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>
/* Reminder to move to uapi when everything works */
#ifdef CONFIG_COMPILE_TEST
#include <linux/user_events.h>
#else
#include <uapi/linux/user_events.h>
#endif
#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 a power of two of PAGE_SIZE.
 */
#define MAX_PAGE_ORDER 0
#define MAX_PAGES (1 << MAX_PAGE_ORDER)
#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
#define MAX_FIELD_ARG_NAME 256

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;
	struct list_head validators;
	atomic_t refcnt;
	int index;
	int flags;
	int min_size;
};

/*
 * 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[];
};

#define VALIDATOR_ENSURE_NULL (1 << 0)
#define VALIDATOR_REL (1 << 1)

struct user_event_validator {
	struct list_head link;
	int offset;
	int flags;
};

typedef void (*user_event_func_t) (struct user_event *user, struct iov_iter *i,
				   void *tpdata, bool *faulted);

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 __always_inline __must_check
size_t copy_nofault(void *addr, size_t bytes, struct iov_iter *i)
{
	size_t ret;

	pagefault_disable();

	ret = copy_from_iter_nocache(addr, bytes, i);

	pagefault_enable();

	return ret;
}

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.
 *
 * Upon success user_event has its ref count increased by 1.
 */
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);