// SPDX-License-Identifier: GPL-2.0
/*
 * Performance events callchain code, extracted from core.c:
 *
 *  Copyright (C) 2008 Linutronix GmbH, Thomas Gleixner <tglx@kernel.org>
 *  Copyright (C) 2008-2011 Red Hat, Inc., Ingo Molnar
 *  Copyright (C) 2008-2011 Red Hat, Inc., Peter Zijlstra
 *  Copyright  ©  2009 Paul Mackerras, IBM Corp. <paulus@au1.ibm.com>
 */

#include <linux/perf_event.h>
#include <linux/slab.h>
#include <linux/sched/task_stack.h>
#include <linux/uprobes.h>

#include "internal.h"

struct callchain_cpus_entries {
        struct rcu_head                 rcu_head;
        struct perf_callchain_entry     *cpu_entries[];
};

int sysctl_perf_event_max_stack __read_mostly = PERF_MAX_STACK_DEPTH;
int sysctl_perf_event_max_contexts_per_stack __read_mostly = PERF_MAX_CONTEXTS_PER_STACK;
static const int six_hundred_forty_kb = 640 * 1024;

static inline size_t perf_callchain_entry__sizeof(void)
{
        return (sizeof(struct perf_callchain_entry) +
                sizeof(__u64) * (sysctl_perf_event_max_stack +
                                 sysctl_perf_event_max_contexts_per_stack));
}

static DEFINE_PER_CPU(u8, callchain_recursion[PERF_NR_CONTEXTS]);
static atomic_t nr_callchain_events;
static DEFINE_MUTEX(callchain_mutex);
static struct callchain_cpus_entries *callchain_cpus_entries;


__weak void perf_callchain_kernel(struct perf_callchain_entry_ctx *entry,
                                  struct pt_regs *regs)
{
}

__weak void perf_callchain_user(struct perf_callchain_entry_ctx *entry,
                                struct pt_regs *regs)
{
}

static void release_callchain_buffers_rcu(struct rcu_head *head)
{
        struct callchain_cpus_entries *entries;
        int cpu;

        entries = container_of(head, struct callchain_cpus_entries, rcu_head);

        for_each_possible_cpu(cpu)
                kfree(entries->cpu_entries[cpu]);

        kfree(entries);
}

static void release_callchain_buffers(void)
{
        struct callchain_cpus_entries *entries;

        entries = callchain_cpus_entries;
        RCU_INIT_POINTER(callchain_cpus_entries, NULL);
        call_rcu(&entries->rcu_head, release_callchain_buffers_rcu);
}

static int alloc_callchain_buffers(void)
{
        int cpu;
        int size;
        struct callchain_cpus_entries *entries;

        /*
         * We can't use the percpu allocation API for data that can be
         * accessed from NMI. Use a temporary manual per cpu allocation
         * until that gets sorted out.
         */
        size = offsetof(struct callchain_cpus_entries, cpu_entries[nr_cpu_ids]);

        entries = kzalloc(size, GFP_KERNEL);
        if (!entries)
                return -ENOMEM;

        size = perf_callchain_entry__sizeof() * PERF_NR_CONTEXTS;

        for_each_possible_cpu(cpu) {
                entries->cpu_entries[cpu] = kmalloc_node(size, GFP_KERNEL,
                                                         cpu_to_node(cpu));
                if (!entries->cpu_entries[cpu])
                        goto fail;
        }

        rcu_assign_pointer(callchain_cpus_entries, entries);

        return 0;

fail:
        for_each_possible_cpu(cpu)
                kfree(entries->cpu_entries[cpu]);
        kfree(entries);

        return -ENOMEM;
}

int get_callchain_buffers(int event_max_stack)
{
        int err = 0;
        int count;

        mutex_lock(&callchain_mutex);

        count = atomic_inc_return(&nr_callchain_events);
        if (WARN_ON_ONCE(count < 1)) {
                err = -EINVAL;
                goto exit;
        }

        /*
         * If requesting per event more than the global cap,
         * return a different error to help userspace figure
         * this out.
         *
         * And also do it here so that we have &callchain_mutex held.
         */
        if (event_max_stack > sysctl_perf_event_max_stack) {
                err = -EOVERFLOW;
                goto exit;
        }

        if (count == 1)
                err = alloc_callchain_buffers();
exit:
        if (err)
                atomic_dec(&nr_callchain_events);

        mutex_unlock(&callchain_mutex);

        return err;
}

void put_callchain_buffers(void)
{
        if (atomic_dec_and_mutex_lock(&nr_callchain_events, &callchain_mutex)) {
                release_callchain_buffers();
                mutex_unlock(&callchain_mutex);
        }
}

struct perf_callchain_entry *get_callchain_entry(int *rctx)
{
        int cpu;
        struct callchain_cpus_entries *entries;

        *rctx = get_recursion_context(this_cpu_ptr(callchain_recursion));
        if (*rctx == -1)
                return NULL;

        entries = rcu_dereference(callchain_cpus_entries);
        if (!entries) {
                put_recursion_context(this_cpu_ptr(callchain_recursion), *rctx);
                return NULL;
        }

        cpu = smp_processor_id();

        return (((void *)entries->cpu_entries[cpu]) +
                (*rctx * perf_callchain_entry__sizeof()));
}

void
put_callchain_entry(int rctx)
{
        put_recursion_context(this_cpu_ptr(callchain_recursion), rctx);
}

static void fixup_uretprobe_trampoline_entries(struct perf_callchain_entry *entry,
                                               int start_entry_idx)
{
#ifdef CONFIG_UPROBES
        struct uprobe_task *utask = current->utask;
        struct return_instance *ri;
        __u64 *cur_ip, *last_ip, tramp_addr;

        if (likely(!utask || !utask->return_instances))
                return;

        cur_ip = &entry->ip[start_entry_idx];
        last_ip = &entry->ip[entry->nr - 1];
        ri = utask->return_instances;
        tramp_addr = uprobe_get_trampoline_vaddr();

        /*
         * If there are pending uretprobes for the current thread, they are
         * recorded in a list inside utask->return_instances; each such
         * pending uretprobe replaces traced user function's return address on
         * the stack, so when stack trace is captured, instead of seeing
         * actual function's return address, we'll have one or many uretprobe
         * trampoline addresses in the stack trace, which are not helpful and
         * misleading to users.
         * So here we go over the pending list of uretprobes, and each
         * encountered trampoline address is replaced with actual return
         * address.
         */
        while (ri && cur_ip <= last_ip) {
                if (*cur_ip == tramp_addr) {
                        *cur_ip = ri->orig_ret_vaddr;
                        ri = ri->next;
                }
                cur_ip++;
        }
#endif
}

struct perf_callchain_entry *
get_perf_callchain(struct pt_regs *regs, bool kernel, bool user,
                   u32 max_stack, bool crosstask, bool add_mark, u64 defer_cookie)
{
        struct perf_callchain_entry *entry;
        struct perf_callchain_entry_ctx ctx;
        int rctx, start_entry_idx;

        /* crosstask is not supported for user stacks */
        if (crosstask && user && !kernel)
                return NULL;

        entry = get_callchain_entry(&rctx);
        if (!entry)
                return NULL;

        ctx.entry               = entry;
        ctx.max_stack           = max_stack;
        ctx.nr                  = entry->nr = 0;
        ctx.contexts            = 0;
        ctx.contexts_maxed      = false;

        if (kernel && !user_mode(regs)) {
                if (add_mark)
                        perf_callchain_store_context(&ctx, PERF_CONTEXT_KERNEL);
                perf_callchain_kernel(&ctx, regs);
        }

        if (user && !crosstask) {
                if (!user_mode(regs)) {
                        if (!is_user_task(current))
                                goto exit_put;
                        regs = task_pt_regs(current);
                }

                if (defer_cookie) {
                        /*
                         * Foretell the coming of PERF_RECORD_CALLCHAIN_DEFERRED
                         * which can be stitched to this one, and add
                         * the cookie after it (it will be cut off when the
                         * user stack is copied to the callchain).
                         */
                        perf_callchain_store_context(&ctx, PERF_CONTEXT_USER_DEFERRED);
                        perf_callchain_store_context(&ctx, defer_cookie);
                        goto exit_put;
                }

                if (add_mark)
                        perf_callchain_store_context(&ctx, PERF_CONTEXT_USER);

                start_entry_idx = entry->nr;
                perf_callchain_user(&ctx, regs);
                fixup_uretprobe_trampoline_entries(entry, start_entry_idx);
        }

exit_put:
        put_callchain_entry(rctx);

        return entry;
}

static int perf_event_max_stack_handler(const struct ctl_table *table, int write,
                                        void *buffer, size_t *lenp, loff_t *ppos)
{
        int *value = table->data;
        int new_value = *value, ret;
        struct ctl_table new_table = *table;

        new_table.data = &new_value;
        ret = proc_dointvec_minmax(&new_table, write, buffer, lenp, ppos);
        if (ret || !write)
                return ret;

        mutex_lock(&callchain_mutex);
        if (atomic_read(&nr_callchain_events))
                ret = -EBUSY;
        else
                *value = new_value;

        mutex_unlock(&callchain_mutex);

        return ret;
}

static const struct ctl_table callchain_sysctl_table[] = {
        {
                .procname       = "perf_event_max_stack",
                .data           = &sysctl_perf_event_max_stack,
                .maxlen         = sizeof(sysctl_perf_event_max_stack),
                .mode           = 0644,
                .proc_handler   = perf_event_max_stack_handler,
                .extra1         = SYSCTL_ZERO,
                .extra2         = (void *)&six_hundred_forty_kb,
        },
        {
                .procname       = "perf_event_max_contexts_per_stack",
                .data           = &sysctl_perf_event_max_contexts_per_stack,
                .maxlen         = sizeof(sysctl_perf_event_max_contexts_per_stack),
                .mode           = 0644,
                .proc_handler   = perf_event_max_stack_handler,
                .extra1         = SYSCTL_ZERO,
                .extra2         = SYSCTL_ONE_THOUSAND,
        },
};

static int __init init_callchain_sysctls(void)
{
        register_sysctl_init("kernel", callchain_sysctl_table);
        return 0;
}
core_initcall(init_callchain_sysctls);