hw_breakpoint.c

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/*
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
 *
 * Copyright (C) 2007 Alan Stern
 * Copyright (C) IBM Corporation, 2009
 * Copyright (C) 2009, Frederic Weisbecker <[email protected]>
 *
 * Thanks to Ingo Molnar for his many suggestions.
 *
 * Authors: Alan Stern <[email protected]>
 *          K.Prasad <[email protected]>
 *          Frederic Weisbecker <[email protected]>
 */

/*
 * HW_breakpoint: a unified kernel/user-space hardware breakpoint facility,
 * using the CPU's debug registers.
 * This file contains the arch-independent routines.
 */

#include <linux/irqflags.h>
#include <linux/kallsyms.h>
#include <linux/notifier.h>
#include <linux/kprobes.h>
#include <linux/kdebug.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/percpu.h>
#include <linux/sched.h>
#include <linux/init.h>
#include <linux/slab.h>
#include <linux/list.h>
#include <linux/cpu.h>
#include <linux/smp.h>

#include <linux/hw_breakpoint.h>


/*
 * Constraints data
 */

/* Number of pinned cpu breakpoints in a cpu */
static DEFINE_PER_CPU(unsigned int, nr_cpu_bp_pinned[TYPE_MAX]);

/* Number of pinned task breakpoints in a cpu */
static DEFINE_PER_CPU(unsigned int *, nr_task_bp_pinned[TYPE_MAX]);

/* Number of non-pinned cpu/task breakpoints in a cpu */
static DEFINE_PER_CPU(unsigned int, nr_bp_flexible[TYPE_MAX]);

static int nr_slots[TYPE_MAX];

/* Keep track of the breakpoints attached to tasks */
static LIST_HEAD(bp_task_head);

static int constraints_initialized;

/* Gather the number of total pinned and un-pinned bp in a cpuset */
struct bp_busy_slots {
    unsigned int pinned;
    unsigned int flexible;
};

/* Serialize accesses to the above constraints */
static DEFINE_MUTEX(nr_bp_mutex);

__weak int hw_breakpoint_weight(struct perf_event *bp)
{
    return 1;
}

static inline enum bp_type_idx find_slot_idx(struct perf_event *bp)
{
    if (bp->attr.bp_type & HW_BREAKPOINT_RW)
        return TYPE_DATA;

    return TYPE_INST;
}

/*
 * Report the maximum number of pinned breakpoints a task
 * have in this cpu
 */
static unsigned int max_task_bp_pinned(int cpu, enum bp_type_idx type)
{
    int i;
    unsigned int *tsk_pinned = per_cpu(nr_task_bp_pinned[type], cpu);

    for (i = nr_slots[type] - 1; i >= 0; i--) {
        if (tsk_pinned[i] > 0)
            return i + 1;
    }

    return 0;
}

/*
 * Count the number of breakpoints of the same type and same task.
 * The given event must be not on the list.
 */
static int task_bp_pinned(int cpu, struct perf_event *bp, enum bp_type_idx type)
{
    struct task_struct *tsk = bp->hw.bp_target;
    struct perf_event *iter;
    int count = 0;

    list_for_each_entry(iter, &bp_task_head, hw.bp_list) {
        if (iter->hw.bp_target == tsk &&
            find_slot_idx(iter) == type &&
            cpu == iter->cpu)
            count += hw_breakpoint_weight(iter);
    }

    return count;
}

/*
 * Report the number of pinned/un-pinned breakpoints we have in
 * a given cpu (cpu > -1) or in all of them (cpu = -1).
 */
static void
fetch_bp_busy_slots(struct bp_busy_slots *slots, struct perf_event *bp,
            enum bp_type_idx type)
{
    int cpu = bp->cpu;
    struct task_struct *tsk = bp->hw.bp_target;

    if (cpu >= 0) {
        slots->pinned = per_cpu(nr_cpu_bp_pinned[type], cpu);
        if (!tsk)
            slots->pinned += max_task_bp_pinned(cpu, type);
        else
            slots->pinned += task_bp_pinned(cpu, bp, type);
        slots->flexible = per_cpu(nr_bp_flexible[type], cpu);

        return;
    }

    for_each_online_cpu(cpu) {
        unsigned int nr;

        nr = per_cpu(nr_cpu_bp_pinned[type], cpu);
        if (!tsk)
            nr += max_task_bp_pinned(cpu, type);
        else
            nr += task_bp_pinned(cpu, bp, type);

        if (nr > slots->pinned)
            slots->pinned = nr;

        nr = per_cpu(nr_bp_flexible[type], cpu);

        if (nr > slots->flexible)
            slots->flexible = nr;
    }
}

/*
 * For now, continue to consider flexible as pinned, until we can
 * ensure no flexible event can ever be scheduled before a pinned event
 * in a same cpu.
 */
static void
fetch_this_slot(struct bp_busy_slots *slots, int weight)
{
    slots->pinned += weight;
}

/*
 * Add a pinned breakpoint for the given task in our constraint table
 */
static void toggle_bp_task_slot(struct perf_event *bp, int cpu, bool enable,
                enum bp_type_idx type, int weight)
{
    unsigned int *tsk_pinned;
    int old_count = 0;
    int old_idx = 0;
    int idx = 0;

    old_count = task_bp_pinned(cpu, bp, type);
    old_idx = old_count - 1;
    idx = old_idx + weight;

    /* tsk_pinned[n] is the number of tasks having n breakpoints */
    tsk_pinned = per_cpu(nr_task_bp_pinned[type], cpu);
    if (enable) {
        tsk_pinned[idx]++;
        if (old_count > 0)
            tsk_pinned[old_idx]--;
    } else {
        tsk_pinned[idx]--;
        if (old_count > 0)
            tsk_pinned[old_idx]++;
    }
}

/*
 * Add/remove the given breakpoint in our constraint table
 */
static void
toggle_bp_slot(struct perf_event *bp, bool enable, enum bp_type_idx type,
           int weight)
{
    int cpu = bp->cpu;
    struct task_struct *tsk = bp->hw.bp_target;

    /* Pinned counter cpu profiling */
    if (!tsk) {

        if (enable)
            per_cpu(nr_cpu_bp_pinned[type], bp->cpu) += weight;
        else
            per_cpu(nr_cpu_bp_pinned[type], bp->cpu) -= weight;
        return;
    }

    /* Pinned counter task profiling */

    if (!enable)
        list_del(&bp->hw.bp_list);

    if (cpu >= 0) {
        toggle_bp_task_slot(bp, cpu, enable, type, weight);
    } else {
        for_each_online_cpu(cpu)
            toggle_bp_task_slot(bp, cpu, enable, type, weight);
    }

    if (enable)
        list_add_tail(&bp->hw.bp_list, &bp_task_head);
}

/*
 * Function to perform processor-specific cleanup during unregistration
 */
__weak void arch_unregister_hw_breakpoint(struct perf_event *bp)
{
    /*
     * A weak stub function here for those archs that don't define
     * it inside arch/.../kernel/hw_breakpoint.c
     */
}

/*
 * Contraints to check before allowing this new breakpoint counter:
 *
 *  == Non-pinned counter == (Considered as pinned for now)
 *
 *   - If attached to a single cpu, check:
 *
 *       (per_cpu(nr_bp_flexible, cpu) || (per_cpu(nr_cpu_bp_pinned, cpu)
 *           + max(per_cpu(nr_task_bp_pinned, cpu)))) < HBP_NUM
 *
 *       -> If there are already non-pinned counters in this cpu, it means
 *          there is already a free slot for them.
 *          Otherwise, we check that the maximum number of per task
 *          breakpoints (for this cpu) plus the number of per cpu breakpoint
 *          (for this cpu) doesn't cover every registers.
 *
 *   - If attached to every cpus, check:
 *
 *       (per_cpu(nr_bp_flexible, *) || (max(per_cpu(nr_cpu_bp_pinned, *))
 *           + max(per_cpu(nr_task_bp_pinned, *)))) < HBP_NUM
 *
 *       -> This is roughly the same, except we check the number of per cpu
 *          bp for every cpu and we keep the max one. Same for the per tasks
 *          breakpoints.
 *
 *
 * == Pinned counter ==
 *
 *   - If attached to a single cpu, check:
 *
 *       ((per_cpu(nr_bp_flexible, cpu) > 1) + per_cpu(nr_cpu_bp_pinned, cpu)
 *            + max(per_cpu(nr_task_bp_pinned, cpu))) < HBP_NUM
 *
 *       -> Same checks as before. But now the nr_bp_flexible, if any, must keep
 *          one register at least (or they will never be fed).
 *
 *   - If attached to every cpus, check:
 *
 *       ((per_cpu(nr_bp_flexible, *) > 1) + max(per_cpu(nr_cpu_bp_pinned, *))
 *            + max(per_cpu(nr_task_bp_pinned, *))) < HBP_NUM
 */
static int __reserve_bp_slot(struct perf_event *bp)
{
    struct bp_busy_slots slots = {0};
    enum bp_type_idx type;
    int weight;

    /* We couldn't initialize breakpoint constraints on boot */
    if (!constraints_initialized)
        return -ENOMEM;

    /* Basic checks */
    if (bp->attr.bp_type == HW_BREAKPOINT_EMPTY ||
        bp->attr.bp_type == HW_BREAKPOINT_INVALID)
        return -EINVAL;

    type = find_slot_idx(bp);
    weight = hw_breakpoint_weight(bp);

    fetch_bp_busy_slots(&slots, bp, type);
    /*
     * Simulate the addition of this breakpoint to the constraints
     * and see the result.
     */
    fetch_this_slot(&slots, weight);

    /* Flexible counters need to keep at least one slot */
    if (slots.pinned + (!!slots.flexible) > nr_slots[type])
        return -ENOSPC;

    toggle_bp_slot(bp, true, type, weight);

    return 0;
}

int reserve_bp_slot(struct perf_event *bp)
{
    int ret;

    mutex_lock(&nr_bp_mutex);

    ret = __reserve_bp_slot(bp);

    mutex_unlock(&nr_bp_mutex);

    return ret;
}

static void __release_bp_slot(struct perf_event *bp)
{
    enum bp_type_idx type;
    int weight;

    type = find_slot_idx(bp);
    weight = hw_breakpoint_weight(bp);
    toggle_bp_slot(bp, false, type, weight);
}

void release_bp_slot(struct perf_event *bp)
{
    mutex_lock(&nr_bp_mutex);

    arch_unregister_hw_breakpoint(bp);
    __release_bp_slot(bp);

    mutex_unlock(&nr_bp_mutex);
}

/*
 * Allow the kernel debugger to reserve breakpoint slots without
 * taking a lock using the dbg_* variant of for the reserve and
 * release breakpoint slots.
 */
int dbg_reserve_bp_slot(struct perf_event *bp)
{
    if (mutex_is_locked(&nr_bp_mutex))
        return -1;

    return __reserve_bp_slot(bp);
}

int dbg_release_bp_slot(struct perf_event *bp)
{
    if (mutex_is_locked(&nr_bp_mutex))
        return -1;

    __release_bp_slot(bp);

    return 0;
}

static int validate_hw_breakpoint(struct perf_event *bp)
{
    int ret;

    ret = arch_validate_hwbkpt_settings(bp);
    if (ret)
        return ret;

    if (arch_check_bp_in_kernelspace(bp)) {
        if (bp->attr.exclude_kernel)
            return -EINVAL;
        /*
         * Don't let unprivileged users set a breakpoint in the trap
         * path to avoid trap recursion attacks.
         */
        if (!capable(CAP_SYS_ADMIN))
            return -EPERM;
    }

    return 0;
}

int register_perf_hw_breakpoint(struct perf_event *bp)
{
    int ret;

    ret = reserve_bp_slot(bp);
    if (ret)
        return ret;

    ret = validate_hw_breakpoint(bp);

    /* if arch_validate_hwbkpt_settings() fails then release bp slot */
    if (ret)
        release_bp_slot(bp);

    return ret;
}

struct perf_event *
register_user_hw_breakpoint(struct perf_event_attr *attr,
                perf_overflow_handler_t triggered,
                void *context,
                struct task_struct *tsk)
{
    return perf_event_create_kernel_counter(attr, -1, tsk, triggered,
                        context);
}
EXPORT_SYMBOL_GPL(register_user_hw_breakpoint);

int modify_user_hw_breakpoint(struct perf_event *bp, struct perf_event_attr *attr)
{
    u64 old_addr = bp->attr.bp_addr;
    u64 old_len = bp->attr.bp_len;
    int old_type = bp->attr.bp_type;
    int err = 0;

    /*
     * modify_user_hw_breakpoint can be invoked with IRQs disabled and hence it
     * will not be possible to raise IPIs that invoke __perf_event_disable.
     * So call the function directly after making sure we are targeting the
     * current task.
     */
    if (irqs_disabled() && bp->ctx && bp->ctx->task == current)
        __perf_event_disable(bp);
    else
        perf_event_disable(bp);

    bp->attr.bp_addr = attr->bp_addr;
    bp->attr.bp_type = attr->bp_type;
    bp->attr.bp_len = attr->bp_len;

    if (attr->disabled)
        goto end;

    err = validate_hw_breakpoint(bp);
    if (!err)
        perf_event_enable(bp);

    if (err) {
        bp->attr.bp_addr = old_addr;
        bp->attr.bp_type = old_type;
        bp->attr.bp_len = old_len;
        if (!bp->attr.disabled)
            perf_event_enable(bp);

        return err;
    }

end:
    bp->attr.disabled = attr->disabled;

    return 0;
}
EXPORT_SYMBOL_GPL(modify_user_hw_breakpoint);

void unregister_hw_breakpoint(struct perf_event *bp)
{
    if (!bp)
        return;
    perf_event_release_kernel(bp);
}
EXPORT_SYMBOL_GPL(unregister_hw_breakpoint);

struct perf_event * __percpu *
register_wide_hw_breakpoint(struct perf_event_attr *attr,
                perf_overflow_handler_t triggered,
                void *context)
{
    struct perf_event * __percpu *cpu_events, **pevent, *bp;
    long err;
    int cpu;

    cpu_events = alloc_percpu(typeof(*cpu_events));
    if (!cpu_events)
        return (void __percpu __force *)ERR_PTR(-ENOMEM);

    get_online_cpus();
    for_each_online_cpu(cpu) {
        pevent = per_cpu_ptr(cpu_events, cpu);
        bp = perf_event_create_kernel_counter(attr, cpu, NULL,
                              triggered, context);

        *pevent = bp;

        if (IS_ERR(bp)) {
            err = PTR_ERR(bp);
            goto fail;
        }
    }
    put_online_cpus();

    return cpu_events;

fail:
    for_each_online_cpu(cpu) {
        pevent = per_cpu_ptr(cpu_events, cpu);
        if (IS_ERR(*pevent))
            break;
        unregister_hw_breakpoint(*pevent);
    }
    put_online_cpus();

    free_percpu(cpu_events);
    return (void __percpu __force *)ERR_PTR(err);
}
EXPORT_SYMBOL_GPL(register_wide_hw_breakpoint);

void unregister_wide_hw_breakpoint(struct perf_event * __percpu *cpu_events)
{
    int cpu;
    struct perf_event **pevent;

    for_each_possible_cpu(cpu) {
        pevent = per_cpu_ptr(cpu_events, cpu);
        unregister_hw_breakpoint(*pevent);
    }
    free_percpu(cpu_events);
}
EXPORT_SYMBOL_GPL(unregister_wide_hw_breakpoint);

static struct notifier_block hw_breakpoint_exceptions_nb = {
    .notifier_call = hw_breakpoint_exceptions_notify,
    /* we need to be notified first */
    .priority = 0x7fffffff
};

static void bp_perf_event_destroy(struct perf_event *event)
{
    release_bp_slot(event);
}

static int hw_breakpoint_event_init(struct perf_event *bp)
{
    int err;

    if (bp->attr.type != PERF_TYPE_BREAKPOINT)
        return -ENOENT;

    /*
     * no branch sampling for breakpoint events
     */
    if (has_branch_stack(bp))
        return -EOPNOTSUPP;

    err = register_perf_hw_breakpoint(bp);
    if (err)
        return err;

    bp->destroy = bp_perf_event_destroy;

    return 0;
}

static int hw_breakpoint_add(struct perf_event *bp, int flags)
{
    if (!(flags & PERF_EF_START))
        bp->hw.state = PERF_HES_STOPPED;

    return arch_install_hw_breakpoint(bp);
}

static void hw_breakpoint_del(struct perf_event *bp, int flags)
{
    arch_uninstall_hw_breakpoint(bp);
}

static void hw_breakpoint_start(struct perf_event *bp, int flags)
{
    bp->hw.state = 0;
}

static void hw_breakpoint_stop(struct perf_event *bp, int flags)
{
    bp->hw.state = PERF_HES_STOPPED;
}

static int hw_breakpoint_event_idx(struct perf_event *bp)
{
    return 0;
}

static struct pmu perf_breakpoint = {
    .task_ctx_nr    = perf_sw_context, /* could eventually get its own */

    .event_init = hw_breakpoint_event_init,
    .add        = hw_breakpoint_add,
    .del        = hw_breakpoint_del,
    .start      = hw_breakpoint_start,
    .stop       = hw_breakpoint_stop,
    .read       = hw_breakpoint_pmu_read,

    .event_idx  = hw_breakpoint_event_idx,
};

int __init init_hw_breakpoint(void)
{
    unsigned int **task_bp_pinned;
    int cpu, err_cpu;
    int i;

    for (i = 0; i < TYPE_MAX; i++)
        nr_slots[i] = hw_breakpoint_slots(i);

    for_each_possible_cpu(cpu) {
        for (i = 0; i < TYPE_MAX; i++) {
            task_bp_pinned = &per_cpu(nr_task_bp_pinned[i], cpu);
            *task_bp_pinned = kzalloc(sizeof(int) * nr_slots[i],
                          GFP_KERNEL);
            if (!*task_bp_pinned)
                goto err_alloc;
        }
    }

    constraints_initialized = 1;

    perf_pmu_register(&perf_breakpoint, "breakpoint", PERF_TYPE_BREAKPOINT);

    return register_die_notifier(&hw_breakpoint_exceptions_nb);

 err_alloc:
    for_each_possible_cpu(err_cpu) {
        for (i = 0; i < TYPE_MAX; i++)
            kfree(per_cpu(nr_task_bp_pinned[i], cpu));
        if (err_cpu == cpu)
            break;
    }

    return -ENOMEM;
}