trace_events_user.c

// SPDX-License-Identifier: GPL-2.0-only
/*
 * Copyright (c) 2021, Microsoft Corporation.
 *
 * Authors:
 *   Beau Belgrave <beaub@linux.microsoft.com>
 */

#include <linux/bitmap.h>
#include <linux/cdev.h>
#include <linux/hashtable.h>
#include <linux/list.h>
#include <linux/io.h>
#include <linux/uio.h>
#include <linux/ioctl.h>
#include <linux/jhash.h>
#include <linux/trace_events.h>
#include <linux/tracefs.h>
#include <linux/types.h>
#include <linux/uaccess.h>
#include <uapi/linux/user_events.h>
#include "trace.h"
#include "trace_dynevent.h"

#define USER_EVENTS_PREFIX_LEN (sizeof(USER_EVENTS_PREFIX)-1)

#define FIELD_DEPTH_TYPE 0
#define FIELD_DEPTH_NAME 1
#define FIELD_DEPTH_SIZE 2

/*
 * Limits how many trace_event calls user processes can create:
 * Must be multiple of PAGE_SIZE.
 */
#define MAX_PAGES 1
#define MAX_EVENTS (MAX_PAGES * PAGE_SIZE)

/* Limit how long of an event name plus args within the subsystem. */
#define MAX_EVENT_DESC 512
#define EVENT_NAME(user_event) ((user_event)->tracepoint.name)
#define MAX_FIELD_ARRAY_SIZE 1024

static char *register_page_data;

static DEFINE_MUTEX(reg_mutex);
static DEFINE_HASHTABLE(register_table, 4);
static DECLARE_BITMAP(page_bitmap, MAX_EVENTS);

/*
 * Stores per-event properties, as users register events
 * within a file a user_event might be created if it does not
 * already exist. These are globally used and their lifetime
 * is tied to the refcnt member. These cannot go away until the
 * refcnt reaches zero.
 */
struct user_event {
	struct tracepoint tracepoint;
	struct trace_event_call call;
	struct trace_event_class class;
	struct dyn_event devent;
	struct hlist_node node;
	struct list_head fields;
	atomic_t refcnt;
	int index;
	int flags;
};

/*
 * Stores per-file events references, as users register events
 * within a file this structure is modified and freed via RCU.
 * The lifetime of this struct is tied to the lifetime of the file.
 * These are not shared and only accessible by the file that created it.
 */
struct user_event_refs {
	struct rcu_head rcu;
	int count;
	struct user_event *events[];
};

typedef void (*user_event_func_t) (struct user_event *user,
				   void *data, u32 datalen,
				   void *tpdata);

static int user_event_parse(char *name, char *args, char *flags,
			    struct user_event **newuser);

static u32 user_event_key(char *name)
{
	return jhash(name, strlen(name), 0);
}

static struct list_head *user_event_get_fields(struct trace_event_call *call)
{
	struct user_event *user = (struct user_event *)call->data;

	return &user->fields;
}

/*
 * Parses a register command for user_events
 * Format: event_name[:FLAG1[,FLAG2...]] [field1[;field2...]]
 *
 * Example event named 'test' with a 20 char 'msg' field with an unsigned int
 * 'id' field after:
 * test char[20] msg;unsigned int id
 *
 * NOTE: Offsets are from the user data perspective, they are not from the
 * trace_entry/buffer perspective. We automatically add the common properties
 * sizes to the offset for the user.
 */
static int user_event_parse_cmd(char *raw_command, struct user_event **newuser)
{
	char *name = raw_command;
	char *args = strpbrk(name, " ");
	char *flags;

	if (args)
		*args++ = '\0';

	flags = strpbrk(name, ":");

	if (flags)
		*flags++ = '\0';

	return user_event_parse(name, args, flags, newuser);
}

static int user_field_array_size(const char *type)
{
	const char *start = strchr(type, '[');
	char val[8];
	char *bracket;
	int size = 0;

	if (start == NULL)
		return -EINVAL;

	if (strscpy(val, start + 1, sizeof(val)) <= 0)
		return -EINVAL;

	bracket = strchr(val, ']');

	if (!bracket)
		return -EINVAL;

	*bracket = '\0';

	if (kstrtouint(val, 0, &size))
		return -EINVAL;

	if (size > MAX_FIELD_ARRAY_SIZE)
		return -EINVAL;

	return size;
}

static int user_field_size(const char *type)
{
	/* long is not allowed from a user, since it's ambigious in size */
	if (strcmp(type, "s64") == 0)
		return sizeof(s64);
	if (strcmp(type, "u64") == 0)
		return sizeof(u64);
	if (strcmp(type, "s32") == 0)
		return sizeof(s32);
	if (strcmp(type, "u32") == 0)
		return sizeof(u32);
	if (strcmp(type, "int") == 0)
		return sizeof(int);
	if (strcmp(type, "unsigned int") == 0)
		return sizeof(unsigned int);
	if (strcmp(type, "s16") == 0)
		return sizeof(s16);
	if (strcmp(type, "u16") == 0)
		return sizeof(u16);
	if (strcmp(type, "short") == 0)
		return sizeof(short);
	if (strcmp(type, "unsigned short") == 0)
		return sizeof(unsigned short);
	if (strcmp(type, "s8") == 0)
		return sizeof(s8);
	if (strcmp(type, "u8") == 0)
		return sizeof(u8);
	if (strcmp(type, "char") == 0)
		return sizeof(char);
	if (strcmp(type, "unsigned char") == 0)
		return sizeof(unsigned char);
	if (str_has_prefix(type, "char["))
		return user_field_array_size(type);
	if (str_has_prefix(type, "unsigned char["))
		return user_field_array_size(type);
	if (str_has_prefix(type, "__data_loc "))
		return sizeof(u32);
	if (str_has_prefix(type, "__rel_loc "))
		return sizeof(u32);

	/* Uknown basic type, error */
	return -EINVAL;
}

static void user_event_destroy_fields(struct user_event *user)
{
	struct ftrace_event_field *field, *next;
	struct list_head *head = &user->fields;

	list_for_each_entry_safe(field, next, head, link) {
		list_del(&field->link);
		kfree(field);
	}
}

static int user_event_add_field(struct user_event *user, const char *type,
				const char *name, int offset, int size,
				int is_signed, int filter_type)
{
	struct ftrace_event_field *field;

	field = kmalloc(sizeof(*field), GFP_KERNEL);

	if (!field)
		return -ENOMEM;

	field->type = type;
	field->name = name;
	field->offset = offset;
	field->size = size;
	field->is_signed = is_signed;
	field->filter_type = filter_type;

	list_add(&field->link, &user->fields);

	return 0;
}

/*
 * Parses the values of a field within the description
 * Format: type name [size]
 */
static int user_event_parse_field(char *field, struct user_event *user,
				  u32 *offset)
{
	char *part, *type, *name;
	u32 depth = 0, saved_offset = *offset;
	int len, size = -EINVAL;
	bool is_struct = false;

	field = skip_spaces(field);

	if (*field == '\0')
		return 0;

	/* Handle types that have a space within */
	len = str_has_prefix(field, "unsigned ");
	if (len)
		goto skip_next;

	len = str_has_prefix(field, "struct ");
	if (len) {
		is_struct = true;
		goto skip_next;
	}

	len = str_has_prefix(field, "__data_loc unsigned ");
	if (len)
		goto skip_next;

	len = str_has_prefix(field, "__data_loc ");
	if (len)
		goto skip_next;

	len = str_has_prefix(field, "__rel_loc unsigned ");
	if (len)
		goto skip_next;

	len = str_has_prefix(field, "__rel_loc ");
	if (len)
		goto skip_next;

	goto parse;
skip_next:
	type = field;
	field = strpbrk(field + len, " ");

	if (field == NULL)
		return -EINVAL;

	*field++ = '\0';
	depth++;
parse:
	while ((part = strsep(&field, " ")) != NULL) {
		switch (depth++) {
		case FIELD_DEPTH_TYPE:
			type = part;
			break;
		case FIELD_DEPTH_NAME:
			name = part;
			break;
		case FIELD_DEPTH_SIZE:
			if (!is_struct)
				return -EINVAL;

			if (kstrtou32(part, 10, &size))
				return -EINVAL;
			break;
		default:
			return -EINVAL;
		}
	}

	if (depth < FIELD_DEPTH_SIZE)
		return -EINVAL;

	if (depth == FIELD_DEPTH_SIZE)
		size = user_field_size(type);

	if (size == 0)
		return -EINVAL;

	if (size < 0)
		return size;

	*offset = saved_offset + size;

	return user_event_add_field(user, type, name, saved_offset, size,
				    type[0] != 'u', FILTER_OTHER);
}

static void user_event_parse_flags(struct user_event *user, char *flags)
{
	char *flag;

	if (flags == NULL)
		return;

	while ((flag = strsep(&flags, ",")) != NULL) {
		if (strcmp(flag, "BPF_ITER") == 0)
			user->flags |= FLAG_BPF_ITER;
	}
}

static int user_event_parse_fields(struct user_event *user, char *args)
{
	char *field;
	u32 offset = sizeof(struct trace_entry);
	int ret = -EINVAL;

	if (args == NULL)
		return 0;

	while ((field = strsep(&args, ";")) != NULL) {
		ret = user_event_parse_field(field, user, &offset);

		if (ret)
			break;
	}

	return ret;
}

static struct trace_event_fields user_event_fields_array[1];

static enum print_line_t user_event_print_trace(struct trace_iterator *iter,
						int flags,
						struct trace_event *event)
{
	/* Unsafe to try to decode user provided print_fmt, use hex */
	trace_print_hex_dump_seq(&iter->seq, "", DUMP_PREFIX_OFFSET, 16,
				 1, iter->ent, iter->ent_size, true);

	return trace_handle_return(&iter->seq);
}

static struct trace_event_functions user_event_funcs = {
	.trace = user_event_print_trace,
};

static int destroy_user_event(struct user_event *user)
{
	int ret = 0;

	/* Must destroy fields before call removal */
	user_event_destroy_fields(user);

	ret = trace_remove_event_call(&user->call);

	if (ret)
		return ret;

	dyn_event_remove(&user->devent);

	register_page_data[user->index] = 0;
	clear_bit(user->index, page_bitmap);
	hash_del(&user->node);

	kfree(EVENT_NAME(user));
	kfree(user);

	return ret;
}

static struct user_event *find_user_event(char *name, u32 *outkey)
{
	struct user_event *user;
	u32 key = user_event_key(name);

	*outkey = key;

	hash_for_each_possible(register_table, user, node, key)
		if (!strcmp(EVENT_NAME(user), name))
			return user;

	return NULL;
}

/*
 * Writes the user supplied payload out to a trace file.
 */
static void user_event_ftrace(struct user_event *user, void *data, u32 datalen,
			      void *tpdata)
{
	struct trace_event_file *file;
	struct trace_entry *entry;
	struct trace_event_buffer event_buffer;

	file = (struct trace_event_file *)tpdata;

	if (!file ||
	    !(file->flags & EVENT_FILE_FL_ENABLED) ||
	    trace_trigger_soft_disabled(file))
		return;

	/* Allocates and fills trace_entry, + 1 of this is data payload */
	entry = trace_event_buffer_reserve(&event_buffer, file,
					   sizeof(*entry) + datalen);

	if (unlikely(!entry))
		return;

	memcpy(entry + 1, data, datalen);

	trace_event_buffer_commit(&event_buffer);
}

/*
 * Update the register page that is shared between user processes.
 */
static void update_reg_page_for(struct user_event *user)
{
	struct tracepoint *tp = &user->tracepoint;
	char status = 0;

	if (atomic_read(&tp->key.enabled) > 0) {
		struct tracepoint_func *probe_func_ptr;
		user_event_func_t probe_func;

		rcu_read_lock_sched();

		probe_func_ptr = rcu_dereference_sched(tp->funcs);

		if (probe_func_ptr) {
			do {
				probe_func = probe_func_ptr->func;

				if (probe_func == user_event_ftrace)
					status |= EVENT_STATUS_FTRACE;
				else
					status |= EVENT_STATUS_OTHER;
			} while ((++probe_func_ptr)->func);
		}

		rcu_read_unlock_sched();
	}

	register_page_data[user->index] = status;
}

/*
 * Register callback for our events from tracing sub-systems.
 */
static int user_event_reg(struct trace_event_call *call,
			  enum trace_reg type,
			  void *data)
{
	struct user_event *user = (struct user_event *)call->data;
	int ret = 0;

	if (!user)
		return -ENOENT;

	switch (type) {
	case TRACE_REG_REGISTER:
		ret = tracepoint_probe_register(call->tp,
						call->class->probe,
						data);
		if (!ret)
			goto inc;
		break;

	case TRACE_REG_UNREGISTER:
		tracepoint_probe_unregister(call->tp,
					    call->class->probe,
					    data);
		goto dec;

	default:
		break;
	}

	return ret;
inc:
	atomic_inc(&user->refcnt);
	update_reg_page_for(user);
	return 0;
dec:
	update_reg_page_for(user);
	atomic_dec(&user->refcnt);
	return 0;
}

static int user_event_create(const char *raw_command)
{
	struct user_event *user;
	char *name;
	int ret;

	if (!str_has_prefix(raw_command, USER_EVENTS_PREFIX))
		return -ECANCELED;

	raw_command += USER_EVENTS_PREFIX_LEN;
	raw_command = skip_spaces(raw_command);

	name = kstrdup(raw_command, GFP_KERNEL);

	if (!name)
		return -ENOMEM;

	mutex_lock(&reg_mutex);
	ret = user_event_parse_cmd(name, &user);
	mutex_unlock(&reg_mutex);

	if (ret)
		kfree(name);

	return ret;
}

static int user_event_show(struct seq_file *m, struct dyn_event *ev)
{
	struct user_event *user = container_of(ev, struct user_event, devent);
	struct ftrace_event_field *field, *next;
	struct list_head *head;
	int depth = 0;

	seq_printf(m, "%s%s", USER_EVENTS_PREFIX, EVENT_NAME(user));

	head = trace_get_fields(&user->call);

	list_for_each_entry_safe_reverse(field, next, head, link) {
		if (depth == 0)
			seq_puts(m, " ");
		else
			seq_puts(m, "; ");

		seq_printf(m, "%s %s", field->type, field->name);

		if (str_has_prefix(field->type, "struct "))
			seq_printf(m, " %d", field->size);

		depth++;
	}

	seq_puts(m, "\n");

	return 0;
}

static bool user_event_is_busy(struct dyn_event *ev)
{
	struct user_event *user = container_of(ev, struct user_event, devent);

	return atomic_read(&user->refcnt) != 0;
}

static int user_event_free(struct dyn_event *ev)
{
	struct user_event *user = container_of(ev, struct user_event, devent);

	if (atomic_read(&user->refcnt) != 0)
		return -EBUSY;

	return destroy_user_event(user);
}

static bool user_event_match(const char *system, const char *event,
			     int argc, const char **argv, struct dyn_event *ev)
{
	struct user_event *user = container_of(ev, struct user_event, devent);

	return strcmp(EVENT_NAME(user), event) == 0 &&
		(!system || strcmp(system, USER_EVENTS_SYSTEM) == 0);
}

static struct dyn_event_operations user_event_dops = {
	.create = user_event_create,
	.show = user_event_show,
	.is_busy = user_event_is_busy,
	.free = user_event_free,
	.match = user_event_match,
};

static int user_event_trace_register(struct user_event *user)
{
	int ret;

	ret = register_trace_event(&user->call.event);

	if (!ret)
		return -ENODEV;

	ret = trace_add_event_call(&user->call);

	if (ret)
		unregister_trace_event(&user->call.event);

	return ret;
}

/*
 * Parses the event name, arguments and flags then registers if successful.
 * The name buffer lifetime is owned by this method for success cases only.
 */
static int user_event_parse(char *name, char *args, char *flags,
			    struct user_event **newuser)
{
	int ret;
	int index;
	u32 key;
	struct user_event *user = find_user_event(name, &key);

	if (user) {
		*newuser = user;
		/*
		 * Name is allocated by caller, free it since it already exists.
		 * Caller only worries about failure cases for freeing.
		 */
		kfree(name);
		return 0;
	}

	index = find_first_zero_bit(page_bitmap, MAX_EVENTS);

	if (index == MAX_EVENTS)
		return -EMFILE;

	user = kzalloc(sizeof(*user), GFP_KERNEL);

	if (!user)
		return -ENOMEM;

	INIT_LIST_HEAD(&user->class.fields);
	INIT_LIST_HEAD(&user->fields);

	user->tracepoint.name = name;

	user_event_parse_flags(user, flags);

	ret = user_event_parse_fields(user, args);

	if (ret)
		goto put_user;

	/* Minimal print format */
	user->call.print_fmt = "\"\"";

	user->call.data = user;
	user->call.class = &user->class;
	user->call.name = name;
	user->call.flags = TRACE_EVENT_FL_TRACEPOINT;
	user->call.tp = &user->tracepoint;
	user->call.event.funcs = &user_event_funcs;

	user->class.system = USER_EVENTS_SYSTEM;
	user->class.fields_array = user_event_fields_array;
	user->class.get_fields = user_event_get_fields;
	user->class.reg = user_event_reg;
	user->class.probe = user_event_ftrace;

	mutex_lock(&event_mutex);
	ret = user_event_trace_register(user);
	mutex_unlock(&event_mutex);

	if (ret)
		goto put_user;

	user->index = index;
	dyn_event_init(&user->devent, &user_event_dops);
	dyn_event_add(&user->devent, &user->call);
	set_bit(user->index, page_bitmap);
	hash_add(register_table, &user->node, key);

	*newuser = user;
	return 0;
put_user:
	user_event_destroy_fields(user);
	kfree(user);
	return ret;
}

/*
 * Deletes a previously created event if it is no longer being used.
 */
static int delete_user_event(char *name)
{
	u32 key;
	int ret;
	struct user_event *user = find_user_event(name, &key);

	if (!user)
		return -ENOENT;

	if (atomic_read(&user->refcnt) != 0)
		return -EBUSY;

	mutex_lock(&event_mutex);
	ret = destroy_user_event(user);
	mutex_unlock(&event_mutex);

	return ret;
}

/*
 * Validates the user payload and writes via iterator.
 */
static ssize_t user_events_write_core(struct file *file, struct iov_iter *i)
{
	struct user_event_refs *refs;
	struct user_event *user = NULL;
	struct tracepoint *tp;
	ssize_t ret = i->count;
	int idx;

	if (unlikely(copy_from_iter(&idx, sizeof(idx), i) != sizeof(idx)))
		return -EFAULT;

	rcu_read_lock_sched();

	refs = rcu_dereference_sched(file->private_data);

	/*
	 * The refs->events array is protected by RCU, and new items may be
	 * added. But the user retrieved from indexing into the events array
	 * shall be immutable while the file is opened.
	 */
	if (likely(refs && idx < refs->count))
		user = refs->events[idx];

	rcu_read_unlock_sched();

	if (unlikely(user == NULL))
		return -ENOENT;

	tp = &user->tracepoint;

	/*
	 * It's possible key.enabled disables after this check, however
	 * we don't mind if a few events are included in this condition.
	 */
	if (likely(atomic_read(&tp->key.enabled) > 0)) {
		struct tracepoint_func *probe_func_ptr;
		user_event_func_t probe_func;
		void *tpdata;
		void *kdata;
		u32 datalen;

		kdata = kmalloc(i->count, GFP_KERNEL);

		if (unlikely(!kdata))
			return -ENOMEM;

		datalen = copy_from_iter(kdata, i->count, i);

		rcu_read_lock_sched();

		probe_func_ptr = rcu_dereference_sched(tp->funcs);

		if (probe_func_ptr) {
			do {
				probe_func = probe_func_ptr->func;
				tpdata = probe_func_ptr->data;
				probe_func(user, kdata, datalen, tpdata);
			} while ((++probe_func_ptr)->func);
		}

		rcu_read_unlock_sched();

		kfree(kdata);
	}

	return ret;
}

static ssize_t user_events_write(struct file *file, const char __user *ubuf,
				 size_t count, loff_t *ppos)
{
	struct iovec iov;
	struct iov_iter i;

	if (unlikely(*ppos != 0))
		return -EFAULT;

	if (unlikely(import_single_range(READ, (char *)ubuf, count, &iov, &i)))
		return -EFAULT;

	return user_events_write_core(file, &i);
}

static ssize_t user_events_write_iter(struct kiocb *kp, struct iov_iter *i)
{
	return user_events_write_core(kp->ki_filp, i);
}

static int user_events_ref_add(struct file *file, struct user_event *user)
{
	struct user_event_refs *refs, *new_refs;
	int i, size, count = 0;

	refs = rcu_dereference_protected(file->private_data,
					 lockdep_is_held(&reg_mutex));

	if (refs) {
		count = refs->count;

		for (i = 0; i < count; ++i)
			if (refs->events[i] == user)
				return i;
	}

	size = struct_size(refs, events, count + 1);

	new_refs = kzalloc(size, GFP_KERNEL);

	if (!new_refs)
		return -ENOMEM;

	new_refs->count = count + 1;

	for (i = 0; i < count; ++i)
		new_refs->events[i] = refs->events[i];

	new_refs->events[i] = user;

	atomic_inc(&user->refcnt);

	rcu_assign_pointer(file->private_data, new_refs);

	if (refs)
		kfree_rcu(refs, rcu);

	return i;
}

static long user_reg_get(struct user_reg __user *ureg, struct user_reg *kreg)
{
	u32 size;
	long ret;

	ret = get_user(size, &ureg->size);

	if (ret)
		return ret;

	if (size > PAGE_SIZE)
		return -E2BIG;

	return copy_struct_from_user(kreg, sizeof(*kreg), ureg, size);
}

/*
 * Registers a user_event on behalf of a user process.
 */
static long user_events_ioctl_reg(struct file *file, unsigned long uarg)
{
	struct user_reg __user *ureg = (struct user_reg __user *)uarg;
	struct user_reg reg;
	struct user_event *user;
	char *name;
	long ret;

	ret = user_reg_get(ureg, &reg);

	if (ret)
		return ret;

	name = strndup_user((const char __user *)(uintptr_t)reg.name_args,
			    MAX_EVENT_DESC);

	if (IS_ERR(name)) {
		ret = PTR_ERR(name);
		return ret;
	}

	ret = user_event_parse_cmd(name, &user);

	if (ret) {
		kfree(name);
		return ret;
	}

	ret = user_events_ref_add(file, user);

	/* Positive number is index and valid */
	if (ret < 0)
		return ret;

	put_user((u32)ret, &ureg->write_index);
	put_user(user->index, &ureg->status_index);

	return 0;
}

/*
 * Deletes a user_event on behalf of a user process.
 */
static long user_events_ioctl_del(struct file *file, unsigned long uarg)
{
	void __user *ubuf = (void __user *)uarg;
	char *name;
	long ret;

	name = strndup_user(ubuf, MAX_EVENT_DESC);

	if (IS_ERR(name))
		return PTR_ERR(name);

	ret = delete_user_event(name);

	kfree(name);

	return ret;
}

/*
 * Handles the ioctl from user mode to register or alter operations.
 */
static long user_events_ioctl(struct file *file, unsigned int cmd,
			      unsigned long uarg)
{
	long ret = -ENOTTY;

	switch (cmd) {
	case DIAG_IOCSREG:
		mutex_lock(&reg_mutex);
		ret = user_events_ioctl_reg(file, uarg);
		mutex_unlock(&reg_mutex);
		break;

	case DIAG_IOCSDEL:
		mutex_lock(&reg_mutex);
		ret = user_events_ioctl_del(file, uarg);
		mutex_unlock(&reg_mutex);
		break;
	}

	return ret;
}

/*
 * Handles the final close of the file from user mode.
 */
static int user_events_release(struct inode *node, struct file *file)
{
	struct user_event_refs *refs;
	struct user_event *user;
	int i;

	/*
	 * Ensure refs cannot change under any situation by taking the
	 * register mutex during the final freeing of the references.
	 */
	mutex_lock(&reg_mutex);

	refs = file->private_data;

	if (!refs)
		goto out;

	/*
	 * The lifetime of refs has reached an end, it's tied to this file.
	 * The underlying user_events are ref counted, and cannot be freed.
	 * After this decrement, the user_events may be freed elsewhere.
	 */
	for (i = 0; i < refs->count; ++i) {
		user = refs->events[i];

		if (user)
			atomic_dec(&user->refcnt);
	}
out:
	file->private_data = NULL;