text: /*
   * 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
   */
  
  #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;
  };
  
  /*
   * 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 vm_special_mapping	xol_mapping;
  	struct page 			*pages[2];
  	/*
  	 * 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,
  			false);
  	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, false);
  	mem_cgroup_commit_charge(kpage, memcg, false, false);
  	lru_cache_add_active_or_unevictable(kpage, vma);
  
  	if (!PageAnon(page)) {
  		dec_mm_counter(mm, mm_counter_file(page));
  		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, false);
  	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, false);
  	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_remote(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);
  	put_page(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 struct uprobe *get_uprobe(struct uprobe *uprobe)
  {
  	atomic_inc(&uprobe->ref);
  	return uprobe;
  }
  
  static void put_uprobe(struct uprobe *uprobe)
  {
  	if (atomic_dec_and_test(&uprobe->ref))
  		kfree(uprobe);
  }
  
  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)
  			return get_uprobe(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)
  			return get_uprobe(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 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_SHIFT, filp);
  	else
  		page = shmem_read_mapping_page(mapping, offset >> PAGE_SHIFT);
  	if (IS_ERR(page))
  		return PTR_ERR(page);
  
  	copy_from_page(page, offset, insn, nbytes);
  	put_page(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);
  			get_uprobe(u);
  		}
  		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);
  			get_uprobe(u);
  		}
  	}
  	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)
  {
  	struct vm_area_struct *vma;
  	int ret;
  
  	if (down_write_killable(&mm->mmap_sem))
  		return -EINTR;
  
  	if (mm->uprobes_state.xol_area) {
  		ret = -EALREADY;
  		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;
  		}
  	}
  
  	vma = _install_special_mapping(mm, area->vaddr, PAGE_SIZE,
  				VM_EXEC|VM_MAYEXEC|VM_DONTCOPY|VM_IO,
  				&area->xol_mapping);
  	if (IS_ERR(vma)) {
  		ret = PTR_ERR(vma);
  		goto fail;
  	}
  
  	ret = 0;
  	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->xol_mapping.name = "[uprobes]";
  	area->xol_mapping.fault = NULL;
  	area->xol_mapping.pages = area->pages;
  	area->pages[0] = alloc_page(GFP_HIGHUSER);
  	if (!area->pages[0])
  		goto free_bitmap;
  	area->pages[1] = NULL;
  
  	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->pages[0], 0, &insn, UPROBE_SWBP_INSN_SIZE);
  
  	if (!xol_add_vma(mm, area))
  		return area;
  
  	__free_page(area->pages[0]);
   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->pages[0]);
  	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->pages[0], 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);
  		smp_mb__after_atomic(); /* pairs with prepare_to_wait() */
  		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);
  }
  
  static struct return_instance *free_ret_instance(struct return_instance *ri)
  {
  	struct return_instance *next = ri->next;
  	put_uprobe(ri->uprobe);
  	kfree(ri);
  	return next;
  }
  
  /*
   * 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;
  
  	if (!utask)
  		return;
  
  	if (utask->active_uprobe)
  		put_uprobe(utask->active_uprobe);
  
  	ri = utask->return_instances;
  	while (ri)
  		ri = free_ret_instance(ri);
  
  	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;
  		get_uprobe(n->uprobe);
  		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) &&
  			!fatal_signal_pending(current))
  		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 cleanup_return_instances(struct uprobe_task *utask, bool chained,
  					struct pt_regs *regs)
  {
  	struct return_instance *ri = utask->return_instances;
  	enum rp_check ctx = chained ? RP_CHECK_CHAIN_CALL : RP_CHECK_CALL;
  
  	while (ri && !arch_uretprobe_is_alive(ri, ctx, regs)) {
  		ri = free_ret_instance(ri);
  		utask->depth--;
  	}
  	utask->return_instances = ri;
  }
  
  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;
  
  	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 = kmalloc(sizeof(struct return_instance), GFP_KERNEL);
  	if (!ri)
  		return;
  
  	trampoline_vaddr = get_trampoline_vaddr();
  	orig_ret_vaddr = arch_uretprobe_hijack_return_addr(trampoline_vaddr, regs);
  	if (orig_ret_vaddr == -1)
  		goto fail;
  
  	/* drop the entries invalidated by longjmp() */
  	chained = (orig_ret_vaddr == trampoline_vaddr);
  	cleanup_return_instances(utask, chained, regs);
  
  	/*
  	 * 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 (chained) {
  		if (!utask->return_instances) {
  			/*
  			 * This situation is not possible. Likely we have an
  			 * attack from user-space.
  			 */
  			uprobe_warn(current, "handle tail call");
  			goto fail;
  		}
  		orig_ret_vaddr = utask->return_instances->orig_ret_vaddr;
  	}
  
  	ri->uprobe = get_uprobe(uprobe);
  	ri->func = instruction_pointer(regs);
  	ri->stack = user_stack_pointer(regs);
  	ri->orig_ret_vaddr = orig_ret_vaddr;
  	ri->chained = chained;
  
  	utask->depth++;
  	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 = __get_user(opcode, (uprobe_opcode_t __user *)vaddr);
  	pagefault_enable();
  
  	if (likely(result == 0))
  		goto out;
  
  	/*
  	 * The NULL 'tsk' here ensures that any faults that occur here
  	 * will not be accounted to the task.  'mm' *is* current->mm,
  	 * but we treat this as a 'remote' access since it is
  	 * essentially a kernel access to the memory.
  	 */
  	result = get_user_pages_remote(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 struct return_instance *find_next_ret_chain(struct return_instance *ri)
  {
  	bool chained;
  
  	do {
  		chained = ri->chained;
  		ri = ri->next;	/* can't be NULL if chained */
  	} while (chained);
  
  	return ri;
  }
  
  static void handle_trampoline(struct pt_regs *regs)
  {
  	struct uprobe_task *utask;
  	struct return_instance *ri, *next;
  	bool valid;
  
  	utask = current->utask;
  	if (!utask)
  		goto sigill;
  
  	ri = utask->return_instances;
  	if (!ri)
  		goto sigill;
  
  	do {
  		/*
  		 * We should throw out the frames invalidated by longjmp().
  		 * If this chain is valid, then the next one should be alive
  		 * or NULL; the latter case means that nobody but ri->func
  		 * could hit this trampoline on return. TODO: sigaltstack().
  		 */
  		next = find_next_ret_chain(ri);
  		valid = !next || arch_uretprobe_is_alive(next, RP_CHECK_RET, regs);
  
  		instruction_pointer_set(regs, ri->orig_ret_vaddr);
  		do {
  			if (valid)
  				handle_uretprobe_chain(ri, regs);
  			ri = free_ret_instance(ri);
  			utask->depth--;
  		} while (ri != next);
  	} while (!valid);
  
  	utask->return_instances = ri;
  	return;
  
   sigill:
  	uprobe_warn(current, "handle uretprobe, sending SIGILL.");
  	force_sig_info(SIGILL, SEND_SIG_FORCED, current);
  
  }
  
  bool __weak arch_uprobe_ignore(struct arch_uprobe *aup, struct pt_regs *regs)
  {
  	return false;
  }
  
  bool __weak arch_uretprobe_is_alive(struct return_instance *ret, enum rp_check ctx,
  					struct pt_regs *regs)
  {
  	return true;
  }
  
  /*
   * 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())
  		return handle_trampoline(regs);
  
  	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);
  