Commit efbbdaa2 authored by Masami Hiramatsu's avatar Masami Hiramatsu Committed by Steven Rostedt (VMware)
Browse files

tracing: Show real address for trace event arguments 

To help debugging kernel, show real address for trace event arguments
in tracefs/trace{,pipe} instead of hashed pointer value.

Since ftrace human-readable format uses vsprintf(), all %p are
translated to hash values instead of pointer address.

However, when debugging the kernel, raw address value gives a
hint when comparing with the memory mapping in the kernel.
(Those are sometimes used with crash log, which is not hashed too)
So converting %p with %px when calling trace_seq_printf().

Moreover, this is not improving the security because the tracefs
can be used only by root user and the raw address values are readable
from tracefs/percpu/cpu*/trace_pipe_raw file.

Link: https://lkml.kernel.org/r/160277370703.29307.5134475491761971203.stgit@devnote2



Signed-off-by: default avatarMasami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: default avatarSteven Rostedt (VMware) <rostedt@goodmis.org>
parent 7d536753

include/linux/trace_events.h

+4 −0
Original line number Diff line number Diff line
@@ -55,6 +55,8 @@ struct trace_event; 


int trace_raw_output_prep(struct trace_iterator *iter,

			  struct trace_event *event);

extern __printf(2, 3)

void trace_event_printf(struct trace_iterator *iter, const char *fmt, ...);



/*

 * The trace entry - the most basic unit of tracing. This is what
@@ -87,6 +89,8 @@ struct trace_iterator { 
	unsigned long		iter_flags;

	void			*temp;	/* temp holder */

	unsigned int		temp_size;

	char			*fmt;	/* modified format holder */

	unsigned int		fmt_size;



	/* trace_seq for __print_flags() and __print_symbolic() etc. */

	struct trace_seq	tmp_seq;

include/trace/trace_events.h

+1 −1
Original line number Diff line number Diff line
@@ -364,7 +364,7 @@ trace_raw_output_##call(struct trace_iterator *iter, int flags, \ 
	if (ret != TRACE_TYPE_HANDLED)					\

		return ret;						\

									\

	trace_seq_printf(s, print);					\

	trace_event_printf(iter, print);				\

									\

	return trace_handle_return(s);					\

}									\

kernel/trace/trace.c

+70 −1
Original line number Diff line number Diff line
@@ -3530,6 +3530,62 @@ __find_next_entry(struct trace_iterator *iter, int *ent_cpu, 
	return next;

}



#define STATIC_FMT_BUF_SIZE	128

static char static_fmt_buf[STATIC_FMT_BUF_SIZE];



static char *trace_iter_expand_format(struct trace_iterator *iter)

{

	char *tmp;



	if (iter->fmt == static_fmt_buf)

		return NULL;



	tmp = krealloc(iter->fmt, iter->fmt_size + STATIC_FMT_BUF_SIZE,

		       GFP_KERNEL);

	if (tmp) {

		iter->fmt_size += STATIC_FMT_BUF_SIZE;

		iter->fmt = tmp;

	}



	return tmp;

}



const char *trace_event_format(struct trace_iterator *iter, const char *fmt)

{

	const char *p, *new_fmt;

	char *q;



	if (WARN_ON_ONCE(!fmt))

		return fmt;



	p = fmt;

	new_fmt = q = iter->fmt;

	while (*p) {

		if (unlikely(q - new_fmt + 3 > iter->fmt_size)) {

			if (!trace_iter_expand_format(iter))

				return fmt;



			q += iter->fmt - new_fmt;

			new_fmt = iter->fmt;

		}



		*q++ = *p++;



		/* Replace %p with %px */

		if (p[-1] == '%') {

			if (p[0] == '%') {

				*q++ = *p++;

			} else if (p[0] == 'p' && !isalnum(p[1])) {

				*q++ = *p++;

				*q++ = 'x';

			}

		}

	}

	*q = '\0';



	return new_fmt;

}



#define STATIC_TEMP_BUF_SIZE	128

static char static_temp_buf[STATIC_TEMP_BUF_SIZE] __aligned(4);
@@ -4322,6 +4378,16 @@ __tracing_open(struct inode *inode, struct file *file, bool snapshot) 
	if (iter->temp)

		iter->temp_size = 128;



	/*

	 * trace_event_printf() may need to modify given format

	 * string to replace %p with %px so that it shows real address

	 * instead of hash value. However, that is only for the event

	 * tracing, other tracer may not need. Defer the allocation

	 * until it is needed.

	 */

	iter->fmt = NULL;

	iter->fmt_size = 0;



	/*

	 * We make a copy of the current tracer to avoid concurrent

	 * changes on it while we are reading.
@@ -4473,6 +4539,7 @@ static int tracing_release(struct inode *inode, struct file *file) 


	mutex_destroy(&iter->mutex);

	free_cpumask_var(iter->started);

	kfree(iter->fmt);

	kfree(iter->temp);

	kfree(iter->trace);

	kfree(iter->buffer_iter);
@@ -9331,9 +9398,11 @@ void ftrace_dump(enum ftrace_dump_mode oops_dump_mode) 


	/* Simulate the iterator */

	trace_init_global_iter(&iter);

	/* Can not use kmalloc for iter.temp */

	/* Can not use kmalloc for iter.temp and iter.fmt */

	iter.temp = static_temp_buf;

	iter.temp_size = STATIC_TEMP_BUF_SIZE;

	iter.fmt = static_fmt_buf;

	iter.fmt_size = STATIC_FMT_BUF_SIZE;



	for_each_tracing_cpu(cpu) {

		atomic_inc(&per_cpu_ptr(iter.array_buffer->data, cpu)->disabled);

kernel/trace/trace.h

+2 −0
Original line number Diff line number Diff line
@@ -581,6 +581,8 @@ struct trace_entry *trace_find_next_entry(struct trace_iterator *iter, 
void trace_buffer_unlock_commit_nostack(struct trace_buffer *buffer,

					struct ring_buffer_event *event);



const char *trace_event_format(struct trace_iterator *iter, const char *fmt);



int trace_empty(struct trace_iterator *iter);



void *trace_find_next_entry_inc(struct trace_iterator *iter);

kernel/trace/trace_output.c

+11 −1
Original line number Diff line number Diff line
@@ -312,13 +312,23 @@ int trace_raw_output_prep(struct trace_iterator *iter, 
}

EXPORT_SYMBOL(trace_raw_output_prep);



void trace_event_printf(struct trace_iterator *iter, const char *fmt, ...)

{

	va_list ap;



	va_start(ap, fmt);

	trace_seq_vprintf(&iter->seq, trace_event_format(iter, fmt), ap);

	va_end(ap);

}

EXPORT_SYMBOL(trace_event_printf);



static int trace_output_raw(struct trace_iterator *iter, char *name,

			    char *fmt, va_list ap)

{

	struct trace_seq *s = &iter->seq;



	trace_seq_printf(s, "%s: ", name);

	trace_seq_vprintf(s, fmt, ap);

	trace_seq_vprintf(s, trace_event_format(iter, fmt), ap);



	return trace_handle_return(s);

}