[PATCH v7 2/4] trace/objtrace: get the value of the object

From: Jeff Xie
Date: Wed Jan 12 2022 - 20:39:01 EST

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@xxxxxxxxx>
---
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;
+ }
+ 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);
- /* 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);
}
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;
+ set_trace_object(obj, obj_data->obj_type_size);
}

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