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SubjectRe: [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@gmail.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@gmail.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@kernel.org>

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