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[v2] tracing: Allow for max buffer data size trace_marker writes

Message ID 20231212090057.41b28efe@gandalf.local.home (mailing list archive)
State Superseded
Headers show
Series [v2] tracing: Allow for max buffer data size trace_marker writes | expand

Commit Message

Steven Rostedt Dec. 12, 2023, 2 p.m. UTC 
From: "Steven Rostedt (Google)" <rostedt@goodmis.org>

Allow a trace write to be as big as the ring buffer tracing data will
allow. Currently, it only allows writes of 1KB in size, but there's no
reason that it cannot allow what the ring buffer can hold.

Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
---
Changes since v1: https://lore.kernel.org/linux-trace-kernel/20231209175003.63db40ab@gandalf.local.home

- Now that there's a new fix for the max event size, there's no more
  BUF_MAX_EVENT_SIZE macro. Now the BUF_MAX_DATA_SIZE can be used again.

- Check if the buffer itself is requesting forced timestamps, and if so,
  decrement from the max size, the timestamp size.

- This no longer depends on the previous fix change, as it's now using
  existing macros.

 include/linux/ring_buffer.h |  1 +
 kernel/trace/ring_buffer.c  | 15 +++++++++++++++
 kernel/trace/trace.c        | 28 +++++++++++++++++++++-------
 3 files changed, 37 insertions(+), 7 deletions(-)

Comments

Mathieu Desnoyers Dec. 12, 2023, 2:33 p.m. UTC | #1 
On 2023-12-12 09:00, Steven Rostedt wrote:
[...]
> --- a/kernel/trace/trace.c
> +++ b/kernel/trace/trace.c
> @@ -7272,6 +7272,7 @@ tracing_mark_write(struct file *filp, const char __user *ubuf,
>   	enum event_trigger_type tt = ETT_NONE;
>   	struct trace_buffer *buffer;
>   	struct print_entry *entry;
> +	int meta_size;
>   	ssize_t written;
>   	int size;
>   	int len;
> @@ -7286,12 +7287,9 @@ tracing_mark_write(struct file *filp, const char __user *ubuf,
>   	if (!(tr->trace_flags & TRACE_ITER_MARKERS))
>   		return -EINVAL;
>   
> -	if (cnt > TRACE_BUF_SIZE)
> -		cnt = TRACE_BUF_SIZE;

You're removing an early bound check for a size_t userspace input...

> -
> -	BUILD_BUG_ON(TRACE_BUF_SIZE >= PAGE_SIZE);
> -
> -	size = sizeof(*entry) + cnt + 2; /* add '\0' and possible '\n' */
> +	meta_size = sizeof(*entry) + 2;  /* add '\0' and possible '\n' */
> + again:
> +	size = cnt + meta_size;

... and then implicitly casting it into a "int" size variable, which
can therefore become a negative value.

Just for the sake of not having to rely on ring_buffer_lock_reserve
catching (length > BUF_MAX_DATA_SIZE), I would recommend to add an
early check for negative here.

>   
>   	/* If less than "<faulted>", then make sure we can still add that */
>   	if (cnt < FAULTED_SIZE)
> @@ -7300,9 +7298,25 @@ tracing_mark_write(struct file *filp, const char __user *ubuf,
>   	buffer = tr->array_buffer.buffer;
>   	event = __trace_buffer_lock_reserve(buffer, TRACE_PRINT, size,
>   					    tracing_gen_ctx());
> -	if (unlikely(!event))
> +	if (unlikely(!event)) {
> +		/*
> +		 * If the size was greated than what was allowed, then

greater ?

Thanks,

Mathieu
Steven Rostedt Dec. 12, 2023, 3:45 p.m. UTC | #2 
On Tue, 12 Dec 2023 09:33:11 -0500
Mathieu Desnoyers <mathieu.desnoyers@efficios.com> wrote:

> On 2023-12-12 09:00, Steven Rostedt wrote:
> [...]
> > --- a/kernel/trace/trace.c
> > +++ b/kernel/trace/trace.c
> > @@ -7272,6 +7272,7 @@ tracing_mark_write(struct file *filp, const char __user *ubuf,
> >   	enum event_trigger_type tt = ETT_NONE;
> >   	struct trace_buffer *buffer;
> >   	struct print_entry *entry;
> > +	int meta_size;
> >   	ssize_t written;
> >   	int size;
> >   	int len;
> > @@ -7286,12 +7287,9 @@ tracing_mark_write(struct file *filp, const char __user *ubuf,
> >   	if (!(tr->trace_flags & TRACE_ITER_MARKERS))
> >   		return -EINVAL;
> >   
> > -	if (cnt > TRACE_BUF_SIZE)
> > -		cnt = TRACE_BUF_SIZE;  
> 
> You're removing an early bound check for a size_t userspace input...
> 
> > -
> > -	BUILD_BUG_ON(TRACE_BUF_SIZE >= PAGE_SIZE);
> > -
> > -	size = sizeof(*entry) + cnt + 2; /* add '\0' and possible '\n' */
> > +	meta_size = sizeof(*entry) + 2;  /* add '\0' and possible '\n' */
> > + again:
> > +	size = cnt + meta_size;  
> 
> ... and then implicitly casting it into a "int" size variable, which
> can therefore become a negative value.
> 
> Just for the sake of not having to rely on ring_buffer_lock_reserve
> catching (length > BUF_MAX_DATA_SIZE), I would recommend to add an
> early check for negative here.

size_t is not signed, so nothing should be negative. But you are right, I
need to have "size" be of size_t type too to prevent the overflow.

And I could make cnt of ssize_t type and check for negative and fail early
in such a case.

Thanks!

> 
> >   
> >   	/* If less than "<faulted>", then make sure we can still add
> > that */ if (cnt < FAULTED_SIZE)
> > @@ -7300,9 +7298,25 @@ tracing_mark_write(struct file *filp, const char
> > __user *ubuf, buffer = tr->array_buffer.buffer;
> >   	event = __trace_buffer_lock_reserve(buffer, TRACE_PRINT, size,
> >   					    tracing_gen_ctx());
> > -	if (unlikely(!event))
> > +	if (unlikely(!event)) {
> > +		/*
> > +		 * If the size was greated than what was allowed, then
> >  
> 
> greater ?

Nah, the size is "greated" like "greated cheese" ;-)

Thanks for the review, I'll send out a v3.

-- Steve
diff mbox series

Patch

diff --git a/include/linux/ring_buffer.h b/include/linux/ring_buffer.h
index 782e14f62201..b1b03b2c0f08 100644
--- a/include/linux/ring_buffer.h
+++ b/include/linux/ring_buffer.h
@@ -141,6 +141,7 @@  int ring_buffer_iter_empty(struct ring_buffer_iter *iter);
 bool ring_buffer_iter_dropped(struct ring_buffer_iter *iter);
 
 unsigned long ring_buffer_size(struct trace_buffer *buffer, int cpu);
+unsigned long ring_buffer_max_event_size(struct trace_buffer *buffer);
 
 void ring_buffer_reset_cpu(struct trace_buffer *buffer, int cpu);
 void ring_buffer_reset_online_cpus(struct trace_buffer *buffer);
diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index a3eaa052f4de..882aab2bede3 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -5250,6 +5250,21 @@  unsigned long ring_buffer_size(struct trace_buffer *buffer, int cpu)
 }
 EXPORT_SYMBOL_GPL(ring_buffer_size);
 
+/**
+ * ring_buffer_max_event_size - return the max data size of an event
+ * @buffer: The ring buffer.
+ *
+ * Returns the maximum size an event can be.
+ */
+unsigned long ring_buffer_max_event_size(struct trace_buffer *buffer)
+{
+	/* If abs timestamp is requested, events have a timestamp too */
+	if (ring_buffer_time_stamp_abs(buffer))
+		return BUF_MAX_DATA_SIZE - RB_LEN_TIME_EXTEND;
+	return BUF_MAX_DATA_SIZE;
+}
+EXPORT_SYMBOL_GPL(ring_buffer_max_event_size);
+
 static void rb_clear_buffer_page(struct buffer_page *page)
 {
 	local_set(&page->write, 0);
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index ef86379555e4..bd6d28dad05d 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -7272,6 +7272,7 @@  tracing_mark_write(struct file *filp, const char __user *ubuf,
 	enum event_trigger_type tt = ETT_NONE;
 	struct trace_buffer *buffer;
 	struct print_entry *entry;
+	int meta_size;
 	ssize_t written;
 	int size;
 	int len;
@@ -7286,12 +7287,9 @@  tracing_mark_write(struct file *filp, const char __user *ubuf,
 	if (!(tr->trace_flags & TRACE_ITER_MARKERS))
 		return -EINVAL;
 
-	if (cnt > TRACE_BUF_SIZE)
-		cnt = TRACE_BUF_SIZE;
-
-	BUILD_BUG_ON(TRACE_BUF_SIZE >= PAGE_SIZE);
-
-	size = sizeof(*entry) + cnt + 2; /* add '\0' and possible '\n' */
+	meta_size = sizeof(*entry) + 2;  /* add '\0' and possible '\n' */
+ again:
+	size = cnt + meta_size;
 
 	/* If less than "<faulted>", then make sure we can still add that */
 	if (cnt < FAULTED_SIZE)
@@ -7300,9 +7298,25 @@  tracing_mark_write(struct file *filp, const char __user *ubuf,
 	buffer = tr->array_buffer.buffer;
 	event = __trace_buffer_lock_reserve(buffer, TRACE_PRINT, size,
 					    tracing_gen_ctx());
-	if (unlikely(!event))
+	if (unlikely(!event)) {
+		/*
+		 * If the size was greated than what was allowed, then
+		 * make it smaller and try again.
+		 */
+		if (size > ring_buffer_max_event_size(buffer)) {
+			/* cnt < FAULTED size should never be bigger than max */
+			if (WARN_ON_ONCE(cnt < FAULTED_SIZE))
+				return -EBADF;
+			cnt = ring_buffer_max_event_size(buffer) - meta_size;
+			/* The above should only happen once */
+			if (WARN_ON_ONCE(cnt + meta_size == size))
+				return -EBADF;
+			goto again;
+		}
+
 		/* Ring buffer disabled, return as if not open for write */
 		return -EBADF;
+	}
 
 	entry = ring_buffer_event_data(event);
 	entry->ip = _THIS_IP_;