mmap locking API: convert mmap_sem comments

[thirdparty/linux.git] / kernel / events / uprobes.c

// SPDX-License-Identifier: GPL-2.0+
/*
 * User-space Probes (UProbes)
 *
 * 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/sched/mm.h>
#include <linux/sched/coredump.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/khugepaged.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])

DEFINE_STATIC_PERCPU_RWSEM(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 */
        refcount_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;
        loff_t                  ref_ctr_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 delayed_uprobe {
        struct list_head list;
        struct uprobe *uprobe;
        struct mm_struct *mm;
};

static DEFINE_MUTEX(delayed_uprobe_lock);
static LIST_HEAD(delayed_uprobe_list);

/*
 * 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
 * @old_page: the page we are replacing by new_page
 * @new_page: the modified page we replace page by
 *
 * If @new_page is NULL, only unmap @old_page.
 *
 * Returns 0 on success, negative error code otherwise.
 */
static int __replace_page(struct vm_area_struct *vma, unsigned long addr,
                                struct page *old_page, struct page *new_page)
{
        struct mm_struct *mm = vma->vm_mm;
        struct page_vma_mapped_walk pvmw = {
                .page = compound_head(old_page),
                .vma = vma,
                .address = addr,
        };
        int err;
        struct mmu_notifier_range range;

        mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, vma, mm, addr,
                                addr + PAGE_SIZE);

        if (new_page) {
                err = mem_cgroup_charge(new_page, vma->vm_mm, GFP_KERNEL);
                if (err)
                        return err;
        }

        /* For try_to_free_swap() and munlock_vma_page() below */
        lock_page(old_page);

        mmu_notifier_invalidate_range_start(&range);
        err = -EAGAIN;
        if (!page_vma_mapped_walk(&pvmw))
                goto unlock;
        VM_BUG_ON_PAGE(addr != pvmw.address, old_page);

        if (new_page) {
                get_page(new_page);
                page_add_new_anon_rmap(new_page, vma, addr, false);
                lru_cache_add_active_or_unevictable(new_page, vma);
        } else
                /* no new page, just dec_mm_counter for old_page */
                dec_mm_counter(mm, MM_ANONPAGES);

        if (!PageAnon(old_page)) {
                dec_mm_counter(mm, mm_counter_file(old_page));
                inc_mm_counter(mm, MM_ANONPAGES);
        }

        flush_cache_page(vma, addr, pte_pfn(*pvmw.pte));
        ptep_clear_flush_notify(vma, addr, pvmw.pte);
        if (new_page)
                set_pte_at_notify(mm, addr, pvmw.pte,
                                  mk_pte(new_page, vma->vm_page_prot));

        page_remove_rmap(old_page, false);
        if (!page_mapped(old_page))
                try_to_free_swap(old_page);
        page_vma_mapped_walk_done(&pvmw);

        if (vma->vm_flags & VM_LOCKED)
                munlock_vma_page(old_page);
        put_page(old_page);

        err = 0;
 unlock:
        mmu_notifier_invalidate_range_end(&range);
        unlock_page(old_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;
}

static struct delayed_uprobe *
delayed_uprobe_check(struct uprobe *uprobe, struct mm_struct *mm)
{
        struct delayed_uprobe *du;

        list_for_each_entry(du, &delayed_uprobe_list, list)
                if (du->uprobe == uprobe && du->mm == mm)
                        return du;
        return NULL;
}

static int delayed_uprobe_add(struct uprobe *uprobe, struct mm_struct *mm)
{
        struct delayed_uprobe *du;

        if (delayed_uprobe_check(uprobe, mm))
                return 0;

        du  = kzalloc(sizeof(*du), GFP_KERNEL);
        if (!du)
                return -ENOMEM;

        du->uprobe = uprobe;
        du->mm = mm;
        list_add(&du->list, &delayed_uprobe_list);
        return 0;
}

static void delayed_uprobe_delete(struct delayed_uprobe *du)
{
        if (WARN_ON(!du))
                return;
        list_del(&du->list);
        kfree(du);
}

static void delayed_uprobe_remove(struct uprobe *uprobe, struct mm_struct *mm)
{
        struct list_head *pos, *q;
        struct delayed_uprobe *du;

        if (!uprobe && !mm)
                return;

        list_for_each_safe(pos, q, &delayed_uprobe_list) {
                du = list_entry(pos, struct delayed_uprobe, list);

                if (uprobe && du->uprobe != uprobe)
                        continue;
                if (mm && du->mm != mm)
                        continue;

                delayed_uprobe_delete(du);
        }
}

static bool valid_ref_ctr_vma(struct uprobe *uprobe,
                              struct vm_area_struct *vma)
{
        unsigned long vaddr = offset_to_vaddr(vma, uprobe->ref_ctr_offset);

        return uprobe->ref_ctr_offset &&
                vma->vm_file &&
                file_inode(vma->vm_file) == uprobe->inode &&
                (vma->vm_flags & (VM_WRITE|VM_SHARED)) == VM_WRITE &&
                vma->vm_start <= vaddr &&
                vma->vm_end > vaddr;
}

static struct vm_area_struct *
find_ref_ctr_vma(struct uprobe *uprobe, struct mm_struct *mm)
{
        struct vm_area_struct *tmp;

        for (tmp = mm->mmap; tmp; tmp = tmp->vm_next)
                if (valid_ref_ctr_vma(uprobe, tmp))
                        return tmp;

        return NULL;
}

static int
__update_ref_ctr(struct mm_struct *mm, unsigned long vaddr, short d)
{
        void *kaddr;
        struct page *page;
        struct vm_area_struct *vma;
        int ret;
        short *ptr;

        if (!vaddr || !d)
                return -EINVAL;

        ret = get_user_pages_remote(NULL, mm, vaddr, 1,
                        FOLL_WRITE, &page, &vma, NULL);
        if (unlikely(ret <= 0)) {
                /*
                 * We are asking for 1 page. If get_user_pages_remote() fails,
                 * it may return 0, in that case we have to return error.
                 */
                return ret == 0 ? -EBUSY : ret;
        }

        kaddr = kmap_atomic(page);
        ptr = kaddr + (vaddr & ~PAGE_MASK);

        if (unlikely(*ptr + d < 0)) {
                pr_warn("ref_ctr going negative. vaddr: 0x%lx, "
                        "curr val: %d, delta: %d\n", vaddr, *ptr, d);
                ret = -EINVAL;
                goto out;
        }

        *ptr += d;
        ret = 0;
out:
        kunmap_atomic(kaddr);
        put_page(page);
        return ret;
}

static void update_ref_ctr_warn(struct uprobe *uprobe,
                                struct mm_struct *mm, short d)
{
        pr_warn("ref_ctr %s failed for inode: 0x%lx offset: "
                "0x%llx ref_ctr_offset: 0x%llx of mm: 0x%pK\n",
                d > 0 ? "increment" : "decrement", uprobe->inode->i_ino,
                (unsigned long long) uprobe->offset,
                (unsigned long long) uprobe->ref_ctr_offset, mm);
}

static int update_ref_ctr(struct uprobe *uprobe, struct mm_struct *mm,
                          short d)
{
        struct vm_area_struct *rc_vma;
        unsigned long rc_vaddr;
        int ret = 0;

        rc_vma = find_ref_ctr_vma(uprobe, mm);

        if (rc_vma) {
                rc_vaddr = offset_to_vaddr(rc_vma, uprobe->ref_ctr_offset);
                ret = __update_ref_ctr(mm, rc_vaddr, d);
                if (ret)
                        update_ref_ctr_warn(uprobe, mm, d);

                if (d > 0)
                        return ret;
        }

        mutex_lock(&delayed_uprobe_lock);
        if (d > 0)
                ret = delayed_uprobe_add(uprobe, mm);
        else
                delayed_uprobe_remove(uprobe, mm);
        mutex_unlock(&delayed_uprobe_lock);

        return ret;
}

/*
 * 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_lock held for write.
 * Return 0 (success) or a negative errno.
 */
int uprobe_write_opcode(struct arch_uprobe *auprobe, struct mm_struct *mm,
                        unsigned long vaddr, uprobe_opcode_t opcode)
{
        struct uprobe *uprobe;
        struct page *old_page, *new_page;
        struct vm_area_struct *vma;
        int ret, is_register, ref_ctr_updated = 0;
        bool orig_page_huge = false;
        unsigned int gup_flags = FOLL_FORCE;

        is_register = is_swbp_insn(&opcode);
        uprobe = container_of(auprobe, struct uprobe, arch);

retry:
        if (is_register)
                gup_flags |= FOLL_SPLIT_PMD;
        /* Read the page with vaddr into memory */
        ret = get_user_pages_remote(NULL, mm, vaddr, 1, gup_flags,
                                    &old_page, &vma, NULL);
        if (ret <= 0)
                return ret;

        ret = verify_opcode(old_page, vaddr, &opcode);
        if (ret <= 0)
                goto put_old;

        if (WARN(!is_register && PageCompound(old_page),
                 "uprobe unregister should never work on compound page\n")) {
                ret = -EINVAL;
                goto put_old;
        }

        /* We are going to replace instruction, update ref_ctr. */
        if (!ref_ctr_updated && uprobe->ref_ctr_offset) {
                ret = update_ref_ctr(uprobe, mm, is_register ? 1 : -1);
                if (ret)
                        goto put_old;

                ref_ctr_updated = 1;
        }

        ret = 0;
        if (!is_register && !PageAnon(old_page))
                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);

        if (!is_register) {
                struct page *orig_page;
                pgoff_t index;

                VM_BUG_ON_PAGE(!PageAnon(old_page), old_page);

                index = vaddr_to_offset(vma, vaddr & PAGE_MASK) >> PAGE_SHIFT;
                orig_page = find_get_page(vma->vm_file->f_inode->i_mapping,
                                          index);

                if (orig_page) {
                        if (PageUptodate(orig_page) &&
                            pages_identical(new_page, orig_page)) {
                                /* let go new_page */
                                put_page(new_page);
                                new_page = NULL;

                                if (PageCompound(orig_page))
                                        orig_page_huge = true;
                        }
                        put_page(orig_page);
                }
        }

        ret = __replace_page(vma, vaddr, old_page, new_page);
        if (new_page)
                put_page(new_page);
put_old:
        put_page(old_page);

        if (unlikely(ret == -EAGAIN))
                goto retry;

        /* Revert back reference counter if instruction update failed. */
        if (ret && is_register && ref_ctr_updated)
                update_ref_ctr(uprobe, mm, -1);

        /* try collapse pmd for compound page */
        if (!ret && orig_page_huge)
                collapse_pte_mapped_thp(mm, vaddr);

        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(auprobe, 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(auprobe, mm, vaddr,
                        *(uprobe_opcode_t *)&auprobe->insn);
}

static struct uprobe *get_uprobe(struct uprobe *uprobe)
{
        refcount_inc(&uprobe->ref);
        return uprobe;
}

static void put_uprobe(struct uprobe *uprobe)
{
        if (refcount_dec_and_test(&uprobe->ref)) {
                /*
                 * If application munmap(exec_vma) before uprobe_unregister()
                 * gets called, we don't get a chance to remove uprobe from
                 * delayed_uprobe_list from remove_breakpoint(). Do it here.
                 */
                mutex_lock(&delayed_uprobe_lock);
                delayed_uprobe_remove(uprobe, NULL);
                mutex_unlock(&delayed_uprobe_lock);
                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 */
        refcount_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
ref_ctr_mismatch_warn(struct uprobe *cur_uprobe, struct uprobe *uprobe)
{
        pr_warn("ref_ctr_offset mismatch. inode: 0x%lx offset: 0x%llx "
                "ref_ctr_offset(old): 0x%llx ref_ctr_offset(new): 0x%llx\n",
                uprobe->inode->i_ino, (unsigned long long) uprobe->offset,
                (unsigned long long) cur_uprobe->ref_ctr_offset,
                (unsigned long long) uprobe->ref_ctr_offset);
}

static struct uprobe *alloc_uprobe(struct inode *inode, loff_t offset,
                                   loff_t ref_ctr_offset)
{
        struct uprobe *uprobe, *cur_uprobe;

        uprobe = kzalloc(sizeof(struct uprobe), GFP_KERNEL);
        if (!uprobe)
                return NULL;

        uprobe->inode = inode;
        uprobe->offset = offset;
        uprobe->ref_ctr_offset = ref_ctr_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) {
                if (cur_uprobe->ref_ctr_offset != uprobe->ref_ctr_offset) {
                        ref_ctr_mismatch_warn(cur_uprobe, uprobe);
                        put_uprobe(cur_uprobe);
                        kfree(uprobe);
                        return ERR_PTR(-EINVAL);
                }
                kfree(uprobe);
                uprobe = cur_uprobe;
        }

        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 the smp_rmb() in handle_swbp() */
        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() */
        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 (!mmget_not_zero(vma->vm_mm))
                        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;

                mmap_write_lock(mm);
                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:
                mmap_write_unlock(mm);
 free:
                mmput(mm);
                info = free_map_info(info);
        }
 out:
        percpu_up_write(&dup_mmap_sem);
        return err;
}

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_unregister - unregister an 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);

/*
 * __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. Caller of __uprobe_register() is required to keep @inode
 * (and the containing mount) referenced.
 *
 * Return errno if it cannot successully install probes
 * else return 0 (success)
 */
static int __uprobe_register(struct inode *inode, loff_t offset,
                             loff_t ref_ctr_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, ref_ctr_offset);
        if (!uprobe)
                return -ENOMEM;
        if (IS_ERR(uprobe))
                return PTR_ERR(uprobe);

        /*
         * 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))) {
                consumer_add(uprobe, uc);
                ret = register_for_each_vma(uprobe, uc);
                if (ret)
                        __uprobe_unregister(uprobe, uc);
        }
        up_write(&uprobe->register_rwsem);
        put_uprobe(uprobe);

        if (unlikely(ret == -EAGAIN))
                goto retry;
        return ret;
}

int uprobe_register(struct inode *inode, loff_t offset,
                    struct uprobe_consumer *uc)
{
        return __uprobe_register(inode, offset, 0, uc);
}
EXPORT_SYMBOL_GPL(uprobe_register);

int uprobe_register_refctr(struct inode *inode, loff_t offset,
                           loff_t ref_ctr_offset, struct uprobe_consumer *uc)
{
        return __uprobe_register(inode, offset, ref_ctr_offset, uc);
}
EXPORT_SYMBOL_GPL(uprobe_register_refctr);

/*
 * uprobe_apply - unregister an 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;
}

static int unapply_uprobe(struct uprobe *uprobe, struct mm_struct *mm)
{
        struct vm_area_struct *vma;
        int err = 0;

        mmap_read_lock(mm);
        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);
        }
        mmap_read_unlock(mm);

        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);
}

/* @vma contains reference counter, not the probed instruction. */
static int delayed_ref_ctr_inc(struct vm_area_struct *vma)
{
        struct list_head *pos, *q;
        struct delayed_uprobe *du;
        unsigned long vaddr;
        int ret = 0, err = 0;

        mutex_lock(&delayed_uprobe_lock);
        list_for_each_safe(pos, q, &delayed_uprobe_list) {
                du = list_entry(pos, struct delayed_uprobe, list);

                if (du->mm != vma->vm_mm ||
                    !valid_ref_ctr_vma(du->uprobe, vma))
                        continue;

                vaddr = offset_to_vaddr(vma, du->uprobe->ref_ctr_offset);
                ret = __update_ref_ctr(vma->vm_mm, vaddr, 1);
                if (ret) {
                        update_ref_ctr_warn(du->uprobe, vma->vm_mm, 1);
                        if (!err)
                                err = ret;
                }
                delayed_uprobe_delete(du);
        }
        mutex_unlock(&delayed_uprobe_lock);
        return err;
}

/*
 * Called from mmap_region/vma_adjust with mm->mmap_lock 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())
                return 0;

        if (vma->vm_file &&
            (vma->vm_flags & (VM_WRITE|VM_SHARED)) == VM_WRITE &&
            test_bit(MMF_HAS_UPROBES, &vma->vm_mm->flags))
                delayed_ref_ctr_inc(vma);

        if (!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 (mmap_write_lock_killable(mm))
                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 (IS_ERR_VALUE(area->vaddr)) {
                        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;
        /* pairs with get_xol_area() */
        smp_store_release(&mm->uprobes_state.xol_area, area); /* ^^^ */
 fail:
        mmap_write_unlock(mm);

        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 = kcalloc(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);
        arch_uprobe_copy_ixol(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);

        /* Pairs with xol_add_vma() smp_store_release() */
        area = READ_ONCE(mm->uprobes_state.xol_area); /* ^^^ */
        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;

        mutex_lock(&delayed_uprobe_lock);
        delayed_uprobe_remove(NULL, mm);
        mutex_unlock(&delayed_uprobe_lock);

        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)
{
        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_page() 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 an exiting or an 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;

        /* Pairs with xol_add_vma() smp_store_release() */
        area = READ_ONCE(current->mm->uprobes_state.xol_area); /* ^^^ */
        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, FOLL_FORCE, &page,
                        NULL, 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;

        mmap_read_lock(mm);
        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);
        mmap_read_unlock(mm);

        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 %ps()\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(SIGILL);

}

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.
         */
        if (unlikely(!test_bit(UPROBE_COPY_INSN, &uprobe->flags)))
                goto out;

        /*
         * Pairs with the smp_wmb() in prepare_uprobe().
         *
         * Guarantees that if we see the UPROBE_COPY_INSN bit set, then
         * we must also see the stores to &uprobe->arch performed by the
         * prepare_uprobe() call.
         */
        smp_rmb();

        /* 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(SIGILL);
        }
}

/*
 * 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 */
};

void __init uprobes_init(void)
{
        int i;

        for (i = 0; i < UPROBES_HASH_SZ; i++)
                mutex_init(&uprobes_mmap_mutex[i]);

        BUG_ON(register_die_notifier(&uprobe_exception_nb));
}