[PATCH v3 17/33] function_graph: Implement fgraph_reserve_data() and fgraph_retrieve_data()

Masami Hiramatsu (Google)
2023-11-27T14:01:22Z

From: Steven Rostedt (VMware) <rostedt@goodmis.org>

Added functions that can be called by a fgraph_ops entryfunc and retfunc to
store state between the entry of the function being traced to the exit of
the same function. The fgraph_ops entryfunc() may call
fgraph_reserve_data() to store up to 32 words onto the task's shadow
ret_stack and this then can be retrieved by fgraph_retrieve_data() called
by the corresponding retfunc().

Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
---
Changes in v3:
- Store fgraph_array index to the data entry.
- Both function requires fgraph_array index to store/retrieve data.
- Reserve correct size of the data.
- Return correct data area.
Changes in v2:
- Retrieve the reserved size by fgraph_retrieve_data().
- Expand the maximum data size to 32 words.
- Update stack index with __get_index(val) if FGRAPH_TYPE_ARRAY entry.
- fix typos and make description lines shorter than 76 chars.
---
include/linux/ftrace.h | 3 +
kernel/trace/fgraph.c | 175 ++++++++++++++++++++++++++++++++++++++++++++++--
2 files changed, 170 insertions(+), 8 deletions(-)

diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
index 09ca4bba63f2..1c121237016e 100644
--- a/include/linux/ftrace.h
+++ b/include/linux/ftrace.h
@@ -1075,6 +1075,9 @@ struct fgraph_ops {
int idx;
};

+void *fgraph_reserve_data(int idx, int size_bytes);
+void *fgraph_retrieve_data(int idx, int *size_bytes);
+
/*
* Stack of return addresses for functions
* of a thread.
diff --git a/kernel/trace/fgraph.c b/kernel/trace/fgraph.c
index d1981fe8edf0..317202943936 100644
--- a/kernel/trace/fgraph.c
+++ b/kernel/trace/fgraph.c
@@ -41,17 +41,29 @@
* bits: 10 - 11 Type of storage
* 0 - reserved
* 1 - bitmap of fgraph_array index
+ * 2 - reserved data
*
* For bitmap of fgraph_array index
* bits: 12 - 27 The bitmap of fgraph_ops fgraph_array index
*
+ * For reserved data:
+ * bits: 12 - 17 The size in words that is stored
+ * bits: 18 - 23 The index of fgraph_array, which shows who is stored
+ *
* That is, at the end of function_graph_enter, if the first and forth
* fgraph_ops on the fgraph_array[] (index 0 and 3) needs their retfunc called
- * on the return of the function being traced, this is what will be on the
- * task's shadow ret_stack: (the stack grows upward)
+ * on the return of the function being traced, and the forth fgraph_ops
+ * stored two words of data, this is what will be on the task's shadow
+ * ret_stack: (the stack grows upward)
*
* | | <- task->curr_ret_stack
* +--------------------------------------------+
+ * | data_type(idx:3, size:2, |
+ * | offset:FGRAPH_RET_INDEX+3) | ( Data with size of 2 words)
+ * +--------------------------------------------+ ( It is 4 words from the ret_stack)
+ * | STORED DATA WORD 2 |
+ * | STORED DATA WORD 1 |
+ * +------i-------------------------------------+
* | bitmap_type(bitmap:(BIT(3)|BIT(0)), |
* | offset:FGRAPH_RET_INDEX) | <- the offset is from here
* +--------------------------------------------+
@@ -78,14 +90,23 @@
enum {
FGRAPH_TYPE_RESERVED = 0,
FGRAPH_TYPE_BITMAP = 1,
+ FGRAPH_TYPE_DATA = 2,
};

#define FGRAPH_INDEX_SIZE 16
#define FGRAPH_INDEX_MASK GENMASK(FGRAPH_INDEX_SIZE - 1, 0)
#define FGRAPH_INDEX_SHIFT (FGRAPH_TYPE_SHIFT + FGRAPH_TYPE_SIZE)

-/* Currently the max stack index can't be more than register callers */
-#define FGRAPH_MAX_INDEX (FGRAPH_INDEX_SIZE + FGRAPH_RET_INDEX)
+#define FGRAPH_DATA_SIZE 5
+#define FGRAPH_DATA_MASK ((1 << FGRAPH_DATA_SIZE) - 1)
+#define FGRAPH_DATA_SHIFT (FGRAPH_TYPE_SHIFT + FGRAPH_TYPE_SIZE)
+
+#define FGRAPH_DATA_INDEX_SIZE 4
+#define FGRAPH_DATA_INDEX_MASK ((1 << FGRAPH_DATA_INDEX_SIZE) - 1)
+#define FGRAPH_DATA_INDEX_SHIFT (FGRAPH_DATA_SHIFT + FGRAPH_DATA_SIZE)
+
+#define FGRAPH_MAX_INDEX \
+ ((FGRAPH_INDEX_SIZE << FGRAPH_DATA_SIZE) + FGRAPH_RET_INDEX)

#define FGRAPH_ARRAY_SIZE FGRAPH_INDEX_SIZE

@@ -97,6 +118,8 @@ enum {

#define RET_STACK(t, index) ((struct ftrace_ret_stack *)(&(t)->ret_stack[index]))

+#define FGRAPH_MAX_DATA_SIZE (sizeof(long) * (1 << FGRAPH_DATA_SIZE))
+
/*
* Each fgraph_ops has a reservered unsigned long at the end (top) of the
* ret_stack to store task specific state.
@@ -111,14 +134,39 @@ static int fgraph_array_cnt;

static struct fgraph_ops *fgraph_array[FGRAPH_ARRAY_SIZE];

+static inline int __get_index(unsigned long val)
+{
+ return val & FGRAPH_RET_INDEX_MASK;
+}
+
+static inline int __get_type(unsigned long val)
+{
+ return (val >> FGRAPH_TYPE_SHIFT) & FGRAPH_TYPE_MASK;
+}
+
+static inline int __get_data_index(unsigned long val)
+{
+ return (val >> FGRAPH_DATA_INDEX_SHIFT) & FGRAPH_DATA_INDEX_MASK;
+}
+
+static inline int __get_data_size(unsigned long val)
+{
+ return (val >> FGRAPH_DATA_SHIFT) & FGRAPH_DATA_MASK;
+}
+
+static inline unsigned long get_fgraph_entry(struct task_struct *t, int index)
+{
+ return t->ret_stack[index];
+}
+
static inline int get_ret_stack_index(struct task_struct *t, int offset)
{
- return t->ret_stack[offset] & FGRAPH_RET_INDEX_MASK;
+ return __get_index(t->ret_stack[offset]);
}

static inline int get_fgraph_type(struct task_struct *t, int offset)
{
- return (t->ret_stack[offset] >> FGRAPH_TYPE_SHIFT) & FGRAPH_TYPE_MASK;
+ return __get_type(t->ret_stack[offset]);
}

static inline unsigned long
@@ -145,6 +193,22 @@ add_fgraph_index_bitmap(struct task_struct *t, int offset, unsigned long bitmap)
t->ret_stack[offset] |= (bitmap << FGRAPH_INDEX_SHIFT);
}

+static inline void *get_fgraph_data(struct task_struct *t, int index)
+{
+ unsigned long val = t->ret_stack[index];
+
+ if (__get_type(val) != FGRAPH_TYPE_DATA)
+ return NULL;
+ index -= __get_data_size(val);
+ return (void *)&t->ret_stack[index];
+}
+
+static inline unsigned long make_fgraph_data(int idx, int size, int offset)
+{
+ return (idx << FGRAPH_DATA_INDEX_SHIFT) | (size << FGRAPH_DATA_SHIFT) |
+ (FGRAPH_TYPE_DATA << FGRAPH_TYPE_SHIFT) | offset;
+}
+
/* ftrace_graph_entry set to this to tell some archs to run function graph */
static int entry_run(struct ftrace_graph_ent *trace, struct fgraph_ops *ops)
{
@@ -178,6 +242,92 @@ static void ret_stack_init_task_vars(unsigned long *ret_stack)
memset(gvals, 0, sizeof(*gvals) * FGRAPH_ARRAY_SIZE);
}

+/**
+ * fgraph_reserve_data - Reserve storage on the task's ret_stack
+ * @idx: The index of fgraph_array
+ * @size_bytes: The size in bytes to reserve
+ *
+ * Reserves space of up to FGRAPH_MAX_DATA_SIZE bytes on the
+ * task's ret_stack shadow stack, for a given fgraph_ops during
+ * the entryfunc() call. If entryfunc() returns zero, the storage
+ * is discarded. An entryfunc() can only call this once per iteration.
+ * The fgraph_ops retfunc() can retrieve this stored data with
+ * fgraph_retrieve_data().
+ *
+ * Returns: On success, a pointer to the data on the stack.
+ * Otherwise, NULL if there's not enough space left on the
+ * ret_stack for the data, or if fgraph_reserve_data() was called
+ * more than once for a single entryfunc() call.
+ */
+void *fgraph_reserve_data(int idx, int size_bytes)
+{
+ unsigned long val;
+ void *data;
+ int curr_ret_stack = current->curr_ret_stack;
+ int data_size;
+
+ if (size_bytes > FGRAPH_MAX_DATA_SIZE)
+ return NULL;
+
+ /* Convert to number of longs + data word */
+ data_size = DIV_ROUND_UP(size_bytes, sizeof(long));
+
+ val = get_fgraph_entry(current, curr_ret_stack - 1);
+ data = &current->ret_stack[curr_ret_stack];
+
+ curr_ret_stack += data_size + 1;
+ if (unlikely(curr_ret_stack >= SHADOW_STACK_MAX_INDEX))
+ return NULL;
+
+ val = make_fgraph_data(idx, data_size, __get_index(val) + data_size + 1);
+
+ /* Set the last word to be reserved */
+ current->ret_stack[curr_ret_stack - 1] = val;
+
+ /* Make sure interrupts see this */
+ barrier();
+ current->curr_ret_stack = curr_ret_stack;
+ /* Again sync with interrupts, and reset reserve */
+ current->ret_stack[curr_ret_stack - 1] = val;
+
+ return data;
+}
+
+/**
+ * fgraph_retrieve_data - Retrieve stored data from fgraph_reserve_data()
+ * @idx: the index of fgraph_array (fgraph_ops::idx)
+ * @size_bytes: pointer to retrieved data size.
+ *
+ * This is to be called by a fgraph_ops retfunc(), to retrieve data that
+ * was stored by the fgraph_ops entryfunc() on the function entry.
+ * That is, this will retrieve the data that was reserved on the
+ * entry of the function that corresponds to the exit of the function
+ * that the fgraph_ops retfunc() is called on.
+ *
+ * Returns: The stored data from fgraph_reserve_data() called by the
+ * matching entryfunc() for the retfunc() this is called from.
+ * Or NULL if there was nothing stored.
+ */
+void *fgraph_retrieve_data(int idx, int *size_bytes)
+{
+ int index = current->curr_ret_stack - 1;
+ unsigned long val;
+
+ val = get_fgraph_entry(current, index);
+ while (__get_type(val) == FGRAPH_TYPE_DATA) {
+ if (__get_data_index(val) == idx)
+ goto found;
+ index -= __get_data_size(val) + 1;
+ val = get_fgraph_entry(current, index);
+ }
+ return NULL;
+found:
+ if (size_bytes)
+ *size_bytes = __get_data_size(val) *
+ sizeof(long);
+ return get_fgraph_data(current, index);
+}
+
/**
* fgraph_get_task_var - retrieve a task specific state variable
* @gops: The ftrace_ops that owns the task specific variable
@@ -424,13 +574,18 @@ int function_graph_enter(unsigned long ret, unsigned long func,

for (i = 0; i < fgraph_array_cnt; i++) {
struct fgraph_ops *gops = fgraph_array[i];
+ int save_curr_ret_stack;

if (gops == &fgraph_stub)
continue;

+ save_curr_ret_stack = current->curr_ret_stack;
if (ftrace_ops_test(&gops->ops, func, NULL) &&
gops->entryfunc(&trace, gops))
bitmap |= BIT(i);
+ else
+ /* Clear out any saved storage */
+ current->curr_ret_stack = save_curr_ret_stack;
}

if (!bitmap)
@@ -452,6 +607,7 @@ int function_graph_enter_ops(unsigned long ret, unsigned long func,
struct fgraph_ops *gops)
{
struct ftrace_graph_ent trace;
+ int save_curr_ret_stack;
int index;
int type;

@@ -468,13 +624,15 @@ int function_graph_enter_ops(unsigned long ret, unsigned long func,

trace.func = func;
trace.depth = current->curr_ret_depth;
+ save_curr_ret_stack = current->curr_ret_stack;
if (gops->entryfunc(&trace, gops)) {
if (type == FGRAPH_TYPE_RESERVED)
set_fgraph_index_bitmap(current, index, BIT(gops->idx));
else
add_fgraph_index_bitmap(current, index, BIT(gops->idx));
return 0;
- }
+ } else
+ current->curr_ret_stack = save_curr_ret_stack;

if (type == FGRAPH_TYPE_RESERVED) {
current->curr_ret_stack -= FGRAPH_RET_INDEX + 1;
@@ -619,7 +777,8 @@ static unsigned long __ftrace_return_to_handler(struct fgraph_ret_regs *ret_regs
* curr_ret_stack is after that.
*/
barrier();
- current->curr_ret_stack -= FGRAPH_RET_INDEX + 1;
+ current->curr_ret_stack = index - FGRAPH_RET_INDEX;
+
current->curr_ret_depth--;
return ret;
}