tracing: Fix trace_check_vprintf() when tp_printk is used

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/
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Link: https://lore.kernel.org/20241003104925.4e1b1fd9@gandalf.local.home
Fixes: 07714b4bb3f98 ("tracing: Handle old buffer mappings for event strings and functions")
Reported-by: Alison Schofield <alison.schofield@intel.com>
Tested-by: Alison Schofield <alison.schofield@intel.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index c01375adc4714a563c71dc0aeeb2b30c78cc9478..1c69ca1f108865e59ad42424890de6233d6161ae 100644 (file)
--- 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;