callchain.c

// SPDX-License-Identifier: GPL-2.0
/*
 * Performance events callchain code, extracted from core.c:
 *
 *  Copyright (C) 2008 Thomas Gleixner <[email protected]>
 *  Copyright (C) 2008-2011 Red Hat, Inc., Ingo Molnar
 *  Copyright (C) 2008-2011 Red Hat, Inc., Peter Zijlstra
 *  Copyright  ©  2009 Paul Mackerras, IBM Corp. <[email protected]>
 */

#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)
{
	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 (current->flags & (PF_KTHREAD | PF_USER_WORKER))
				goto exit_put;
			regs = task_pt_regs(current);
		}

		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);