inline void xpfo_alloc_page(struct page *page, int order, gfp_t gfp) { } > +static inline void xpfo_free_page(struct page *page, int order) { } > + > +static inline bool xpfo_page_is_unmapped(struct page *page) { return false; } > + > +#endif /* CONFIG_XPFO */ > + > +#endif /* _LINUX_XPFO_H */ > diff --git a/lib/swiotlb.c b/lib/swiotlb.c > index 22e13a0e19d7..455eff44604e 100644 > --- a/lib/swiotlb.c > +++ b/lib/swiotlb.c > @@ -390,8 +390,9 @@ static void swiotlb_bounce(phys_addr_t orig_addr, phys_addr_t tlb_addr, > { > unsigned long pfn = PFN_DOWN(orig_addr); > unsigned char *vaddr = phys_to_virt(tlb_addr); > + struct page *page = pfn_to_page(pfn); > > - if (PageHighMem(pfn_to_page(pfn))) { > + if (PageHighMem(page) || xpfo_page_is_unmapped(page)) { > /* The buffer does not have a mapping. Map it in and copy */ > unsigned int offset = orig_addr & ~PAGE_MASK; > char *buffer; > diff --git a/mm/Makefile b/mm/Makefile > index 295bd7a9f76b..175680f516aa 100644 > --- a/mm/Makefile > +++ b/mm/Makefile > @@ -100,3 +100,4 @@ obj-$(CONFIG_IDLE_PAGE_TRACKING) += page_idle.o > obj-$(CONFIG_FRAME_VECTOR) += frame_vector.o > obj-$(CONFIG_DEBUG_PAGE_REF) += debug_page_ref.o > obj-$(CONFIG_HARDENED_USERCOPY) += usercopy.o > +obj-$(CONFIG_XPFO) += xpfo.o > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index 8fd42aa7c4bd..100e80e008e2 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -1045,6 +1045,7 @@ static __always_inline bool free_pages_prepare(struct page *page, > kernel_poison_pages(page, 1 << order, 0); > kernel_map_pages(page, 1 << order, 0); > kasan_free_pages(page, order); > + xpfo_free_page(page, order); > > return true; > } > @@ -1745,6 +1746,7 @@ inline void post_alloc_hook(struct page *page, unsigned int order, > kernel_map_pages(page, 1 << order, 1); > kernel_poison_pages(page, 1 << order, 1); > kasan_alloc_pages(page, order); > + xpfo_alloc_page(page, order, gfp_flags); > set_page_owner(page, order, gfp_flags); > } > > diff --git a/mm/page_ext.c b/mm/page_ext.c > index 121dcffc4ec1..ba6dbcacc2db 100644 > --- a/mm/page_ext.c > +++ b/mm/page_ext.c > @@ -7,6 +7,7 @@ > #include <linux/kmemleak.h> > #include <linux/page_owner.h> > #include <linux/page_idle.h> > +#include <linux/xpfo.h> > > /* > * struct page extension > @@ -68,6 +69,9 @@ static struct page_ext_operations *page_ext_ops[] = { > #if defined(CONFIG_IDLE_PAGE_TRACKING) && !defined(CONFIG_64BIT) > &page_idle_ops, > #endif > +#ifdef CONFIG_XPFO > + &page_xpfo_ops, > +#endif > }; > > static unsigned long total_usage; > diff --git a/mm/xpfo.c b/mm/xpfo.c > new file mode 100644 > index 000000000000..8e3a6a694b6a > --- /dev/null > +++ b/mm/xpfo.c > @@ -0,0 +1,206 @@ > +/* > + * Copyright (C) 2016 Hewlett Packard Enterprise Development, L.P. > + * Copyright (C) 2016 Brown University. All rights reserved. > + * > + * Authors: > + * Juerg Haefliger <juerg.haefliger@xxxxxxx> > + * Vasileios P. Kemerlis <vpk@xxxxxxxxxxxx> > + * > + * This program is free software; you can redistribute it and/or modify it > + * under the terms of the GNU General Public License version 2 as published by > + * the Free Software Foundation. > + */ > + > +#include <linux/mm.h> > +#include <linux/module.h> > +#include <linux/page_ext.h> > +#include <linux/xpfo.h> > + > +#include <asm/tlbflush.h> > + > +DEFINE_STATIC_KEY_FALSE(xpfo_inited); > + > +static bool need_xpfo(void) > +{ > + return true; > +} > + > +static void init_xpfo(void) > +{ > + printk(KERN_INFO "XPFO enabled\n"); > + static_branch_enable(&xpfo_inited); > +} > + > +struct page_ext_operations page_xpfo_ops = { > + .need = need_xpfo, > + .init = init_xpfo, > +}; > + > +/* > + * Update a single kernel page table entry > + */ > +static inline void set_kpte(struct page *page, unsigned long kaddr, > + pgprot_t prot) { > + unsigned int level; > + pte_t *kpte = lookup_address(kaddr, &level); > + > + /* We only support 4k pages for now */ > + BUG_ON(!kpte || level != PG_LEVEL_4K); > + > + set_pte_atomic(kpte, pfn_pte(page_to_pfn(page), canon_pgprot(prot))); > +} > + > +void xpfo_alloc_page(struct page *page, int order, gfp_t gfp) > +{ > + int i, flush_tlb = 0; > + struct page_ext *page_ext; > + unsigned long kaddr; > + > + if (!static_branch_unlikely(&xpfo_inited)) > + return; > + > + for (i = 0; i < (1 << order); i++) { > + page_ext = lookup_page_ext(page + i); > + > + BUG_ON(test_bit(PAGE_EXT_XPFO_UNMAPPED, &page_ext->flags)); > + > + /* Initialize the map lock and map counter */ > + if (!page_ext->inited) { > + spin_lock_init(&page_ext->maplock); > + atomic_set(&page_ext->mapcount, 0); > + page_ext->inited = 1; > + } > + BUG_ON(atomic_read(&page_ext->mapcount)); > + > + if ((gfp & GFP_HIGHUSER) == GFP_HIGHUSER) { > + /* > + * Flush the TLB if the page was previously allocated > + * to the kernel. > + */ > + if (test_and_clear_bit(PAGE_EXT_XPFO_KERNEL, > + &page_ext->flags)) > + flush_tlb = 1; > + } else { > + /* Tag the page as a kernel page */ > + set_bit(PAGE_EXT_XPFO_KERNEL, &page_ext->flags); > + } > + } > + > + if (flush_tlb) { > + kaddr = (unsigned long)page_address(page); > + flush_tlb_kernel_range(kaddr, kaddr + (1 << order) * > + PAGE_SIZE); > + } > +} > + > +void xpfo_free_page(struct page *page, int order) > +{ > + int i; > + struct page_ext *page_ext; > + unsigned long kaddr; > + > + if (!static_branch_unlikely(&xpfo_inited)) > + return; > + > + for (i = 0; i < (1 << order); i++) { > + page_ext = lookup_page_ext(page + i); > + > + if (!page_ext->inited) { > + /* > + * The page was allocated before page_ext was > + * initialized, so it is a kernel page and it needs to > + * be tagged accordingly. > + */ > + set_bit(PAGE_EXT_XPFO_KERNEL, &page_ext->flags); > + continue; > + } > + > + /* > + * Map the page back into the kernel if it was previously > + * allocated to user space. > + */ > + if (test_and_clear_bit(PAGE_EXT_XPFO_UNMAPPED, > + &page_ext->flags)) { > + kaddr = (unsigned long)page_address(page + i); > + set_kpte(page + i, kaddr, __pgprot(__PAGE_KERNEL)); > + } > + } > +} > + > +void xpfo_kmap(void *kaddr, struct page *page) > +{ > + struct page_ext *page_ext; > + unsigned long flags; > + > + if (!static_branch_unlikely(&xpfo_inited)) > + return; > + > + page_ext = lookup_page_ext(page); > + > + /* > + * The page was allocated before page_ext was initialized (which means > + * it's a kernel page) or it's allocated to the kernel, so nothing to > + * do. > + */ > + if (!page_ext->inited || > + test_bit(PAGE_EXT_XPFO_KERNEL, &page_ext->flags)) > + return; > + > + spin_lock_irqsave(&page_ext->maplock, flags); > + > + /* > + * The page was previously allocated to user space, so map it back > + * into the kernel. No TLB flush required. > + */ > + if ((atomic_inc_return(&page_ext->mapcount) == 1) && > + test_and_clear_bit(PAGE_EXT_XPFO_UNMAPPED, &page_ext->flags)) > + set_kpte(page, (unsigned long)kaddr, __pgprot(__PAGE_KERNEL)); > + > + spin_unlock_irqrestore(&page_ext->maplock, flags); > +} > +EXPORT_SYMBOL(xpfo_kmap); > + > +void xpfo_kunmap(void *kaddr, struct page *page) > +{ > + struct page_ext *page_ext; > + unsigned long flags; > + > + if (!static_branch_unlikely(&xpfo_inited)) > + return; > + > + page_ext = lookup_page_ext(page); > + > + /* > + * The page was allocated before page_ext was initialized (which means > + * it's a kernel page) or it's allocated to the kernel, so nothing to > + * do. > + */ > + if (!page_ext->inited || > + test_bit(PAGE_EXT_XPFO_KERNEL, &page_ext->flags)) > + return; > + > + spin_lock_irqsave(&page_ext->maplock, flags); > + > + /* > + * The page is to be allocated back to user space, so unmap it from the > + * kernel, flush the TLB and tag it as a user page. > + */ > + if (atomic_dec_return(&page_ext->mapcount) == 0) { > + BUG_ON(test_bit(PAGE_EXT_XPFO_UNMAPPED, &page_ext->flags)); > + set_bit(PAGE_EXT_XPFO_UNMAPPED, &page_ext->flags); > + set_kpte(page, (unsigned long)kaddr, __pgprot(0)); > + __flush_tlb_one((unsigned long)kaddr); > + } > + > + spin_unlock_irqrestore(&page_ext->maplock, flags); > +} > +EXPORT_SYMBOL(xpfo_kunmap); > + > +inline bool xpfo_page_is_unmapped(struct page *page) > +{ > + if (!static_branch_unlikely(&xpfo_inited)) > + return false; > + > + return test_bit(PAGE_EXT_XPFO_UNMAPPED, &lookup_page_ext(page)->flags); > +} > +EXPORT_SYMBOL(xpfo_page_is_unmapped); > diff --git a/security/Kconfig b/security/Kconfig > index 118f4549404e..4502e15c8419 100644 > --- a/security/Kconfig > +++ b/security/Kconfig > @@ -6,6 +6,25 @@ menu "Security options" > > source security/keys/Kconfig > > +config ARCH_SUPPORTS_XPFO > + bool Can you include a "help" section here to describe what requirements an architecture needs to support XPFO? See HAVE_ARCH_SECCOMP_FILTER and HAVE_ARCH_VMAP_STACK or some examples. > +config XPFO > + bool "Enable eXclusive Page Frame Ownership (XPFO)" > + default n > + depends on ARCH_SUPPORTS_XPFO > + select PAGE_EXTENSION > + help > + This option offers protection against 'ret2dir' kernel attacks. > + When enabled, every time a page frame is allocated to user space, it > + is unmapped from the direct mapped RAM region in kernel space > + (physmap). Similarly, when a page frame is freed/reclaimed, it is > + mapped back to physmap. > + > + There is a slight performance impact when this option is enabled. > + > + If in doubt, say "N". > + > config SECURITY_DMESG_RESTRICT > bool "Restrict unprivileged access to the kernel syslog" > default n > -- > 2.10.1 > I've added these patches to my kspp tree on kernel.org, so it should get some 0-day testing now... Thanks! -Kees -- Kees Cook Nexus Security -- To unsubscribe from this list: send the line "unsubscribe linux-x86_64" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
