[PATCH] tracing: Fix trace_check_vprintf() when tp_printk is used

[PATCH] tracing: Fix trace_check_vprintf() when tp_printk is used

[Steven Rostedt]

From: Steven Rostedt <rostedt@goodmis.org>

When the tp_printk kernel command line is used, the trace events go
directly to printk(). It is still checked via the trace_check_vprintf()
function to make sure the pointers of the trace event are legit.

The addition of reading buffers from previous boots required adding a
delta between the addresses of the previous boot and the current boot so
that the pointers in the old buffer can still be used. But this required
adding a trace_array pointer to acquire the delta offsets.

The tp_printk code does not provide a trace_array (tr) pointer, so when
the offsets were examined, a NULL pointer dereference happened and the
kernel crashed.

If the trace_array does not exist, just default the delta offsets to zero,
as that also means the trace event is not being read from a previous boot.

Link: https://lore.kernel.org/all/Zv3z5UsG_jsO9_Tb@aschofie-mobl2.lan/

Reported-by: Alison Schofield <alison.schofield@intel.com>
Fixes: 07714b4bb3f98 ("tracing: Handle old buffer mappings for event strings and functions")
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
---
 kernel/trace/trace.c | 15 +++++++++++++--
 1 file changed, 13 insertions(+), 2 deletions(-)

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index c01375adc471..1c69ca1f1088 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -3697,8 +3697,8 @@ static void test_can_verify(void)
 void trace_check_vprintf(struct trace_iterator *iter, const char *fmt,
 			 va_list ap)
 {
-	long text_delta = iter->tr->text_delta;
-	long data_delta = iter->tr->data_delta;
+	long text_delta = 0;
+	long data_delta = 0;
 	const char *p = fmt;
 	const char *str;
 	bool good;
@@ -3710,6 +3710,17 @@ void trace_check_vprintf(struct trace_iterator *iter, const char *fmt,
 	if (static_branch_unlikely(&trace_no_verify))
 		goto print;
 
+	/*
+	 * When the kernel is booted with the tp_printk command line
+	 * parameter, trace events go directly through to printk().
+	 * It also is checked by this function, but it does not
+	 * have an associated trace_array (tr) for it.
+	 */
+	if (iter->tr) {
+		text_delta = iter->tr->text_delta;
+		data_delta = iter->tr->data_delta;
+	}
+
 	/* Don't bother checking when doing a ftrace_dump() */
 	if (iter->fmt == static_fmt_buf)
 		goto print;
-- 
2.45.2

Re: [PATCH] tracing: Fix trace_check_vprintf() when tp_printk is used

[Alison Schofield]

On Thu, Oct 03, 2024 at 10:49:25AM -0400, Steven Rostedt wrote:
> From: Steven Rostedt <rostedt@goodmis.org>
> 
> When the tp_printk kernel command line is used, the trace events go
> directly to printk(). It is still checked via the trace_check_vprintf()
> function to make sure the pointers of the trace event are legit.
> 
> The addition of reading buffers from previous boots required adding a
> delta between the addresses of the previous boot and the current boot so
> that the pointers in the old buffer can still be used. But this required
> adding a trace_array pointer to acquire the delta offsets.
> 
> The tp_printk code does not provide a trace_array (tr) pointer, so when
> the offsets were examined, a NULL pointer dereference happened and the
> kernel crashed.
> 
> If the trace_array does not exist, just default the delta offsets to zero,
> as that also means the trace event is not being read from a previous boot.
> 
> Link: https://lore.kernel.org/all/Zv3z5UsG_jsO9_Tb@aschofie-mobl2.lan/
> 

Thanks Steve!

Tested-by: Alison Schofield <alison.schofield@intel.com>


> Reported-by: Alison Schofield <alison.schofield@intel.com>
> Fixes: 07714b4bb3f98 ("tracing: Handle old buffer mappings for event strings and functions")
> Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
> ---
>  kernel/trace/trace.c | 15 +++++++++++++--
>  1 file changed, 13 insertions(+), 2 deletions(-)
> 
>
snip