[RFC PATCH v2 3/3] tracing: Add ptr-hash option to show the hashed pointer value

[Masami Hiramatsu]

Add tracefs/options/hash-ptr option to show hashed pointer
value by %p in event printk format string.

For the security reason, normal printk will show the hashed
pointer value (encrypted by random number) with %p to printk
buffer to hide the real address. But the tracefs/trace always
shows real address for debug. To bridge those outputs, add an
option to switch the output format. Ftrace users can use it
to find the hashed value corresponding to the real address
in trace log.

Signed-off-by: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
---
 Documentation/trace/ftrace.rst |    6 ++++++
 kernel/trace/trace.c           |    4 ++++
 kernel/trace/trace.h           |    1 +
 3 files changed, 11 insertions(+)

diff --git a/Documentation/trace/ftrace.rst b/Documentation/trace/ftrace.rst
index 87cf5c010d5d..62c98e9bbdd9 100644
--- a/Documentation/trace/ftrace.rst
+++ b/Documentation/trace/ftrace.rst
@@ -1159,6 +1159,12 @@ Here are the available options:
 	This simulates the original behavior of the trace file.
 	When the file is closed, tracing will be enabled again.
 
+  hash-ptr
+        When set, "%p" in the event printk format displays the
+        hashed pointer value instead of real address.
+        This will be useful if you want to find out which hashed
+        value is corresponding to the real value in trace log.
+
   record-cmd
 	When any event or tracer is enabled, a hook is enabled
 	in the sched_switch trace point to fill comm cache
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 1ebcc83b1e23..414c40a579be 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -3525,6 +3525,10 @@ const char *trace_event_format(struct trace_iterator *iter, const char *fmt)
 
 	if (WARN_ON_ONCE(!fmt))
 		return fmt;
+
+	if (iter->tr->trace_flags & TRACE_ITER_HASH_PTR)
+		return fmt;
+
 retry:
 	p = fmt;
 	new_fmt = q = iter->fmt;
diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index 524502d1f60a..c34187bd22a9 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -1347,6 +1347,7 @@ extern int trace_get_user(struct trace_parser *parser, const char __user *ubuf,
 		C(MARKERS,		"markers"),		\
 		C(EVENT_FORK,		"event-fork"),		\
 		C(PAUSE_ON_TRACE,	"pause-on-trace"),	\
+		C(HASH_PTR,		"hash-ptr"),	/* Print hashed pointer */ \
 		FUNCTION_FLAGS					\
 		FGRAPH_FLAGS					\
 		STACK_FLAGS					\