// 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/export.h>
#include <linux/rmap.h>         /* anon_vma_prepare */
#include <linux/mmu_notifier.h>
#include <linux/swap.h>         /* folio_free_swap */
#include <linux/ptrace.h>       /* user_enable_single_step */
#include <linux/kdebug.h>       /* notifier mechanism */
#include <linux/percpu-rwsem.h>
#include <linux/task_work.h>
#include <linux/shmem_fs.h>
#include <linux/khugepaged.h>
#include <linux/rcupdate_trace.h>
#include <linux/workqueue.h>
#include <linux/srcu.h>
#include <linux/oom.h>          /* check_stable_address_space */
#include <linux/pagewalk.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_RWLOCK(uprobes_treelock); /* serialize rbtree access */
static seqcount_rwlock_t uprobes_seqcount = SEQCNT_RWLOCK_ZERO(uprobes_seqcount, &uprobes_treelock);

#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);

/* Covers return_instance's uprobe lifetime. */
DEFINE_STATIC_SRCU(uretprobes_srcu);

/* 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 list_head        consumers;
        struct inode            *inode;         /* Also hold a ref to inode */
        union {
                struct rcu_head         rcu;
                struct work_struct      work;
        };
        loff_t                  offset;
        loff_t                  ref_ctr_offset;
        unsigned long           flags;          /* "unsigned long" so bitops work */

        /*
         * 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 */
        unsigned long                   *bitmap;        /* 0 = free slot */

        struct page                     *page;
        /*
         * We keep the vma's vm_start rather than a pointer to the vma
         * itself.  The probed process or a naughty kernel module could make
         * the vma go away, and we must handle that reasonably gracefully.
         */
        unsigned long                   vaddr;          /* Page(s) of instruction slots */
};

static void uprobe_warn(struct task_struct *t, const char *msg)
{
        pr_warn("uprobe: %s:%d failed to %s\n", t->comm, t->pid, msg);
}

/*
 * 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);
}

/**
 * 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);
}

void uprobe_copy_from_page(struct page *page, unsigned long vaddr, void *dst, int len)
{
        void *kaddr = kmap_local_page(page);
        memcpy(dst, kaddr + (vaddr & ~PAGE_MASK), len);
        kunmap_local(kaddr);
}

static void copy_to_page(struct page *page, unsigned long vaddr, const void *src, int len)
{
        void *kaddr = kmap_local_page(page);
        memcpy(kaddr + (vaddr & ~PAGE_MASK), src, len);
        kunmap_local(kaddr);
}

static int verify_opcode(struct page *page, unsigned long vaddr, uprobe_opcode_t *insn,
                         int nbytes, void *data)
{
        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.
         */
        uprobe_copy_from_page(page, vaddr, &old_opcode, UPROBE_SWBP_INSN_SIZE);
        is_swbp = is_swbp_insn(&old_opcode);

        if (is_swbp_insn(insn)) {
                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_obj(*du);
        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)
{
        VMA_ITERATOR(vmi, mm, 0);
        struct vm_area_struct *tmp;

        for_each_vma(vmi, tmp)
                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;
        int ret;
        short *ptr;

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

        ret = get_user_pages_remote(mm, vaddr, 1,
                                    FOLL_WRITE, &page, 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_local_page(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_local(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%p\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;
}

static bool orig_page_is_identical(struct vm_area_struct *vma,
                unsigned long vaddr, struct page *page, bool *pmd_mappable)
{
        const pgoff_t index = vaddr_to_offset(vma, vaddr) >> PAGE_SHIFT;
        struct folio *orig_folio = filemap_get_folio(vma->vm_file->f_mapping,
                                                    index);
        struct page *orig_page;
        bool identical;

        if (IS_ERR(orig_folio))
                return false;
        orig_page = folio_file_page(orig_folio, index);

        *pmd_mappable = folio_test_pmd_mappable(orig_folio);
        identical = folio_test_uptodate(orig_folio) &&
                    pages_identical(page, orig_page);
        folio_put(orig_folio);
        return identical;
}

static int __uprobe_write(struct vm_area_struct *vma,
                struct folio_walk *fw, struct folio *folio,
                unsigned long insn_vaddr, uprobe_opcode_t *insn, int nbytes,
                bool is_register)
{
        const unsigned long vaddr = insn_vaddr & PAGE_MASK;
        bool pmd_mappable;

        /* For now, we'll only handle PTE-mapped folios. */
        if (fw->level != FW_LEVEL_PTE)
                return -EFAULT;

        /*
         * See can_follow_write_pte(): we'd actually prefer a writable PTE here,
         * but the VMA might not be writable.
         */
        if (!pte_write(fw->pte)) {
                if (!PageAnonExclusive(fw->page))
                        return -EFAULT;
                if (unlikely(userfaultfd_pte_wp(vma, fw->pte)))
                        return -EFAULT;
                /* SOFTDIRTY is handled via pte_mkdirty() below. */
        }

        /*
         * We'll temporarily unmap the page and flush the TLB, such that we can
         * modify the page atomically.
         */
        flush_cache_page(vma, vaddr, pte_pfn(fw->pte));
        fw->pte = ptep_clear_flush(vma, vaddr, fw->ptep);
        copy_to_page(fw->page, insn_vaddr, insn, nbytes);

        /*
         * When unregistering, we may only zap a PTE if uffd is disabled and
         * there are no unexpected folio references ...
         */
        if (is_register || userfaultfd_missing(vma) ||
            (folio_ref_count(folio) != folio_expected_ref_count(folio) + 1))
                goto remap;

        /*
         * ... and the mapped page is identical to the original page that
         * would get faulted in on next access.
         */
        if (!orig_page_is_identical(vma, vaddr, fw->page, &pmd_mappable))
                goto remap;

        dec_mm_counter(vma->vm_mm, MM_ANONPAGES);
        folio_remove_rmap_pte(folio, fw->page, vma);
        if (!folio_mapped(folio) && folio_test_swapcache(folio) &&
             folio_trylock(folio)) {
                folio_free_swap(folio);
                folio_unlock(folio);
        }
        folio_put(folio);

        return pmd_mappable;
remap:
        /*
         * Make sure that our copy_to_page() changes become visible before the
         * set_pte_at() write.
         */
        smp_wmb();
        /* We modified the page. Make sure to mark the PTE dirty. */
        set_pte_at(vma->vm_mm, vaddr, fw->ptep, pte_mkdirty(fw->pte));
        return 0;
}

/*
 * 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.
 * @auprobe: arch specific probepoint information.
 * @vma: the probed virtual memory area.
 * @opcode_vaddr: the virtual address to store the opcode.
 * @opcode: opcode to be written at @opcode_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 vm_area_struct *vma,
                const unsigned long opcode_vaddr, uprobe_opcode_t opcode,
                bool is_register)
{
        return uprobe_write(auprobe, vma, opcode_vaddr, &opcode, UPROBE_SWBP_INSN_SIZE,
                            verify_opcode, is_register, true /* do_update_ref_ctr */, NULL);
}

int uprobe_write(struct arch_uprobe *auprobe, struct vm_area_struct *vma,
                 const unsigned long insn_vaddr, uprobe_opcode_t *insn, int nbytes,
                 uprobe_write_verify_t verify, bool is_register, bool do_update_ref_ctr,
                 void *data)
{
        const unsigned long vaddr = insn_vaddr & PAGE_MASK;
        struct mm_struct *mm = vma->vm_mm;
        struct uprobe *uprobe;
        int ret, ref_ctr_updated = 0;
        unsigned int gup_flags = FOLL_FORCE;
        struct mmu_notifier_range range;
        struct folio_walk fw;
        struct folio *folio;
        struct page *page;

        uprobe = container_of(auprobe, struct uprobe, arch);

        if (WARN_ON_ONCE(!is_cow_mapping(vma->vm_flags)))
                return -EINVAL;

        /*
         * When registering, we have to break COW to get an exclusive anonymous
         * page that we can safely modify. Use FOLL_WRITE to trigger a write
         * fault if required. When unregistering, we might be lucky and the
         * anon page is already gone. So defer write faults until really
         * required. Use FOLL_SPLIT_PMD, because __uprobe_write()
         * cannot deal with PMDs yet.
         */
        if (is_register)
                gup_flags |= FOLL_WRITE | FOLL_SPLIT_PMD;

retry:
        ret = get_user_pages_remote(mm, vaddr, 1, gup_flags, &page, NULL);
        if (ret <= 0)
                goto out;
        folio = page_folio(page);

        ret = verify(page, insn_vaddr, insn, nbytes, data);
        if (ret <= 0) {
                folio_put(folio);
                goto out;
        }

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

                ref_ctr_updated = 1;
        }

        ret = 0;
        if (unlikely(!folio_test_anon(folio) || folio_is_zone_device(folio))) {
                VM_WARN_ON_ONCE(is_register);
                folio_put(folio);
                goto out;
        }

        if (!is_register) {
                /*
                 * In the common case, we'll be able to zap the page when
                 * unregistering. So trigger MMU notifiers now, as we won't
                 * be able to do it under PTL.
                 */
                mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, mm,
                                        vaddr, vaddr + PAGE_SIZE);
                mmu_notifier_invalidate_range_start(&range);
        }

        ret = -EAGAIN;
        /* Walk the page tables again, to perform the actual update. */
        if (folio_walk_start(&fw, vma, vaddr, 0)) {
                if (fw.page == page)
                        ret = __uprobe_write(vma, &fw, folio, insn_vaddr, insn, nbytes, is_register);
                folio_walk_end(&fw, vma);
        }

        if (!is_register)
                mmu_notifier_invalidate_range_end(&range);

        folio_put(folio);
        switch (ret) {
        case -EFAULT:
                gup_flags |= FOLL_WRITE | FOLL_SPLIT_PMD;
                fallthrough;
        case -EAGAIN:
                goto retry;
        default:
                break;
        }

out:
        /* Revert back reference counter if instruction update failed. */
        if (do_update_ref_ctr && ret < 0 && ref_ctr_updated)
                update_ref_ctr(uprobe, mm, is_register ? -1 : 1);

        /* try collapse pmd for compound page */
        if (ret > 0)
                collapse_pte_mapped_thp(mm, vaddr, false);

        return ret < 0 ? ret : 0;
}

/**
 * set_swbp - store breakpoint at a given address.
 * @auprobe: arch specific probepoint information.
 * @vma: the probed virtual memory area.
 * @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 vm_area_struct *vma,
                unsigned long vaddr)
{
        return uprobe_write_opcode(auprobe, vma, vaddr, UPROBE_SWBP_INSN, true);
}

/**
 * set_orig_insn - Restore the original instruction.
 * @vma: the probed virtual memory area.
 * @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 vm_area_struct *vma, unsigned long vaddr)
{
        return uprobe_write_opcode(auprobe, vma, vaddr,
                        *(uprobe_opcode_t *)&auprobe->insn, false);
}

/* uprobe should have guaranteed positive refcount */
static struct uprobe *get_uprobe(struct uprobe *uprobe)
{
        refcount_inc(&uprobe->ref);
        return uprobe;
}

/*
 * uprobe should have guaranteed lifetime, which can be either of:
 *   - caller already has refcount taken (and wants an extra one);
 *   - uprobe is RCU protected and won't be freed until after grace period;
 *   - we are holding uprobes_treelock (for read or write, doesn't matter).
 */
static struct uprobe *try_get_uprobe(struct uprobe *uprobe)
{
        if (refcount_inc_not_zero(&uprobe->ref))
                return uprobe;
        return NULL;
}

static inline bool uprobe_is_active(struct uprobe *uprobe)
{
        return !RB_EMPTY_NODE(&uprobe->rb_node);
}

static void uprobe_free_rcu_tasks_trace(struct rcu_head *rcu)
{
        struct uprobe *uprobe = container_of(rcu, struct uprobe, rcu);

        kfree(uprobe);
}

static void uprobe_free_srcu(struct rcu_head *rcu)
{
        struct uprobe *uprobe = container_of(rcu, struct uprobe, rcu);

        call_rcu_tasks_trace(&uprobe->rcu, uprobe_free_rcu_tasks_trace);
}

static void uprobe_free_deferred(struct work_struct *work)
{
        struct uprobe *uprobe = container_of(work, struct uprobe, work);

        write_lock(&uprobes_treelock);

        if (uprobe_is_active(uprobe)) {
                write_seqcount_begin(&uprobes_seqcount);
                rb_erase(&uprobe->rb_node, &uprobes_tree);
                write_seqcount_end(&uprobes_seqcount);
        }

        write_unlock(&uprobes_treelock);

        /*
         * 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);

        /* start srcu -> rcu_tasks_trace -> kfree chain */
        call_srcu(&uretprobes_srcu, &uprobe->rcu, uprobe_free_srcu);
}

static void put_uprobe(struct uprobe *uprobe)
{
        if (!refcount_dec_and_test(&uprobe->ref))
                return;

        INIT_WORK(&uprobe->work, uprobe_free_deferred);
        schedule_work(&uprobe->work);
}

/* Initialize hprobe as SRCU-protected "leased" uprobe */
static void hprobe_init_leased(struct hprobe *hprobe, struct uprobe *uprobe, int srcu_idx)
{
        WARN_ON(!uprobe);
        hprobe->state = HPROBE_LEASED;
        hprobe->uprobe = uprobe;
        hprobe->srcu_idx = srcu_idx;
}

/* Initialize hprobe as refcounted ("stable") uprobe (uprobe can be NULL). */
static void hprobe_init_stable(struct hprobe *hprobe, struct uprobe *uprobe)
{
        hprobe->state = uprobe ? HPROBE_STABLE : HPROBE_GONE;
        hprobe->uprobe = uprobe;
        hprobe->srcu_idx = -1;
}

/*
 * hprobe_consume() fetches hprobe's underlying uprobe and detects whether
 * uprobe is SRCU protected or is refcounted. hprobe_consume() can be
 * used only once for a given hprobe.
 *
 * Caller has to call hprobe_finalize() and pass previous hprobe_state, so
 * that hprobe_finalize() can perform SRCU unlock or put uprobe, whichever
 * is appropriate.
 */
static inline struct uprobe *hprobe_consume(struct hprobe *hprobe, enum hprobe_state *hstate)
{
        *hstate = xchg(&hprobe->state, HPROBE_CONSUMED);
        switch (*hstate) {
        case HPROBE_LEASED:
        case HPROBE_STABLE:
                return hprobe->uprobe;
        case HPROBE_GONE:       /* uprobe is NULL, no SRCU */
        case HPROBE_CONSUMED:   /* uprobe was finalized already, do nothing */
                return NULL;
        default:
                WARN(1, "hprobe invalid state %d", *hstate);
                return NULL;
        }
}

/*
 * Reset hprobe state and, if hprobe was LEASED, release SRCU lock.
 * hprobe_finalize() can only be used from current context after
 * hprobe_consume() call (which determines uprobe and hstate value).
 */
static void hprobe_finalize(struct hprobe *hprobe, enum hprobe_state hstate)
{
        switch (hstate) {
        case HPROBE_LEASED:
                __srcu_read_unlock(&uretprobes_srcu, hprobe->srcu_idx);
                break;
        case HPROBE_STABLE:
                put_uprobe(hprobe->uprobe);
                break;
        case HPROBE_GONE:
        case HPROBE_CONSUMED:
                break;
        default:
                WARN(1, "hprobe invalid state %d", hstate);
                break;
        }
}

/*
 * Attempt to switch (atomically) uprobe from being SRCU protected (LEASED)
 * to refcounted (STABLE) state. Competes with hprobe_consume(); only one of
 * them can win the race to perform SRCU unlocking. Whoever wins must perform
 * SRCU unlock.
 *
 * Returns underlying valid uprobe or NULL, if there was no underlying uprobe
 * to begin with or we failed to bump its refcount and it's going away.
 *
 * Returned non-NULL uprobe can be still safely used within an ongoing SRCU
 * locked region. If `get` is true, it's guaranteed that non-NULL uprobe has
 * an extra refcount for caller to assume and use. Otherwise, it's not
 * guaranteed that returned uprobe has a positive refcount, so caller has to
 * attempt try_get_uprobe(), if it needs to preserve uprobe beyond current
 * SRCU lock region. See dup_utask().
 */
static struct uprobe *hprobe_expire(struct hprobe *hprobe, bool get)
{
        enum hprobe_state hstate;

        /*
         * Caller should guarantee that return_instance is not going to be
         * freed from under us. This can be achieved either through holding
         * rcu_read_lock() or by owning return_instance in the first place.
         *
         * Underlying uprobe is itself protected from reuse by SRCU, so ensure
         * SRCU lock is held properly.
         */
        lockdep_assert(srcu_read_lock_held(&uretprobes_srcu));

        hstate = READ_ONCE(hprobe->state);
        switch (hstate) {
        case HPROBE_STABLE:
                /* uprobe has positive refcount, bump refcount, if necessary */
                return get ? get_uprobe(hprobe->uprobe) : hprobe->uprobe;
        case HPROBE_GONE:
                /*
                 * SRCU was unlocked earlier and we didn't manage to take
                 * uprobe refcnt, so it's effectively NULL
                 */
                return NULL;
        case HPROBE_CONSUMED:
                /*
                 * uprobe was consumed, so it's effectively NULL as far as
                 * uretprobe processing logic is concerned
                 */
                return NULL;
        case HPROBE_LEASED: {
                struct uprobe *uprobe = try_get_uprobe(hprobe->uprobe);
                /*
                 * Try to switch hprobe state, guarding against
                 * hprobe_consume() or another hprobe_expire() racing with us.
                 * Note, if we failed to get uprobe refcount, we use special
                 * HPROBE_GONE state to signal that hprobe->uprobe shouldn't
                 * be used as it will be freed after SRCU is unlocked.
                 */
                if (try_cmpxchg(&hprobe->state, &hstate, uprobe ? HPROBE_STABLE : HPROBE_GONE)) {
                        /* We won the race, we are the ones to unlock SRCU */
                        __srcu_read_unlock(&uretprobes_srcu, hprobe->srcu_idx);
                        return get ? get_uprobe(uprobe) : uprobe;
                }

                /*
                 * We lost the race, undo refcount bump (if it ever happened),
                 * unless caller would like an extra refcount anyways.
                 */
                if (uprobe && !get)
                        put_uprobe(uprobe);
                /*
                 * Even if hprobe_consume() or another hprobe_expire() wins
                 * the state update race and unlocks SRCU from under us, we
                 * still have a guarantee that underyling uprobe won't be
                 * freed due to ongoing caller's SRCU lock region, so we can
                 * return it regardless. Also, if `get` was true, we also have
                 * an extra ref for the caller to own. This is used in dup_utask().
                 */
                return uprobe;
        }
        default:
                WARN(1, "unknown hprobe state %d", hstate);
                return NULL;
        }
}

static __always_inline
int uprobe_cmp(const struct inode *l_inode, const loff_t l_offset,
               const 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;
}

#define __node_2_uprobe(node) \
        rb_entry((node), struct uprobe, rb_node)

struct __uprobe_key {
        struct inode *inode;
        loff_t offset;
};

static inline int __uprobe_cmp_key(const void *key, const struct rb_node *b)
{
        const struct __uprobe_key *a = key;
        return uprobe_cmp(a->inode, a->offset, __node_2_uprobe(b));
}

static inline int __uprobe_cmp(struct rb_node *a, const struct rb_node *b)
{
        struct uprobe *u = __node_2_uprobe(a);
        return uprobe_cmp(u->inode, u->offset, __node_2_uprobe(b));
}

/*
 * Assumes being inside RCU protected region.
 * No refcount is taken on returned uprobe.
 */
static struct uprobe *find_uprobe_rcu(struct inode *inode, loff_t offset)
{
        struct __uprobe_key key = {
                .inode = inode,
                .offset = offset,
        };
        struct rb_node *node;
        unsigned int seq;

        lockdep_assert(rcu_read_lock_trace_held());

        do {
                seq = read_seqcount_begin(&uprobes_seqcount);
                node = rb_find_rcu(&key, &uprobes_tree, __uprobe_cmp_key);
                /*
                 * Lockless RB-tree lookups can result only in false negatives.
                 * If the element is found, it is correct and can be returned
                 * under RCU protection. If we find nothing, we need to
                 * validate that seqcount didn't change. If it did, we have to
                 * try again as we might have missed the element (false
                 * negative). If seqcount is unchanged, search truly failed.
                 */
                if (node)
                        return __node_2_uprobe(node);
        } while (read_seqcount_retry(&uprobes_seqcount, seq));

        return NULL;
}

/*
 * Attempt to insert a new uprobe into uprobes_tree.
 *
 * If uprobe already exists (for given inode+offset), we just increment
 * refcount of previously existing uprobe.
 *
 * If not, a provided new instance of uprobe is inserted into the tree (with
 * assumed initial refcount == 1).
 *
 * In any case, we return a uprobe instance that ends up being in uprobes_tree.
 * Caller has to clean up new uprobe instance, if it ended up not being
 * inserted into the tree.
 *
 * We assume that uprobes_treelock is held for writing.
 */
static struct uprobe *__insert_uprobe(struct uprobe *uprobe)
{
        struct rb_node *node;
again:
        node = rb_find_add_rcu(&uprobe->rb_node, &uprobes_tree, __uprobe_cmp);
        if (node) {
                struct uprobe *u = __node_2_uprobe(node);

                if (!try_get_uprobe(u)) {
                        rb_erase(node, &uprobes_tree);
                        RB_CLEAR_NODE(&u->rb_node);
                        goto again;
                }

                return u;
        }

        return uprobe;
}

/*
 * Acquire uprobes_treelock and insert uprobe into uprobes_tree
 * (or reuse existing one, see __insert_uprobe() comments above).
 */
static struct uprobe *insert_uprobe(struct uprobe *uprobe)
{
        struct uprobe *u;

        write_lock(&uprobes_treelock);
        write_seqcount_begin(&uprobes_seqcount);
        u = __insert_uprobe(uprobe);
        write_seqcount_end(&uprobes_seqcount);
        write_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_obj(struct uprobe);
        if (!uprobe)
                return ERR_PTR(-ENOMEM);

        uprobe->inode = inode;
        uprobe->offset = offset;
        uprobe->ref_ctr_offset = ref_ctr_offset;
        INIT_LIST_HEAD(&uprobe->consumers);
        init_rwsem(&uprobe->register_rwsem);
        init_rwsem(&uprobe->consumer_rwsem);
        RB_CLEAR_NODE(&uprobe->rb_node);
        refcount_set(&uprobe->ref, 1);

        /* add to uprobes_tree, sorted on inode:offset */
        cur_uprobe = insert_uprobe(uprobe);
        /* a uprobe exists for this inode:offset combination */
        if (cur_uprobe != 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)
{
        static atomic64_t id;

        down_write(&uprobe->consumer_rwsem);
        list_add_rcu(&uc->cons_node, &uprobe->consumers);
        uc->id = (__u64) atomic64_inc_return(&id);
        up_write(&uprobe->consumer_rwsem);
}

/*
 * For uprobe @uprobe, delete the consumer @uc.
 * Should never be called with consumer that's not part of @uprobe->consumers.
 */
static void consumer_del(struct uprobe *uprobe, struct uprobe_consumer *uc)
{
        down_write(&uprobe->consumer_rwsem);
        list_del_rcu(&uc->cons_node);
        up_write(&uprobe->consumer_rwsem);
}

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 ->read_folio == NULL it must be shmem_mapping(),
         * see uprobe_register().
         */
        if (mapping->a_ops->read_folio)
                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);

        uprobe_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;

        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, struct mm_struct *mm)
{
        return !uc->filter || uc->filter(uc, mm);
}

static bool filter_chain(struct uprobe *uprobe, struct mm_struct *mm)
{
        struct uprobe_consumer *uc;
        bool ret = false;

        down_read(&uprobe->consumer_rwsem);
        list_for_each_entry(uc, &uprobe->consumers, cons_node) {
                ret = consumer_filter(uc, mm);
                if (ret)
                        break;
        }
        up_read(&uprobe->consumer_rwsem);

        return ret;
}

static int install_breakpoint(struct uprobe *uprobe, struct vm_area_struct *vma,
                unsigned long vaddr)
{
        struct mm_struct *mm = vma->vm_mm;
        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 = !mm_flags_test(MMF_HAS_UPROBES, mm);
        if (first_uprobe)
                mm_flags_set(MMF_HAS_UPROBES, mm);

        ret = set_swbp(&uprobe->arch, vma, vaddr);
        if (!ret)
                mm_flags_clear(MMF_RECALC_UPROBES, mm);
        else if (first_uprobe)
                mm_flags_clear(MMF_HAS_UPROBES, mm);

        return ret;
}

static int remove_breakpoint(struct uprobe *uprobe, struct vm_area_struct *vma,
                unsigned long vaddr)
{
        struct mm_struct *mm = vma->vm_mm;

        mm_flags_set(MMF_RECALC_UPROBES, mm);
        return set_orig_insn(&uprobe->arch, vma, vaddr);
}

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_obj(struct map_info,
                                           GFP_NOWAIT | __GFP_NOMEMALLOC);
                        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_obj(struct map_info);
                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;
                /*
                 * We take mmap_lock for writing to avoid the race with
                 * find_active_uprobe_rcu() which takes mmap_lock for reading.
                 * Thus this install_breakpoint() can not make
                 * is_trap_at_addr() true right after find_uprobe_rcu()
                 * returns NULL in find_active_uprobe_rcu().
                 */
                mmap_write_lock(mm);
                if (check_stable_address_space(mm))
                        goto unlock;

                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, mm))
                                err = install_breakpoint(uprobe, vma, info->vaddr);
                } else if (mm_flags_test(MMF_HAS_UPROBES, mm)) {
                        if (!filter_chain(uprobe, mm))
                                err |= remove_breakpoint(uprobe, vma, info->vaddr);
                }

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

/**
 * uprobe_unregister_nosync - unregister an already registered probe.
 * @uprobe: uprobe to remove
 * @uc: identify which probe if multiple probes are colocated.
 */
void uprobe_unregister_nosync(struct uprobe *uprobe, struct uprobe_consumer *uc)
{
        int err;

        down_write(&uprobe->register_rwsem);
        consumer_del(uprobe, uc);
        err = register_for_each_vma(uprobe, NULL);
        up_write(&uprobe->register_rwsem);

        /* TODO : cant unregister? schedule a worker thread */
        if (unlikely(err)) {
                uprobe_warn(current, "unregister, leaking uprobe");
                return;
        }

        put_uprobe(uprobe);
}
EXPORT_SYMBOL_GPL(uprobe_unregister_nosync);

void uprobe_unregister_sync(void)
{
        /*
         * Now that handler_chain() and handle_uretprobe_chain() iterate over
         * uprobe->consumers list under RCU protection without holding
         * uprobe->register_rwsem, we need to wait for RCU grace period to
         * make sure that we can't call into just unregistered
         * uprobe_consumer's callbacks anymore. If we don't do that, fast and
         * unlucky enough caller can free consumer's memory and cause
         * handler_chain() or handle_uretprobe_chain() to do an use-after-free.
         */
        synchronize_rcu_tasks_trace();
        synchronize_srcu(&uretprobes_srcu);
}
EXPORT_SYMBOL_GPL(uprobe_unregister_sync);

/**
 * uprobe_register - register a probe
 * @inode: the file in which the probe has to be placed.
 * @offset: offset from the start of the file.
 * @ref_ctr_offset: offset of SDT marker / reference counter
 * @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: pointer to the new uprobe on success or an ERR_PTR on failure.
 */
struct uprobe *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 ERR_PTR(-EINVAL);

        /* copy_insn() uses read_mapping_page() or shmem_read_mapping_page() */
        if (!inode->i_mapping->a_ops->read_folio &&
            !shmem_mapping(inode->i_mapping))
                return ERR_PTR(-EIO);
        /* Racy, just to catch the obvious mistakes */
        if (offset > i_size_read(inode))
                return ERR_PTR(-EINVAL);

        /*
         * This ensures that uprobe_copy_from_page(), copy_to_page() and
         * __update_ref_ctr() can't cross page boundary.
         */
        if (!IS_ALIGNED(offset, UPROBE_SWBP_INSN_SIZE))
                return ERR_PTR(-EINVAL);
        if (!IS_ALIGNED(ref_ctr_offset, sizeof(short)))
                return ERR_PTR(-EINVAL);

        uprobe = alloc_uprobe(inode, offset, ref_ctr_offset);
        if (IS_ERR(uprobe))
                return uprobe;

        down_write(&uprobe->register_rwsem);
        consumer_add(uprobe, uc);
        ret = register_for_each_vma(uprobe, uc);
        up_write(&uprobe->register_rwsem);

        if (ret) {
                uprobe_unregister_nosync(uprobe, uc);
                /*
                 * Registration might have partially succeeded, so we can have
                 * this consumer being called right at this time. We need to
                 * sync here. It's ok, it's unlikely slow path.
                 */
                uprobe_unregister_sync();
                return ERR_PTR(ret);
        }

        return uprobe;
}
EXPORT_SYMBOL_GPL(uprobe_register);

/**
 * uprobe_apply - add or remove the breakpoints according to @uc->filter
 * @uprobe: uprobe which "owns" the breakpoint
 * @uc: consumer which wants to add more or remove some breakpoints
 * @add: add or remove the breakpoints
 * Return: 0 on success or negative error code.
 */
int uprobe_apply(struct uprobe *uprobe, struct uprobe_consumer *uc, bool add)
{
        struct uprobe_consumer *con;
        int ret = -ENOENT;

        down_write(&uprobe->register_rwsem);

        rcu_read_lock_trace();
        list_for_each_entry_rcu(con, &uprobe->consumers, cons_node, rcu_read_lock_trace_held()) {
                if (con == uc) {
                        ret = register_for_each_vma(uprobe, add ? uc : NULL);
                        break;
                }
        }
        rcu_read_unlock_trace();

        up_write(&uprobe->register_rwsem);

        return ret;
}

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

        mmap_write_lock(mm);
        for_each_vma(vmi, vma) {
                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, vma, vaddr);
        }
        mmap_write_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;

        read_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;
                        /* if uprobe went away, it's safe to ignore it */
                        if (try_get_uprobe(u))
                                list_add(&u->pending_list, head);
                }
                for (t = n; (t = rb_next(t)); ) {
                        u = rb_entry(t, struct uprobe, rb_node);
                        if (u->inode != inode || u->offset > max)
                                break;
                        /* if uprobe went away, it's safe to ignore it */
                        if (try_get_uprobe(u))
                                list_add(&u->pending_list, head);
                }
        }
        read_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_merge 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 &&
            mm_flags_test(MMF_HAS_UPROBES, vma->vm_mm))
                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, vma->vm_mm)) {
                        unsigned long vaddr = offset_to_vaddr(vma, uprobe->offset);
                        install_breakpoint(uprobe, 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;

        read_lock(&uprobes_treelock);
        n = find_node_in_range(inode, min, max);
        read_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 (!mm_flags_test(MMF_HAS_UPROBES, vma->vm_mm) ||
             mm_flags_test(MMF_RECALC_UPROBES, vma->vm_mm))
                return;

        if (vma_has_uprobes(vma, start, end))
                mm_flags_set(MMF_RECALC_UPROBES, vma->vm_mm);
}

static vm_fault_t xol_fault(const struct vm_special_mapping *sm,
                            struct vm_area_struct *vma, struct vm_fault *vmf)
{
        struct xol_area *area = vma->vm_mm->uprobes_state.xol_area;

        vmf->page = area->page;
        get_page(vmf->page);
        return 0;
}

static int xol_mremap(const struct vm_special_mapping *sm, struct vm_area_struct *new_vma)
{
        return -EPERM;
}

static const struct vm_special_mapping xol_mapping = {
        .name = "[uprobes]",
        .fault = xol_fault,
        .mremap = xol_mremap,
};

unsigned long __weak arch_uprobe_get_xol_area(void)
{
        /* Try to map as high as possible, this is only a hint. */
        return get_unmapped_area(NULL, TASK_SIZE - PAGE_SIZE, PAGE_SIZE, 0, 0);
}

/* 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) {
                area->vaddr = arch_uprobe_get_xol_area();
                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|
                                VM_SEALED_SYSMAP,
                                &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;
}

void * __weak arch_uretprobe_trampoline(unsigned long *psize)
{
        static uprobe_opcode_t insn = UPROBE_SWBP_INSN;

        *psize = UPROBE_SWBP_INSN_SIZE;
        return &insn;
}

static struct xol_area *__create_xol_area(unsigned long vaddr)
{
        struct mm_struct *mm = current->mm;
        unsigned long insns_size;
        struct xol_area *area;
        void *insns;

        area = kzalloc_obj(*area);
        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->page = alloc_page(GFP_HIGHUSER | __GFP_ZERO);
        if (!area->page)
                goto free_bitmap;

        area->vaddr = vaddr;
        init_waitqueue_head(&area->wq);
        /* Reserve the 1st slot for get_trampoline_vaddr() */
        set_bit(0, area->bitmap);
        insns = arch_uretprobe_trampoline(&insns_size);
        arch_uprobe_copy_ixol(area->page, 0, insns, insns_size);

        if (!xol_add_vma(mm, area))
                return area;

        __free_page(area->page);
 free_bitmap:
        kfree(area->bitmap);
 free_area:
        kfree(area);
 out:
        return NULL;
}

/*
 * get_xol_area - Allocate process's xol_area if necessary.
 * This area will be used for storing instructions for execution out of line.
 *
 * Returns the allocated area or NULL.
 */
static struct xol_area *get_xol_area(void)
{
        struct mm_struct *mm = current->mm;
        struct xol_area *area;

        if (!mm->uprobes_state.xol_area)
                __create_xol_area(0);

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

void __weak arch_uprobe_clear_state(struct mm_struct *mm)
{
}

void __weak arch_uprobe_init_state(struct mm_struct *mm)
{
}

/*
 * 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);

        arch_uprobe_clear_state(mm);

        if (!area)
                return;

        put_page(area->page);
        kfree(area->bitmap);
        kfree(area);
}

void uprobe_start_dup_mmap(void)
{
        percpu_down_read(&dup_mmap_sem);
}

void uprobe_end_dup_mmap(void)
{
        percpu_up_read(&dup_mmap_sem);
}

void uprobe_dup_mmap(struct mm_struct *oldmm, struct mm_struct *newmm)
{
        if (mm_flags_test(MMF_HAS_UPROBES, oldmm)) {
                mm_flags_set(MMF_HAS_UPROBES, newmm);
                /* unconditionally, dup_mmap() skips VM_DONTCOPY vmas */
                mm_flags_set(MMF_RECALC_UPROBES, newmm);
        }
}

static unsigned long xol_get_slot_nr(struct xol_area *area)
{
        unsigned long slot_nr;

        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))
                        return slot_nr;
        }

        return UINSNS_PER_PAGE;
}

/*
 * xol_get_insn_slot - allocate a slot for xol.
 */
static bool xol_get_insn_slot(struct uprobe *uprobe, struct uprobe_task *utask)
{
        struct xol_area *area = get_xol_area();
        unsigned long slot_nr;

        if (!area)
                return false;

        wait_event(area->wq, (slot_nr = xol_get_slot_nr(area)) < UINSNS_PER_PAGE);

        utask->xol_vaddr = area->vaddr + slot_nr * UPROBE_XOL_SLOT_BYTES;
        arch_uprobe_copy_ixol(area->page, utask->xol_vaddr,
                              &uprobe->arch.ixol, sizeof(uprobe->arch.ixol));
        return true;
}

/*
 * xol_free_insn_slot - free the slot allocated by xol_get_insn_slot()
 */
static void xol_free_insn_slot(struct uprobe_task *utask)
{
        struct xol_area *area = current->mm->uprobes_state.xol_area;
        unsigned long offset = utask->xol_vaddr - area->vaddr;
        unsigned int slot_nr;

        utask->xol_vaddr = 0;
        /* xol_vaddr must fit into [area->vaddr, area->vaddr + PAGE_SIZE) */
        if (WARN_ON_ONCE(offset >= PAGE_SIZE))
                return;

        slot_nr = offset / UPROBE_XOL_SLOT_BYTES;
        clear_bit(slot_nr, area->bitmap);
        smp_mb__after_atomic(); /* pairs with prepare_to_wait() */
        if (waitqueue_active(&area->wq))
                wake_up(&area->wq);
}

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 void ri_pool_push(struct uprobe_task *utask, struct return_instance *ri)
{
        ri->cons_cnt = 0;
        ri->next = utask->ri_pool;
        utask->ri_pool = ri;
}

static struct return_instance *ri_pool_pop(struct uprobe_task *utask)
{
        struct return_instance *ri = utask->ri_pool;

        if (likely(ri))
                utask->ri_pool = ri->next;

        return ri;
}

static void ri_free(struct return_instance *ri)
{
        kfree(ri->extra_consumers);
        kfree_rcu(ri, rcu);
}

static void free_ret_instance(struct uprobe_task *utask,
                              struct return_instance *ri, bool cleanup_hprobe)
{
        unsigned seq;

        if (cleanup_hprobe) {
                enum hprobe_state hstate;

                (void)hprobe_consume(&ri->hprobe, &hstate);
                hprobe_finalize(&ri->hprobe, hstate);
        }

        /*
         * At this point return_instance is unlinked from utask's
         * return_instances list and this has become visible to ri_timer().
         * If seqcount now indicates that ri_timer's return instance
         * processing loop isn't active, we can return ri into the pool of
         * to-be-reused return instances for future uretprobes. If ri_timer()
         * happens to be running right now, though, we fallback to safety and
         * just perform RCU-delated freeing of ri.
         * Admittedly, this is a rather simple use of seqcount, but it nicely
         * abstracts away all the necessary memory barriers, so we use
         * a well-supported kernel primitive here.
         */
        if (raw_seqcount_try_begin(&utask->ri_seqcount, seq)) {
                /* immediate reuse of ri without RCU GP is OK */
                ri_pool_push(utask, ri);
        } else {
                /* we might be racing with ri_timer(), so play it safe */
                ri_free(ri);
        }
}

/*
 * 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, *ri_next;

        if (!utask)
                return;

        t->utask = NULL;
        WARN_ON_ONCE(utask->active_uprobe || utask->xol_vaddr);

        timer_delete_sync(&utask->ri_timer);

        ri = utask->return_instances;
        while (ri) {
                ri_next = ri->next;
                free_ret_instance(utask, ri, true /* cleanup_hprobe */);
                ri = ri_next;
        }

        /* free_ret_instance() above might add to ri_pool, so this loop should come last */
        ri = utask->ri_pool;
        while (ri) {
                ri_next = ri->next;
                ri_free(ri);
                ri = ri_next;
        }

        kfree(utask);
}

#define RI_TIMER_PERIOD (HZ / 10) /* 100 ms */

#define for_each_ret_instance_rcu(pos, head) \
        for (pos = rcu_dereference_raw(head); pos; pos = rcu_dereference_raw(pos->next))

static void ri_timer(struct timer_list *timer)
{
        struct uprobe_task *utask = container_of(timer, struct uprobe_task, ri_timer);
        struct return_instance *ri;

        /* SRCU protects uprobe from reuse for the cmpxchg() inside hprobe_expire(). */
        guard(srcu)(&uretprobes_srcu);
        /* RCU protects return_instance from freeing. */
        guard(rcu)();

        /*
         * See free_ret_instance() for notes on seqcount use.
         * We also employ raw API variants to avoid lockdep false-positive
         * warning complaining about enabled preemption. The timer can only be
         * invoked once for a uprobe_task. Therefore there can only be one
         * writer. The reader does not require an even sequence count to make
         * progress, so it is OK to remain preemptible on PREEMPT_RT.
         */
        raw_write_seqcount_begin(&utask->ri_seqcount);

        for_each_ret_instance_rcu(ri, utask->return_instances)
                hprobe_expire(&ri->hprobe, false);

        raw_write_seqcount_end(&utask->ri_seqcount);
}

static struct uprobe_task *alloc_utask(void)
{
        struct uprobe_task *utask;

        utask = kzalloc_obj(*utask);
        if (!utask)
                return NULL;

        timer_setup(&utask->ri_timer, ri_timer, 0);
        seqcount_init(&utask->ri_seqcount);

        return utask;
}

/*
 * Allocate a uprobe_task object for the task 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 = alloc_utask();
        return current->utask;
}

static struct return_instance *alloc_return_instance(struct uprobe_task *utask)
{
        struct return_instance *ri;

        ri = ri_pool_pop(utask);
        if (ri)
                return ri;

        ri = kzalloc_obj(*ri);
        if (!ri)
                return ZERO_SIZE_PTR;

        return ri;
}

static struct return_instance *dup_return_instance(struct return_instance *old)
{
        struct return_instance *ri;

        ri = kmemdup(old, sizeof(*ri), GFP_KERNEL);
        if (!ri)
                return NULL;

        if (unlikely(old->cons_cnt > 1)) {
                ri->extra_consumers = kmemdup(old->extra_consumers,
                                              sizeof(ri->extra_consumers[0]) * (old->cons_cnt - 1),
                                              GFP_KERNEL);
                if (!ri->extra_consumers) {
                        kfree(ri);
                        return NULL;
                }
        }

        return ri;
}

static int dup_utask(struct task_struct *t, struct uprobe_task *o_utask)
{
        struct uprobe_task *n_utask;
        struct return_instance **p, *o, *n;
        struct uprobe *uprobe;

        n_utask = alloc_utask();
        if (!n_utask)
                return -ENOMEM;
        t->utask = n_utask;

        /* protect uprobes from freeing, we'll need try_get_uprobe() them */
        guard(srcu)(&uretprobes_srcu);

        p = &n_utask->return_instances;
        for (o = o_utask->return_instances; o; o = o->next) {
                n = dup_return_instance(o);
                if (!n)
                        return -ENOMEM;

                /* if uprobe is non-NULL, we'll have an extra refcount for uprobe */
                uprobe = hprobe_expire(&o->hprobe, true);

                /*
                 * New utask will have stable properly refcounted uprobe or
                 * NULL. Even if we failed to get refcounted uprobe, we still
                 * need to preserve full set of return_instances for proper
                 * uretprobe handling and nesting in forked task.
                 */
                hprobe_init_stable(&n->hprobe, uprobe);

                n->next = NULL;
                rcu_assign_pointer(*p, n);
                p = &n->next;

                n_utask->depth++;
        }

        return 0;
}

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, u64 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, TWA_RESUME);
}

/*
 * Current area->vaddr notion assume the trampoline address is always
 * equal area->vaddr.
 *
 * Returns -1 in case the xol_area is not allocated.
 */
unsigned long uprobe_get_trampoline_vaddr(void)
{
        unsigned long trampoline_vaddr = UPROBE_NO_TRAMPOLINE_VADDR;
        struct xol_area *area;

        /* 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, *ri_next;
        enum rp_check ctx = chained ? RP_CHECK_CHAIN_CALL : RP_CHECK_CALL;

        while (ri && !arch_uretprobe_is_alive(ri, ctx, regs)) {
                ri_next = ri->next;
                rcu_assign_pointer(utask->return_instances, ri_next);
                utask->depth--;

                free_ret_instance(utask, ri, true /* cleanup_hprobe */);
                ri = ri_next;
        }
}

static void prepare_uretprobe(struct uprobe *uprobe, struct pt_regs *regs,
                              struct return_instance *ri)
{
        struct uprobe_task *utask = current->utask;
        unsigned long orig_ret_vaddr, trampoline_vaddr;
        bool chained;
        int srcu_idx;

        if (!get_xol_area())
                goto free;

        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);
                goto free;
        }

        trampoline_vaddr = uprobe_get_trampoline_vaddr();
        orig_ret_vaddr = arch_uretprobe_hijack_return_addr(trampoline_vaddr, regs);
        if (orig_ret_vaddr == -1)
                goto free;

        /* 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 free;
                }
                orig_ret_vaddr = utask->return_instances->orig_ret_vaddr;
        }

        /* __srcu_read_lock() because SRCU lock survives switch to user space */
        srcu_idx = __srcu_read_lock(&uretprobes_srcu);

        ri->func = instruction_pointer(regs);
        ri->stack = user_stack_pointer(regs);
        ri->orig_ret_vaddr = orig_ret_vaddr;
        ri->chained = chained;

        utask->depth++;

        hprobe_init_leased(&ri->hprobe, uprobe, srcu_idx);
        ri->next = utask->return_instances;
        rcu_assign_pointer(utask->return_instances, ri);

        mod_timer(&utask->ri_timer, jiffies + RI_TIMER_PERIOD);

        return;
free:
        ri_free(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 = current->utask;
        int err;

        if (!try_get_uprobe(uprobe))
                return -EINVAL;

        if (!xol_get_insn_slot(uprobe, utask)) {
                err = -ENOMEM;
                goto err_out;
        }

        utask->vaddr = bp_vaddr;
        err = arch_uprobe_pre_xol(&uprobe->arch, regs);
        if (unlikely(err)) {
                xol_free_insn_slot(utask);
                goto err_out;
        }

        utask->active_uprobe = uprobe;
        utask->state = UTASK_SSTEP;
        return 0;
err_out:
        put_uprobe(uprobe);
        return err;
}

/*
 * 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 (task_sigpending(t)) {
                utask->signal_denied = true;
                clear_tsk_thread_flag(t, TIF_SIGPENDING);

                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)
{
        VMA_ITERATOR(vmi, mm, 0);
        struct vm_area_struct *vma;

        for_each_vma(vmi, vma) {
                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;
        }

        mm_flags_clear(MMF_HAS_UPROBES, mm);
}

static int is_trap_at_addr(struct mm_struct *mm, unsigned long vaddr)
{
        struct page *page;
        uprobe_opcode_t opcode;
        int result;

        if (WARN_ON_ONCE(!IS_ALIGNED(vaddr, UPROBE_SWBP_INSN_SIZE)))
                return -EINVAL;

        pagefault_disable();
        result = __get_user(opcode, (uprobe_opcode_t __user *)vaddr);
        pagefault_enable();

        if (likely(result == 0))
                goto out;

        result = get_user_pages(vaddr, 1, FOLL_FORCE, &page);
        if (result < 0)
                return result;

        uprobe_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_speculative(unsigned long bp_vaddr)
{
        struct mm_struct *mm = current->mm;
        struct uprobe *uprobe = NULL;
        struct vm_area_struct *vma;
        struct file *vm_file;
        loff_t offset;
        unsigned int seq;

        guard(rcu)();

        if (!mmap_lock_speculate_try_begin(mm, &seq))
                return NULL;

        vma = vma_lookup(mm, bp_vaddr);
        if (!vma)
                return NULL;

        /*
         * vm_file memory can be reused for another instance of struct file,
         * but can't be freed from under us, so it's safe to read fields from
         * it, even if the values are some garbage values; ultimately
         * find_uprobe_rcu() + mmap_lock_speculation_end() check will ensure
         * that whatever we speculatively found is correct
         */
        vm_file = READ_ONCE(vma->vm_file);
        if (!vm_file)
                return NULL;

        offset = (loff_t)(vma->vm_pgoff << PAGE_SHIFT) + (bp_vaddr - vma->vm_start);
        uprobe = find_uprobe_rcu(vm_file->f_inode, offset);
        if (!uprobe)
                return NULL;

        /* now double check that nothing about MM changed */
        if (mmap_lock_speculate_retry(mm, seq))
                return NULL;

        return uprobe;
}

/* assumes being inside RCU protected region */
static struct uprobe *find_active_uprobe_rcu(unsigned long bp_vaddr, int *is_swbp)
{
        struct mm_struct *mm = current->mm;
        struct uprobe *uprobe = NULL;
        struct vm_area_struct *vma;

        uprobe = find_active_uprobe_speculative(bp_vaddr);
        if (uprobe)
                return uprobe;

        mmap_read_lock(mm);
        vma = vma_lookup(mm, bp_vaddr);
        if (vma) {
                if (vma->vm_file) {
                        struct inode *inode = file_inode(vma->vm_file);
                        loff_t offset = vaddr_to_offset(vma, bp_vaddr);

                        uprobe = find_uprobe_rcu(inode, offset);
                }

                if (!uprobe)
                        *is_swbp = is_trap_at_addr(mm, bp_vaddr);
        } else {
                *is_swbp = -EFAULT;
        }

        if (!uprobe && mm_flags_test_and_clear(MMF_RECALC_UPROBES, mm))
                mmf_recalc_uprobes(mm);
        mmap_read_unlock(mm);

        return uprobe;
}

static struct return_instance *push_consumer(struct return_instance *ri, __u64 id, __u64 cookie)
{
        struct return_consumer *ric;

        if (unlikely(ri == ZERO_SIZE_PTR))
                return ri;

        if (unlikely(ri->cons_cnt > 0)) {
                ric = krealloc(ri->extra_consumers, sizeof(*ric) * ri->cons_cnt, GFP_KERNEL);
                if (!ric) {
                        ri_free(ri);
                        return ZERO_SIZE_PTR;
                }
                ri->extra_consumers = ric;
        }

        ric = likely(ri->cons_cnt == 0) ? &ri->consumer : &ri->extra_consumers[ri->cons_cnt - 1];
        ric->id = id;
        ric->cookie = cookie;

        ri->cons_cnt++;
        return ri;
}

static struct return_consumer *
return_consumer_find(struct return_instance *ri, int *iter, int id)
{
        struct return_consumer *ric;
        int idx;

        for (idx = *iter; idx < ri->cons_cnt; idx++)
        {
                ric = likely(idx == 0) ? &ri->consumer : &ri->extra_consumers[idx - 1];
                if (ric->id == id) {
                        *iter = idx + 1;
                        return ric;
                }
        }

        return NULL;
}

static bool ignore_ret_handler(int rc)
{
        return rc == UPROBE_HANDLER_REMOVE || rc == UPROBE_HANDLER_IGNORE;
}

static void handler_chain(struct uprobe *uprobe, struct pt_regs *regs)
{
        struct uprobe_consumer *uc;
        bool has_consumers = false, remove = true;
        struct return_instance *ri = NULL;
        struct uprobe_task *utask = current->utask;

        utask->auprobe = &uprobe->arch;

        list_for_each_entry_rcu(uc, &uprobe->consumers, cons_node, rcu_read_lock_trace_held()) {
                bool session = uc->handler && uc->ret_handler;
                __u64 cookie = 0;
                int rc = 0;

                if (uc->handler) {
                        rc = uc->handler(uc, regs, &cookie);
                        WARN(rc < 0 || rc > 2,
                                "bad rc=0x%x from %ps()\n", rc, uc->handler);
                }

                remove &= rc == UPROBE_HANDLER_REMOVE;
                has_consumers = true;

                if (!uc->ret_handler || ignore_ret_handler(rc))
                        continue;

                if (!ri)
                        ri = alloc_return_instance(utask);

                if (session)
                        ri = push_consumer(ri, uc->id, cookie);
        }
        utask->auprobe = NULL;

        if (!ZERO_OR_NULL_PTR(ri))
                prepare_uretprobe(uprobe, regs, ri);

        if (remove && has_consumers) {
                down_read(&uprobe->register_rwsem);

                /* re-check that removal is still required, this time under lock */
                if (!filter_chain(uprobe, current->mm)) {
                        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 uprobe *uprobe, struct pt_regs *regs)
{
        struct return_consumer *ric;
        struct uprobe_consumer *uc;
        int ric_idx = 0;

        /* all consumers unsubscribed meanwhile */
        if (unlikely(!uprobe))
                return;

        rcu_read_lock_trace();
        list_for_each_entry_rcu(uc, &uprobe->consumers, cons_node, rcu_read_lock_trace_held()) {
                bool session = uc->handler && uc->ret_handler;

                if (uc->ret_handler) {
                        ric = return_consumer_find(ri, &ric_idx, uc->id);
                        if (!session || ric)
                                uc->ret_handler(uc, ri->func, regs, ric ? &ric->cookie : NULL);
                }
        }
        rcu_read_unlock_trace();
}

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;
}

void uprobe_handle_trampoline(struct pt_regs *regs)
{
        struct uprobe_task *utask;
        struct return_instance *ri, *ri_next, *next_chain;
        struct uprobe *uprobe;
        enum hprobe_state hstate;
        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_chain = find_next_ret_chain(ri);
                valid = !next_chain || arch_uretprobe_is_alive(next_chain, RP_CHECK_RET, regs);

                instruction_pointer_set(regs, ri->orig_ret_vaddr);
                do {
                        /* pop current instance from the stack of pending return instances,
                         * as it's not pending anymore: we just fixed up original
                         * instruction pointer in regs and are about to call handlers;
                         * this allows fixup_uretprobe_trampoline_entries() to properly fix up
                         * captured stack traces from uretprobe handlers, in which pending
                         * trampoline addresses on the stack are replaced with correct
                         * original return addresses
                         */
                        ri_next = ri->next;
                        rcu_assign_pointer(utask->return_instances, ri_next);
                        utask->depth--;

                        uprobe = hprobe_consume(&ri->hprobe, &hstate);
                        if (valid)
                                handle_uretprobe_chain(ri, uprobe, regs);
                        hprobe_finalize(&ri->hprobe, hstate);

                        /* We already took care of hprobe, no need to waste more time on that. */
                        free_ret_instance(utask, ri, false /* !cleanup_hprobe */);
                        ri = ri_next;
                } while (ri != next_chain);
        } while (!valid);

        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;
}

void __weak arch_uprobe_optimize(struct arch_uprobe *auprobe, unsigned long vaddr)
{
}

/*
 * 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 is_swbp;

        bp_vaddr = uprobe_get_swbp_addr(regs);
        if (bp_vaddr == uprobe_get_trampoline_vaddr())
                return uprobe_handle_trampoline(regs);

        rcu_read_lock_trace();

        uprobe = find_active_uprobe_rcu(bp_vaddr, &is_swbp);
        if (!uprobe) {
                if (is_swbp > 0) {
                        /* No matching uprobe; signal SIGTRAP. */
                        force_sig(SIGTRAP);
                } 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);
                }
                goto out;
        }

        /* 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);

        /* Try to optimize after first hit. */
        arch_uprobe_optimize(&uprobe->arch, bp_vaddr);

        /*
         * If user decided to take execution elsewhere, it makes little sense
         * to execute the original instruction, so let's skip it.
         */
        if (instruction_pointer(regs) != bp_vaddr)
                goto out;

        if (arch_uprobe_skip_sstep(&uprobe->arch, regs))
                goto out;

        if (pre_ssout(uprobe, regs, bp_vaddr))
                goto out;

out:
        /* arch_uprobe_skip_sstep() succeeded, or restart if can't singlestep */
        rcu_read_unlock_trace();
}

void handle_syscall_uprobe(struct pt_regs *regs, unsigned long bp_vaddr)
{
        struct uprobe *uprobe;
        int is_swbp;

        guard(rcu_tasks_trace)();

        uprobe = find_active_uprobe_rcu(bp_vaddr, &is_swbp);
        if (!uprobe)
                return;
        if (!get_utask())
                return;
        if (arch_uprobe_ignore(&uprobe->arch, regs))
                return;
        handler_chain(uprobe, regs);
}

/*
 * 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(utask);

        if (utask->signal_denied) {
                set_thread_flag(TIF_SIGPENDING);
                utask->signal_denied = false;
        }

        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 (!mm_flags_test(MMF_HAS_UPROBES, current->mm) &&
            (!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));
}