Date:   Wed, 19 Jan 2022 00:13:43 +0900
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     Jeff Xie <xiehuan09@...il.com>
Cc:     rostedt@...dmis.org, mhiramat@...nel.org, mingo@...hat.com,
        zanussi@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v7 2/4] trace/objtrace: get the value of the object

Hi Jeff,

On Thu, 13 Jan 2022 09:38:33 +0800
Jeff Xie <xiehuan09@...il.com> wrote:

> Using objtrace trigger to get the value of the object which from the kernel
> function parameter.
> 
> Syntax:
> 	objtrace:add:obj[,offset][:type][:count][if <filter>]
> 
> Usage:
> 	# echo 'p bio_add_page arg1=$arg1' > ./kprobe_events
> 	# gdb vmlinux
> 	(gdb) p &(((struct bio *)0)->bi_iter.bi_size)
> 	$1 = (unsigned int *) 0x28
> 	# echo 'objtrace:add:arg1,0x28:u32:1 if comm == "cat"' > ./events/kprobes/ \
> 		 p_bio_add_page_0/trigger
> 	# cat /test.txt
> 
> Signed-off-by: Jeff Xie <xiehuan09@...il.com>
> ---
>  kernel/trace/trace.c         |   2 +-
>  kernel/trace/trace_entries.h |   5 +-
>  kernel/trace/trace_object.c  | 190 +++++++++++++++++++++++++++++------
>  kernel/trace/trace_output.c  |   6 +-
>  4 files changed, 169 insertions(+), 34 deletions(-)
> 
> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> index 0b627963e343..d5332ece4c67 100644
> --- a/kernel/trace/trace.c
> +++ b/kernel/trace/trace.c
> @@ -5591,7 +5591,7 @@ static const char readme_msg[] =
>  	"\t            disable_hist:<system>:<event>\n"
>  #endif
>  #ifdef CONFIG_TRACE_OBJECT
> -	"\t            objtrace:add:obj[:count][if <filter>]\n"
> +	"\t            objtrace:add:obj[,offset][:type][:count][if <filter>]\n"
>  #endif
>  #ifdef CONFIG_STACKTRACE
>  	"\t\t    stacktrace\n"
> diff --git a/kernel/trace/trace_entries.h b/kernel/trace/trace_entries.h
> index bb120d9498a9..2407c45a568c 100644
> --- a/kernel/trace/trace_entries.h
> +++ b/kernel/trace/trace_entries.h
> @@ -413,8 +413,9 @@ FTRACE_ENTRY(object, trace_object_entry,
>  		__field(	unsigned long,		ip		)
>  		__field(	unsigned long,		parent_ip	)
>  		__field(	unsigned long,		object		)
> +		__field(	unsigned long,		value		)
>  	),
>  
> -	F_printk(" %ps <-- %ps object:%lx\n",
> -		 (void *)__entry->ip, (void *)__entry->parent_ip, __entry->object)
> +	F_printk(" %ps <-- %ps object:%lx value:%lx\n", (void *)__entry->ip,
> +	       (void *)__entry->parent_ip, __entry->object, __entry->value)
>  );
> diff --git a/kernel/trace/trace_object.c b/kernel/trace/trace_object.c
> index 4af1c117cbfa..774a9dff4d0a 100644
> --- a/kernel/trace/trace_object.c
> +++ b/kernel/trace/trace_object.c
> @@ -11,7 +11,6 @@
>  #define MAX_TRACED_OBJECT 5
>  static DEFINE_RAW_SPINLOCK(trace_obj_lock);
>  static struct trace_event_file event_trace_file;
> -static const int max_args_num = 6;
>  static atomic_t trace_object_ref;
>  static atomic_t num_traced_obj;
>  static int exit_trace_object(void);
> @@ -19,8 +18,22 @@ static int init_trace_object(void);
>  
>  static struct object_instance {
>  	void *obj;
> +	int obj_type_size;
>  } traced_obj[MAX_TRACED_OBJECT];
>  
> +/* objtrace private data */
> +struct objtrace_trigger_data {
> +	struct ftrace_event_field *field;
> +	int offset;
> +	int obj_type_size;
> +};
> +
> +/* get the type size for the special object */
> +struct objtrace_fetch_type {
> +	char *name;
> +	int type_size;
> +};
> +
>  static bool object_exist(void *obj)
>  {
>  	int i, max;
> @@ -39,7 +52,7 @@ static bool object_empty(void)
>  	return !atomic_read(&num_traced_obj);
>  }
>  
> -static void set_trace_object(void *obj)
> +static void set_trace_object(void *obj, int obj_type_size)
>  {
>  	unsigned long flags;
>  
> @@ -59,6 +72,7 @@ static void set_trace_object(void *obj)
>  		goto out;
>  	}
>  	traced_obj[atomic_read(&num_traced_obj)].obj = obj;
> +	traced_obj[atomic_read(&num_traced_obj)].obj_type_size = obj_type_size;
>  	/* make sure the num_traced_obj update always appears after traced_obj update */
>  	smp_wmb();
>  	atomic_inc(&num_traced_obj);
> @@ -67,7 +81,7 @@ static void set_trace_object(void *obj)
>  }
>  
>  static void submit_trace_object(unsigned long ip, unsigned long parent_ip,
> -				 unsigned long object)
> +				 unsigned long object, unsigned long value)
>  {
>  
>  	struct trace_buffer *buffer;
> @@ -84,18 +98,66 @@ static void submit_trace_object(unsigned long ip, unsigned long parent_ip,
>  	entry->ip                       = ip;
>  	entry->parent_ip                = parent_ip;
>  	entry->object			= object;
> +	entry->value			= value;
>  
>  	event_trigger_unlock_commit(&event_trace_file, buffer, event,
>  		entry, pc);
>  }
>  
> +static inline long get_object_value(unsigned long *val, void *obj, int type_size)
> +{
> +	long ret = 0;
> +
> +	switch (type_size) {
> +	case 1: {
> +		u8 tmp;
> +
> +		ret = copy_from_kernel_nofault(&tmp, obj, sizeof(tmp));
> +		if (ret)
> +			goto out;
> +		*val = tmp;
> +		break;
> +	}
> +	case 2: {
> +		u16 tmp;
> +
> +		ret = copy_from_kernel_nofault(&tmp, obj, sizeof(tmp));
> +		if (ret)
> +			goto out;
> +		*val = tmp;
> +		break;
> +	}
> +	case 4: {
> +		u32 tmp;
> +
> +		ret = copy_from_kernel_nofault(&tmp, obj, sizeof(tmp));
> +		if (ret)
> +			goto out;
> +		*val = tmp;
> +		break;
> +	}
> +	case 8: {
> +		u64 tmp;
> +
> +		ret = copy_from_kernel_nofault(&tmp, obj, sizeof(tmp));
> +		if (ret)
> +			goto out;
> +		*val = tmp;
> +		break;
> +	}

Can't you move the copy_from_kernel_nofault() outside of the switch-case?
e.g.

	char tmp[sizeof(u64)];

	ret = copy_from_kernel_nofault(tmp, obj, sizeof(tmp));
	if (ret)
		return ret;

	switch (type_size) {
		case 1:
			*val = (unsigned long)*(u8 *)tmp;
			break;
		...
	}
	return 0;

Thank you,


> +	default:
> +		return -EINVAL;
> +	}
> +out:
> +	return ret;
> +}
> +
>  static void
>  trace_object_events_call(unsigned long ip, unsigned long parent_ip,
>  		struct ftrace_ops *op, struct ftrace_regs *fregs)
>  {
> -	struct pt_regs *pt_regs = ftrace_get_regs(fregs);
> -	unsigned long obj;
> -	int bit, n;
> +	unsigned long val = 0;
> +	int bit, n, max;
>  
>  	bit = ftrace_test_recursion_trylock(ip, parent_ip);
>  	if (bit < 0)
> @@ -104,11 +166,12 @@ trace_object_events_call(unsigned long ip, unsigned long parent_ip,
>  	if (object_empty())
>  		goto out;
>  
> -	for (n = 0; n < max_args_num; n++) {
> -		obj = regs_get_kernel_argument(pt_regs, n);
> -		if (object_exist((void *)obj))
> -			submit_trace_object(ip, parent_ip, obj);

This actually filtered the (function call) event which is related to the object.

> -	/* The parameters of a function may match multiple objects */
> +	max = atomic_read(&num_traced_obj);
> +	smp_rmb();
> +	for (n = 0; n < max; n++) {
> +		if (get_object_value(&val, traced_obj[n].obj, traced_obj[n].obj_type_size))
> +			goto out;
> +		submit_trace_object(ip, parent_ip, (unsigned long)traced_obj[n].obj, val);

But you lost the filter here.
This is because you saves the "object + offset" address below;


>  	}
>  out:
>  	ftrace_test_recursion_unlock(bit);
> @@ -124,12 +187,15 @@ trace_object_trigger(struct event_trigger_data *data,
>  		   struct trace_buffer *buffer,  void *rec,
>  		   struct ring_buffer_event *event)
>  {
> +	struct objtrace_trigger_data *obj_data = data->private_data;
> +	struct ftrace_event_field *field;
> +	void *obj, *val = NULL;
>  
> -	struct ftrace_event_field *field = data->private_data;
> -	void *obj = NULL;
> -
> -	memcpy(&obj, rec + field->offset, sizeof(obj));
> -	set_trace_object(obj);
> +	field = obj_data->field;
> +	memcpy(&val, rec + field->offset, sizeof(val));
> +	/* get the final object */
> +	obj = val + obj_data->offset;

Here, you saved the object address including offset. This means
you can not filter the actual function related to the object.

Please recover the filter.

> +	set_trace_object(obj, obj_data->obj_type_size);

You can save the offset with type-size and object address itself. 

Thank you,

>  }
>  
>  static void
> @@ -140,8 +206,10 @@ trace_object_trigger_free(struct event_trigger_ops *ops,
>  		return;
>  
>  	data->ref--;
> -	if (!data->ref)
> +	if (!data->ref) {
> +		kfree(data->private_data);
>  		trigger_data_free(data);
> +	}
>  }
>  
>  static void
> @@ -276,6 +344,22 @@ static void unregister_object_trigger(char *glob, struct event_trigger_ops *ops,
>  	}
>  }
>  
> +static const struct objtrace_fetch_type objtrace_fetch_types[] = {
> +	{"u8", 1},
> +	{"s8", 1},
> +	{"x8", 1},
> +	{"u16", 2},
> +	{"s16", 2},
> +	{"x16", 2},
> +	{"u32", 4},
> +	{"s32", 4},
> +	{"x32", 4},
> +	{"u64", 8},
> +	{"s64", 8},
> +	{"x64", 8},
> +	{}
> +};
> +
>  static int
>  event_object_trigger_callback(struct event_command *cmd_ops,
>  		       struct trace_event_file *file,
> @@ -283,19 +367,22 @@ event_object_trigger_callback(struct event_command *cmd_ops,
>  {
>  	struct event_trigger_data *trigger_data;
>  	struct event_trigger_ops *trigger_ops;
> +	struct objtrace_trigger_data *obj_data;
>  	struct trace_event_call *call;
>  	struct ftrace_event_field *field;
> -	char *objtrace_cmd;
> -	char *trigger = NULL;
> -	char *arg;
> -	char *number;
> -	int ret;
> +	char *type, *tr, *obj, *tmp, *trigger = NULL;
> +	char *number, *objtrace_cmd;
> +	int ret, i, def_type_size, obj_type_size = 0;
> +	long offset = 0;
>  
>  	ret = -EINVAL;
>  	if (!param)
>  		goto out;
>  
> -	/* separate the trigger from the filter (c:a:n [if filter]) */
> +	/*
> +	 * separate the trigger from the filter:
> +	 * objtrace:add:OBJ[,OFFS][:TYPE][:COUNT] [if filter]
> +	 */
>  	trigger = strsep(&param, " \t");
>  	if (!trigger)
>  		goto out;
> @@ -309,33 +396,79 @@ event_object_trigger_callback(struct event_command *cmd_ops,
>  	if (!objtrace_cmd || strcmp(objtrace_cmd, "add"))
>  		goto out;
>  
> -	arg = strsep(&trigger, ":");
> -	if (!arg)
> +	obj = strsep(&trigger, ":");
> +	if (!obj)
>  		goto out;
> +
> +	tr = strchr(obj, ',');
> +	if (!tr)
> +		offset = 0;
> +	else {
> +		*tr++ = '\0';
> +		ret = kstrtol(tr, 0, &offset);
> +		if (ret)
> +			goto out;
> +	}
> +
> +	ret = -EINVAL;
>  	call = file->event_call;
> -	field = trace_find_event_field(call, arg);
> +	field = trace_find_event_field(call, obj);
>  	if (!field)
>  		goto out;
>  
>  	if (field->size != sizeof(void *))
>  		goto out;
> +	def_type_size = sizeof(void *);
> +	if (!trigger) {
> +		obj_type_size = def_type_size;
> +		goto skip_get_type;
> +	}
>  
> +	tmp = trigger;
> +	type = strsep(&trigger, ":");
> +	if (!type)
> +		obj_type_size = def_type_size;
> +	else if (isdigit(type[0])) {
> +		obj_type_size = def_type_size;
> +		trigger = tmp;
> +	} else {
> +		for (i = 0; objtrace_fetch_types[i].name; i++) {
> +			if (strcmp(objtrace_fetch_types[i].name, type) == 0) {
> +				obj_type_size = objtrace_fetch_types[i].type_size;
> +				break;
> +			}
> +		}
> +	}
> +	if (!obj_type_size)
> +		goto out;
> +skip_get_type:
>  	trigger_ops = cmd_ops->get_trigger_ops(cmd, trigger);
>  
>  	ret = -ENOMEM;
> +	obj_data = kzalloc(sizeof(*obj_data), GFP_KERNEL);
> +	if (!obj_data)
> +		goto out;
> +
> +	obj_data->field = field;
> +	obj_data->offset = offset;
> +	obj_data->obj_type_size = obj_type_size;
> +
>  	trigger_data = kzalloc(sizeof(*trigger_data), GFP_KERNEL);
> -	if (!trigger_data)
> +	if (!trigger_data) {
> +		kfree(obj_data);
>  		goto out;
> +	}
>  
>  	trigger_data->count = -1;
>  	trigger_data->ops = trigger_ops;
>  	trigger_data->cmd_ops = cmd_ops;
> -	trigger_data->private_data = field;
> +	trigger_data->private_data = obj_data;
>  	INIT_LIST_HEAD(&trigger_data->list);
>  	INIT_LIST_HEAD(&trigger_data->named_list);
>  
>  	if (glob[0] == '!') {
>  		cmd_ops->unreg(glob+1, trigger_ops, trigger_data, file);
> +		kfree(obj_data);
>  		kfree(trigger_data);
>  		ret = 0;
>  		goto out;
> @@ -390,6 +523,7 @@ event_object_trigger_callback(struct event_command *cmd_ops,
>   out_free:
>  	if (cmd_ops->set_filter)
>  		cmd_ops->set_filter(NULL, trigger_data, NULL);
> +	kfree(obj_data);
>  	kfree(trigger_data);
>  	goto out;
>  }
> diff --git a/kernel/trace/trace_output.c b/kernel/trace/trace_output.c
> index d747aed27104..12a971927d8c 100644
> --- a/kernel/trace/trace_output.c
> +++ b/kernel/trace/trace_output.c
> @@ -1553,6 +1553,7 @@ static enum print_line_t trace_object_print(struct trace_iterator *iter, int fla
>  	trace_assign_type(field, iter->ent);
>  	print_fn_trace(s, field->ip, field->parent_ip, flags);
>  	trace_seq_printf(s, " object:0x%lx", field->object);
> +	trace_seq_printf(s, " value:0x%lx", field->value);
>  	trace_seq_putc(s, '\n');
>  
>  	return trace_handle_return(s);
> @@ -1565,9 +1566,8 @@ static enum print_line_t trace_object_raw(struct trace_iterator *iter, int flags
>  
>  	trace_assign_type(field, iter->ent);
>  
> -	trace_seq_printf(&iter->seq, "%lx %lx\n",
> -			 field->ip,
> -			 field->parent_ip);
> +	trace_seq_printf(&iter->seq, "%lx %lx %lx %lx\n", field->ip,
> +			field->parent_ip, field->object, field->value);
>  
>  	return trace_handle_return(&iter->seq);
>  }
> -- 
> 2.25.1
> 


-- 
Masami Hiramatsu <mhiramat@...nel.org>

Powered by blists - more mailing lists