Initial import

1 files changed, 1993 insertions, 0 deletions

diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
new file mode 100644
index 000000000..cb346f26a
--- /dev/null
+++ b/kernel/events/uprobes.c
@@ -0,0 +1,1993 @@
+/*
+ * User-space Probes (UProbes)
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
+ *
+ * Copyright (C) IBM Corporation, 2008-2012
+ * Authors:
+ *	Srikar Dronamraju
+ *	Jim Keniston
+ * Copyright (C) 2011-2012 Red Hat, Inc., Peter Zijlstra <pzijlstr@redhat.com>
+ */
+
+#include <linux/kernel.h>
+#include <linux/highmem.h>
+#include <linux/pagemap.h>	/* read_mapping_page */
+#include <linux/slab.h>
+#include <linux/sched.h>
+#include <linux/export.h>
+#include <linux/rmap.h>		/* anon_vma_prepare */
+#include <linux/mmu_notifier.h>	/* set_pte_at_notify */
+#include <linux/swap.h>		/* try_to_free_swap */
+#include <linux/ptrace.h>	/* user_enable_single_step */
+#include <linux/kdebug.h>	/* notifier mechanism */
+#include "../../mm/internal.h"	/* munlock_vma_page */
+#include <linux/percpu-rwsem.h>
+#include <linux/task_work.h>
+#include <linux/shmem_fs.h>
+
+#include <linux/uprobes.h>
+
+#define UINSNS_PER_PAGE			(PAGE_SIZE/UPROBE_XOL_SLOT_BYTES)
+#define MAX_UPROBE_XOL_SLOTS		UINSNS_PER_PAGE
+
+static struct rb_root uprobes_tree = RB_ROOT;
+/*
+ * allows us to skip the uprobe_mmap if there are no uprobe events active
+ * at this time.  Probably a fine grained per inode count is better?
+ */
+#define no_uprobe_events()	RB_EMPTY_ROOT(&uprobes_tree)
+
+static DEFINE_SPINLOCK(uprobes_treelock);	/* serialize rbtree access */
+
+#define UPROBES_HASH_SZ	13
+/* serialize uprobe->pending_list */
+static struct mutex uprobes_mmap_mutex[UPROBES_HASH_SZ];
+#define uprobes_mmap_hash(v)	(&uprobes_mmap_mutex[((unsigned long)(v)) % UPROBES_HASH_SZ])
+
+static struct percpu_rw_semaphore dup_mmap_sem;
+
+/* Have a copy of original instruction */
+#define UPROBE_COPY_INSN	0
+
+struct uprobe {
+	struct rb_node		rb_node;	/* node in the rb tree */
+	atomic_t		ref;
+	struct rw_semaphore	register_rwsem;
+	struct rw_semaphore	consumer_rwsem;
+	struct list_head	pending_list;
+	struct uprobe_consumer	*consumers;
+	struct inode		*inode;		/* Also hold a ref to inode */
+	loff_t			offset;
+	unsigned long		flags;
+
+	/*
+	 * The generic code assumes that it has two members of unknown type
+	 * owned by the arch-specific code:
+	 *
+	 * 	insn -	copy_insn() saves the original instruction here for
+	 *		arch_uprobe_analyze_insn().
+	 *
+	 *	ixol -	potentially modified instruction to execute out of
+	 *		line, copied to xol_area by xol_get_insn_slot().
+	 */
+	struct arch_uprobe	arch;
+};
+
+struct return_instance {
+	struct uprobe		*uprobe;
+	unsigned long		func;
+	unsigned long		orig_ret_vaddr; /* original return address */
+	bool			chained;	/* true, if instance is nested */
+
+	struct return_instance	*next;		/* keep as stack */
+};
+
+/*
+ * Execute out of line area: anonymous executable mapping installed
+ * by the probed task to execute the copy of the original instruction
+ * mangled by set_swbp().
+ *
+ * On a breakpoint hit, thread contests for a slot.  It frees the
+ * slot after singlestep. Currently a fixed number of slots are
+ * allocated.
+ */
+struct xol_area {
+	wait_queue_head_t 	wq;		/* if all slots are busy */
+	atomic_t 		slot_count;	/* number of in-use slots */
+	unsigned long 		*bitmap;	/* 0 = free slot */
+	struct page 		*page;
+
+	/*
+	 * We keep the vma's vm_start rather than a pointer to the vma
+	 * itself.  The probed process or a naughty kernel module could make
+	 * the vma go away, and we must handle that reasonably gracefully.
+	 */
+	unsigned long 		vaddr;		/* Page(s) of instruction slots */
+};
+
+/*
+ * valid_vma: Verify if the specified vma is an executable vma
+ * Relax restrictions while unregistering: vm_flags might have
+ * changed after breakpoint was inserted.
+ *	- is_register: indicates if we are in register context.
+ *	- Return 1 if the specified virtual address is in an
+ *	  executable vma.
+ */
+static bool valid_vma(struct vm_area_struct *vma, bool is_register)
+{
+	vm_flags_t flags = VM_HUGETLB | VM_MAYEXEC | VM_MAYSHARE;
+
+	if (is_register)
+		flags |= VM_WRITE;
+
+	return vma->vm_file && (vma->vm_flags & flags) == VM_MAYEXEC;
+}
+
+static unsigned long offset_to_vaddr(struct vm_area_struct *vma, loff_t offset)
+{
+	return vma->vm_start + offset - ((loff_t)vma->vm_pgoff << PAGE_SHIFT);
+}
+
+static loff_t vaddr_to_offset(struct vm_area_struct *vma, unsigned long vaddr)
+{
+	return ((loff_t)vma->vm_pgoff << PAGE_SHIFT) + (vaddr - vma->vm_start);
+}
+
+/**
+ * __replace_page - replace page in vma by new page.
+ * based on replace_page in mm/ksm.c
+ *
+ * @vma:      vma that holds the pte pointing to page
+ * @addr:     address the old @page is mapped at
+ * @page:     the cowed page we are replacing by kpage
+ * @kpage:    the modified page we replace page by
+ *
+ * Returns 0 on success, -EFAULT on failure.
+ */
+static int __replace_page(struct vm_area_struct *vma, unsigned long addr,
+				struct page *page, struct page *kpage)
+{
+	struct mm_struct *mm = vma->vm_mm;
+	spinlock_t *ptl;
+	pte_t *ptep;
+	int err;
+	/* For mmu_notifiers */
+	const unsigned long mmun_start = addr;
+	const unsigned long mmun_end   = addr + PAGE_SIZE;
+	struct mem_cgroup *memcg;
+
+	err = mem_cgroup_try_charge(kpage, vma->vm_mm, GFP_KERNEL, &memcg);
+	if (err)
+		return err;
+
+	/* For try_to_free_swap() and munlock_vma_page() below */
+	lock_page(page);
+
+	mmu_notifier_invalidate_range_start(mm, mmun_start, mmun_end);
+	err = -EAGAIN;
+	ptep = page_check_address(page, mm, addr, &ptl, 0);
+	if (!ptep)
+		goto unlock;
+
+	get_page(kpage);
+	page_add_new_anon_rmap(kpage, vma, addr);
+	mem_cgroup_commit_charge(kpage, memcg, false);
+	lru_cache_add_active_or_unevictable(kpage, vma);
+
+	if (!PageAnon(page)) {
+		dec_mm_counter(mm, MM_FILEPAGES);
+		inc_mm_counter(mm, MM_ANONPAGES);
+	}
+
+	flush_cache_page(vma, addr, pte_pfn(*ptep));
+	ptep_clear_flush_notify(vma, addr, ptep);
+	set_pte_at_notify(mm, addr, ptep, mk_pte(kpage, vma->vm_page_prot));
+
+	page_remove_rmap(page);
+	if (!page_mapped(page))
+		try_to_free_swap(page);
+	pte_unmap_unlock(ptep, ptl);
+
+	if (vma->vm_flags & VM_LOCKED)
+		munlock_vma_page(page);
+	put_page(page);
+
+	err = 0;
+ unlock:
+	mem_cgroup_cancel_charge(kpage, memcg);
+	mmu_notifier_invalidate_range_end(mm, mmun_start, mmun_end);
+	unlock_page(page);
+	return err;
+}
+
+/**
+ * is_swbp_insn - check if instruction is breakpoint instruction.
+ * @insn: instruction to be checked.
+ * Default implementation of is_swbp_insn
+ * Returns true if @insn is a breakpoint instruction.
+ */
+bool __weak is_swbp_insn(uprobe_opcode_t *insn)
+{
+	return *insn == UPROBE_SWBP_INSN;
+}
+
+/**
+ * is_trap_insn - check if instruction is breakpoint instruction.
+ * @insn: instruction to be checked.
+ * Default implementation of is_trap_insn
+ * Returns true if @insn is a breakpoint instruction.
+ *
+ * This function is needed for the case where an architecture has multiple
+ * trap instructions (like powerpc).
+ */
+bool __weak is_trap_insn(uprobe_opcode_t *insn)
+{
+	return is_swbp_insn(insn);
+}
+
+static void copy_from_page(struct page *page, unsigned long vaddr, void *dst, int len)
+{
+	void *kaddr = kmap_atomic(page);
+	memcpy(dst, kaddr + (vaddr & ~PAGE_MASK), len);
+	kunmap_atomic(kaddr);
+}
+
+static void copy_to_page(struct page *page, unsigned long vaddr, const void *src, int len)
+{
+	void *kaddr = kmap_atomic(page);
+	memcpy(kaddr + (vaddr & ~PAGE_MASK), src, len);
+	kunmap_atomic(kaddr);
+}
+
+static int verify_opcode(struct page *page, unsigned long vaddr, uprobe_opcode_t *new_opcode)
+{
+	uprobe_opcode_t old_opcode;
+	bool is_swbp;
+
+	/*
+	 * Note: We only check if the old_opcode is UPROBE_SWBP_INSN here.
+	 * We do not check if it is any other 'trap variant' which could
+	 * be conditional trap instruction such as the one powerpc supports.
+	 *
+	 * The logic is that we do not care if the underlying instruction
+	 * is a trap variant; uprobes always wins over any other (gdb)
+	 * breakpoint.
+	 */
+	copy_from_page(page, vaddr, &old_opcode, UPROBE_SWBP_INSN_SIZE);
+	is_swbp = is_swbp_insn(&old_opcode);
+
+	if (is_swbp_insn(new_opcode)) {
+		if (is_swbp)		/* register: already installed? */
+			return 0;
+	} else {
+		if (!is_swbp)		/* unregister: was it changed by us? */
+			return 0;
+	}
+
+	return 1;
+}
+
+/*
+ * NOTE:
+ * Expect the breakpoint instruction to be the smallest size instruction for
+ * the architecture. If an arch has variable length instruction and the
+ * breakpoint instruction is not of the smallest length instruction
+ * supported by that architecture then we need to modify is_trap_at_addr and
+ * uprobe_write_opcode accordingly. This would never be a problem for archs
+ * that have fixed length instructions.
+ *
+ * uprobe_write_opcode - write the opcode at a given virtual address.
+ * @mm: the probed process address space.
+ * @vaddr: the virtual address to store the opcode.
+ * @opcode: opcode to be written at @vaddr.
+ *
+ * Called with mm->mmap_sem held for write.
+ * Return 0 (success) or a negative errno.
+ */
+int uprobe_write_opcode(struct mm_struct *mm, unsigned long vaddr,
+			uprobe_opcode_t opcode)
+{
+	struct page *old_page, *new_page;
+	struct vm_area_struct *vma;
+	int ret;
+
+retry:
+	/* Read the page with vaddr into memory */
+	ret = get_user_pages(NULL, mm, vaddr, 1, 0, 1, &old_page, &vma);
+	if (ret <= 0)
+		return ret;
+
+	ret = verify_opcode(old_page, vaddr, &opcode);
+	if (ret <= 0)
+		goto put_old;
+
+	ret = anon_vma_prepare(vma);
+	if (ret)
+		goto put_old;
+
+	ret = -ENOMEM;
+	new_page = alloc_page_vma(GFP_HIGHUSER_MOVABLE, vma, vaddr);
+	if (!new_page)
+		goto put_old;
+
+	__SetPageUptodate(new_page);
+	copy_highpage(new_page, old_page);
+	copy_to_page(new_page, vaddr, &opcode, UPROBE_SWBP_INSN_SIZE);
+
+	ret = __replace_page(vma, vaddr, old_page, new_page);
+	page_cache_release(new_page);
+put_old:
+	put_page(old_page);
+
+	if (unlikely(ret == -EAGAIN))
+		goto retry;
+	return ret;
+}
+
+/**
+ * set_swbp - store breakpoint at a given address.
+ * @auprobe: arch specific probepoint information.
+ * @mm: the probed process address space.
+ * @vaddr: the virtual address to insert the opcode.
+ *
+ * For mm @mm, store the breakpoint instruction at @vaddr.
+ * Return 0 (success) or a negative errno.
+ */
+int __weak set_swbp(struct arch_uprobe *auprobe, struct mm_struct *mm, unsigned long vaddr)
+{
+	return uprobe_write_opcode(mm, vaddr, UPROBE_SWBP_INSN);
+}
+
+/**
+ * set_orig_insn - Restore the original instruction.
+ * @mm: the probed process address space.
+ * @auprobe: arch specific probepoint information.
+ * @vaddr: the virtual address to insert the opcode.
+ *
+ * For mm @mm, restore the original opcode (opcode) at @vaddr.
+ * Return 0 (success) or a negative errno.
+ */
+int __weak
+set_orig_insn(struct arch_uprobe *auprobe, struct mm_struct *mm, unsigned long vaddr)
+{
+	return uprobe_write_opcode(mm, vaddr, *(uprobe_opcode_t *)&auprobe->insn);
+}
+
+static int match_uprobe(struct uprobe *l, struct uprobe *r)
+{
+	if (l->inode < r->inode)
+		return -1;
+
+	if (l->inode > r->inode)
+		return 1;
+
+	if (l->offset < r->offset)
+		return -1;
+
+	if (l->offset > r->offset)
+		return 1;
+
+	return 0;
+}
+
+static struct uprobe *__find_uprobe(struct inode *inode, loff_t offset)
+{
+	struct uprobe u = { .inode = inode, .offset = offset };
+	struct rb_node *n = uprobes_tree.rb_node;
+	struct uprobe *uprobe;
+	int match;
+
+	while (n) {
+		uprobe = rb_entry(n, struct uprobe, rb_node);
+		match = match_uprobe(&u, uprobe);
+		if (!match) {
+			atomic_inc(&uprobe->ref);
+			return uprobe;
+		}
+
+		if (match < 0)
+			n = n->rb_left;
+		else
+			n = n->rb_right;
+	}
+	return NULL;
+}
+
+/*
+ * Find a uprobe corresponding to a given inode:offset
+ * Acquires uprobes_treelock
+ */
+static struct uprobe *find_uprobe(struct inode *inode, loff_t offset)
+{
+	struct uprobe *uprobe;
+
+	spin_lock(&uprobes_treelock);
+	uprobe = __find_uprobe(inode, offset);
+	spin_unlock(&uprobes_treelock);
+
+	return uprobe;
+}
+
+static struct uprobe *__insert_uprobe(struct uprobe *uprobe)
+{
+	struct rb_node **p = &uprobes_tree.rb_node;
+	struct rb_node *parent = NULL;
+	struct uprobe *u;
+	int match;
+
+	while (*p) {
+		parent = *p;
+		u = rb_entry(parent, struct uprobe, rb_node);
+		match = match_uprobe(uprobe, u);
+		if (!match) {
+			atomic_inc(&u->ref);
+			return u;
+		}
+
+		if (match < 0)
+			p = &parent->rb_left;
+		else
+			p = &parent->rb_right;
+
+	}
+
+	u = NULL;
+	rb_link_node(&uprobe->rb_node, parent, p);
+	rb_insert_color(&uprobe->rb_node, &uprobes_tree);
+	/* get access + creation ref */
+	atomic_set(&uprobe->ref, 2);
+
+	return u;
+}
+
+/*
+ * Acquire uprobes_treelock.
+ * Matching uprobe already exists in rbtree;
+ *	increment (access refcount) and return the matching uprobe.
+ *
+ * No matching uprobe; insert the uprobe in rb_tree;
+ *	get a double refcount (access + creation) and return NULL.
+ */
+static struct uprobe *insert_uprobe(struct uprobe *uprobe)
+{
+	struct uprobe *u;
+
+	spin_lock(&uprobes_treelock);
+	u = __insert_uprobe(uprobe);
+	spin_unlock(&uprobes_treelock);
+
+	return u;
+}
+
+static void put_uprobe(struct uprobe *uprobe)
+{
+	if (atomic_dec_and_test(&uprobe->ref))
+		kfree(uprobe);
+}
+
+static struct uprobe *alloc_uprobe(struct inode *inode, loff_t offset)
+{
+	struct uprobe *uprobe, *cur_uprobe;
+
+	uprobe = kzalloc(sizeof(struct uprobe), GFP_KERNEL);
+	if (!uprobe)
+		return NULL;
+
+	uprobe->inode = igrab(inode);
+	uprobe->offset = offset;
+	init_rwsem(&uprobe->register_rwsem);
+	init_rwsem(&uprobe->consumer_rwsem);
+
+	/* add to uprobes_tree, sorted on inode:offset */
+	cur_uprobe = insert_uprobe(uprobe);
+	/* a uprobe exists for this inode:offset combination */
+	if (cur_uprobe) {
+		kfree(uprobe);
+		uprobe = cur_uprobe;
+		iput(inode);
+	}
+
+	return uprobe;
+}
+
+static void consumer_add(struct uprobe *uprobe, struct uprobe_consumer *uc)
+{
+	down_write(&uprobe->consumer_rwsem);
+	uc->next = uprobe->consumers;
+	uprobe->consumers = uc;
+	up_write(&uprobe->consumer_rwsem);
+}
+
+/*
+ * For uprobe @uprobe, delete the consumer @uc.
+ * Return true if the @uc is deleted successfully
+ * or return false.
+ */
+static bool consumer_del(struct uprobe *uprobe, struct uprobe_consumer *uc)
+{
+	struct uprobe_consumer **con;
+	bool ret = false;
+
+	down_write(&uprobe->consumer_rwsem);
+	for (con = &uprobe->consumers; *con; con = &(*con)->next) {
+		if (*con == uc) {
+			*con = uc->next;
+			ret = true;
+			break;
+		}
+	}
+	up_write(&uprobe->consumer_rwsem);
+
+	return ret;
+}
+
+static int __copy_insn(struct address_space *mapping, struct file *filp,
+			void *insn, int nbytes, loff_t offset)
+{
+	struct page *page;
+	/*
+	 * Ensure that the page that has the original instruction is populated
+	 * and in page-cache. If ->readpage == NULL it must be shmem_mapping(),
+	 * see uprobe_register().
+	 */
+	if (mapping->a_ops->readpage)
+		page = read_mapping_page(mapping, offset >> PAGE_CACHE_SHIFT, filp);
+	else
+		page = shmem_read_mapping_page(mapping, offset >> PAGE_CACHE_SHIFT);
+	if (IS_ERR(page))
+		return PTR_ERR(page);
+
+	copy_from_page(page, offset, insn, nbytes);
+	page_cache_release(page);
+
+	return 0;
+}
+
+static int copy_insn(struct uprobe *uprobe, struct file *filp)
+{
+	struct address_space *mapping = uprobe->inode->i_mapping;
+	loff_t offs = uprobe->offset;
+	void *insn = &uprobe->arch.insn;
+	int size = sizeof(uprobe->arch.insn);
+	int len, err = -EIO;
+
+	/* Copy only available bytes, -EIO if nothing was read */
+	do {
+		if (offs >= i_size_read(uprobe->inode))
+			break;
+
+		len = min_t(int, size, PAGE_SIZE - (offs & ~PAGE_MASK));
+		err = __copy_insn(mapping, filp, insn, len, offs);
+		if (err)
+			break;
+
+		insn += len;
+		offs += len;
+		size -= len;
+	} while (size);
+
+	return err;
+}
+
+static int prepare_uprobe(struct uprobe *uprobe, struct file *file,
+				struct mm_struct *mm, unsigned long vaddr)
+{
+	int ret = 0;
+
+	if (test_bit(UPROBE_COPY_INSN, &uprobe->flags))
+		return ret;
+
+	/* TODO: move this into _register, until then we abuse this sem. */
+	down_write(&uprobe->consumer_rwsem);
+	if (test_bit(UPROBE_COPY_INSN, &uprobe->flags))
+		goto out;
+
+	ret = copy_insn(uprobe, file);
+	if (ret)
+		goto out;
+
+	ret = -ENOTSUPP;
+	if (is_trap_insn((uprobe_opcode_t *)&uprobe->arch.insn))
+		goto out;
+
+	ret = arch_uprobe_analyze_insn(&uprobe->arch, mm, vaddr);
+	if (ret)
+		goto out;
+
+	/* uprobe_write_opcode() assumes we don't cross page boundary */
+	BUG_ON((uprobe->offset & ~PAGE_MASK) +
+			UPROBE_SWBP_INSN_SIZE > PAGE_SIZE);
+
+	smp_wmb(); /* pairs with rmb() in find_active_uprobe() */
+	set_bit(UPROBE_COPY_INSN, &uprobe->flags);
+
+ out:
+	up_write(&uprobe->consumer_rwsem);
+
+	return ret;
+}
+
+static inline bool consumer_filter(struct uprobe_consumer *uc,
+				   enum uprobe_filter_ctx ctx, struct mm_struct *mm)
+{
+	return !uc->filter || uc->filter(uc, ctx, mm);
+}
+
+static bool filter_chain(struct uprobe *uprobe,
+			 enum uprobe_filter_ctx ctx, struct mm_struct *mm)
+{
+	struct uprobe_consumer *uc;
+	bool ret = false;
+
+	down_read(&uprobe->consumer_rwsem);
+	for (uc = uprobe->consumers; uc; uc = uc->next) {
+		ret = consumer_filter(uc, ctx, mm);
+		if (ret)
+			break;
+	}
+	up_read(&uprobe->consumer_rwsem);
+
+	return ret;
+}
+
+static int
+install_breakpoint(struct uprobe *uprobe, struct mm_struct *mm,
+			struct vm_area_struct *vma, unsigned long vaddr)
+{
+	bool first_uprobe;
+	int ret;
+
+	ret = prepare_uprobe(uprobe, vma->vm_file, mm, vaddr);
+	if (ret)
+		return ret;
+
+	/*
+	 * set MMF_HAS_UPROBES in advance for uprobe_pre_sstep_notifier(),
+	 * the task can hit this breakpoint right after __replace_page().
+	 */
+	first_uprobe = !test_bit(MMF_HAS_UPROBES, &mm->flags);
+	if (first_uprobe)
+		set_bit(MMF_HAS_UPROBES, &mm->flags);
+
+	ret = set_swbp(&uprobe->arch, mm, vaddr);
+	if (!ret)
+		clear_bit(MMF_RECALC_UPROBES, &mm->flags);
+	else if (first_uprobe)
+		clear_bit(MMF_HAS_UPROBES, &mm->flags);
+
+	return ret;
+}
+
+static int
+remove_breakpoint(struct uprobe *uprobe, struct mm_struct *mm, unsigned long vaddr)
+{
+	set_bit(MMF_RECALC_UPROBES, &mm->flags);
+	return set_orig_insn(&uprobe->arch, mm, vaddr);
+}
+
+static inline bool uprobe_is_active(struct uprobe *uprobe)
+{
+	return !RB_EMPTY_NODE(&uprobe->rb_node);
+}
+/*
+ * There could be threads that have already hit the breakpoint. They
+ * will recheck the current insn and restart if find_uprobe() fails.
+ * See find_active_uprobe().
+ */
+static void delete_uprobe(struct uprobe *uprobe)
+{
+	if (WARN_ON(!uprobe_is_active(uprobe)))
+		return;
+
+	spin_lock(&uprobes_treelock);
+	rb_erase(&uprobe->rb_node, &uprobes_tree);
+	spin_unlock(&uprobes_treelock);
+	RB_CLEAR_NODE(&uprobe->rb_node); /* for uprobe_is_active() */
+	iput(uprobe->inode);
+	put_uprobe(uprobe);
+}
+
+struct map_info {
+	struct map_info *next;
+	struct mm_struct *mm;
+	unsigned long vaddr;
+};
+
+static inline struct map_info *free_map_info(struct map_info *info)
+{
+	struct map_info *next = info->next;
+	kfree(info);
+	return next;
+}
+
+static struct map_info *
+build_map_info(struct address_space *mapping, loff_t offset, bool is_register)
+{
+	unsigned long pgoff = offset >> PAGE_SHIFT;
+	struct vm_area_struct *vma;
+	struct map_info *curr = NULL;
+	struct map_info *prev = NULL;
+	struct map_info *info;
+	int more = 0;
+
+ again:
+	i_mmap_lock_read(mapping);
+	vma_interval_tree_foreach(vma, &mapping->i_mmap, pgoff, pgoff) {
+		if (!valid_vma(vma, is_register))
+			continue;
+
+		if (!prev && !more) {
+			/*
+			 * Needs GFP_NOWAIT to avoid i_mmap_rwsem recursion through
+			 * reclaim. This is optimistic, no harm done if it fails.
+			 */
+			prev = kmalloc(sizeof(struct map_info),
+					GFP_NOWAIT | __GFP_NOMEMALLOC | __GFP_NOWARN);
+			if (prev)
+				prev->next = NULL;
+		}
+		if (!prev) {
+			more++;
+			continue;
+		}
+
+		if (!atomic_inc_not_zero(&vma->vm_mm->mm_users))
+			continue;
+
+		info = prev;
+		prev = prev->next;
+		info->next = curr;
+		curr = info;
+
+		info->mm = vma->vm_mm;
+		info->vaddr = offset_to_vaddr(vma, offset);
+	}
+	i_mmap_unlock_read(mapping);
+
+	if (!more)
+		goto out;
+
+	prev = curr;
+	while (curr) {
+		mmput(curr->mm);
+		curr = curr->next;
+	}
+
+	do {
+		info = kmalloc(sizeof(struct map_info), GFP_KERNEL);
+		if (!info) {
+			curr = ERR_PTR(-ENOMEM);
+			goto out;
+		}
+		info->next = prev;
+		prev = info;
+	} while (--more);
+
+	goto again;
+ out:
+	while (prev)
+		prev = free_map_info(prev);
+	return curr;
+}
+
+static int
+register_for_each_vma(struct uprobe *uprobe, struct uprobe_consumer *new)
+{
+	bool is_register = !!new;
+	struct map_info *info;
+	int err = 0;
+
+	percpu_down_write(&dup_mmap_sem);
+	info = build_map_info(uprobe->inode->i_mapping,
+					uprobe->offset, is_register);
+	if (IS_ERR(info)) {
+		err = PTR_ERR(info);
+		goto out;
+	}
+
+	while (info) {
+		struct mm_struct *mm = info->mm;
+		struct vm_area_struct *vma;
+
+		if (err && is_register)
+			goto free;
+
+		down_write(&mm->mmap_sem);
+		vma = find_vma(mm, info->vaddr);
+		if (!vma || !valid_vma(vma, is_register) ||
+		    file_inode(vma->vm_file) != uprobe->inode)
+			goto unlock;
+
+		if (vma->vm_start > info->vaddr ||
+		    vaddr_to_offset(vma, info->vaddr) != uprobe->offset)
+			goto unlock;
+
+		if (is_register) {
+			/* consult only the "caller", new consumer. */
+			if (consumer_filter(new,
+					UPROBE_FILTER_REGISTER, mm))
+				err = install_breakpoint(uprobe, mm, vma, info->vaddr);
+		} else if (test_bit(MMF_HAS_UPROBES, &mm->flags)) {
+			if (!filter_chain(uprobe,
+					UPROBE_FILTER_UNREGISTER, mm))
+				err |= remove_breakpoint(uprobe, mm, info->vaddr);
+		}
+
+ unlock:
+		up_write(&mm->mmap_sem);
+ free:
+		mmput(mm);
+		info = free_map_info(info);
+	}
+ out:
+	percpu_up_write(&dup_mmap_sem);
+	return err;
+}
+
+static int __uprobe_register(struct uprobe *uprobe, struct uprobe_consumer *uc)
+{
+	consumer_add(uprobe, uc);
+	return register_for_each_vma(uprobe, uc);
+}
+
+static void __uprobe_unregister(struct uprobe *uprobe, struct uprobe_consumer *uc)
+{
+	int err;
+
+	if (WARN_ON(!consumer_del(uprobe, uc)))
+		return;
+
+	err = register_for_each_vma(uprobe, NULL);
+	/* TODO : cant unregister? schedule a worker thread */
+	if (!uprobe->consumers && !err)
+		delete_uprobe(uprobe);
+}
+
+/*
+ * uprobe_register - register a probe
+ * @inode: the file in which the probe has to be placed.
+ * @offset: offset from the start of the file.
+ * @uc: information on howto handle the probe..
+ *
+ * Apart from the access refcount, uprobe_register() takes a creation
+ * refcount (thro alloc_uprobe) if and only if this @uprobe is getting
+ * inserted into the rbtree (i.e first consumer for a @inode:@offset
+ * tuple).  Creation refcount stops uprobe_unregister from freeing the
+ * @uprobe even before the register operation is complete. Creation
+ * refcount is released when the last @uc for the @uprobe
+ * unregisters.
+ *
+ * Return errno if it cannot successully install probes
+ * else return 0 (success)
+ */
+int uprobe_register(struct inode *inode, loff_t offset, struct uprobe_consumer *uc)
+{
+	struct uprobe *uprobe;
+	int ret;
+
+	/* Uprobe must have at least one set consumer */
+	if (!uc->handler && !uc->ret_handler)
+		return -EINVAL;
+
+	/* copy_insn() uses read_mapping_page() or shmem_read_mapping_page() */
+	if (!inode->i_mapping->a_ops->readpage && !shmem_mapping(inode->i_mapping))
+		return -EIO;
+	/* Racy, just to catch the obvious mistakes */
+	if (offset > i_size_read(inode))
+		return -EINVAL;
+
+ retry:
+	uprobe = alloc_uprobe(inode, offset);
+	if (!uprobe)
+		return -ENOMEM;
+	/*
+	 * We can race with uprobe_unregister()->delete_uprobe().
+	 * Check uprobe_is_active() and retry if it is false.
+	 */
+	down_write(&uprobe->register_rwsem);
+	ret = -EAGAIN;
+	if (likely(uprobe_is_active(uprobe))) {
+		ret = __uprobe_register(uprobe, uc);
+		if (ret)
+			__uprobe_unregister(uprobe, uc);
+	}
+	up_write(&uprobe->register_rwsem);
+	put_uprobe(uprobe);
+
+	if (unlikely(ret == -EAGAIN))
+		goto retry;
+	return ret;
+}
+EXPORT_SYMBOL_GPL(uprobe_register);
+
+/*
+ * uprobe_apply - unregister a already registered probe.
+ * @inode: the file in which the probe has to be removed.
+ * @offset: offset from the start of the file.
+ * @uc: consumer which wants to add more or remove some breakpoints
+ * @add: add or remove the breakpoints
+ */
+int uprobe_apply(struct inode *inode, loff_t offset,
+			struct uprobe_consumer *uc, bool add)
+{
+	struct uprobe *uprobe;
+	struct uprobe_consumer *con;
+	int ret = -ENOENT;
+
+	uprobe = find_uprobe(inode, offset);
+	if (WARN_ON(!uprobe))
+		return ret;
+
+	down_write(&uprobe->register_rwsem);
+	for (con = uprobe->consumers; con && con != uc ; con = con->next)
+		;
+	if (con)
+		ret = register_for_each_vma(uprobe, add ? uc : NULL);
+	up_write(&uprobe->register_rwsem);
+	put_uprobe(uprobe);
+
+	return ret;
+}
+
+/*
+ * uprobe_unregister - unregister a already registered probe.
+ * @inode: the file in which the probe has to be removed.
+ * @offset: offset from the start of the file.
+ * @uc: identify which probe if multiple probes are colocated.
+ */
+void uprobe_unregister(struct inode *inode, loff_t offset, struct uprobe_consumer *uc)
+{
+	struct uprobe *uprobe;
+
+	uprobe = find_uprobe(inode, offset);
+	if (WARN_ON(!uprobe))
+		return;
+
+	down_write(&uprobe->register_rwsem);
+	__uprobe_unregister(uprobe, uc);
+	up_write(&uprobe->register_rwsem);
+	put_uprobe(uprobe);
+}
+EXPORT_SYMBOL_GPL(uprobe_unregister);
+
+static int unapply_uprobe(struct uprobe *uprobe, struct mm_struct *mm)
+{
+	struct vm_area_struct *vma;
+	int err = 0;
+
+	down_read(&mm->mmap_sem);
+	for (vma = mm->mmap; vma; vma = vma->vm_next) {
+		unsigned long vaddr;
+		loff_t offset;
+
+		if (!valid_vma(vma, false) ||
+		    file_inode(vma->vm_file) != uprobe->inode)
+			continue;
+
+		offset = (loff_t)vma->vm_pgoff << PAGE_SHIFT;
+		if (uprobe->offset <  offset ||
+		    uprobe->offset >= offset + vma->vm_end - vma->vm_start)
+			continue;
+
+		vaddr = offset_to_vaddr(vma, uprobe->offset);
+		err |= remove_breakpoint(uprobe, mm, vaddr);
+	}
+	up_read(&mm->mmap_sem);
+
+	return err;
+}
+
+static struct rb_node *
+find_node_in_range(struct inode *inode, loff_t min, loff_t max)
+{
+	struct rb_node *n = uprobes_tree.rb_node;
+
+	while (n) {
+		struct uprobe *u = rb_entry(n, struct uprobe, rb_node);
+
+		if (inode < u->inode) {
+			n = n->rb_left;
+		} else if (inode > u->inode) {
+			n = n->rb_right;
+		} else {
+			if (max < u->offset)
+				n = n->rb_left;
+			else if (min > u->offset)
+				n = n->rb_right;
+			else
+				break;
+		}
+	}
+
+	return n;
+}
+
+/*
+ * For a given range in vma, build a list of probes that need to be inserted.
+ */
+static void build_probe_list(struct inode *inode,
+				struct vm_area_struct *vma,
+				unsigned long start, unsigned long end,
+				struct list_head *head)
+{
+	loff_t min, max;
+	struct rb_node *n, *t;
+	struct uprobe *u;
+
+	INIT_LIST_HEAD(head);
+	min = vaddr_to_offset(vma, start);
+	max = min + (end - start) - 1;
+
+	spin_lock(&uprobes_treelock);
+	n = find_node_in_range(inode, min, max);
+	if (n) {
+		for (t = n; t; t = rb_prev(t)) {
+			u = rb_entry(t, struct uprobe, rb_node);
+			if (u->inode != inode || u->offset < min)
+				break;
+			list_add(&u->pending_list, head);
+			atomic_inc(&u->ref);
+		}
+		for (t = n; (t = rb_next(t)); ) {
+			u = rb_entry(t, struct uprobe, rb_node);
+			if (u->inode != inode || u->offset > max)
+				break;
+			list_add(&u->pending_list, head);
+			atomic_inc(&u->ref);
+		}
+	}
+	spin_unlock(&uprobes_treelock);
+}
+
+/*
+ * Called from mmap_region/vma_adjust with mm->mmap_sem acquired.
+ *
+ * Currently we ignore all errors and always return 0, the callers
+ * can't handle the failure anyway.
+ */
+int uprobe_mmap(struct vm_area_struct *vma)
+{
+	struct list_head tmp_list;
+	struct uprobe *uprobe, *u;
+	struct inode *inode;
+
+	if (no_uprobe_events() || !valid_vma(vma, true))
+		return 0;
+
+	inode = file_inode(vma->vm_file);
+	if (!inode)
+		return 0;
+
+	mutex_lock(uprobes_mmap_hash(inode));
+	build_probe_list(inode, vma, vma->vm_start, vma->vm_end, &tmp_list);
+	/*
+	 * We can race with uprobe_unregister(), this uprobe can be already
+	 * removed. But in this case filter_chain() must return false, all
+	 * consumers have gone away.
+	 */
+	list_for_each_entry_safe(uprobe, u, &tmp_list, pending_list) {
+		if (!fatal_signal_pending(current) &&
+		    filter_chain(uprobe, UPROBE_FILTER_MMAP, vma->vm_mm)) {
+			unsigned long vaddr = offset_to_vaddr(vma, uprobe->offset);
+			install_breakpoint(uprobe, vma->vm_mm, vma, vaddr);
+		}
+		put_uprobe(uprobe);
+	}
+	mutex_unlock(uprobes_mmap_hash(inode));
+
+	return 0;
+}
+
+static bool
+vma_has_uprobes(struct vm_area_struct *vma, unsigned long start, unsigned long end)
+{
+	loff_t min, max;
+	struct inode *inode;
+	struct rb_node *n;
+
+	inode = file_inode(vma->vm_file);
+
+	min = vaddr_to_offset(vma, start);
+	max = min + (end - start) - 1;
+
+	spin_lock(&uprobes_treelock);
+	n = find_node_in_range(inode, min, max);
+	spin_unlock(&uprobes_treelock);
+
+	return !!n;
+}
+
+/*
+ * Called in context of a munmap of a vma.
+ */
+void uprobe_munmap(struct vm_area_struct *vma, unsigned long start, unsigned long end)
+{
+	if (no_uprobe_events() || !valid_vma(vma, false))
+		return;
+
+	if (!atomic_read(&vma->vm_mm->mm_users)) /* called by mmput() ? */
+		return;
+
+	if (!test_bit(MMF_HAS_UPROBES, &vma->vm_mm->flags) ||
+	     test_bit(MMF_RECALC_UPROBES, &vma->vm_mm->flags))
+		return;
+
+	if (vma_has_uprobes(vma, start, end))
+		set_bit(MMF_RECALC_UPROBES, &vma->vm_mm->flags);
+}
+
+/* Slot allocation for XOL */
+static int xol_add_vma(struct mm_struct *mm, struct xol_area *area)
+{
+	int ret = -EALREADY;
+
+	down_write(&mm->mmap_sem);
+	if (mm->uprobes_state.xol_area)
+		goto fail;
+
+	if (!area->vaddr) {
+		/* Try to map as high as possible, this is only a hint. */
+		area->vaddr = get_unmapped_area(NULL, TASK_SIZE - PAGE_SIZE,
+						PAGE_SIZE, 0, 0);
+		if (area->vaddr & ~PAGE_MASK) {
+			ret = area->vaddr;
+			goto fail;
+		}
+	}
+
+	ret = install_special_mapping(mm, area->vaddr, PAGE_SIZE,
+				VM_EXEC|VM_MAYEXEC|VM_DONTCOPY|VM_IO, &area->page);
+	if (ret)
+		goto fail;
+
+	smp_wmb();	/* pairs with get_xol_area() */
+	mm->uprobes_state.xol_area = area;
+ fail:
+	up_write(&mm->mmap_sem);
+
+	return ret;
+}
+
+static struct xol_area *__create_xol_area(unsigned long vaddr)
+{
+	struct mm_struct *mm = current->mm;
+	uprobe_opcode_t insn = UPROBE_SWBP_INSN;
+	struct xol_area *area;
+
+	area = kmalloc(sizeof(*area), GFP_KERNEL);
+	if (unlikely(!area))
+		goto out;
+
+	area->bitmap = kzalloc(BITS_TO_LONGS(UINSNS_PER_PAGE) * sizeof(long), GFP_KERNEL);
+	if (!area->bitmap)
+		goto free_area;
+
+	area->page = alloc_page(GFP_HIGHUSER);
+	if (!area->page)
+		goto free_bitmap;
+
+	area->vaddr = vaddr;
+	init_waitqueue_head(&area->wq);
+	/* Reserve the 1st slot for get_trampoline_vaddr() */
+	set_bit(0, area->bitmap);
+	atomic_set(&area->slot_count, 1);
+	copy_to_page(area->page, 0, &insn, UPROBE_SWBP_INSN_SIZE);
+
+	if (!xol_add_vma(mm, area))
+		return area;
+
+	__free_page(area->page);
+ free_bitmap:
+	kfree(area->bitmap);
+ free_area:
+	kfree(area);
+ out:
+	return NULL;
+}
+
+/*
+ * get_xol_area - Allocate process's xol_area if necessary.
+ * This area will be used for storing instructions for execution out of line.
+ *
+ * Returns the allocated area or NULL.
+ */
+static struct xol_area *get_xol_area(void)
+{
+	struct mm_struct *mm = current->mm;
+	struct xol_area *area;
+
+	if (!mm->uprobes_state.xol_area)
+		__create_xol_area(0);
+
+	area = mm->uprobes_state.xol_area;
+	smp_read_barrier_depends();	/* pairs with wmb in xol_add_vma() */
+	return area;
+}
+
+/*
+ * uprobe_clear_state - Free the area allocated for slots.
+ */
+void uprobe_clear_state(struct mm_struct *mm)
+{
+	struct xol_area *area = mm->uprobes_state.xol_area;
+
+	if (!area)
+		return;
+
+	put_page(area->page);
+	kfree(area->bitmap);
+	kfree(area);
+}
+
+void uprobe_start_dup_mmap(void)
+{
+	percpu_down_read(&dup_mmap_sem);
+}
+
+void uprobe_end_dup_mmap(void)
+{
+	percpu_up_read(&dup_mmap_sem);
+}
+
+void uprobe_dup_mmap(struct mm_struct *oldmm, struct mm_struct *newmm)
+{
+	newmm->uprobes_state.xol_area = NULL;
+
+	if (test_bit(MMF_HAS_UPROBES, &oldmm->flags)) {
+		set_bit(MMF_HAS_UPROBES, &newmm->flags);
+		/* unconditionally, dup_mmap() skips VM_DONTCOPY vmas */
+		set_bit(MMF_RECALC_UPROBES, &newmm->flags);
+	}
+}
+
+/*
+ *  - search for a free slot.
+ */
+static unsigned long xol_take_insn_slot(struct xol_area *area)
+{
+	unsigned long slot_addr;
+	int slot_nr;
+
+	do {
+		slot_nr = find_first_zero_bit(area->bitmap, UINSNS_PER_PAGE);
+		if (slot_nr < UINSNS_PER_PAGE) {
+			if (!test_and_set_bit(slot_nr, area->bitmap))
+				break;
+
+			slot_nr = UINSNS_PER_PAGE;
+			continue;
+		}
+		wait_event(area->wq, (atomic_read(&area->slot_count) < UINSNS_PER_PAGE));
+	} while (slot_nr >= UINSNS_PER_PAGE);
+
+	slot_addr = area->vaddr + (slot_nr * UPROBE_XOL_SLOT_BYTES);
+	atomic_inc(&area->slot_count);
+
+	return slot_addr;
+}
+
+/*
+ * xol_get_insn_slot - allocate a slot for xol.
+ * Returns the allocated slot address or 0.
+ */
+static unsigned long xol_get_insn_slot(struct uprobe *uprobe)
+{
+	struct xol_area *area;
+	unsigned long xol_vaddr;
+
+	area = get_xol_area();
+	if (!area)
+		return 0;
+
+	xol_vaddr = xol_take_insn_slot(area);
+	if (unlikely(!xol_vaddr))
+		return 0;
+
+	arch_uprobe_copy_ixol(area->page, xol_vaddr,
+			      &uprobe->arch.ixol, sizeof(uprobe->arch.ixol));
+
+	return xol_vaddr;
+}
+
+/*
+ * xol_free_insn_slot - If slot was earlier allocated by
+ * @xol_get_insn_slot(), make the slot available for
+ * subsequent requests.
+ */
+static void xol_free_insn_slot(struct task_struct *tsk)
+{
+	struct xol_area *area;
+	unsigned long vma_end;
+	unsigned long slot_addr;
+
+	if (!tsk->mm || !tsk->mm->uprobes_state.xol_area || !tsk->utask)
+		return;
+
+	slot_addr = tsk->utask->xol_vaddr;
+	if (unlikely(!slot_addr))
+		return;
+
+	area = tsk->mm->uprobes_state.xol_area;
+	vma_end = area->vaddr + PAGE_SIZE;
+	if (area->vaddr <= slot_addr && slot_addr < vma_end) {
+		unsigned long offset;
+		int slot_nr;
+
+		offset = slot_addr - area->vaddr;
+		slot_nr = offset / UPROBE_XOL_SLOT_BYTES;
+		if (slot_nr >= UINSNS_PER_PAGE)
+			return;
+
+		clear_bit(slot_nr, area->bitmap);
+		atomic_dec(&area->slot_count);
+		if (waitqueue_active(&area->wq))
+			wake_up(&area->wq);
+
+		tsk->utask->xol_vaddr = 0;
+	}
+}
+
+void __weak arch_uprobe_copy_ixol(struct page *page, unsigned long vaddr,
+				  void *src, unsigned long len)
+{
+	/* Initialize the slot */
+	copy_to_page(page, vaddr, src, len);
+
+	/*
+	 * We probably need flush_icache_user_range() but it needs vma.
+	 * This should work on most of architectures by default. If
+	 * architecture needs to do something different it can define
+	 * its own version of the function.
+	 */
+	flush_dcache_page(page);
+}
+
+/**
+ * uprobe_get_swbp_addr - compute address of swbp given post-swbp regs
+ * @regs: Reflects the saved state of the task after it has hit a breakpoint
+ * instruction.
+ * Return the address of the breakpoint instruction.
+ */
+unsigned long __weak uprobe_get_swbp_addr(struct pt_regs *regs)
+{
+	return instruction_pointer(regs) - UPROBE_SWBP_INSN_SIZE;
+}
+
+unsigned long uprobe_get_trap_addr(struct pt_regs *regs)
+{
+	struct uprobe_task *utask = current->utask;
+
+	if (unlikely(utask && utask->active_uprobe))
+		return utask->vaddr;
+
+	return instruction_pointer(regs);
+}
+
+/*
+ * Called with no locks held.
+ * Called in context of a exiting or a exec-ing thread.
+ */
+void uprobe_free_utask(struct task_struct *t)
+{
+	struct uprobe_task *utask = t->utask;
+	struct return_instance *ri, *tmp;
+
+	if (!utask)
+		return;
+
+	if (utask->active_uprobe)
+		put_uprobe(utask->active_uprobe);
+
+	ri = utask->return_instances;
+	while (ri) {
+		tmp = ri;
+		ri = ri->next;
+
+		put_uprobe(tmp->uprobe);
+		kfree(tmp);
+	}
+
+	xol_free_insn_slot(t);
+	kfree(utask);
+	t->utask = NULL;
+}
+
+/*
+ * Allocate a uprobe_task object for the task if if necessary.
+ * Called when the thread hits a breakpoint.
+ *
+ * Returns:
+ * - pointer to new uprobe_task on success
+ * - NULL otherwise
+ */
+static struct uprobe_task *get_utask(void)
+{
+	if (!current->utask)
+		current->utask = kzalloc(sizeof(struct uprobe_task), GFP_KERNEL);
+	return current->utask;
+}
+
+static int dup_utask(struct task_struct *t, struct uprobe_task *o_utask)
+{
+	struct uprobe_task *n_utask;
+	struct return_instance **p, *o, *n;
+
+	n_utask = kzalloc(sizeof(struct uprobe_task), GFP_KERNEL);
+	if (!n_utask)
+		return -ENOMEM;
+	t->utask = n_utask;
+
+	p = &n_utask->return_instances;
+	for (o = o_utask->return_instances; o; o = o->next) {
+		n = kmalloc(sizeof(struct return_instance), GFP_KERNEL);
+		if (!n)
+			return -ENOMEM;
+
+		*n = *o;
+		atomic_inc(&n->uprobe->ref);
+		n->next = NULL;
+
+		*p = n;
+		p = &n->next;
+		n_utask->depth++;
+	}
+
+	return 0;
+}
+
+static void uprobe_warn(struct task_struct *t, const char *msg)
+{
+	pr_warn("uprobe: %s:%d failed to %s\n",
+			current->comm, current->pid, msg);
+}
+
+static void dup_xol_work(struct callback_head *work)
+{
+	if (current->flags & PF_EXITING)
+		return;
+
+	if (!__create_xol_area(current->utask->dup_xol_addr))
+		uprobe_warn(current, "dup xol area");
+}
+
+/*
+ * Called in context of a new clone/fork from copy_process.
+ */
+void uprobe_copy_process(struct task_struct *t, unsigned long flags)
+{
+	struct uprobe_task *utask = current->utask;
+	struct mm_struct *mm = current->mm;
+	struct xol_area *area;
+
+	t->utask = NULL;
+
+	if (!utask || !utask->return_instances)
+		return;
+
+	if (mm == t->mm && !(flags & CLONE_VFORK))
+		return;
+
+	if (dup_utask(t, utask))
+		return uprobe_warn(t, "dup ret instances");
+
+	/* The task can fork() after dup_xol_work() fails */
+	area = mm->uprobes_state.xol_area;
+	if (!area)
+		return uprobe_warn(t, "dup xol area");
+
+	if (mm == t->mm)
+		return;
+
+	t->utask->dup_xol_addr = area->vaddr;
+	init_task_work(&t->utask->dup_xol_work, dup_xol_work);
+	task_work_add(t, &t->utask->dup_xol_work, true);
+}
+
+/*
+ * Current area->vaddr notion assume the trampoline address is always
+ * equal area->vaddr.
+ *
+ * Returns -1 in case the xol_area is not allocated.
+ */
+static unsigned long get_trampoline_vaddr(void)
+{
+	struct xol_area *area;
+	unsigned long trampoline_vaddr = -1;
+
+	area = current->mm->uprobes_state.xol_area;
+	smp_read_barrier_depends();
+	if (area)
+		trampoline_vaddr = area->vaddr;
+
+	return trampoline_vaddr;
+}
+
+static void prepare_uretprobe(struct uprobe *uprobe, struct pt_regs *regs)
+{
+	struct return_instance *ri;
+	struct uprobe_task *utask;
+	unsigned long orig_ret_vaddr, trampoline_vaddr;
+	bool chained = false;
+
+	if (!get_xol_area())
+		return;
+
+	utask = get_utask();
+	if (!utask)
+		return;
+
+	if (utask->depth >= MAX_URETPROBE_DEPTH) {
+		printk_ratelimited(KERN_INFO "uprobe: omit uretprobe due to"
+				" nestedness limit pid/tgid=%d/%d\n",
+				current->pid, current->tgid);
+		return;
+	}
+
+	ri = kzalloc(sizeof(struct return_instance), GFP_KERNEL);
+	if (!ri)
+		goto fail;
+
+	trampoline_vaddr = get_trampoline_vaddr();
+	orig_ret_vaddr = arch_uretprobe_hijack_return_addr(trampoline_vaddr, regs);
+	if (orig_ret_vaddr == -1)
+		goto fail;
+
+	/*
+	 * We don't want to keep trampoline address in stack, rather keep the
+	 * original return address of first caller thru all the consequent
+	 * instances. This also makes breakpoint unwrapping easier.
+	 */
+	if (orig_ret_vaddr == trampoline_vaddr) {
+		if (!utask->return_instances) {
+			/*
+			 * This situation is not possible. Likely we have an
+			 * attack from user-space.
+			 */
+			pr_warn("uprobe: unable to set uretprobe pid/tgid=%d/%d\n",
+						current->pid, current->tgid);
+			goto fail;
+		}
+
+		chained = true;
+		orig_ret_vaddr = utask->return_instances->orig_ret_vaddr;
+	}
+
+	atomic_inc(&uprobe->ref);
+	ri->uprobe = uprobe;
+	ri->func = instruction_pointer(regs);
+	ri->orig_ret_vaddr = orig_ret_vaddr;
+	ri->chained = chained;
+
+	utask->depth++;
+
+	/* add instance to the stack */
+	ri->next = utask->return_instances;
+	utask->return_instances = ri;
+
+	return;
+
+ fail:
+	kfree(ri);
+}
+
+/* Prepare to single-step probed instruction out of line. */
+static int
+pre_ssout(struct uprobe *uprobe, struct pt_regs *regs, unsigned long bp_vaddr)
+{
+	struct uprobe_task *utask;
+	unsigned long xol_vaddr;
+	int err;
+
+	utask = get_utask();
+	if (!utask)
+		return -ENOMEM;
+
+	xol_vaddr = xol_get_insn_slot(uprobe);
+	if (!xol_vaddr)
+		return -ENOMEM;
+
+	utask->xol_vaddr = xol_vaddr;
+	utask->vaddr = bp_vaddr;
+
+	err = arch_uprobe_pre_xol(&uprobe->arch, regs);
+	if (unlikely(err)) {
+		xol_free_insn_slot(current);
+		return err;
+	}
+
+	utask->active_uprobe = uprobe;
+	utask->state = UTASK_SSTEP;
+	return 0;
+}
+
+/*
+ * If we are singlestepping, then ensure this thread is not connected to
+ * non-fatal signals until completion of singlestep.  When xol insn itself
+ * triggers the signal,  restart the original insn even if the task is
+ * already SIGKILL'ed (since coredump should report the correct ip).  This
+ * is even more important if the task has a handler for SIGSEGV/etc, The
+ * _same_ instruction should be repeated again after return from the signal
+ * handler, and SSTEP can never finish in this case.
+ */
+bool uprobe_deny_signal(void)
+{
+	struct task_struct *t = current;
+	struct uprobe_task *utask = t->utask;
+
+	if (likely(!utask || !utask->active_uprobe))
+		return false;
+
+	WARN_ON_ONCE(utask->state != UTASK_SSTEP);
+
+	if (signal_pending(t)) {
+		spin_lock_irq(&t->sighand->siglock);
+		clear_tsk_thread_flag(t, TIF_SIGPENDING);
+		spin_unlock_irq(&t->sighand->siglock);
+
+		if (__fatal_signal_pending(t) || arch_uprobe_xol_was_trapped(t)) {
+			utask->state = UTASK_SSTEP_TRAPPED;
+			set_tsk_thread_flag(t, TIF_UPROBE);
+		}
+	}
+
+	return true;
+}
+
+static void mmf_recalc_uprobes(struct mm_struct *mm)
+{
+	struct vm_area_struct *vma;
+
+	for (vma = mm->mmap; vma; vma = vma->vm_next) {
+		if (!valid_vma(vma, false))
+			continue;
+		/*
+		 * This is not strictly accurate, we can race with
+		 * uprobe_unregister() and see the already removed
+		 * uprobe if delete_uprobe() was not yet called.
+		 * Or this uprobe can be filtered out.
+		 */
+		if (vma_has_uprobes(vma, vma->vm_start, vma->vm_end))
+			return;
+	}
+
+	clear_bit(MMF_HAS_UPROBES, &mm->flags);
+}
+
+static int is_trap_at_addr(struct mm_struct *mm, unsigned long vaddr)
+{
+	struct page *page;
+	uprobe_opcode_t opcode;
+	int result;
+
+	pagefault_disable();
+	result = __copy_from_user_inatomic(&opcode, (void __user*)vaddr,
+							sizeof(opcode));
+	pagefault_enable();
+
+	if (likely(result == 0))
+		goto out;
+
+	result = get_user_pages(NULL, mm, vaddr, 1, 0, 1, &page, NULL);
+	if (result < 0)
+		return result;
+
+	copy_from_page(page, vaddr, &opcode, UPROBE_SWBP_INSN_SIZE);
+	put_page(page);
+ out:
+	/* This needs to return true for any variant of the trap insn */
+	return is_trap_insn(&opcode);
+}
+
+static struct uprobe *find_active_uprobe(unsigned long bp_vaddr, int *is_swbp)
+{
+	struct mm_struct *mm = current->mm;
+	struct uprobe *uprobe = NULL;
+	struct vm_area_struct *vma;
+
+	down_read(&mm->mmap_sem);
+	vma = find_vma(mm, bp_vaddr);
+	if (vma && vma->vm_start <= bp_vaddr) {
+		if (valid_vma(vma, false)) {
+			struct inode *inode = file_inode(vma->vm_file);
+			loff_t offset = vaddr_to_offset(vma, bp_vaddr);
+
+			uprobe = find_uprobe(inode, offset);
+		}
+
+		if (!uprobe)
+			*is_swbp = is_trap_at_addr(mm, bp_vaddr);
+	} else {
+		*is_swbp = -EFAULT;
+	}
+
+	if (!uprobe && test_and_clear_bit(MMF_RECALC_UPROBES, &mm->flags))
+		mmf_recalc_uprobes(mm);
+	up_read(&mm->mmap_sem);
+
+	return uprobe;
+}
+
+static void handler_chain(struct uprobe *uprobe, struct pt_regs *regs)
+{
+	struct uprobe_consumer *uc;
+	int remove = UPROBE_HANDLER_REMOVE;
+	bool need_prep = false; /* prepare return uprobe, when needed */
+
+	down_read(&uprobe->register_rwsem);
+	for (uc = uprobe->consumers; uc; uc = uc->next) {
+		int rc = 0;
+
+		if (uc->handler) {
+			rc = uc->handler(uc, regs);
+			WARN(rc & ~UPROBE_HANDLER_MASK,
+				"bad rc=0x%x from %pf()\n", rc, uc->handler);
+		}
+
+		if (uc->ret_handler)
+			need_prep = true;
+
+		remove &= rc;
+	}
+
+	if (need_prep && !remove)
+		prepare_uretprobe(uprobe, regs); /* put bp at return */
+
+	if (remove && uprobe->consumers) {
+		WARN_ON(!uprobe_is_active(uprobe));
+		unapply_uprobe(uprobe, current->mm);
+	}
+	up_read(&uprobe->register_rwsem);
+}
+
+static void
+handle_uretprobe_chain(struct return_instance *ri, struct pt_regs *regs)
+{
+	struct uprobe *uprobe = ri->uprobe;
+	struct uprobe_consumer *uc;
+
+	down_read(&uprobe->register_rwsem);
+	for (uc = uprobe->consumers; uc; uc = uc->next) {
+		if (uc->ret_handler)
+			uc->ret_handler(uc, ri->func, regs);
+	}
+	up_read(&uprobe->register_rwsem);
+}
+
+static bool handle_trampoline(struct pt_regs *regs)
+{
+	struct uprobe_task *utask;
+	struct return_instance *ri, *tmp;
+	bool chained;
+
+	utask = current->utask;
+	if (!utask)
+		return false;
+
+	ri = utask->return_instances;
+	if (!ri)
+		return false;
+
+	/*
+	 * TODO: we should throw out return_instance's invalidated by
+	 * longjmp(), currently we assume that the probed function always
+	 * returns.
+	 */
+	instruction_pointer_set(regs, ri->orig_ret_vaddr);
+
+	for (;;) {
+		handle_uretprobe_chain(ri, regs);
+
+		chained = ri->chained;
+		put_uprobe(ri->uprobe);
+
+		tmp = ri;
+		ri = ri->next;
+		kfree(tmp);
+		utask->depth--;
+
+		if (!chained)
+			break;
+		BUG_ON(!ri);
+	}
+
+	utask->return_instances = ri;
+
+	return true;
+}
+
+bool __weak arch_uprobe_ignore(struct arch_uprobe *aup, struct pt_regs *regs)
+{
+	return false;
+}
+
+/*
+ * Run handler and ask thread to singlestep.
+ * Ensure all non-fatal signals cannot interrupt thread while it singlesteps.
+ */
+static void handle_swbp(struct pt_regs *regs)
+{
+	struct uprobe *uprobe;
+	unsigned long bp_vaddr;
+	int uninitialized_var(is_swbp);
+
+	bp_vaddr = uprobe_get_swbp_addr(regs);
+	if (bp_vaddr == get_trampoline_vaddr()) {
+		if (handle_trampoline(regs))
+			return;
+
+		pr_warn("uprobe: unable to handle uretprobe pid/tgid=%d/%d\n",
+						current->pid, current->tgid);
+	}
+
+	uprobe = find_active_uprobe(bp_vaddr, &is_swbp);
+	if (!uprobe) {
+		if (is_swbp > 0) {
+			/* No matching uprobe; signal SIGTRAP. */
+			send_sig(SIGTRAP, current, 0);
+		} else {
+			/*
+			 * Either we raced with uprobe_unregister() or we can't
+			 * access this memory. The latter is only possible if
+			 * another thread plays with our ->mm. In both cases
+			 * we can simply restart. If this vma was unmapped we
+			 * can pretend this insn was not executed yet and get
+			 * the (correct) SIGSEGV after restart.
+			 */
+			instruction_pointer_set(regs, bp_vaddr);
+		}
+		return;
+	}
+
+	/* change it in advance for ->handler() and restart */
+	instruction_pointer_set(regs, bp_vaddr);
+
+	/*
+	 * TODO: move copy_insn/etc into _register and remove this hack.
+	 * After we hit the bp, _unregister + _register can install the
+	 * new and not-yet-analyzed uprobe at the same address, restart.
+	 */
+	smp_rmb(); /* pairs with wmb() in install_breakpoint() */
+	if (unlikely(!test_bit(UPROBE_COPY_INSN, &uprobe->flags)))
+		goto out;
+
+	/* Tracing handlers use ->utask to communicate with fetch methods */
+	if (!get_utask())
+		goto out;
+
+	if (arch_uprobe_ignore(&uprobe->arch, regs))
+		goto out;
+
+	handler_chain(uprobe, regs);
+
+	if (arch_uprobe_skip_sstep(&uprobe->arch, regs))
+		goto out;
+
+	if (!pre_ssout(uprobe, regs, bp_vaddr))
+		return;
+
+	/* arch_uprobe_skip_sstep() succeeded, or restart if can't singlestep */
+out:
+	put_uprobe(uprobe);
+}
+
+/*
+ * Perform required fix-ups and disable singlestep.
+ * Allow pending signals to take effect.
+ */
+static void handle_singlestep(struct uprobe_task *utask, struct pt_regs *regs)
+{
+	struct uprobe *uprobe;
+	int err = 0;
+
+	uprobe = utask->active_uprobe;
+	if (utask->state == UTASK_SSTEP_ACK)
+		err = arch_uprobe_post_xol(&uprobe->arch, regs);
+	else if (utask->state == UTASK_SSTEP_TRAPPED)
+		arch_uprobe_abort_xol(&uprobe->arch, regs);
+	else
+		WARN_ON_ONCE(1);
+
+	put_uprobe(uprobe);
+	utask->active_uprobe = NULL;
+	utask->state = UTASK_RUNNING;
+	xol_free_insn_slot(current);
+
+	spin_lock_irq(&current->sighand->siglock);
+	recalc_sigpending(); /* see uprobe_deny_signal() */
+	spin_unlock_irq(&current->sighand->siglock);
+
+	if (unlikely(err)) {
+		uprobe_warn(current, "execute the probed insn, sending SIGILL.");
+		force_sig_info(SIGILL, SEND_SIG_FORCED, current);
+	}
+}
+
+/*
+ * On breakpoint hit, breakpoint notifier sets the TIF_UPROBE flag and
+ * allows the thread to return from interrupt. After that handle_swbp()
+ * sets utask->active_uprobe.
+ *
+ * On singlestep exception, singlestep notifier sets the TIF_UPROBE flag
+ * and allows the thread to return from interrupt.
+ *
+ * While returning to userspace, thread notices the TIF_UPROBE flag and calls
+ * uprobe_notify_resume().
+ */
+void uprobe_notify_resume(struct pt_regs *regs)
+{
+	struct uprobe_task *utask;
+
+	clear_thread_flag(TIF_UPROBE);
+
+	utask = current->utask;
+	if (utask && utask->active_uprobe)
+		handle_singlestep(utask, regs);
+	else
+		handle_swbp(regs);
+}
+
+/*
+ * uprobe_pre_sstep_notifier gets called from interrupt context as part of
+ * notifier mechanism. Set TIF_UPROBE flag and indicate breakpoint hit.
+ */
+int uprobe_pre_sstep_notifier(struct pt_regs *regs)
+{
+	if (!current->mm)
+		return 0;
+
+	if (!test_bit(MMF_HAS_UPROBES, &current->mm->flags) &&
+	    (!current->utask || !current->utask->return_instances))
+		return 0;
+
+	set_thread_flag(TIF_UPROBE);
+	return 1;
+}
+
+/*
+ * uprobe_post_sstep_notifier gets called in interrupt context as part of notifier
+ * mechanism. Set TIF_UPROBE flag and indicate completion of singlestep.
+ */
+int uprobe_post_sstep_notifier(struct pt_regs *regs)
+{
+	struct uprobe_task *utask = current->utask;
+
+	if (!current->mm || !utask || !utask->active_uprobe)
+		/* task is currently not uprobed */
+		return 0;
+
+	utask->state = UTASK_SSTEP_ACK;
+	set_thread_flag(TIF_UPROBE);
+	return 1;
+}
+
+static struct notifier_block uprobe_exception_nb = {
+	.notifier_call		= arch_uprobe_exception_notify,
+	.priority		= INT_MAX-1,	/* notified after kprobes, kgdb */
+};
+
+static int __init init_uprobes(void)
+{
+	int i;
+
+	for (i = 0; i < UPROBES_HASH_SZ; i++)
+		mutex_init(&uprobes_mmap_mutex[i]);
+
+	if (percpu_init_rwsem(&dup_mmap_sem))
+		return -ENOMEM;
+
+	return register_die_notifier(&uprobe_exception_nb);
+}
+__initcall(init_uprobes);